geology of the united arab emirates
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Farzad Irani Page 1 9/12/2001
Geology of the United Arab Emirates
A Project by Farzad. N. Irani
Schlumberger Drilling and Measurements
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Table of contents
Table of contents 2 List of figures 3 Introduction 6 Geology of Abu – Dhabi 7 Geology of Dubai 36 Geology of the Northern Emirates 39 Oil in the United Arab Emirates 43 Gas in the United Arab Emirates 43 Geological Time Scale 44 Sedimentary Rocks 53 Knowledge 88 Fossils of the United Arab Emirates 103 Desert of the United Arab Emirates 116 Descriptive Glossary 118
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List of figures Figure 1 – Main Structural Province of Arabian Peninsula................................................ 7 Figure 2- Paleogeography of the Arabian Region (red outline) during the Albian times
(Lower Cretaceous)..................................................................................................... 8 Figure 3- Regional lithostratigraphic correlations ............................................................ 10 Figure 4- Upper Jurassic nomenclature in Abu Dhabi...................................................... 15 Figure 5- Thamama Group terminology and reservoir classification............................... 16 Figure 6- Jurassic/Cretaceous contact............................................................................... 17 Figure 7- Aptian Limestones (Shuaiba) outcropping in Wadi Dhayah, Ras Al Khaimah,
UAE .......................................................................................................................... 20 Figure 8- Startigraphic correlation of Abu Dhabi onshore wells...................................... 22 Figure 9-Startigraphic correlation of Abu Dhabi offshore wells ...................................... 24 Figure 10- Fields of UAE ................................................................................................. 28 Figure 11- Structural cross section of ADCO’s Fields ..................................................... 30 Figure 12- Generalized lithostratigraphic column of Offshore Abu Dhabi ...................... 31 Figure 14- First rig at Umm Shaif..................................................................................... 34 Figure 16- Generalized geological cross-section of the Northern United Arab Emirates 39 Figure 17-Shuaiba facies relationships in the Northern Arab Emirates ........................... 40 Figure 18-Mishrif facies relationships in the Northern United Arab Emirates ................ 41 Figure 19- Geological Time scale (source www.geology.com) .................................... 45 Figure 20-Cenozoic Era .................................................................................................... 47 Figure 21-Mesozoic .......................................................................................................... 48 Figure 22-Triassic ............................................................................................................. 49 Figure 23-Jurassic ............................................................................................................. 50 Figure 24-Cretaceous ........................................................................................................ 52 Figure 25- Rock Cycle........................................................................................................ 53 Figure 26-– Igneous Rock classification........................................................................... 54 Figure 27-Constituents of sedimentary rocks ................................................................... 56 Figure 28-Composition of Siliciclastic sedimentary rocks............................................... 57 Figure 29- Udden-Wentworth Scale ................................................................................. 60 Figure 30- Grain size distribution (Sorting)...................................................................... 61 Figure 31- Roundness of grains ........................................................................................ 62 Figure 32- Roundness of grains chart ............................................................................... 62 Figure 33- Sandstone specimen ........................................................................................ 63 Figure 34- Sediment is composed of shelly debris ............................................................... 64 Figure 35- A brief description of differences between carbonate and Siliciclastic
sediments................................................................................................................... 64 Figure 36- Carbonate Factory ........................................................................................... 65 Figure 37- Icehouse and Greenhouse conditions during ancient times ............................ 65 Figure 38- Relative importance of groups of Organisms to carbonate sediment production
through time.............................................................................................................. 66 Figure 39- Carbonate buildup phase during the ancient geologic times........................... 66 Figure 40- Ramp Margin .................................................................................................. 68 Figure 41- Rimmed Margin .............................................................................................. 69 Figure 42- Isolated Carbonate Platform............................................................................ 70
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Figure 43- Carbonate chemistry........................................................................................ 71 Figure 44– Calcite crystal structure and a Calcite crystal................................................. 72 Figure 45 - Aragonite........................................................................................................ 73 Figure 46- Lime Mudstone (chalk) ................................................................................... 74 Figure 47– wackestone ..................................................................................................... 75 Figure 48- crinoidal packstone. The crinoid skeletal fragments are an off white to grayish
brown color, whereas the matrix is yellowish brown. .............................................. 75 Figure 49- Silicified Oolitic Grainstone ........................................................................... 76 Figure 50- Algal Boundstone Coral Boundstone........................ 77 Figure 51– Oolitic Limestone ........................................................................................... 78 Figure 52- Shale................................................................................................................ 80 Figure 53- Mudstone......................................................................................................... 80 Figure 54- Specimens of Anhydrite.................................................................................. 85 Figure 55- Chert................................................................................................................ 86 Figure 56- Pyrite Crystals ................................................................................................. 87 Figure 57- Stalactites and Stalagmites.............................................................................. 89 Figure 58- Mohs Scale of Hardness.................................................................................. 90 Figure 59- Chalk Cliffs ..................................................................................................... 91 Figure 60- Limestone Pinnacles in China......................................................................... 91 Figure 61- Limestone Features ......................................................................................... 92 Figure 62- Limestone Pavement, North Yorkshire........................................................... 92 Figure 63- Dolines, Ural Mountains, Russia .................................................................... 93 Figure 64- Stratigraphy..................................................................................................... 94 Figure 65- Idealized cross section of an Ophiolite ........................................................... 95 Figure 66– Vein Quartz grains.......................................................................................... 96 Figure 67- Diagenesis Compaction................................................................................... 97 Figure 68- Diagenesis Solution......................................................................................... 98 Figure 69- Diagenesis Cementation.................................................................................. 99 Figure 70- Diagenesis Replacement (Wood Opal) ......................................................... 100 Figure 71- Diagenesis Bioturbation................................................................................ 100 Figure 72- Biostratigraphy of the Shuaiba formation in the Shaybah field (Late Aptian
nannofossil evidence is confined to localities off the eastern flank of the Shaybah104 Figure 73- Plate 1 Rudist species from the Shuaiba formation of the Shaybah field ..... 105 Figure 74 - Plate 2 Rudist species from the Shuaiba formation of the Shaybah field .... 106 Figure 75- Plate 3 Rudist species from the Shuaiba formation of the Shaybah field ..... 107 Figure 76- Plate 4............................................................................................................ 108 Figure 77- Plate 4. (Cont) ............................................................................................... 109 Figure 78- Plate 5 Various Shuaiba formation fossils typical of the “middle Shuaiba”
lagoonal sediments in the Shaybah field (see previous page)................................. 110 Figure 79- Plate 6 Various Shuaiba formation fossils typical of the “upper Shuaiba” in the
Shaybah field (see next page) ..................................................................................... 111 Figure 80- Cretaceous Fossils of the Simsima Limestone Formation ............................ 113 Figure 81- Micene fossil ................................................................................................. 114 Figure 82- Vertebrate fossil of Miocene......................................................................... 114 Figure 83- Nummulite of Jebel Hafit.............................................................................. 115 Figure 84- Desert of UAE............................................................................................... 116 Figure 85- Sabkha ........................................................................................................... 118
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Figure 86- Bivalve Mollusc ............................................................................................ 119 Figure 87- Dinosaur Shapes and Sizes............................................................................ 119 Figure 88- Ferns.............................................................................................................. 120 Figure 89- Cycads ........................................................................................................... 120 Figure 90- Ginkgo........................................................................................................... 121 Figure 91- Club Moss ..................................................................................................... 122 Figure 92- Fossilized Glossopterid leaf .......................................................................... 122 Figure 93- Dicynodonts .................................................................................................. 122 Figure 94- Ammonite...................................................................................................... 123 Figure 95- Feldspar ......................................................................................................... 123 Figure 96- Scanning Electron Microscope ..................................................................... 126 Figure 97- Plankton in a Drop of Water ......................................................................... 127 Figure 98- Green Algae .................................................................................................. 128 Figure 99- Red Coralline Algae...................................................................................... 129 Figure 100- Gastropods................................................................................................... 129 Figure 101- Corals .......................................................................................................... 130 Figure 102- Bryozoans.................................................................................................... 131 Figure 103- Trilobites fossilized..................................................................................... 131 Figure 104- Sea Lily, or Crinoid..................................................................................... 132 Figure 105- Sea Urchin................................................................................................... 133 Figure 106- Bioherms ..................................................................................................... 133 Figure 108- Twinning ..................................................................................................... 135 Figure 109- Polarized Light ............................................................................................ 135 Figure 110- Euhedral Crystals ........................................................................................ 136 Figure 111- Gypsum and Crystal Structure .................................................................... 137 Figure 112- Halimeda ..................................................................................................... 138 Figure 113- Heteraster Musandamensis.......................................................................... 140 Figure 114- Facies........................................................................................................... 141
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Project The purpose of this project is to give the New Engineer a good picture about the Geology and Formations of UAE. This could also be a useful document for experienced Engineers going out to the field, as it will provide them with a good insight about the formations expected in that particular field. I will try to make this as interesting and knowledge providing as possible. Some of the material for making this document is obtained from different websites, which are given on the last page.
A Brief Summary about the Project All these topics are explained with respect to the Geology of the UAE. The topics included in this document, such as Geologic time scale, Stratigraphy and Sedimentary rocks will give us good information about the type of litho logy, how they were formed, the ages of formations including the different Eras, Periods, and Epochs etc. It will also cover the different Lithologies and how they were formed including their depositional environments, fossil content, Hydrocarbon content etc. There will be a good explanation about the Lithologies of all the fields in the UAE, including Onshore and Offshore. The Sedimentary rocks section gives a good explanation about the types of sedimentary rocks including carbonates, siliciclastics, shales, clays etc.
Many of the new engineers ask questions like how are the rocks formed? What is a mineral? How to identify between minerals and rocks? And many more. This document will try to answer all of those questions.
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Geology of Abu – Dhabi Introduction The Arabian Peninsula as a whole shows two main geological provinces (Fig 1):
1. The Arabian Shield: an area to the west composed mostly of Precambrian Igneous and Metamorphic rocks, which has remained a largely positive region since the Cambrian.
2. The Arabian Platform: a vast area to the east of the Arabian Shield including Qatar and the UAE, which has undergone periodic subsidence and which has accumulated a sequence of sedimentary rocks ranging in age from Cambrian to Recent.
Figure 1 – Main Structural Province of Arabian Peninsula
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Paleogeography of the Arabian Peninsula
Figure 2- Paleogeography of the Arabian Region (red ou(Lower Cretaceous).
The world's landmasses have not always been in the place wh700 million years they have moved, broken apart and joined toinclude the landmasses - continental plates - and the material bThis movement of continental plates continues today and somcontinental plate drifting away from Africa, travel at a rate of of these plates there are two types of phenomena; "active" eve"passive" events where the plates are spreading apart. Materiathat of a continental plate; so that when the two collide the ocecontinental plate. This process, called subduction, can result insuch as the Zagros Mountains of Iran and activities associatedearthquakes and intense volcanicity, sometimes with catastrop When the "active" and "passive" margins have been identifiedpast magnetic fields that have been fossilized within the iron mmargins of spreading oceanic plates, the positions of the land parts of geological time. The result from this plotting is called
The Arabian Peninsula during the Albian time was located approximately 8º S of the Equator and the Aptian palaeogeography was similar to that of the Albian
tline) during the Albian times
ere they are today. During the past gether. The earth's crustal plates eneath the oceans - oceanic plates.
e plates, such as the Arabian 5 centimeters a year. At the margins nts caused by colliding plates and l of an oceanic plate is denser than anic plate is forced beneath the the formation of mountain ranges
with this process are deep-seated hic results.
, and by using data from the earth's inerals of basalts found at the
masses can be plotted for various palaeogeography.
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• 140 million years ago, the massive continental plate of Africa, the northeastern part of
which was to become Arabia, steadily moved northeastwards. This movement was due to sea floor spreading along the mid-Atlantic ridge - a "passive" plate margin.
• 70 million years ago the rocks of ancient Nubia, linking Arabia with Egypt at that time, began to drift apart to form the beginnings of what is now the Red Sea rift. At this time Arabia was still isolated from both Europe and Asia by a seaway named the Tethys that once connected the ancient Mediterranean with the Arabian Gulf and the Indian Ocean.
• 23 million years ago, approximately, the pace of movement of Arabia away from Africa increased by an anticlockwise motion to the northeast that closed the Tethys Sea. This event prompted the formation of the Zagros and Taurus Mountains of Iran and Turkey respectively and, in Arabia, most of the volcanicity linked with this movement was confined to the southern Red Sea area, namely the Republic of Yemen and the Kingdom of Saudi Arabia.
A land connection to Africa was still in place in southwestern Arabia; the Ethiopian-Yemen isthmus existed until Pliocene times (about 5 million years ago) when the Red Sea was connected to the Mediterranean but cut off from the Gulf of Aden. This land bridge allowed migrations of terrestrial animals to and from Africa and Asia via Arabia. Stratigraphic History The structural evolution of the Arabian Platform has strongly influenced the sedimentation patterns in the United Arab Emirates and Qatar. After the Upper Paleozoic the prevailing sedimentary conditions changed drastically from mainly clastics to predominantly shallow-marine carbonates until the Eocene:
1. Permian-Triassic: predominantly dolomites with subordinate evaporates (Anhydrites) and clastics in the upper part of the section.
2. Jurassic: Shallow marine limestones with subordinate dolomites and extensive massive anhydrite in the Tithonian times (Hith)
3. Cretaceous: predominantly shallow-marine limestones without evaporates, but with clastic influxes in the Albian-Turonian times.
4. Paleocene-Eocene: shallow marine limestone with subordinate gypsum/anhydrite in the lower Eocene.
5. Mio-Pliocene: during the late Tertiary the clastic deposits with subordinate carbonates were re-established.
A broad correlation of lithostratigraphic units is shown in Fig-3 below.
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Figure 3- Regional lithostratigraphic correlations
Surface Geology The surface geology of United Arab Emirates is concealed under a cover of sand. Out crops are confined only to the Al-Ain area to the East where the Oman mountains form part of that region. The sands form dune ridges reaching heights of 150m inland. Plain gravel areas - the so-called “desert floor”, separate the dune ridges. Evaporatic flats (sabkha) dominate the coastal plains, which extend more than 80km southwards into the sand deserts. Consequently the geology of this area is based exclusively on subsurface information. Data from below the Permian is quite scarce, as only 3 wells have penetrated the Permian sequences of Abu-Dhabi. Offshore Abu-Dhabi the sedimentary section from Upper-Permian to Recent has a maximum thickness of more than 17,000 ft.
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Structural Features Two main features had a profound influence on the structural development of Abu Dhabi: the central Arabian arch and the Rub al Khali basin. These two structures plunge gently towards the Arabian Gulf (i.e. North east). General thickening of sedimentation is observed in this direction indicating an increasing rate of subsidence. Gentle and simple folds are common features. The main fold axes directions in Abu-Dhabi near the top of Thamama are N-S, E-W/NE-SW, and NW-SE. The “Arabian folds” aligned N-S is the most dominant and probably related to deep-seated basement tectonics. Diapiric salts are believed to underlie most of the structures of Abu-Dhabi. In some wells (e.g. Mandous) salt has been found intruding the Tertiary formations. Furthermore, in western Abu-Dhabi islands and the Jebel Dhanna peninsula are salt piercement structures surrounded by Tertiary and Quaternary deposits associated with Cambrian sediments carried up by salt plugs. Stratigraphic History Some believe the Stratigraphy of the Middle East oil province is “all done”. However an in depth examination of the extent Stratigraphic scheme reveals it merely consists of a jigsaw puzzle of units. In the late 60’s - early 70’s, some companies operating in the Middle East oil province (Abu Dhabi, Dubai, Oman, Qatar, Sharjah) arranged “Geological Liaison Meetings” to standardize the regional Stratigraphic nomenclature. Many operational units defined at the time fall into the category of ‘unconformity-bounded units’, as their boundaries commonly correspond either to a ‘sequence boundary’ (SB) or to a ‘transgressive surface’ (TS), i.e. an unconformity onto the shelf, which passes basin ward into its correlative conformity. Unconformity-bounded units are the reference rock-unit on which is based allostratigraphy, a classification that was not introduced until recently into the Code of Stratigraphic Nomenclature. In the subsurface, such boundaries, which are usually easily picked from well logs, are traceable far away from the reference locality; cores or cuttings provide additional physical evidence for these key bounding surface features (erosional surface, hard ground, karst, etc.). The interplay of changes in sea level, crustal movements (Plate Tectonics) and climatic variations controlled to a large extent the sedimentation process in Abu-Dhabi. Refer to Fig-3 for a broad correlation on a regional basis with neighboring Arabian Gulf Countries.
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Paleozoic As the Permo-Triassic structural evolution results in a comprehensive sedimentary sequence, the Triassic period is described here together with the Permian in the Paleozoic section. Evidence from the nearby areas suggest that the carbonates, clastics and evaporates of the Huqf Group, infra Cambrian in age, are the first non-metamorphosed sediments that covered the Arabian Shield. A predominantly clastic regime during the Early Paleozoic then followed resulting in the deposition of terrestrial to very shallow marine sandstones, with subordinate shales and silts over the entire shield area. Carbonate rocks are rare and restricted to the Middle-Late Cambrian, Early-Middle Devonian and Early-Middle Carboniferous. In Abu-Dhabi the oldest rocks exposed at Jebel Dhanna and in a number of Islands (Das, Dalma, Arzana, Zirkouh, etc) located in the west of the area. These rocks consist of a mixture of shales,dolomites and volcanics that have been brought to the surface as a result of salt Tectonics. In the Late Carboniferous the Middle East Craton was affected by the main phase of the Hercynian orogeny that led to considerable up warping and erosion. On the unconformity so developed the clastics of the late Carboniferous to Early Permian. These clastics consist of quartzitic sandstones and variably colored shales, siltstones with thin beds of dolomite, and anhydrites, which were probably deposited in a terrestrial to coastal marine environment. Permo-Triassic In the Middle-Permian the climate became gradually warmer and more arid. As a result of marine transgression a carbonate platform was established throughout the region. On this platform a thick sequence of shallow-water carbonates and subordinate evaporates of the Khuff formation were deposited. In the early Triassic the Carbonate platform was maintained, climatic conditions became hotter and more arid, and the Arabian Shield was pronouncedly uplifted to the west. Under these conditions the succeeding Sudair Formation was deposited. The restricted peritidal conditions established during the Sudair times persisted later leading to the deposition of Gulailah (Offshore Abu-Dhabi) or Jilh formation (Onshore Abu-Dhabi). Late in the Triassic, continental clastic beds of the Minjur Formation were deposited indicating a widespread regressive phase. Khuff The Khuff formation has been incompletely penetrated onshore Abu-Dhabi. Offshore the formation is 2800-2970 ft thick and consists of microcrystalline dolomites with subordinate limestones and minor anhydrites. The Khuff Carbonates consists of five regressive megacycles: fig 1-17
1. The lower megacycle (K-5) consists of tight dolomites slightly argillaceous at the base, becoming cleaner upwards with occasional interbedded anhydrites. The cycle terminates with a 60 ft thick massive anhydrite layer (Median Anhydrite), which has a considerable aerial extent. Locally, however, lateral facies changes occur over a short distance and the anhydrite is replaced by a highly radioactive dolomite (argillaceous, organic rich paleosoil, Uranium bearing).
2. The overlying four megacycles include a number of reservoir units, each of them consisting of various regressive sub cycles.
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Sudair The Sudair is 800-900 ft thick and consists of three units:
1. A lower dolomite and argillaceous limestone, 2. Overlain by a thick middle section of dolomite and thin anhydrite with some shale
interbeds 3. Terminated by an interbedding of shale and dolomite.
Gulailah and Jilh The Gulailah formation is 881-1023 ft thick, while the Jilh in the extreme S-E part of Abu-Dhabi (Mender region) is 1370 ft thick. These rocks consist of microcrystalline dolomite interbedded with subordinate anhydrite, minor shales and argillaceous limestones. Minjur Minjur consists of continental sandstones, lacustrine clastics, fresh water, sandy limestones etc. Minjur has been penetrated in the extreme SE part of Abu-Dhabi at Mender. However in Offshore Abu-Dhabi the Minjur Formation is non-existent – a fact that indicates the large unconformity marking the termination of the Triassic period?
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Mesozoic Lower Jurassic The Onset of the Jurassic evidenced a major marine Transgression that produced a vast carbonate-evaporite platform, which still received substantial clastic influx from the west. On this platform the initial deposits of the Jurassic represented by the Hamlah Formation were laid. Hamlah The Hamlah is 172-442 ft thick and consists of a thick middle section of argillaceous limestone; mudstone and subordinate shales bounded on top and bottom by thin intervals of clean limestone, dominantly lime-mudstone and wackestone. Middle Jurassic Shallow to very shallow, warm and clear water shelf conditions prevailed. This promoted the deposition of the clean carbonates of the Araej Formation. Araej Three units can be distinguished within the Araej, which are (top to bottom):
1. Upper Araej: Argillaceous limestone overlain by clean grainstone/packstones, 128-335 ft thick.
2. Uweinat Member: Very clean wackestones, and packstones with minor grainstones, 130-179 ft thick.
3. Lower Araej: Packstone/grainstones and lime-mudstones, 307-391 ft thick.
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Figure 4- Upper Jurassic nomenclature in Abu Dhabi
The upper Jurassic sequence of Abu-Dhabi rests on the unconformity surface that marks the end of the middle Jurassic period. It is a fairly thick sequence of carbonates and evaporates which constitute one megacycle of sedimentation recoding a gradual change from relatively deep-water shelf conditions grading through shoal-lagoonal and culminating in sub aerial supratidal conditions. Early in the Upper Jurassic times, active subsidence of the western and SW part of Abu-Dhabi resulted in the development of an intra-shelf basin in that region with a subsequent rapid marine transgression from the east to the west. Onto this basin the deep-water carbonates of the Diyab (or Dukhan) were laid down. The bulk of the formation consists of argillaceous lime-mudstones and wackestones and passes laterally eastwards into the cleaner limestone facies of the Fateh Formation. Towards the Upper Jurassic gradual shallowing of the depositional environment resulted in cyclic sedimentation of carbonates and evaporates referred to as the Arab Formation (Qatar-Fahahil equivalent). This carbonate/anhydrite cyclic sequence is well defined in the western part of the area but loses its identity eastwards. The Hith Formation represents the final regressive supratidal phase of the Upper Jurassic megacycle. This formation has a thickness range of 187-325 ft and consists principally of anhydrite with subordinate dolomite in the western part of the area, while to the east the anhydrite content of the formation decreases gradually. In Zakum and Bab fields the Hith is represented by a thin anhydrite at the top, which is underlain by shoal grainstones, and the bulk of the formation is represented by anhydritic dolomite. East of Zakum (Offshore eastern area), the anhydrite disappears and the Hith consists of partly anhydritic dolomite. In the area the distinction between Arab and Hith is no longer valid and both formations are referred to as the Hith/Arab equivalent.
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The overall picture is that of two contrasting sedimentary environments, the supratidal anhydrite/subordinate dolomite in the west, and the oolite/dolomite shoal environment (Asab Formation) in the east. The end of the Jurassic was marked by a period of non-deposition, perhaps erosion in some areas (e.g. in the south-east and central parts of onshore Abu-Dhabi). However, the structural relationship with the overlying Cretaceous sediments is for the most part one of conformity. Lower Cretaceous In the late 60’s - early 70’s, some companies operating in the Middle East oil province (Abu Dhabi, Dubai, Oman, Qatar, Sharjah) arranged “Geological Liaison Meetings” to standardize the regional Stratigraphic nomenclature. They came up with a practical scheme for the so-called “Thamama Group”. The Jurassic-Cretaceous boundary is placed at the top of the Hith Formation, which marks the cessation of the evaporitic phase and the resumption of the normal marine shelf, carbonate sedimentation. The Thamama group, coincident with the Lower cretaceous, is split into formations as tabulated in fig 1-6. Thamama Platform/Ramp Basin. In Abu Dhabi includes the section from the base of the Nahr Umr Formation down to the top of the Hith Formation, and consists of:
Figure 5- Thamama Group terminology and reservoir classification
Habshan Supposedly passes gradually eastward and downward into the Salil Fm, which in turn passes downward into the Rayda Formation.
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The Habshan Formation is an informal lithostratigraphic unit based on ADCO (ex ADPC) well Bab N°2, in onshore Abu Dhabi; the ADMA well Zakum N° 1 is the reference section for the offshore. The name “Habshan” was introduced as a substitute for the double-barreled name “Yamama/Sulaiy” which was used previously in Abu Dhabi. Deposition of the Habshan commences with a wide marine transgression, but the prevailing environment of deposition was largely restricted or semi-restricted. The Habshan was dominated by largely lagoonal lime-mudstone and wackestone. To the east the early phase of the Habshan sedimentation is characterized by partly oolitic grainstones interbedded with lagoonal, supratidal dolomite and anhydritic dolomite, while the later phase is represented by lagoonal/intertidal carbonates – mostly limestone and subordinate dolomites.
Figure 6- Jurassic/Cretaceous contact
Most unconformities found in the Tithonian section of the type-Habshan are probably intercepted by the pre-Kahmah unconformity. It is therefore suggested to split the type-Habshan into at least two formations, one that covers the lower and median parts bearing Tithonian microfossils and
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the other corresponding to the upper part bearing Berriasian microfossils. The use of "Habshan" as a formation name is presently restricted to the lower and median parts of the type section; two new formation names, “Bu Haseer” and “Belbazem”, are introduced to cover respectively the lower part and the upper part of its Cretaceous section. The new “Bu Haseer” unit displays distinctive facies associations, notably brackish environment facies with Charophytes, Salpingoporella (Hensonella), dinarica Radoicic, Calpionella and Pseudocyclammina.
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Lekhwair An Unconformity, which is of low magnitude offshore Abu Dhabi, terminates the Habshan sedimentation. The Lekhwair Formation represents the establishment of normal unrestricted marine-shelf conditions and is developed in a number of cyclic sequences. Each cycle starts with variably argillaceous limestone (mostly lime-mudstone/wackestone with minor packstone) which grades upwards into porous clean limestone (represented by packstone/wackestone with some grainstone). The argillaceous limestone represents the transgressive phase of an open-shelf sub tidal environment whereas the clean limestone represents regressive shallow-water shelf conditions occasionally above wave-base level. In general, the transgressive phase formed the dominant part of the cycle. It is composed of mainly white-weathering nodular limestone, usually radiolarian or miliolid and mainly white-weathering chalky limestone with Choffatella decipiens Lekhwair comprises of the Zakum Member in its lower part. Zakum Member It is an informal lithostratigraphic unit based on ADMA well Zakum N° 1 in offshore Abu Dhabi and should correspond to the lower unit of the so-called “Lekhwair Formation” in Abu Dhabi. It is bracketed by two unconformities; the lower one corresponds to the pre-Buwaib unconformity, which recorded the drowning of the eastern Arabian carbonate platforms. This interval covers both the so-called “Chrysalidina zone” or “Valvulinella zone”, and the section immediately below down to the pre-Buwaib unconformity. The latter biostratigraphic zone “near the middle of the Buwaib Formation” provides highly reliable correlations over most of Saudi Arabia and neighboring countries; it is identified by the presence of the fossil marker, Paravalvulina arabica or Pseudocyclammina lituus Kharaib A break in the sedimentation, which is again of minor significance, terminated the Lekhwair deposition. The overlying Kharaib formation exhibits the cyclic pattern of carbonate sedimentation already seen in the Lekhwair. The Kharaib commences with a limestone unit representing the regressive phase of a cycle which started late in the Lekhwair. This followed by a complete transgressive/regressive cycle and a thin unit consisting of the transgressive phase of the next cycle terminates the formation. The main characteristics of the Kharaib were the greater prevalence of the regressive portions of the cycles. The regressive limestones themselves exhibit shallowing-upward features with mudsuported limestone in the lower part Consists of Dictyoconus arabicus, occasional radiolarian cherts, molluscan limestone with Heteraster musandamensis In Umm Shaif field, offshore Abu Dhabi, the Kharaib can be split into 4 third-order transgressive-regressive cycles Hawar It is a unit on its own. In the ADMA Umm Shaif field, the base of the Hawar Formation consists of transgressive beach deposits which cut through the underlying shallow-water carbonates; in some locations, relicts of a pre-existing karstic surface are still preserved; therefore this lower boundary is associated to a sea-level fall. The rest of the unit consists predominantly of offshore carbonate-sand deposits with abundant Palorbitolina lenticularis. The maximum flooding is possibly reached at the base of the uppermost shale interval that lies on top of a glauconitic carbonate-sand layer. The top of the Hawar Fm coincides with an abrupt break in sedimentation from the latter shale interval to very shallow-water carbonates above. As far the lower boundary, the upper one also records a forced regression. The Hawar is a unit on its own, i.e. an unconformity-bounded unit.
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Shuaiba The terminal rock unit of the lower Cretaceous continues the cyclic pattern of shelf deposition observed in the Lekhwair and Kharaib Formations. The initial deposit of the Shuaiba consists of clean wackestone packstones and represents the regressive phase of a cycle, which had commenced late in the Kharaib. This was followed by deeper-water transgressive limestone consisting mainly of argillaceous lime-mudstone/wackestone with very minor shales. The deep-water shelf conditions persisted over most of offshore Abu Dhabi until the end of the lower Cretaceous. However in some localized areas, anomalously thick shallow-water rudistid carbonates are encountered. This differentiation into shallow- and deeper-water facies is expressed in Stratigraphic terms as:
1. Shuaiba Formation if composed of shelf carbonates and/or rudistid reefs. 2. Bab Member if dense limestone of a basinal nature. The Bab Member, which should
corresponds to the upper unit of the “Shuaiba Formation” in Abu Dhabi, is an informal lithostratigraphic unit based on ADCO well Bab N° 2, in onshore Abu Dhabi.
The existence of such localized build-ups offshore in the Shuaiba is due to the rise of salt plugs at depths, which resulted in the development of submarine topographic highs in this otherwise generally deep-water environment. These highs were sufficiently shallow for the limestone build-up to develop. Onshore from Ruwais through Salabikh and across Bu Hasa the Shuaiba forms a complex reef belt trending NW-SE. In Bu Hasa the first depositional phase of the Shuaiba (fine-grained chalky limestone of shallow-marine shelf) shows a graduation from predominantly algal growth over southern Bu Hasa to slightly deeper marine conditions northwards. The Late Shuaiba phase in central Bu Hasa is characterized by a shallow-shelf sea causing marked variations and in places widespread rudistid facies through the remaining Shuaiba times.
Figure 7- Aptian Limestones (Shuaiba) outcropping in Wadi Dhayah, Ras Al Khaimah,
UAE The Shuaiba consist of the following fossil indicators:
• The Upper part of the Shuaiba is limestone with breccias, with Orbitolina spp. (48 my), • The Lower part is molluscan limestone with Heteraster musandamensis (38 my),
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Geological description of the Shuaiba: Covered an interval ranging from the top of the Bab Member down to the base of the Hawar Formation it included:
• Top Shuaiba: Crystalline limestone with large thick shelled globigerinids and traces of glauconite.
• Middle Shuaiba: Dominantly fine grained limestone the top chalkier and the lower part more argillaceous.
• Bottom Shuaiba: Pseudo-oolitic limestone with clear calcite matrix and angular sand grains. The fauna of this limestone formation is on the whole rather poor with the exception of a rich zone Orbitolina discoidea at the base.”
Macrofossils. - Ammonites identified from ADMA well Umm Shaif N° 2 comprise one Ancyloceratinid specimen; those identified from Umm Shaif N°3 comprise of. Pseudohaploceras sp. and Diadochoceras SP. These observations point toward a Middle Aptian (Gargasian) age
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Middle Cretaceous The Middle Cretaceous formations are known collectively as the Wasia Group both in Abu Dhabi and Qatar. The Wasia group in Abu Dhabi comprises in ascending order: Nahr Umr, Salabikh (Mauddud, Shilaif, Tuwayil and Ruwaydha Members) and Mishrif Formations. Following the Thamama sedimentation a regional uplift and erosion affected most of Abu Dhabi. The effect is more pronounced in the Southeastern high of Abu Dhabi (Mender-Lekhwair region: Fig 8).
Figure 8- Startigraphic correlation of Abu Dhabi onshore wells
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Nahr Umr By Middle Cretaceous times, renewed subsidence took place leading to the deposition of the Nahr Umr formation. This formation thickens gradually from about 220 ft in the north to a maximum of 600 ft in the south and southwest and thins to approximately 300 ft in the extreme east of the offshore area towards the Northern Emirates. The Nahr Umr consists of a sequence of variegated shales with some rare sand lenses, glauconitic silts and occasional beds of limestone—mostly packstones and wackestone. Nahr Umr comprises dark brown-black silty and micaceous shales with small phosphates. Both macro and microfossils are very rare and a conspicuous bed of black-green clay full of glauconite and small black phosphates. The deposition of the Nahr Umr took place in mixed carbonate/clay ramp systems. A gradual increase in the volumetric importance of benthic foraminifera (orbitolinids) is observed during the Barremian and Aptian, leading to a climax in the Albian, where it is the dominant and rock-forming component of the Nahr Umr Formation. Mauddud With the termination of the Nahr Umr sedimentation, influx of terrigeneous sediments ceased and a transgression phase resulted in the deposition of the normal marine clear-water sediments of the Mauddud Member. The Mauddud is thinly developed in the Abu Dhabi and consists of bioclastic and foraminiferal wackestone and packstones. Shilaif Continued subsidence resulted in the establishment of a deep-water basin, the depocentre of which was located in the onshore Abu Dhabi. The axis of this basin ran north south through central offshore Abu Dhabi. The Shilaif Member deposited in this basin is in the range of 100- 200 ft thick in the east and west, but reaches 600 ft in the central parts of the area. The Shilaif consists of a succession of variably argillaceous oligosteginal limestones—mostly fine-grained packstone and wackestones—together with subordinate calcareous shales in the lower part of the formation. Mishrif Within this Shilaif basin, shallow-water carbonates of the Mishrif were deposited. This shelf progradation occurred progressively from the east and the west towards the central area. The Mishrif Formation reaches a maximum thickness of 1600 ft in the western offshore area (Dalma and Hair Dalmah) whilst in the east the maximum thickness is 865 ft in Umm Addalkh field. The formation is absent in the central part of Abu Dhabi (Fig 1-8) The Mishrif consist of a complex sequence of limestones. In the east the formation is made up of a lower unit composed of fine-grained bioclastic packstones and wackestones, which represent distal shelf slope environment. This unit is succeeded by medium-grained packstones indicative of proximal shelf slope sediments, which in turn pass upward into medium—to very coarse-grained bioclastic, and shelly packstones and grainstones. Rudist shells and debris dominate the latter lithofacies and represents shoal deposits which separate low energy lagoonal environment (represented by foraminiferal wackestone) from the Shilaif basin.
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Figure 9-Startigraphic correlation of Abu Dhabi offshore wells
In central Abu Dhabi the basinal facies of the Tuwayil and Ruwaydha members, probably deposited synchronously with the Mishrif, were laid down in a gradually constricting basin. The Middle Cretaceous was terminated by a major unconformity, the evidence of which can be inferred from the complete absence of the Wasia Group over the southeast of Abu Dhabi (Mender—Lekhwair: fig-8).
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Upper Cretaceous The Upper Cretaceous is known as the Aruma in Abu Dhabi. Aruma The Aruma consist of two major transgressive-regressive cycles of deposition. The Laffan and Halul Formations constitute the first cycle, while the Fiqa and Simsima represent the second cycle Laffan Towards the end of the Turonian a large unconformity terminated the Middle Cretaceous. Renewed subsidence led once again to the incursion of the seas and consequent deposition of the Laffan Formation. The Laffan comprises mainly shales with minor argillaceous limestones. The initial deposits of the Laffan were of deltaic origin but the bulk of the formation was laid down in an open marine-shelf environment. Halul The succeeding Halul Formation overlies the Laffan conformably and registers a gradual regression as shown by the prevalence of shallow clear-water marine carbonate sediments. The Halul consists of thin lower interbeds of calcareous shales and lime-mudstone passing upwards into “clean” chalky bioclastic and foraminiferal wackestone and subordinate packstone and lime-mudstone. Fiqa The Fiqa Formation represents the Upper-Cretaceous, second cycle, transgressive phase. It is a deep open marine-shelf environment deposit that ranges in thickness from 335 ft to more than 1100 ft offshore Abu Dhabi. Its Lower part consists of soft marl, calcareous shales and argillaceous limestone and grades upwards into mainly argillaceous lime-wackestone. Simsima Represents the regressive phase of the second cycle. It consists of limestones—mainly packstones and wackestone—and dolomites of shallow-water origin. Offshore Abu Dhabi the formation is about 600 ft thick in the north west of the area and reaches a maximum thickness of 1200 ft in the southeast. Both Simsima and Fiqa lose their characteristics in eastern offshore Abu Dhabi where they pass into the deeper limestones of the Gurpi Formation. This formation was laid down in a basin centered in the Northern UAE.
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Cenozoic A general recession of the seas affected the end of the cretaceous causing a disconfomity, evidenced by the lack of the Aruma in the Mender area. Lower Tertiary During the Lower Tertiary the Qatar arch was a rather stable area. Abu Dhabi lay at the margin of two basins:
• The Rub al Khali Basin to the south, and • The Pabdeh-Gurpi centered in the Northern Emirates.
In the west the Lower Tertiary consists of three formations, known as the Hasa Group:
• The Umm Er Radhuma • Rus • Dammam.
These formations gradually lose their characteristic litho logy when traced to the east and in the extreme eastern offshore Abu Dhabi are replaced almost completely by the Pabdeh Formation, which was laid down in basin centered east of the area. The Pabdeh offshore Abu Dhabi consists of more than 2200 ft of argillaceous limestones and shales. Hasa group Umm Er Radhuma It ranges in thickness from 1150 ft in the northwest to 1500 ft in the south and more than 2300 ft in the east. The UER indicates a widespread transgression at the beginning of the Paleocene. At the base, the formation is comprised of thin shales but the bulk of the UER consists have shelly and bioclastic limestones and dolomites, argillaceous in parts, representing shallow-water conditions. In some localities, such as Zakum and Umm Shaif, the initial shales of the UER are overlain by sabkha cycles, each cycle being terminated by thin anhydrite. Rus In the Lower Eocene a wide evaporitic platform existed over most of the Abu Dhabi region-giving rise to the evaporitic/carbonate sequence of the Rus Formation. The formation thickens from about 200 ft in the north to more than 840 ft in the south and consists dominantly of massive anhydrite representing sub aerial supratidal conditions. Minor argillaceous limestones at the base represent lagoonal conditions. Dammam A transgressive phase with less saline water in the Middle Eocene again brought about normal marine shallow shelf conditions and resulted in widespread deposition of the nummulitic carbonates of the Dammam Formation. The Dammam is made up of calcareous shales and argillaceous limestones in the lower part succeeded by foraminiferal packstones and grainstones representing very shallow high-energy shoal conditions and ending with sub tidal limestones, dolomites and subordinate shales.
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Upper Tertiary In the Upper Eocene and Lower Oligocene times, uplift and erosion affected the area. The uplift was more effective in Qatar and the western part of Abu Dhabi causing some erosion of the Eocene platform. Asmari A transgressive phase then followed resulting in the deposition of the Asmari Formation in the extreme east of Abu Dhabi. The Asmari is a shallow-water fossiliferous limestone deposited offshore in the Northern Emirates during the Oligocene. It is partly dolomitic and represents the shelf edge facies bordering the Pabdeh/Gurpi basin that developed east of the offshore area. Gachsaran The succeeding Gachsaran Formation of the Early Miocene age gradually thickens from about 400 ft in the west to nearly 2800 ft in the extreme east. It consists of three distinct units—
• An upper unit of anhydrites, shales, marl and carbonates. • A middle unit of dolomite and limestone, and • A lower unit of predominantly anhydrite with minor dolomite and terrigeneous clastics.
The Gachsaran was laid down in a restricted evaporitic basin with a depocentre in onshore Abu Dhabi. In the Upper Miocene/Pliocene times further uplift and erosion occurred over most of Abu Dhabi and adjacent areas. This is known as the Alpine Orogeny during which the Abu Dhabi landscape as we see it today was moulded together with the development of the Zagros and the Oman mountains. Severe erosion took place from the Oligocene to the Maastrichtian exposing the jebels, which outcrop in the Oman mountain area. Quaternary At the onset of the Quaternary, the Qatar peninsula was emerged and exposed to continuous erosion. Surficial deposits include pseudo-oolitic and conglomeratic limestones, beach gravels, silts, muds and eolian sands (deposited in thin sheets or forming dunes) and sabkha deposits.
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Hydrocarbon Habitat Abu Dhabi is by far the biggest oil producer in the UAE, controlling more than 85 percent of the UAE’s total oil output capacity and over 90 percent of its crude reserves. Principal offshore oil fields are Umm Shaif, Lower Zakum, Upper Zakum, Al Bunduq and Abu al-Bukhoosh. The main onshore fields are Asab, Bab, Bu Hasa, Sahil and Shah. Almost 92 per cent of the country's gas reserves are also located in Abu Dhabi and the Khuff reservoir beneath the oil fields of Umm Shaif and Abu al-Bukhoosh ranks among the largest single gas reservoirs in the world.
Figure 10- Fields of UAE
The best reservoirs are formed by the regressive high-energy ooidal grainstones terminating the carbonate cycles. Other favorable facies are the Rudist “ reefs” in particular cases. Khuff Formation (Permo-Triassic) At Umm Shaif field, the Khuff proved the presence of large volumes of gas composed predominantly of methane (89 %) with small amounts of N2, CO2, and C2-C5 hydrocarbon gases. Porosities are generally moderate to low and best developed (up to 20 %) in the uppermost part of the formation. Permeability is generally low, yet at some levels it is greatly enhanced by fractures. In Zakum field, the Khuff tested hydrocarbon gas with a high percentage of H2S (up to 35%), CO2 and N2. Porosities are generally lower than those of Umm Shaif field. Permeabilities are usually low with occasional high-permeability streaks.
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Araej Formation (Middle Jurassic) Hydrocarbons in Araej occur in the western and central parts of the offshore area. The Most important occurrence is in the Umm Shaif field where light oil (API gravity 350) occurs in all three members of the Araej Formation. In other structures such as Hair Dalmah, Jarnain, Satah, Ghasha and Zakum, only non-associated gas is present. In Umm Shaif, the Araej, especially the two upper members, is characterized by good reservoir qualities: porosity in range of 20-25% is developed with permeability occasionally exceeding 100 md in grainstones. In other structures, poroperm characteristics of the Araej are much lower. Arab Formation (Upper Jurassic) The Arab Formation forms the principal oil reservoir in the western half of the offshore area while in the onshore area the Arab equivalent is still in the exploration and evaluation stage. The most important Hydrocarbon occurrence in the Arab is in Umm Shaif. Oil (38o API) occurs in the four Arab zones. The lowermost D and C zones are the most important reservoirs (see fig 1-5). Porosities of upto 30% and permeabilities exceeding 100 md are variably distributed through the Arab reservoir in the Umm Shaif field. In the Bab Field, the Upper Jurassic Hith/Qatar Formation and the Fahahil Member have proved to be gas bearing so far. The main gas component is methane with H2S in the 28-32% range. The Arab Formation is hydrocarbon bearing also in Saath Al Raaz Boot, Ghasha-Bu Tini, Hair Dalmah, Dalma, Jarnain, Satah, Nasr, Abu Al Bukhoosh, Bunduq and Arzana. Thamama Group (Lower Cretaceous) Volumetrically the oil accumulations in the Thamama are the largest in Abu Dhabi. The Thamama hydrocarbon-producing zones occur in the onshore-developed fields of Bu Hasa, Asab, Bab, Sahil (see Fig) and in the offshore fields of Zakum, Mubaraz, Abu Al Bukhoosh and Umm Shaif. Onshore Abu Dhabi, oil is produced mainly from zones A, B and C and from the Shuaiba reef facies in the case of Bu Hasa field. The oil gravity is in the range of 39.2-40.7O API. Offshore Abu Dhabi in the Zakum field, oil occurs in all the six zones of the Thamama Group. The oil in the lowermost three zones is characterized by gravities in the 37-40O API range. In the upper three zones the API gravity is in the 32.6-35O ranges.
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Figure 11- Structural cross section of ADCO’s Fields Reservoir characteristics in the Thamama are very variable. Porosity in general is high, in some cases exceeding 30%, but permeability is normally moderate to low and is controlled by limestone texture. The Nahr Umr shales act as a regional sealing formation for the Thamama reservoirs. Mishrif (Middle Cretaceous) The Mishrif Formation receives special attention in the eastern offshore area where it is oil-bearing in Umm Addalkh field and Fateh field of Dubai. In Umm Addalkh, the Mishrif forms a reefal build up which pinches westwards against the dense limestone of the Shilaif and the overlying Laffan cap rock. Porosity, vuggy and fracture type, is moderate to good, but permeability is only moderate to low. The oil gravity varies from about 27 O API near the Oil/Water contact to about 30O API in the uppermost part. Halul (Upper Cretaceous) Small accumulations of heavy oil in the Halul Formation occur only in Mandous and Al Khair, northeast of offshore Abu Dhabi. In Mandous, a gas cap overlies the oil zone. Porosities in the Halul are moderate but permeability is low. Simsima Formation (Uppermost Cretaceous)
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The Simsima Formation is only oil-bearing in the undeveloped Shah Field. The Shah Simsima reservoir possesses moldic, vugular, and Karstic porosities associated with good permeabilities. Reservoir characteristics improve locally by fracturing. Simsima crude has a gravity of 30O API. Asmari Formation (Oligocene) A small heavy oil accumulation (24O API gravity) occurs in the uppermost part of the Asmari Formation in Mandous. This is the only oil accumulation in the Tertiary of Abu Dhabi.
Figure 12- Generalized lithostratigraphic column of Offshore Abu Dhabi
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Source of Oil To date detailed geochemical studies envisaged two principal source rocks: the Diyab Formation (offshore equivalent of the Dukhan), and the Shilaif Formation. The Mauddud shows some source rock characteristics onshore Abu Dhabi. The Diyab occurs in source rock facies only in the western offshore area where it consists mainly of restricted intra-shelf argillaceous limestone. It is at a late stage of maturity, i.e. post main oil generation. Kerogen in the Diyab Formation consists typically of oil-prone sapropelic material and the mean organic carbon content varies from 0.72% to 1.8%. In the offshore Abu Dhabi the Diyab is believed to be the major source for the Arab Oil and possibly the geochemically similar Thamama oil. But is the Diyab organically rich enough to have been the source of all the Thamama and Arab oils? The Diyab itself is capable of generating condensate and gas. The Dukhan Formation, the onshore equivalent of the Diyab, has poor to moderate total organic carbon content although a value of 1.6% at 12300 ft is recorded. The hydrocarbon generating potential of the Dukhan is very small and Kerogen consists mainly of inertinite. The Dukhan is at a high level of maturity. Geochemical studies have established that the Shilaif is a high quality source rock across the whole of Abu Dhabi. The Kerogen is oil prone sapropelic (30-50%) and total organic carbon content ranges from moderate to high, at some levels reaching 15%. The main constraint on the source potential of the Shilaif is its immature state in most of the area. On the other hand, the Shilaif has the potential to generate large quantities of oil if present at increased maturity off-structure. These are the site where regional dip or salt tectonics have taken the formation deep enough to become mature. The Shilaif is one possible source of onshore oil accumulations found in Abu Dhabi. The Shilaif is also believed to be the source of the oil in the Mishrif reservoir of Umm Addalkh. Other minor potential source rocks have also been identified. These include the Izhara Formation, which probably charged the Araej and Pabdeh/Gurpi, which could have sourced oil to the Halul and Asmari of Mandous.The Minjur Formation, which contains coaly material, rates as a gas source while the Jilh Formation also contains abundant humic Kerogen and is rated as minor source of gas. Regressive shales such as the Nahr Umr, Laffan and the intraformational marls and argillaceous limestone of the Thamama do not possess source rock characteristics. They are of limited thickness, organically lean and with little or no hydrocarbon-generating potential. Seals (Cap rock) There are two principal sealing formations, the Hith Anhydrite and the Nahr Umr Shales, which limit to a large extent vertical migration and hence oil and gas distribution. The Hith is ultimate cap rock for the Arab reservoirs. Its absence as in the eastern offshore area, justifies Arab oil absence. Where the Hith is present, the overlying Lower Cretaceous reservoirs are devoid of charge, as in western offshore (e.g. Bunduq, Arzana, Dalmah, Satah). There are exceptions, however, where the Hith is breached through faulting and Arab oil could escape upward (Abu Al Bukhoosh field).
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E R A M illio n Y r s P e r io d E p o c h
up A v gT h ic k .
F tT V D f t L i th o lo g y G e o lo g ic a l
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9 3 8 4 9 8 A n h y d r it ic -5 6 8 5 9 1 D o lo m ite1 0 8 6 4 71 0 8 6 5 75 8 6 6 75 8 6 7 2
7 0 8 6 7 71 5 8 7 4 7 A n h y d r ite8 4 8 7 6 26 4 8 8 4 64 0 8 9 1 0
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L im e s to n eA ra b D 3 L
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A ra b C 2A ra b C 2 D e n s e
A ra b C 3A n h y d r i te -5
A ra b D 2A ra b D 3 UA ra b D 3 M
A ra b B
Figure 13- Lithostratigraphic column of Umm Shaif field
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Umm Shaif Umm Shaif field is located in the Abu Dhabi offshore areas, about 20 miles northeast of Das Island. The picture below shows "ADMA Enterprise" at Umm Shaif One. Drilling started on January 14th, 1958 for this first wildcat well; oil was found there at about 5,500 feet in Thamama Zone I, i.e. in "the Lower Cretaceous Shuaiba Limestone” on March 28th, 1958. Though the results of Well No. 2 were disappointing, Well No. 3 was completed after finding oil at about 9,600 feet in the Arab Fm.
Figure 14- First rig at Umm Shaif
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Zakum Zakum field is located in the Abu Dhabi offshore areas, about 50 miles southeast of Umm Shaif, halfway between Das Island and the mainland. Zakum One began drilling in April 1963. The original Zakum collector platform has been extended into a super complex that is an archipelago of steel islands.
E R A M illio n Yr s P e r io d E p o c h
up A v gT h ic k .
F tL ith o lo g y G e o lo g ic a l
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Figure 15-Lithostratigraphic column of Zakum field
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Geology of Dubai General Geological Framework Thousands of feet of carbonate rocks with minor local facies variations deposited in a “Layer-cake” fashion from Upper Permian to Lower Cretaceous indicate a relatively stable shelf area of deposition in the Dubai area. At the close of the Lower Cretaceous a transgression marked the end of these stable conditions. The Nahr Umr shales deposited on top of the Thamama covers the whole area of the Northern Emirates. The Mauddud shallow-water limestone semi-regressive phase overlays the Nahr Umr shales. The Mauddud is of uniform thickness in the offshore field areas but thickens to the east and south of the fields. Subsidence of the Shilaif Basin occurred to the west of Dubai and the Shilaif (Khatiyah) bituminous oligosteginal limestone and shale sequence was deposited over the Mauddud. Concurrently the Mishrif began to encroach on the margins of the Shilaif basin in a major regressive phase. The high-energy shoal/reef complex prograded over its own talus to the west, northwest and southwest of the oil field areas towards the basin center. Movement of the deep-seated (Cambrian) salt plugs marked the end of the Middle Cretaceous and resulted in a major inconformity. Typical fault patterns developed as uplift intensified. Some of the porous Mishrif high blocks were quickly eroded and redeposited in lower block areas. This reworked rudist debris is a prime exploitation target but accurate fault location is as yet difficult to determine. The Laffan shale overlies the Middle Cretaceous unconformity, thinning south and finally disappearing in the Northern Emirates. It forms the cap rock of the Mishrif reservoirs of Dubai and is succeeded by the shallow-water limestone of the Illam (Halul). Above the Illam, a lower shale unit and an upper marl and mudstone unit typify Aruma deposition. At the end of the Cretaceous period plate movements led to major tectonic rearrangement in the Dubai area. What was formerly a stable shelf or near-shelf became a shelf-basin area with a North-west/south-east hinge line. The formation of this basin had begun during Aruma deposition due to renewed upward movement of deep-seated salt plugs. The climax of this crustal instability was the Zagros (Laramide) Orogeny, which caused nappe folding, and faulting in the Oman mountains. These had begun to form at the end of the Middle Cretaceous. From Upper Cretaceous until the Miocene times the Tertiary basin was the major feature of the Northern Emirates area, other than the continued growth of the Oman Mountains. In Late Miocene time renewed movement of deep-seated salt plugs resulted in piercement to surface forming the islands of the Arabian Gulf.
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Stratigraphy A typical section of Dubai area (Offshore) is displayed in Fig 1-9 and well correlation in Fig 1-10. Stratigraphic Reservoir Description Thamama (Lower Cretaceous) The beginning of the Lower Cretaceous marked the end of the evaporitic episode and the start of shallow-water carbonate deposition. This phase began with deposition of Thamama zone 6 oolitic packstone/grainstones, which varies in thickness from 0 ft in the west to 400 ft in the east. This zone, where developed, is an excellent reservoir. No commercial hydrocarbons have been found in this zone to date. Thamama zones 5 and 4 consist of hard and tight, pyretic, cherty mudstones with occasional streaks of dolomite and shale. Some porosity is present in zones 4A and 4B in pelletal wackestone/packstone, but does not contain hydrocarbons. Thamama zone 3 is divided into 8 porosity zones consisting of pelletal chalky wackestones/packstones with interporosity of tight mudstones with minor shale streaks. Zone 3G is the deepest to test oil; the main producer is zone 3A. Thamama zone 2 is a grainstone/packstone with occasional rudistid development near the top. Stylolites are characteristic of streaks of reduced porosity. Zone 2 becomes chalkier, stylolitic and finer grained in its lower part generally. This is the major productive Thamama zone. The base of the Thamama zone 1B corresponds to the base of the Shuaiba formation/top of Hawar shale in other areas. The Hawar equivalent is 55 to 60 ft thick. Zones 1A and 1B consist of chalky, pyretic, stylolitic wackestones/packstones which are locally dolomitic. Zone 1A thickens to the east as one approaches the Shuaiba barrier reef. Mishrif (Middle Cretaceous) The uppermost Middle Cretaceous began with a transgressive sea depositing the Khatiyah basal bituminous shale and mudstones. The Khatiyah (Shilaif) intra-shelf basin in the west was filled with this shale and mudstone as the contemporaneous Mishrif rudistid reef developed along the basin margins. As the reef complex grew out westwards, a backreef (lagoonal) facies became established behind the advancing front. The backreef section is the thickest in the east and thins to the west conforming the direction of reef growth. This progradation probably occurred in response to moderate basin subsidence (a slow rise in relative sea level) but with carbonate deposition greater than the rate of subsidence. The Mishrif advanced not only over the previous deposits of the Khatiyah, but also over its own fore reef section. Finally this advance was halted by a change in a palaeowater depth. This may have been a lateral change—a marked deepening towards the center of the subsiding basin. Alternatively, there may have been a sudden fall in relative sea level, the effect of which upon reef-forming organisms is well documented. These events resulted in a reef/fore reef section of porous and permeable rock overlying a rich source rock (Khatiyah). The back reef section has numerous rudistid patch reefs with reservoir qualities comparable to the main reef section. Stratigraphic trap possibilities are thus excellent in the back reef section. In addition the wedge edge of the Mishrif is an excellent Stratigraphic trap (e.g. Falah field).
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Illam (Upper Cretaceous) The Illam (Halul) limestone was deposited in a very shallow-water environment. It consists of stylolitic, pyretic, wackestones/packstones with miliolids, pellets and minor shales and argillaceous streaks. Porosity zones represent changes in the energy levels and consist of packstone/grainstones with occasional rudistid fragments. The Illam is a secondary reservoir in the Fateh field and contains non-commercial oil at SW Fateh and Sirri A, D, and C fields. The oil is very similar to that of the Mishrif and probably migrated upwards along fault zones. The Illam thins rapidly to the east and south to disappear onshore in the east. The uppermost horizons and the basal part of the Aruma shale have glauconite and occasional limonite with a trace of silica. An unconformity possibly exists therefore at the top of the Illam.
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Geology of the Northern Emirates Geological Overview Lack of available data precludes an in-depth review of the geology of the Northern Emirates. Only post – Jurassic information is available. Fig -16 is a schematic cross-section from northeast Abu Dhabi to the Oman Mountains foothills.
Figure 16- Generalized geological cross-section of the Northern United Arab Emirates
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Mesozoic Lower Cretaceous The Lower Cretaceous (Thamama group) is typified by broad shelf carbonate sedimentation. A series of minor transgressions and regressions caused cyclic deposition of widespread low- and high-energy carbonates. This cyclic deposition style has resulted in a number of porous high-energy carbonate reservoir units capped and sealed by dense open marine lime-mudstones. The first indication of the formation of an intracratonic basin occurs towards the end of the Thamama during the deposition of the Shuaiba. During this end phase the broad Arabian shelf area developed a shallow basin with minor ramifications extending into Dubai to the northeast and to Oman in the south. A peripheral shelf mostly accumulating quiet-water lagoonal sediments is separated from the basin by a narrow belt of high-energy sediments. Along this well-oxygenated high-energy zone rudists proliferated forming banks and bioherms. Major build-ups, up to 450 ft thick, developed preferentially over topographic highs along the shelf margin. There are some indications that similar rudistid bioherms developed along the eastern margin of the basin in the offshore Dubai area. Wells drilled in the central and western offshore Dubai penetrated a basinal facies (Bab Member), whilst most of the wells in the other parts of the Northern Emirates have encountered the quiet-water lagoonal environment associated with a shelf area. It is possible that a Shuaiba shelf edge runs through central offshore Dubai and the northeast of Abu Dhabi (see Fig 17)
Figure 17-Shuaiba facies relationships in the Northern Arab Emirates
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Middle Cretaceous The Nahr Umr transgressive event starting the Middle Cretaceous is represented by deep marine shales. The form of the underlying Shuaiba Basin to a great extent controls the regional thickness of the Nahr Umr. In Dubai, in the Northern Emirates and in the southeast of Abu Dhabi the Nahr Umr is typically 150 to 300 ft thick while in the basinal area (central Abu Dhabi) thickness of 600 ft are normal. Overlying the Nahr Umr the remainder of the Wasia Group exhibits a semi-regressive phase, which was never completed. A two-fold facies relationship was set up during the remainder of Wasia times:
• To the south-east in Oman a thick shelf carbonate section—the Natih Formation (Lateral and time equivalent of the Shilaif/Mauddud/Mishrif)
• In central onshore and offshore Abu Dhabi a thick basinal oligosteginal lime-mudstone and shale sequence.
The Mauddud Member (basal unit of the Natih) is thickly developed in Oman but only represented as a tongue of shelf carbonates in eastern Abu Dhabi and Dubai where it is confined to the periphery of the basin. The Mauddud is overlain by a basinal Shilaif facies in Dubai. This in turn is overlain by Mishrif shelf carbonates. The eastern limit of the Shilaif basinal facies is located in the central offshore Dubai area; the Shilaif is absent in the Northern Emirates to the east where the Mishrif directly overlies the Mauddud. Regional truncation at the top of the Wasia Group has progressively cut down the section to the extent that only Mauddud is preserved in many parts of the Northern Emirates. The depositional pattern that emerges during the Middle Cretaceous is one of a peripheral prograding Mishrif shelf area surrounding a basinal Shilaif area in central and offshore Abu Dhabi (Fig -18)
Figure 18-Mishrif facies relationships in the Northern United Arab Emirates
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Upper Cretaceous Down warping in offshore areas of the Northern Emirates gave rise to the deposition of the Aruma, a thick monotonous sequence of deep-water shales. The lower section of the Aruma is represented by exceedingly thin Laffan shale overlain by the Illam, a high-energy limestone (lateral equivalent of Halul in Abu Dhabi). In the Northern Emirates, the Illam limestone is thin or absent and the Aruma shale is frequently interbedded or replaced by a flysch sequence of eroded carbonates and silicified shales in areas adjacent to the Oman Mountains foothills. Limestone inclusions in the flysch range in age from Lower Jurassic to Lower Cretaceous but the matrix shale material has been dated as Campanian. The whole sequence is partly silicified and contains abundant Radiolarians indicating a deep bathyal depositional environment. Significant uplift along the fringe of the Oman Mountains towards the end of the Campanian resulted in the deposition of the Maastrichtian limestones similar in character to the Simsima of shelf areas of Abu Dhabi. Cenozoic Lower Tertiary In the Northern Emirates the shelf limestone/evaporitic Pabdeh basinal shales, reflecting the continuing basinal depositional environment set up in the Upper Cretaceous; represent sequence of Umm Er Radhuma, Rus and Dammam. Shelf carbonates similar to the Umm Er Radhuma have been recognized onshore Umm Al Quwain, on the periphery of the basin. Upper Tertiary A thick deep marine salt section of Oligo-Miocene age referred to as “massive salt” was deposited in remnant Pabdeh basin. The periodic closing of the Straits of Hormuz in reaction to the opening of the Red Sea during the Miocene and subsequent rotation of the Arabian plate towards the North west created: --- An environment in which deep-marine salts were precipitated from the super saline remnant of the Pabdeh basin whilst evaporates of the Gachsaran developed in Abu Dhabi. --- A northward plunge of the Qatar arch with a consequent southward uplift where fluviatile deposition prevailed with gravels, sands and conglomerates. The Gachsaran or Fars sequence represents the end-phase filling of the Pabdeh basin with deposition of halite and anhydrite with occasional dolomites and terrigeneous clastics.
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Oil in the United Arab Emirates The UAE contains proven crude oil reserves of 97.8 billion barrels, or slightly less than 10% of the world total. Abu Dhabi holds 94% of this amount, or about 92.2 billion barrels. Dubai contains an estimated 4.0 billion barrels, followed by Sharjah and Ras al-Khaimah, with 1.5 billion and 100 million barrels of oil, respectively. The majority of the UAE’s crude oil is considered light, with gravities in the 32O to 44O API range. Abu Dhabi's Murban 39O and Dubai's Fateh 32O blends are the UAE's primary export crudes. Most of the UAE’s oil fields have been producing since the 1960s or early 1970s. Proven oil reserves in Abu Dhabi have doubled in the last decade, mainly due to significant increases in rates of recovery. Abu Dhabi has continued to identify new finds, especially offshore, and to discover new oil-rich structures in existing fields. Under the UAE's constitution, each Emirate controls its own oil production and resource development. Although Abu Dhabi joined OPEC in 1967 (four years before the UAE was formed), Dubai does not consider itself part of OPEC or bound by its quotas. In response to the period of low oil prices in 1998 and early 1999, OPEC agreed in March 1999 to reduce output in an effort to shore up the price of crude. The UAE’s production quota was lowered to 2.00 million bbl/d. Actual production fell from a 1999 high of 2.25 million bbl/d in February 1999 to 2.05 million bbl/d in May 1999. After three rounds of OPEC quota increases in 2000, the UAE quota rose to 2.29 million bbl/d on October 1, 2000. Production in the third quarter of 2000 was 2.27 million bbl/d, and may climb to 2.35 million bbl/d in the fourth quarter of 2000. The UAE's total capacity is 2.60 million bbl/d, making it second only to Saudi Arabia for excess production capacity among OPEC member states.
Gas in the United Arab Emirates The UAE’s natural gas reserves of 212 trillion cubic feet (Tcf) are the world's fourth largest after Russia, Iran, and Qatar. The largest reserves of 196.1 Tcf are located in Abu Dhabi. Sharjah, Dubai, and Ras al-Khaimah contain smaller reserves of 10.7 Tcf, 4.1 Tcf, and 1.1 Tcf, respectively. In Abu Dhabi, the non-associated Khuff gas reservoirs beneath the Umm Shaif and Abu al-Bukhoosh oil fields rank among the world's largest. Current gas reserves are projected to last for about 150-170 years. Increased domestic consumption of electricity and growing demand from the petrochemical industry has provided incentives for the UAE to increase its use of natural gas. Over the last decade, gas consumption in Abu Dhabi has doubled, and is projected to reach 4 billion cubic feet per day (bcf/d) by 2005. The development of gas fields also increases exports of condensates, which are not subject to OPEC quotas.
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Geological Time Scale What is the origin of the geologic time scale? The first people who needed to understand the geological relationships of different rock units were miners. Mining had been of commercial interest since at least the days of the Romans, but it wasn't until the 1500s and 1600s that these efforts produced an interest in local rock relationships. By noting the relationships of different rock units, Nicolaus Steno in 1669 described two basic geologic principles. The first stated that sedimentary rocks are laid down in a horizontal manner, and the second stated that younger rock units were deposited on top of older rock units. To envision this latter principle think of the layers of paint on a wall. The oldest layer was put on first and is at the bottom, while the newest layer is at the top. Steno's principles allowed workers in the 1600s and early 1700s to begin to recognize rock successions. However, because rocks were locally described by the color, texture, or even smell, comparisons between rock sequences of different areas were often not possible. Fossils provided the opportunity for workers to correlate between geographically distinct areas. This contribution was possible because fossils are found over wide regions of the earth's crust. For the next major contribution to the geologic time scale we turn to William Smith, a surveyor, canal builder, and amateur geologist from England. In 1815 Smith produced a geologic map of England in which he successfully demonstrated the validity of the principle of faunal succession. This principle simply stated that fossils are found in rocks in a very definite order. This principle led others that followed to use fossils to define increments within a relative time scale.
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What do the divisions of the geologic time scale signify? The history of the earth is broken up into a hierarchical set of divisions for describing geologic time. As increasingly smaller units of time, the generally accepted divisions are eon, era, period, and epoch, age.
Figure 19- Geological Time scale (source www.geology.com)
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Phanerozoic Eon The Phanerozoic Eon represents the time during which the majority of macroscopic organisms, algal, fungal, plant and animal, lived. When first proposed as a division of geologic time, the beginning of the Phanerozoic (approximately 540 million years ago) was thought to coincide with the beginning of life. In reality, this eon coincides with the appearance of animals that evolved external skeletons, like shells, and the somewhat later animals that formed internal skeletons, such as the bony elements of vertebrates. The time before the Phanerozoic is usually referred to as the Precambrian, and exactly what qualifies as an "eon" or "era" varies somewhat depending on whom you talk to. The Phanerozoic also consists of three major divisions...the Cenozoic, the Mesozoic, and the Paleozoic Eras. The "zoic" part of the word comes from the root "zoo", which means animal. This is the same root as in the words Zoology and Zoological Park (or Zoo). "Cen" means recent, "Meso" means middle, and "Paleo" means ancient. These divisions reflect major changes in the composition of ancient faunas, each era being recognized by its domination by a particular group of animals. The Cenozoic has sometimes been called the "Age of Mammals", the Mesozoic the "Age of Dinosaurs" and the Paleozoic the "Age of Fishes". This is an overly simplified view, which has some value for the newcomer but can be a bit misleading. For instance, other groups of animals lived during the Mesozoic. In addition to the dinosaurs, animals such as mammals, turtles, crocodiles, frogs, and countless varieties of insects also lived on land. Additionally, there were many kinds of plants living in the past that no longer live today. Ancient floras went through great changes too, and not always at the same times that the animal groups changed. For our Purpose Cenozoic and Mesozoic will be briefly described.
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Cenozoic Era: The Cenozoic is divided into two main sub-divisions: the Tertiary and the Quaternary. Most of the Cenozoic is the Tertiary, from 65 million years ago to 1.8 million years ago. The Quaternary includes only the last 1.8 million years.
Figure 20-Cenozoic Era
Extensive Tertiary age rocks were recognized in the Paris Basin, which is the area around Paris, France. In the 1820's and 1830's Charles Lyell, a noted English geologist who had a great influence on Charles Darwin, subdivided the Tertiary rocks of the Paris Basin on their fossils. Lyell came up with an ingenious idea. He noticed that the rocks at the top of the section had a very high percentage of fossils of living Mollusc species. Those at the bottom of the section had very few living forms. He deduced that this difference was because of the extinction of older forms and the evolution of living forms during the time that the rocks were being deposited. He divided the Tertiary rocks into three sub-ages: the Pliocene, the Miocene, and the Eocene. 90% of the fossil molluscs in Pliocene rocks were living today. In the Miocene rocks, only 18% of the molluscs were of living species, and in Eocene rocks, only 9.5%. These subdivisions of the Tertiary have been correlated around the world using the fossil species in them. Rocks with the same species as Lyell's Eocene, are considered to be the same age as those in the Paris Basin. The same goes for the other subdivisions. Some time later it was noted that in areas other than the Paris Basin, there were rocks that seemed to be from time periods that were not represented in Lyell's sequence. This was because during those periods there had been no deposition in what would later be the Paris Basin. These two periods, later designated Oligocene and Paleocene, were inserted into the Tertiary in their proper places. Cenozoic In Abu-Dhabi Cenozoic formations include the Hasa group, Pabdeh, Umm Er Radhuma, Rus, Dammam, Asmari, Gachsaran and Mishan.
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Mesozoic Era The Mesozoic is divided into three time periods: the Triassic (245-208 Million Years Ago), the Jurassic (208-146 Million Years Ago), and the Cretaceous (146-65 Million Years Ago).
Mesozoic means, "middle animals", and is the time during which the world fauna changed drastically from that which had been seen in the Paleozoic. Dinosaurs, which are perhaps the most popular organisms of the Mesozoic, evolved in the Triassic, but were not very diverse until the Jurassic. Except for birds, dinosaurs became extinct at the end of the Cretaceous. Some of the last dinosaurs to have lived are found in the late Cretaceous deposits of Montana in the United States. The Mesozoic was also a time of great change in the terrestrial vegetation. Ferns, cycads, ginkgophytes, bennettitaleans, and other unusual plants dominated the early Mesozoic. Modern gymnosperms, such as conifers, first appeared in their current recognizable forms in the early Triassic. By the middle of the Cretaceous, the earliest angiosperms had appeared and began to diversify, largely taking over from the other plant groups.
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Triassic Period 245 to 208 Million Years Ago
In many ways, the Triassic was a time of transition. It was at this time that the world-continent of Pangaea existed, altering global climate and ocean circulation. The Triassic also follows the largest extinction event in the history of life, and so is a time when the survivors of that event spread and recolonized. The organisms of the Triassic can be considered to belong to one of three groups: holdovers from the Permo-Triassic extinction, new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. The holdovers included the lycophytes, glossopterids, and dicynodonts. While those that went on to dominate the Mesozoic world include modern conifers, cycadeoids, and the dinosaurs.
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Jurassic Period 208 to 146 Million Years Ago
Great plant-eating dinosaurs roaming the earth, feeding on lush growths of ferns and palm-like cycads and bennettitaleans . . . smaller but vicious carnivores stalking the great herbivores . . . oceans full of fish, squid, and coiled ammonites, plus great ichthyosaurs and long-necked plesiosaurs . . . vertebrates taking to the air, like the pterosaurs and the first birds . . . this was the Jurassic Period, beginning 210 million years ago and lasting for 70 million years of the Mesozoic Era. Named for the Jura Mountains on the border between France and Switzerland, where rocks of this age were first studied, the Jurassic has become a household word with the success of the movie Jurassic Park. Outside of Hollywood, the Jurassic is still important to us today, both because of its wealth of fossils and because of its economic importance -- the oilfields of the North Sea, for instance, are Jurassic in age.
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Jurassic in Abu- Dhabi The Hamlah and Izhara formations (lower Jurassic) consisting of dolomite interval overlain by argillaceous limestone and subordinate shales. The Araej formation and the Uweinat member (middle Jurassic), which are clean depositions of carbonates. The Diyab or Dukhan, Fateh, Arab, Hith and Asab formations (upper Jurassic), which are deposition of carbonates, anhydrite, wackestones and mudstones in the Diyab. The Arab formation is a well-defined cyclic sequence of carbonate/anhydrite.
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Cretaceous Period 146 to 65 Million Years Ago
The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants. The breakup of the world-continent Pangaea, which began to disperse during the Jurassic, continued. This led to increased regional differences in floras and faunas between the northern and southern continents. The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together. Cretaceous in the UAE The cretaceous rocks include the Thamama group, Lekhwair, Kharaib, Shuaiba, Wasia, Nahr Umr, Shilaif, Mishrif, ILAM, Tuwayil, Ruwaydha, Halul, Fiqa, Aruma, Laffan, Simsima and the Gurpi formations with compositions ranging from carbonates to calcareous shales.
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Sedimentary Rocks Definition Sedimentary rocks are those rocks, which form at or near the earth's surface at relatively low temperatures and pressures primarily by either: 1. Deposition by water, wind or ice 2. Precipitation from solution (may be biologically mediated); 3. Growth in position by organic processes (e.g., carbonate reefs) Rock Cycle
Figure 25- Rock Cycle
If we examine the rock cycle in terms of plate tectonics, as depicted in the figure above, we see that mafic (tholeiitic) igneous rocks form at sea floor-spreading ridges. Fluid intrusion of these rocks, both during and after formation, results in some low-grade metamorphism. As the rocks cool, and more magma is introduced from below, the plate is forced away from the spreading ridge, and acquires a sediment cover. As shown in the figure, in this case, the plate is eventually subducted under a continental plate. In the trench of the subduction zone, at relatively shallow depths, high pressure – low-high temperature metamorphism of the plate and its sediment cover occur. As the plate travels deeper, high temperature conditions cause partial melting of the crustal slab. Fluid intrusion plays a key role in partial melting. As the partial melt rises, and intrudes into the continental plate, the surrounding country rock is contact metamorphosed at high temperature conditions. This melt is either driven to the surface as volcanic eruptions, or crystallizes at depth to form plutonic igneous rocks. Sedimentary rocks form from the weathering, erosion, transport and deposition of arc material onto the continental platform and shelf.
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Igneous Rock Igneous rocks form by direct crystallization of minerals from a magma melt; we see a surface expression of magmatic activity at sea-floor spreading ridges and other rift zones, volcanic arcs (subduction zones) and hot spots (intraplate volcanism). Intrusive (plutonic) rocks crystallize at depth, whereas extrusive (volcanic and pyroclastic rocks) rocks crystallize after the magma reaches the earth's surface. In general, extrusive rocks have a finer grained texture than intrusive rocks. Igneous rocks are often classified according to the percentage of SiO2. The figure below is a general guide to igneous rock classification, showing the rock names and the differences in mineralogy.
Figure 26-– Igneous Rock classification
Metamorphic Rock Metamorphic rocks are formed where a parent rock, called the protolith, is subjected to changes in pressure, temperature or chemistry (such as addition of fluids). The rock cycle picture shows several areas where metamorphism is common. 1. In subduction zones: as the oceanic plate descends into the mantle, both the sediments and the basalt floor are subjected to high pressure and low to high temperature conditions. Fluids may play an important role chemically change the rocks' composition. 2. Adjacent igneous intrusions - contact metamorphism, where cooler (country) rocks are altered by contact with a hot igneous intrusion, is another common type of metamorphism. This type of metamorphism commonly produces a 3. At spreading centers (mid-ocean ridge): Fluids play an important role in hydrothermal alteration associated with magma emplacement on the sea floor at mid-ocean ridges. Note: You can read more about Ophiolite Sequence in the knowledge page.
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Sedimentary Rock origin Sedimentary rocks form from pre-existing rock particles - igneous, metamorphic or sedimentary. The Parent rock undergoes WEATHERING by chemical and/or physical mechanisms into smaller particles. These particles are TRANSPORTED by ice, air or water to a region of lower energy called a sedimentary basin. DEPOSITION takes place as a result of a lowering of hydraulic energy, organic biochemical activity or chemical changes (e.g., solubility). Once deposited, the sediments are LITHIFIED (turned into rock) through COMPACTION (decrease in rock volume due to weight of overlying sediment) and CEMENTATION (chemical precipitation in pore spaces between grains, which "glues" the rock together. The primary mineralogical and textural characteristics of the rock can be modified as the sediments are buried deeper in the earth's crust and undergo an increase in both temperature and pressure. This low pressure, low temperature changes are termed DIAGENESIS. Sedimentary rocks accumulate in Depositional basins. Sedimentary rocks may be: 1. Extrabasinal in origin - sediments formed from the weathering of pre-existing rocks outside the basin 2. Intrabasinal in origin - sediments form inside the basin; includes chemical, biochemical, and organic sedimentary rocks
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Constituents Of Sedimentary Rocks Sedimentary rock constitutes of three basic constituents:
1. Silicate fragments and associated grains (S), 2. Allochems (A), 3. Chemical and biochemical precipitates (P).
In this document we will concentrate on becoming familiar with the SILICICLASTICS (Sandstones) and CARBONATES (Limestones)
Figure 27-Constituents of sedimentary rocks
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Siliciclastic Sedimentary rocks Igneous and metamorphic rocks ('crystalline' rocks) make up about 95% of the earth's crust. All inorganic materials in the sedimentary environment are derived either directly or, more commonly, indirectly from igneous or metamorphic precursors (protolith). The total area of the earth above sea level, which is the area subject to erosion, is about 150,106 km2. Sedimentary Rocks are exposed over approximately 75% of that area, leaving only about 25% for igneous and metamorphic rocks combined. Thus, most terrigeneous (derived from the land) sedimentary grains represent recycled material, derived from the weathering and erosion of pre-existing sedimentary rocks, not directly from 'crystalline' precursors. Composition In sedimentary rocks the constituents are organized into framework grains, matrix and cement. Framework grains and matrix are allogenic (transported to the site of deposition), whereas cements are authigenic (precipitated at the site of deposition).
Figure 28-Composition of Siliciclastic sedimentary rocks
The three most common framework grain types are:
1. Quartz: both monocrystalline (single grains) and polycrystalline (e.g., chert) 2. Feldspar 3. Lithic Fragments (any pre-existing rock fragment)
Common cementing minerals include:
• The carbonate minerals: calcite, dolomite, ankerite and siderite • Quartz (as overgrowths on quartz framework grains), • Feldspars such as orthoclase (as overgrowths on detrital orthoclase grains) and albite
(neomorphic), and clays of the mica, smectite, kaolinite and chlorite groups. Note that clays occur both as terrigeneous matrix, the products of hydrolysis reactions in the soils of the source area for the sediments, and as diagenetic cements, which are the result of similar reactions occurring within the sediments themselves. Distinguishing the mineralogy of the matrix and cement clays requires the use of the scanning electron microscope and is beyond the (optical) scope of this project.
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Siliciclastic: Diagenesis Diagenesis: the physical, chemical or biological processes that turn sediment into sedimentary rock by modifying the mineralogy and/or texture. Diagenesis occurs where the mineralogy of the rock becomes unstable as a result of changes in the conditions or chemistry. Instability usually occurs at grain contacts and in pore space between the grains. Changes in pressure and temperature cause new minerals to form or preexisting minerals to become modified as the sediment (or rock) adjusts to new equilibrium conditions. There are 7 main diagenetic processes: Compaction Recrystallization Solution Cementation Authigenesis Replacement Bioturbation (To learn more about these see the Knowledge page). The degree to which each of these processes contributes to the diagenesis of any given sediment is controlled by such factors as Composition Pressure (due to burial) Temperature The composition and nature of the pore fluids Grain size Porosity, permeability The amount of fluid flow Note that any sediment that has been deposited is subject to diagenesis, not just siliciclastics. The diagenesis of carbonate rocks has also been studied in great detail.
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Siliciclastics: Provenance The provenance, or source area from which the sediment is derived, is the main control on sediment composition. The tectonic setting also has some influence on the accumulation of sediment and hence, its provenance. The mineralogy/petrology of a sedimentary rock provides information concerning the nature of the source rocks. The variation from the original host rock composition is dependent upon:
• Lithology of rocks in the source region. For example, if only quartz sandstone is exposed in the source area, the sediments derived from that source region will be quartz-rich.
• Climate and relief in area: controls weathering and erosion rates. In general, those areas
of high relief (especially those in which uplift is active) undergo rapid erosion. Flat areas serve as local base levels, places where potential energy is at a minimum. Here, the degree to which downward erosion and disintegration of a landscape will occur is reduced.
• The nature of sediment transport process (selective destruction of some minerals,
selective sorting by shape, size, specific gravity)
• Depositional environment: more selective sorting, alteration. Mixing of rocks from different sources.
• Diagenesis: all of the surface, sub-surface physical, chemical, and biological processes
that collectively result in transformation of sediment into sedimentary rock and modification of the texture and mineralogy of a rock.
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Siliciclastics: Texture The Siliciclastics are texturally described in the following ways: Grain size Grain shape Grain Size The scales used to define grain sizes in sediments and sedimentary rocks are grade scales; that is, imposing arbitrary subdivisions on a natural continuum creates them. The terminology, which is most familiar to us, is that of the Wentworth Scale, which includes the major classes: gravel, sand and clay, with their numerous subdivisions. Because the range of grain sizes found in nature is so large, a logarithmic scale, such as the Udden-Wentworth scale shown below, is more practical than a linear scale.
Figure 29- Udden-Wentworth Scale
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Grain Size Distribution The range in grain size in a siliclastic rock is commonly known as sorting. The sorting can be computed by from a histogram of the grain size distribution; it is most often estimated using a visual chart such as the one you see below. Sorting is one of the parameters used to determine Textural Maturity.
Figure 30- Grain size distribution (Sorting)
Grain Shape Grain shape comprises attributes, which refer to the external morphology of particles. These include surface texture, roundness and form. Surface Texture Surface texture refers to irregularities on the surface so small that they do not affect the overall shape of the grain. Features include various types of pits, frosting, etc. These features MAY have something to do with depositional environment. However, they are difficult to determine without an SEM (scanning electron microscope). We'll basically ignore the property in this course.
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Roundness Roundness is defined as the average radius of curvature of corners (ri in figure) to that of the largest inscribing circle (R in figure).
Figure 31- Roundness of grains
As you can see, that type of measurement is very tricky. Most geologists compare the roundness of the grains in a rock or sediment to prepared charts such as the one illustrated below.
Figure 32- Roundness of grains chart
Form Form refers to attributes involving the three dimensional morphology: i.e., the variation in proportion of the three axes, which define the geometric shape
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Sandstone Sandstone is the most common Siliciclastic sedimentary rock.
Figure 33- Sandstone specimen
Color: Very variable, frequently red, brown, greenish, yellow, gray, white. Texture: Medium-grained, usually well sorted, the grains are all about the same size, grains are sub-angular to rounded. Structure: Bedding usually apparent, current bedding and ripple marks are common, graded bedding may also occur. Concretions and fossils may also occur. Mineralogy: Quartz is the main component but it is often accompanied feldspar, mica or other minerals. Cementation: Grains may be cemented by silica, calcite or iron oxides. Note: Read, “Examination of Sedimentary rocks in hand specimens” in the knowledge section.
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Carbonates: Overview Carbonate rocks are those in which the matrix and framework are composed of greater than 50% carbonate minerals (this definition excludes cement). Unlike siliclastic sediments, where structures and textures reflect the physical factors in the depositional environment, the structures and Textures of carbonate rocks
Figure 34- Sediment is composed of shelly debris
Commonly reflect Intrabasinal, biological factors. The source for carbonate sediments is almost exclusively biological. Although carbonates form in colder water and more specialized settings such as 'hot' springs and caves, most thick buildups represent high organic accumulation in shallow, warm seas in areas removed from significant Siliciclastic input.
Figure 35- A brief description of differences between carbonate and Siliciclastic sediments.
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These shallow marine areas where carbonate sediments are created by calcareous organisms are referred to as the "carbonate factory" See Figure.
Figure 36- Carbonate Factory
Presently, we live in what is known as an "icehouse" world. Permanent ice is found at both poles, resulting in a strong equator to pole temperature gradient. Although carbonate-producing organisms are currently found all over the globe, due to temperature and light restrictions, significant carbonate production is essentially limited to ±40 latitude. However, this icehouse condition is relatively rare in the Phanerozoic, as shown in FIGURE below, and "greenhouse" conditions were more common.
Figure 37- Icehouse and Greenhouse conditions during ancient times
Common Carbonate-Producing Organisms An appreciation for the types and varieties of carbonate-producing organisms, and how they have changed in time and space, is important in order to be able to reconstruct Paleozoic and other ancient carbonate depositional environments. Both the organisms and types of carbonate buildups (reefs versus mounds) have changed through time, as shown in Fig - 1 and Fig-2 and Table below
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Figure 38- Relative importance of groups of Organisms to carbonate sediment
production through time Note – Description of the Organisms can be found in the definition and description page.
Figure 39- Carbonate buildup phase during the ancient geologic times
Spending some time and examining the morphology of the most common carbonate fossils. Familiarity with the basic fossil groups will help you give a more accurate name to a carbonate rock, as well as interpret the depositional environment. (Read the Definitions)
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Table 1- Source and type of sediments produced in modern and ancient carbonate environments
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Depositional Environment Carbonate depositional systems forming in the geologic past, and in modern settings, fall into three general types: 1.Ramp margins, 2.Rimmed margins and 3.Isolated platforms.
Figure 40- Ramp Margin
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Carbonate Chemistry Carbonates are composed largely of both calcium and magnesium carbonate minerals as well as carbon dioxide. As well, in most carbonate rocks, the silica composition is quite low. There are three main sedimentary carbonate minerals: aragonite, calcite, and dolomite. The composition of most carbonates lies somewhere between calcite (CaCO3) and dolomite (CaMg (CO3) 2. For example, most contain some magnesium, but not as much as pure dolomite. Carbonate sediment may be formed by biological processes as well as by physical weathering and erosion; however, the main control on the formation of these sediments is chemistry. The partial pressure of CO2 in the water greatly controls the amount of carbonate solubility. If the amount of CO2 in the water decreases, the carbonate equilibrium is altered and precipitation may occur.
Figure 43- Carbonate chemistry
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Mineralogy The carbonate minerals are divided on the basis of crystallography into three groups: Calcite Group (hexagonal) CaCO3 Dolomite Group (hexagonal) CaMg (CO3) 2 Aragonite Group (orthorhombic) CaCO3 Other minerals in minute quantities are Magnesite MgCO3 Ankerite Ca (Mg, Fe)(CO3) 2, Witherite BaCO3, Siderite FeCO3, Kutnohorite CaMn (CO3) 2, Strontianite SrCO3 Rhodochrosite MnCO3 Calcite Characteristics: ( Read more in Knowledge section) Usually white/colorless in hand sample; reacts strongly with HCl Colorless in plane polarized light Perfect rhombohedral cleavage Twin lamellae common, usually parallel to one edge or long diagonal of cleavage rhomb Commonly white
Figure 44– Calcite crystal structure and a Calcite crystal
Distinguishing calcite vs. dolomite: Calcite has lower indices of refraction Calcite more commonly twinned Dolomite more commonly euhedral Dolomite shows lamellae parallel to short or long diagonal of cleavage rhomb Calcite commonly colorless; dolomite may be cloudy or stained by iron oxide Dolomite less reactive with HCl
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Dolomite Dolomite is commonly found with calcite in limestone, dolomite, marble and related rocks. In evaporites, it may be associated with halite, sylvite, gypsum, calcite, anhydrite, and related minerals. It is also commonly found in metamorphosed carbonates. Often it is optically difficult to distinguish calcite and dolomite. Characteristics: Usually white/colorless in hand sample; reacts strongly with HCl only if powdered or if the acid is hot. Fe-rich varieties may become magnetic on heating. Colorless in plane polarized light, although weathered or altered iron-rich samples may be brownish due to the presence of iron oxides and hydroxides. Perfect rhombohedral cleavage Aragonite Aragonite is most easily confused with calcite and the two may be difficult to distinguish if fine grained. Characteristics: Usually white/colorless in hand sample; white streak; vitreous lustre. Colorless in thin section; effervesces vigorously in cold dilute HCl. Commonly inverts to its polymorph calcite. May be replaced by dolomite or other minerals
Figure 45 - Aragonite
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Classification of Carbonates Dunham classification scheme: the names used are straightforward, and the approach is similar to that of Siliciclastic rock classification.
Table 2– Dunham’s Classification of Carbonates
Mudstone Lime mudstones are composed of clay sized carbonate particles. These particles can be derived from the disaggregation of relatively complex organisms such as Halimeda, or they can be tests of organisms such as coccolithophorids or foraminifers. These rocks can be of any color, and, like siliclastic mud rocks the color is primarily determined by the red ox conditions at the time of deposition.
Figure 46- Lime Mudstone (chalk)
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Wackestone Wackestones are carbonate rocks, which are matrix-supported; i.e., there are more than 10% grains, but the fine grain clay size matrix essentially surrounds the grains.
Figure 47– wackestone
Packstone Packstones are grain-supported carbonate rocks; i.e., there is less clay size matrix than Allochems. Sometimes it is difficult to differentiate between a packstone and a wackestone, depending on the surface you are examining. Try and look at all sides of the rock! The two pictures below show a cut and a weathered surface. Notice the weathered surface allows a better view of the relationship between the grains and the matrix!
Figure 48- crinoidal packstone. The crinoid skeletal fragments are an off white to grayish brown color, whereas the matrix is yellowish brown.
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Grainstone Grainstones are grain-supported carbonate rocks with NO mud. Often the interstices of these rocks are filled with sparry cement. The photo below is a bit of a stretch for a carbonate because the original carbonate has been replaced by quartz. However, the concentrically laminated texture of the oolites has been preserved, making it a good photo for showing texture!
Figure 49- Silicified Oolitic Grainstone
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Boundstone Boundstones are carbonate rocks which are bound together in the original depositional environment by framework building organisms such as coral, encrusting organisms such as bryozoans or sediment trapping mechanisms such as those of the cyanobacteria. They can have complex structures, which show cellular detail, or appear laminated. The two photos below illustrate two of these types.
Figure 50- Algal Boundstone Coral Boundstone
This type of rock is more commonly
Known as a stromatolite.
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Textures of Carbonates Calcite and aragonite are primarily found in three forms:
1. Grains: silt size or larger aggregates of crystals. Five general types of grains are found as outlined below.
2. Mud: 1 - 5 µ size crystals) - texturally analogous to siliceous muds. This size class is commonly called micrite
3. Spar: coarser grained crystals, which appear translucent in, plane light (clear to white), 0.02-0.1 mm range. Crystals fill pore spaces, often due to recrystallization
Grains Also known as Allochems Five types of grains occur in carbonate rocks: 1. Carbonate clasts (rock fragments): These can be very difficult to differentiate!!
• Intraclasts - formed, transported and redeposited within the basin • Lithoclasts -formed outside of basin • Limeclasts -nonspecific origin • Ooliths: concentrically laminated carbonate structures, including: • Oolites -concentrically laminated structures, less than 2mm in diameter, thought to be
abiogenic in origin
Figure 51– Oolitic Limestone
2. Pisolites - same as oolites, but greater than 2mm in diameter 3. Oncolites - spheroidal stromatolites (> 1-2 cm) 4. Superficial oolites/pseudoolites - uncertain origin 5. Peloids: silt to fine grained sand sized carbonate particles with no distinctive internal structure; most thought to be fecal pellets
• Composite particles: crystal aggregates and crystalline lumps. These are irregularly shaped composite or aggregate grains, which are bound together by dark, organic rich, very fine-grained calcium carbonate. These grains tend to get distorted during diagenesis - rarely reported in ancient sediments.
• Skeletal particles: A. Whole microfossils, whole mega fossils, broken shell fragments. B. Skeletal and mud size carbonate grains can be derived from any organism (cyanobacteria, algae, a variety of invertebrates and vertebrates) with a calcareous skeleton or body parts. Types of fossils dependent on environment and geologic age. Groups and organisms variable, sizes range from micrite to "boulder".
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Facts about Carbonates
1. Carbonates cover 7% land surface 2. Greater than 50% oil and gas reservoirs worldwide are contained in carbonate rocks 3. 70% giant oil fields in Cretaceous rudistid reefs 4. In Western Canada, carbonate-hosted petroleum deposits are primarily found in
Devonian reefs. 5. Major economic importance as industrial "mineral" (agriculture stone, cement)
(Read More about Limestones in Knowledge section)
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Shales and Clays Shale is a common name applied to fine-grained varieties of sedimentary rock formed by the consolidation of beds of clay or mud. Most shales exhibit fine laminations that are parallel to the bedding plane and along which the rock breaks in an irregular, curving fracture. Shales are usually composed of mica and clay minerals, but the grains are so fine that the rock seems to have a homogeneous appearance, and individual minerals cannot be identified without the aid of a microscope. Most varieties of shale are colored in various shades of gray, but other colors, such as red, pink, green, brown, and black, are often present. Shales are soft enough to be scratched with a knife and feel smooth and almost greasy to the touch. All gradations in consistency exist between shales and clay; true shales differ from clays in their lack of plasticity in water. Many shales yield oil when distilled by heat, and the sedimentary rocks containing larger quantities of oil are called oil shales. Widely distributed throughout the world, oil shales are a source of oil for countries lacking petroleum. Note – See Mica in descriptive glossary
Figure 52- Shale
Figure 53- Mudstone
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Clays Clay is earth or soil that is plastic and tenacious when moist and that becomes permanently hard when baked or fired. Of widespread importance in industry, clays consist of a group of hydrous aluminosilicate minerals formed by the weathering of feldspathic rocks, such as granite. Individual mineral grains are microscopic in size and shaped like flakes. This makes their aggregate surface area much greater than their thickness and allows them to take up large amounts of water by adhesion, giving them plasticity and causing some varieties to swell. Common clay is a mixture of kaolin, or china clay (hydrated clay), and the fine powder of some feldspathic mineral that is anhydrous (without water) and not decomposed. Clays vary in plasticity, all being more or less malleable and capable of being moulded into any form when moistened with water. The plastic clays are used for making pottery of all kinds, bricks and tiles, tobacco pipes, firebricks, and other products. The commoner varieties of clay and clay rocks are china clay, or kaolin; pipe clay, similar to kaolin, but containing a larger percentage of silica; potter's clay, not as pure as pipe clay; sculptor's clay, or modelling clay, a fine potter's clay, sometimes mixed with fine sand; brick clay, a mixture of clay and sand with some ferruginous (iron-containing) matter; fire clay, containing little or no lime, alkaline earth, or iron (which act as fluxes), and hence infusible or highly refractory; shale; loam; and marl. Note – read more about weathering in descriptive glossary Clay Minerals Clay Minerals, group of fine-grained, earthy minerals that become plastic when mixed with small amounts of water, and which can be made permanently hard by baking. There is no universally agreed definition of "fine-grained": some authorities say that the maximum particle size for clay is 0.02 mm; others give 0.04 mm. Though first defined in terms of particle size, naturally occurring clay minerals have since been found to comprise mostly hydrous silicates of aluminum, sometimes containing appreciable amounts of other elements, notably magnesium, iron, calcium, sodium, and potassium. However, particle size is still significant in that any material ground down to the appropriate size is classified generically as clay. The name comes from the Old English clæg. As well as being related chemically, clay minerals are also similar structurally, being made up of minute flaky crystals that tend to form thin sheets. Because the crystals of clay minerals are so small-in some cases too small to be regarded as crystals at all-they cannot readily be separated for microscopic examination. As a result, precise identification of individual minerals has to be done using X-ray diffraction analysis or a scanning electron microscope. Clay minerals have a hardness of only 2 to 3 on Mohs scale. Clay minerals are most commonly formed by the weathering of igneous rocks (especially granites) containing feldspars, although they may also be produced from feldspars during diagenesis. The weathered material either stays where it is and gives rise to residual clays, or is transported by agencies such as water, ice, and wind, and then precipitated to form a sedimentary deposit. As a result of diagenetic processes, notably compaction, such sedimentary deposits may become hard. Clay minerals are the main constituent of most argillaceous rocks-the siltstones, mudstones, shales, and marls that make up more than half of all sedimentary rocks. The principal clay minerals are the kaolinite (or kandite) group, the montmorillonite (or smectite) group, the illite (or clay-mica) group, the serpentine group, and the vermiculite group.
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Kaolinite Group Kaolinite has the chemical formula Al4Si4O10 (OH) 8; its name derives from the Chinese kauling ("high ridge"), a reference to the hill near Jauchau Fu where it was first found. It has a relative density (specific gravity) of 2.6, and a hardness of only 2 to 2.5. Kaolinite is white when pure, but is often stained brown, reddish, or gray by impurities. It has a pearly lustre and is translucent. Kaolinite is the most important mineral of a group that includes the rarer dickite, nacrite, and halloysite; these differ from kaolinite and each other only by the way in which the silicate sheets are arranged. Kaolinite is formed from the alteration of feldspars in granite, either as a result of the weathering process or because of the hydrothermal action of gases on the feldspar. Important deposits are found in the United States, Britain, the Czech Republic, China, Germany, Italy, Spain, and France. Kaolinite is very important industrially. It is the main constituent of kaolin, or china clay, which is used in its pure form to make fine china and porcelain. Less pure varieties are used to make pottery, stoneware, and bricks, and as filler in paint and paper manufacture. In Britain, the famous china clay deposits around St Austell in Cornwall are among the best examples of hydrothermal action as a cause of kaolinite. Montmorillonite Group Montmorillonite has the chemical formula (NaCa) 0.33(Al, Mg) 2Si4O10(OH) 2.nH20 and was named after its discovery locality, Montmorillonite, France. It has a relative density (specific gravity) of 2.0 to 2.7, and a hardness of 2. It is typically white, gray, or buff in color but may have tints of yellow, pink, or blue. Montmorillonite has a pearly or dull lustre and is translucent. It is formed chiefly through the alteration of volcanic ash; other members of the group are derived from it by the substitution of other elements. It is the main constituent of the rock bentonite, most of which, for industrial use, is mined in Wyoming, Texas, and Mississippi, in the United States. Other producers of bentonite include Italy, Cyprus, and the Philippines. Montmorillonite absorbs water readily, swelling to a gel-like mass. This property makes it useful economically. Many industries, including textiles and chemicals, use it as an absorbent to refine out impurities. Montmorillonite is also used in drilling lubricants and as a plasticizer in molding sands used in foundries. Illite Group Illite has the chemical formula (K, H3O)(Al, Mg, Fe) 2(Si, Al) 4O10[(OH) 2,H2O], and was named after its discovery locality, Illinois, United States. It has a relative density (specific gravity) of 2.6 to 2.9, and is white, gray, or buff in color. It has a silky-to-dull lustre and is opaque. Illite and its associated minerals, formed by the substitution of other elements, are the main constituents of argillaceous rocks such as shales and mudstones. They are formed by the weathering or hydrothermal alteration of muscovite, or common mica, and feldspars. The illite group of minerals has no major industrial use. Serpentine Group Serpentine has the chemical formula (Mg, Fe, Ni) 3Si2O5(OH) 4 and is the basis of a group of clay minerals that are very similar in structure to the kaolinite minerals. It has a relative density (specific gravity) of 2.5 to 2.6 and a hardness of 2.5 to 3.5. It is typically green in color, but can be yellow, brown, or gray, and has a waxy lustre. It is transparent to translucent. Formed by alteration of olivine or pyroxene, serpentine can form large masses that may be cut and polished for use as an ornamental stone. It also exists in a fibrous form known as chrysotile, a form of asbestos.
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Vermiculite Group Vermiculite has the chemical formula (Mg, Fe, Al) 3(Al, Si) 4O10(OH) 2.4H2O; its name derives from the Latin for "to grow worms". It is the basis of a group of minerals that are very similar in structure to the montmorillonite minerals. The group includes the rare minerals palygorskite, attapulgite, and sepiolite, as well as meerschaum, a variety of sepiolite famed for its use in making pipes and pipe bowls. Vermiculite has a relative density (specific gravity) of 2.4, is yellow to brown in color, has a pearly lustre, and is translucent. Vermiculite is formed from the hydrothermal alteration or weathering of biotite. It is mined widely and is used in concretes and plasters, as a packing material, for insulation, and in agriculture. Many of its uses depend on its ability to expand up to 30 times its original volume when heated quickly to 250-300º C (480-570º F).
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Anhydrite THE MINERAL ANHYDRITE or ANGELITE Chemistry: CaSO4, Calcium Sulfate Class: Sulfates Uses: in the manufacture of some cement, a source of sulfate for sulfuric acid. Specimens Anhydrite is a relatively common sedimentary mineral that forms massive rock layers. Anhydrite does not form directly, but is the result of the dewatering of the rock-forming mineral Gypsum (CaSO4-2H2O). This loss of water produces a reduction in volume of the rock layer and can cause the formation of caverns as the rock shrinks. Good mineral specimens of Anhydrite were extremely rare dispite its common occurrence. However, fine specimens of Anhydrite have been found in Mexico and Peru that show good crystal habit, a nice blue color and even a play of light internally in the crystal. Lilac blue Anhydrate is sometimes called Angelite, for it's "Angelic" color. PHYSICAL CHARACTERISTICS:
1. Color is ordinarily white, gray or colorless but also blue to violet. 2. Luster is vitreous. 3. Transparency crystals are transparent to translucent. 4. Crystal System is orthorhombic; 2/m 5. Crystal Habits include the tabular, rectangular box formed by three pinacoids, often
elongated in one direction forming a prismatic crystal. Most commonly massive and granular.
6. Cleavage is in three directions forming rectangles, but perfect in one, very good in another and only marginally good in the third direction.
7. Fracture is conchoidal. 8. Hardness is 3.5 9. Specific Gravity is approximately 3.0 (average for translucent minerals) 10. Streak is white. 11. Associated Minerals are calcite, halite, and occasionally sulfides such as galena and
pyrite. 12. Other Characteristics: some specimens fluoresce under UV light. 13. Notable Occurrences include Mexico; Peru; Germany and New Mexico. 14. Best Field Indicators are crystal habit, rectangular and non-uniform cleavage and low
Some examples of Anhydrite crystals
Figure 54- Specimens
Marl Marl is a rock containingrocks during weathering;on top of each other. Evea new rock. The type of and on the nature of the ecarbonate, it is called ma Composition: SedimentaFormation: A form of caweathers into small cubicbecomes an earthy (argillThe most common use fo(lime).
This small hand specimen consists of a partly polished chunk of massive Anhydrite, which is sometimes known as Angelite. Where rough, it appears to be coated with a thin layer of white, massive calcite. Cutting has revealed the pale, gray-blue Anhydrite, which is dimly translucent and has been polished to a moderate gloss.
Piece has no visible crystal form. Three flat faces have been cut into the piece, and one slightly convex face has been polished to a moderately high gloss. It has the classic pale blue color with a tinge of gray that is its hallmark, and is essentially opaque at this thickness. Several fracture lines are visible in the polished face, and there is a thin crust of a dull, pale brown
This small hand specimen consists of 4 partly intersecting Anhydrite crystals. Two of these crystals are quite small and are generally heavily intergrown with the largest crystal, all are in very good condition, showing only minor damage if any, and their orthorhombic bladed form is very good. They have the standard pale blue color and almost silky, pearly luster of their species,
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clay and calcium carbonate. It is formed from the erosion of other as rocks erode, small sedimentary particles--sand, silt, and clay--pile up ntually, these sedimentary particles become compacted together to form
new rock that is formed depends on the original rock that was eroded rosion. If the new rock contains predominantly clay and calcium rl.
ry rock. lcareous mudstone. Usually shows only indistinct bedding planes and al pieces. If the amount of calcareous matter present increases, the marl aceous) limestone. r marl is as a fertilizer for soils that are deficient in calcium carbonate
Several intergrown Anhydrite blades make up this small hand specimen. , And like the others, is in very good condition, all have excellent orthorhombic form, with well-defined edges and clean faces that possess the standard pearly luster. All have the classic pale blue color of Anhydrite and are translucent. Besides a few small, thin crusts of almost massive pyrite, there is no other material present.
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Chert Chert is a very hard sedimentary rock that is usually found in nodules in limestone. Chert is light gray to dark gray in color. It probably formed from the remains of ancient sea sponges or other ocean animals that have been fossilized. Silica has replaced the tissue forming the sedimentary rock. Flint is a very dark form of chert. It breaks like obsidian with conchoidal fractures making it widely used by ancient people to make arrowheads, spearheads, and knives.
Figure 55- Chert
Pyrite THE MINERAL PYRITE
1. Chemistry: FeS2, Iron Sulfide 2. Class: Sulfides 3. Group: Pyrite 4. Uses: A very minor ore of sulfur for sulfuric acid, used in jewelry under the trade name
"marcasite" and as mineral specimens. Specimens Pyrite is the classic "Fool's Gold". There are other shiny brassy yellow minerals, but pyrite is by far the most common and the most often mistaken for gold. Whether it is the golden look or something else, pyrite is a favorite among rock collectors. It can have a beautiful luster and interesting crystals. It is so common in the earth's crust that it is found in almost every possible environment; hence it has a vast number of forms and varieties. Although pyrite is common and contains a high percentage of iron, it has never been used as a significant source of iron. Iron oxides such as hematite and magnetite are the primary iron ores.
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1. Color is brassy yellow. 2. Luster is metallic. 3. Transparency: Crystals are opaque. 4. Crystal System is isometric; bar 3 2/m 5. Crystal Habits include the cube, octahedron and pyritohedron (a dodecahedron with
pentagonal faces) and crystals with combinations of these forms. Good interpenetration twins called iron crosses are rare. Found commonly in nodules. Also massive, reniform and replaces other minerals and fossils forming pseudomorphs or copies.
6. Cleavage is very indistinct. 7. Fracture is conchoidal. 8. Hardness is 6 - 6.5 9. Specific Gravity is approximately 5.1+ (heavier than average for metallic minerals) 10. Streak is greenish black. 11. Other Characteristics: Brittle, striations on cubic faces caused by crossing of pyritohedron
with cube. Pyrite unlike gold is not malleable. 12. Associated Minerals are quartz, calcite, gold, sphalerite, galena, fluorite and many other
minerals. Pyrite is so common it may be quicker to name the unassociated minerals. 13. Notable Occurrences include Illinois and Missouri, USA; Peru; Germany; Russia; Spain;
and South Africa among many others. 14. Best Field Indicators are crystal habit, hardness, streak, luster and brittleness.
Figure 56- Pyrite Crystals
Iron Pyrite Composition: Iron Sulphide (FeS2) Crystal system: Cubic, commonly in cubes with striated faces, also in dodecahedra with pentagonal faces. Cleavage: None. It breaks with an irregular conchoidal fracture. Hardness: Just over 6. Specific Gravity: Around 5.0
Pictures – Pyrite Crystals
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Knowledge Limestone A sedimentary rock consisting largely of calcium carbonate (CaCO3), usually in the form of the mineral calcite. It may be produced biologically, chemically, or physically. Most of the world’s ocean floors contain limestone that formed from the shells of dead marine organisms (such as foraminifera) that drifted downwards through the water and settled on the sea floor. A particular form of biological limestone, generated mainly in shallow waters, is chalk, but not all limestone is chalk. Coquina and oolite are also organic forms of limestone. However, limestone may also be produced chemically, being forced to precipitate out from saturated seawater that can dissolve no more carbonate. In rarer instances it may also be produced physically, by the deposition of pre-existing limestone particles that have been washed down by rivers, although rivers would probably dissolve much of the limestone that entered them. Limestone may contain a small percentage of the calcium-magnesium carbonate mineral dolomite, CaMg (CO3)2, and still be called a limestone, or sometimes-dolomitic limestone. Moreover, unlike chalk, a particularly pure form of limestone, “limestone” may contain significant amounts of non-carbonate material such as silica, feldspar, clay, or pyrite. When heated to a high temperature in a furnace, limestone is converted to lime (calcium oxide, CaO), one of the chief uses of which is as a fertilizer. However, limestone is also useful in its own right, for example, as Portland stone, in building. Metamorphosed limestone is known as marble, and is used for building and as an ornamental stone. However, not all the so-called marble used by builders is of true limestone origin. See also Limestone Features.
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Calcite Calcite, mineral consisting largely of calcium carbonate (CaCO3). Next to quartz, it is the most abundant of the Earth's minerals. Crystallizing in the hexagonal system. Calcite is noted for its wide variety of crystalline forms. It also occurs in massive or cryptocrystalline formations. Examples of the crystalline varieties are nail head spar, dogtooth spar, satin spar, and Iceland spar. The last named is the only pure form of calcite found in nature. Limestone, chalk, travertine, Oriental alabaster, and marble are among the most common of the massive forms of the mineral. Calcite is also found as stalactites and calcareous tufas, forms deposited by mineral waters. It is also the chief component of many molluscs' shells.
Figure 57- Stalactites and Stalagmites Stalactites and Stalagmites “Hall of Giants” in Carlsbad Caverns, New Mexico, has both stalagmites and stalactites in its vaulted interior. The icicle-like formations grow as water containing dissolved rock seeps through the cave. As the water evaporates, minerals (primarily calcium carbonate) precipitate out, gradually forming stalactites on the ceiling and stalagmites on the floor. Columns are created where stalactites and stalagmites meet and grow together.
Colorless, with a hardness of 3 and a relative density of 2.72, pure calcite is readily identified by the ease with which it is cut or cleaved and by the rapidity with which it reacts with dilute Acids. Such contaminants as magnesium, ferrous iron, manganese, and zinc alter the properties of the mineral in varying degrees, depending on the amounts present.
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TEST MINERAL HARDNESS (H) SUPPLEMENTARY TESTS
Scratched by fingernail (H: 2+)
Calcite 3 Scratched by copper coin (H: about 3)
Fluorite 4 Scratched by penknife blade or window glass (H: 5.5)
Orthoclase (Alkali Feldspar) 6 Scratches a penknife blade or window glass (H: 5.5)
Diamond 10 Scratches all natural materials
Hardness is one of the main ways of classifying minerals, and is also one of the most useful ways of identifying them. The standard used is the scale developed in 1812 by Friedrich Mohs, which ranks ten test minerals according to their relative hardness (H). The scale represents a steady increase in hardness until H9, but diamond (H10) is ten times harder than corundum (H9) The scratch test is usually carried out with a known test mineral, otherwise a fingernail, copper coin, penknife blade, or window glass is used.
Figure 58- Mohs Scale of Hardness
Chalk Chalk is soft to very soft (powdery or crumbly), pure or nearly pure, porous, fine-textured form of marine limestone. White, light-gray, or sometimes buff in color, it consists largely of the mineral calcite, or calcium carbonate (CaCO3), that has formed by the accumulation, usually in shallow waters, of the tests (the hard parts) of dead, once-floating micro-organisms such as foraminifera and/or of tiny hard fragments of algae, such as coccoliths and rhabdoliths. It may also include the remains of such organisms as ammonites and echinoderms that lived on the sea floor.
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Figure 59- Chalk Cliffs Composed of the same form of limestone as the White Cliffs of Dover, the Cliffs of Normandy are a distinctive landmark on the French coastline. Geological evidence suggests that a land bridge connected the two landmasses during the Cretaceous Period. The arches shown here are a result of the action of water on softer sections of the rock.
Figure 60- Limestone Pinnacles in China Rising 30 to 182 m (100 to 600 ft) high, these limestone pinnacles, or mogotes, are found near the city of Guilin in the southern uplands of China. The karst area of southern China is the largest in the world and is noted for the extraordinary tower karst landscape created by
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the mogotes, steep-sided, residual limestone hills characteristic of humid tropical and subtropical areas
Figure 61- Limestone Features The often-distinctive landscape of limestone areas is caused by the solvent action of water on the rock, in a chemical weathering process known as solution. Some of the most characteristic features, such as solution caves and limestone pavements, form best in rock which is relatively thick, well-jointed, and hard.
Figure 62- Limestone Pavement, North Yorkshire
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This limestone pavement, above Litton dale in the Pennine Hills of northern England, shows clearly how the solution action of water has caused the widening of the joints in the limestone into channels, or grikes. The slabs of limestone separated by the grikes are called Clints. Towards the background the grikes have developed so much that the Clints have almost disappeared.
Figure 63- Dolines, Ural Mountains, Russia The limestone of the Middle Urals near Kungur, pictured here, is noted for the Dolines, or solution hollows, that pockmark the landscape. Dolines are formed by the solution action of water on limestone, often at the juncture of two or more joints in the rock. They may be associated, as here, with cave systems. In this case, solution action is combined with the collapse of the underlying limestone strata into the caves beneath.
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Stratigraphy Stratigraphy is branch of geology concerned with the study of rocks as layers or strata. Concerned mainly with sedimentary rocks, the subject has extended to all types of rocks and their connections, especially chronological, with one another.
Figure 64- Stratigraphy Geologists use the principles of Stratigraphy to unravel the geological history of a region by using information in the region’s rocks. In this cliff face, for example, the faults cut through the granite intrusions but not through the horizontal sedimentary rock. By relating the different strata to each other, geologists can deduce that the granite intrusions were present before the faults and are therefore older than the faults. In addition, the faults must have occurred before the sediments above were deposited and are therefore older than the horizontal sedimentary rocks.
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Ophiolite Sequence An oceanic spreading ridge is an area of rifting where two oceanic plates are being forced apart by addition of new magma from below. These areas can be located at major crustal plate boundaries such as the mid-Atlantic Ridge (separating the North American Plate from the Eurasian Plate), or in back arc basins such as parts of the Japan Sea. The types of rocks, which form at spreading ridges, are strongly influenced by both igneous and metamorphic processes. These regions are mixing zones, where both solids (lavas) and fluids from the Earth's crust and mantle interact with seawater, resulting in extensive low temperature and low-pressure alteration (prehnite-pumpellyite facies metamorphism) of existing minerals and precipitation of new ones. These areas are particularly important in terms of understanding the formation of some ore deposits! The characteristic assemblage of rocks, which form at spreading ridges, is called an Ophiolite sequence. The typical rock types are illustrated below, and include ocean sediments, mafic extrusive and intrusive igneous rocks, and ultramafic rocks. These rocks commonly have a metamorphic sole or base (not shown), which is thought to have formed during emplacement of the sequence onto continental lithosphere. These sequences are commonly revealed in areas characterized by accretionary tectonics, such as the western margin of North America.
Figure 65- Idealized cross section of an Ophiolite
The top of the Ophiolite sequence consists of fine-grained, ocean sediments (cherts, lime mudstones, etc.). Below this are PILLOW BASALTS, which form when hot magma is extruded onto the ocean floor. These rocks are often extensively altered by interaction with seawater. Sheeted or intruded dikes occur below the pillow basalts. These dikes represent the feeders to the sub aqueous pillow basalts, and typically intrude consecutively into one another before cooling is complete. Underlying the basalts is a layer of its intrusive equivalent - a gabbro. The upper part of the gabbro is typically not stratified, but the basal part of the gabbro commonly contains cumulate layers. The cumulates were the first formed crystals which sank to the base of the chamber. The base of the gabbro layer, where the cumulate gabbro passes into an ultramafic cumulate, marks the geophysical base of the crust known as the Moho. Here the density contrast causes a marked attenuation in seismic velocity. The petrological contact between the earth's crust and the mantle lies at the base of this ultramafic layer. The harzburgite layer at the top of the mantle is considered "depleted" - it is composed of only orthopyroxene and olivine, and lacks the typical clinopyroxene and spinel of the underlying fertile mantle rocks (the lherzolite).
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Examination of sedimentary rocks in hand specimens Here are some clues to identify most common particles: Mineral Grains: 1. Quartz: commonly transparent, but will appear dull and translucent if the grain surfaces are pitted. Grain shape is best seen on weathered, rather than fresh, sample surfaces. Vein quartz is usually white, due to presence of abundant fluid inclusions, but is also vitreous.
Figure 66– Vein Quartz grains
2. Feldspars: Potassium feldspars and Sodic plagioclase are most common.
• White to light gray colors may indicate Orthoclase or Sodic plagioclase. • Pink colors generally indicate either orthoclase or microcline. • Unaltered and unweathered feldspars mat be difficult to distinguish from quartz because
of their vitreous luster. If the sandstone was collected from a weathered outcrop, however, the feldspars will be altered on the surface to white or light gray clay. The grain shape indicates their origin and they should be listed as framework feldspars, NOT as matrix clay. Be careful, slightly weathered carbonate rock fragments (rare) or calcite cement patches can give similar white spots with a grain shape.
3. Micas: Both muscovite and biotite are common and relatively easy to identify. They are generally larger than adjacent quartz and feldspars, as their large surface area to weight ratio makes them easy to transport. Rock Fragments: 1. Chert: The most stable rock fragment, and thus the most common, even in mature sandstones. Commonly dark to light gray, less commonly white, black, brown, greasy luster. Very hard, makes up the “pepper” of the “salt and pepper” sandstones. Chert is included with monocrystalline quartz rather than with rock fragments in some, but not all, sandstones classification schemes. 2. Metamorphic rock fragments: Commonly black or dark to light gray, often with yellowish, greenish or brownish hues. Dull luster. Soft. Shape commonly rounded disk. Cleavage may show under the hand lens. Most common types are slate, phyllite and schist.
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3. Volcanic rock fragments: May be any color except blue. Dull to greasy luster, may be difficult to distinguish from chert. Hard (unless weathered), but not so hard as chert. 4. Carbonate rock fragments: Rather rare as sand size grains because of their instability under weathering conditions. Commonly gray, white or pale yellowish brown, with an earthy luster. Quite soft, sandstones containing carbonate rock fragments commonly contain calcite cement, making it impossible to test potential carbonate rock fragments for effervescence with 10% HCL. 5. Mudclasts: Common in some sandstone from fluvial, intertidal and submarine fan environments. Black, dark gray or brown. Soft. May be hard to distinguish from weathered slate and phyllite fragments. Diagenesis The physical, chemical or biological processes that turn sediment into sedimentary rock by modifying the mineralogy and/or texture. There are 7 main diagenetic processes:
1. Compaction 2. Recrystallization 3. Solution 4. Cementation 5. Authigenesis 6. Replacement 7. Bioturbation
Compaction Compaction is the process by which the volume of sediment is reduced as the grains are squeezed together. The weight of the overlying sediment and rock causes a reorganization of the packing of grains and the expulsion of intergranular fluid. As a result, the porosity of the sediment is reduced. The degree of compaction is controlled by such factors as grain shape, sorting, original porosity, and the amount of pore fluid present.
Figure 67- Diagenesis Compaction
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Recrystallization Recrystallization is a process in which physical or chemical conditions induce a reorientation of the crystal lattices of mineral grains. These textural changes cause the sediment to become lithified. It occurs in response to such factors as pressure, temperature, and fluid phase changes. It also occurs as a result of solution and reprecipitation of mineral phases already present in the rock. Solution Solution refers to the process in which a mineral is dissolved. As fluids pass through the sediment, the unstable constituents will dissolve and are either transported away or are reprecipitated in nearby pores where conditions are different. Pressure solution is a process, which occurs, as pressure is concentrated at the point of contact between two grains in the sediment. This causes solution and subsequent migration of ions or molecules away from the point of contact, towards an area of lower pressure where the dissolved phase can be reprecipitated.
Figure 68- Diagenesis Solution
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Cementation Cementation is the process in which chemical precipitates (in the form of new crystals) form in the pores of a sediment or rock, binding the grains together. Some common cement is quartz, calcite and hematite, but a wide variety of cements are known, such as aragonite, gypsum, and dolomite. Pressure solution produces locally derived cement, but many types of cement consist of new minerals previously in solution in the fluid phase. Cementation reduces porosity by filling in the pore spaces between the grains. See Fig.
Figure 69- Diagenesis Cementation
Authigenesis Authigenesis (neocrystallization) is the process in which new mineral phases are crystallized in the sediment or rock during diagenesis. These new minerals may be produced:
1. By reactions involving phases already present in the sediment (or rock) 2. Through precipitation of materials introduced in the fluid phase, or 3. From a combination of primary sedimentary and introduced components.
This process overlaps with weathering and cementation, usually involves recrystallization, and may result in replacement. Authigenic phases include silicates such as quartz, alkali feldspar, clays and zeolites; carbonates such as calcite and dolomite; evaporite minerals such as halite, sylvite and gypsum, as well as many others.
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Replacement Replacement occurs when a newly formed mineral replaces a preexisting one in situ. Replacement may be:
1. Neomorphic: where the new grain is the same phase as the old grain, or is a polymorph of it (i.e. albitization; replacing a grain with a more Na-rich plagioclase grain).
2. Pseudomorphic: where the old grain is replaced with a new mineral but the relict crystal form is retained,
3. Allomorphic: an old phase is replaced with a new phase with a new crystal form Although there are many replacement phases, dolomite, opal, quartz, and illite are some of the most important phases.
Figure 70- Diagenesis Replacement (Wood Opal)
Bioturbation Bioturbation refers to the physical and biological activities that occur at or near the sediment surface which cause the sediment to become mixed. Burrowing and boring by organisms in this way, can increase the compaction of the sediment and usually destroys any laminations or bedding. During bioturbation, some organisms precipitate minerals that act as cement.
Figure 71- Diagenesis Bioturbation
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Petroleum Petroleum, or crude oil, naturally occurring oily, bituminous liquid composed of various organic chemicals. It is found in large quantities below the surface of the Earth and is used as a fuel and as a raw material in the chemical industry. Modern industrial societies use it primarily to achieve a degree of mobility-on land, at sea, and in the air-that was barely imaginable less than a hundred years ago. In addition, petroleum and its derivatives are used in the manufacture of medicines and fertilizers, foodstuffs, plastic ware, building materials, paints, and cloth, and to generate electricity. In fact, modern industrial civilization depends on petroleum and its products; the physical structure and way of life of the suburban communities that surround the great cities are the result of an ample and inexpensive supply of petroleum. In addition, the goals of developing countries-to exploit their natural resources and to supply foodstuffs for the burgeoning populations-are based on the assumption of petroleum availability. Politically imposed restrictions on the oil supply drove up prices for periods during the 1970s. These prompted fears of a global scarcity of petroleum, but by the mid-1990s prices were down to half of what they had been ten years before. See Energy Supply, World. Characteristics All petroleum consists principally of hydrocarbons, although a few sulphur-containing and oxygen-containing compounds are usually present; the sulphur content varies from about 0.1 to 5 per cent. Petroleum contains gaseous, liquid, and solid elements. The consistency of petroleum varies from liquid as thin as petrol to liquid so thick that it will barely pour. Small quantities of gaseous compounds are usually dissolved in the liquid; when larger quantities of these compounds are present, the petroleum deposit is associated with a deposit of natural gas (see Gases, Fuel). Three broad classes of crude petroleum exist: the paraffin types, the asphaltic types, and the mixed-base types. The paraffin types are composed of molecules in which the number of hydrogen atoms is always two more than twice the number of carbon atoms. The characteristic molecules in the asphaltic types are naphthenes, composed of twice as many hydrogen atoms as carbon atoms. In the mixed-base group are both paraffin hydrocarbons and naphthenes. See Asphalt; Naphtha; Wax. How is Petroleum formed? Petroleum is formed under the Earth's surface by the decomposition of marine organisms. The remains of tiny organisms that live in the sea-and, to a lesser extent, those of land organisms that are carried down to the sea in rivers and of plants that grow on the ocean bottoms-are mixed with the fine sands and silts that settle to the bottom in quiet sea basins. Such deposits, which are rich in organic materials, become the source rocks for the generation of crude oil. The process began many millions of years ago with the development of abundant life, and it continues to this day. The sediments grow thicker and sink into the sea floor under their own weight. As additional deposits pile up, the pressure on the ones below increases several thousand times, and the temperature rises by several hundred degrees. The mud and sand harden into shale and sandstone; carbonate precipitates and skeletal shells harden into limestone; and the remains of the dead organisms are transformed into crude oil and natural gas. Once the petroleum forms, it flows upward in the Earth's crust because it has a lower density than the brines that saturate the interstices of the shales, sands, and carbonate rocks that constitute the crust of the Earth. The crude oil and natural gas rise into the microscopic pores of the coarser sediments lying above. Frequently, the rising material encounters an impermeable shale or dense layer of rock that prevents further migration; the oil has become trapped, and a reservoir of
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petroleum is formed. A significant amount of the upward-migrating petroleum, however, does not encounter impermeable rock but instead flows out at the surface of the Earth or on to the ocean floor. Surface deposits also include bituminous lakes and escaping natural gas. Asphalt Asphalt, black, cement-like material varying in consistency at room temperature from solid to semi-solid. It can be poured when heated to the temperature of boiling water and is used in surfacing roads, in lining the walls of water-retaining structures such as reservoirs and swimming pools, and in manufacturing floor tiles and roofing materials. It is not to be confused with tar, a black substance derived from coal, wood, and other substances. Asphalt is found in natural deposits, but almost all of the asphalt used commercially is now derived from petroleum. Straight-run asphalts, which are made up of the non-volatile hydrocarbons left after petroleum has been refined into petrol products, are used for paving. Air-blown asphalts, produced from petroleum residues at temperatures of from 204° to 316° C (400° to 600° F), are used to make roofing materials and similar products. A small amount of asphalt is "cracked" at temperatures of about 500° C (about 930° F) to make some insulation materials. Natural asphalt was used extensively in ancient times. Ancient Babylonians used it as a building material, and it is referred to several times in the Old Testament books of Genesis and Exodus as a caulking material (see Bitumen). Natural deposits of asphalt occur in pits or lakes as residue from crude petroleum that has seeped up through fissures in the earth. Typical of these deposits are the La Brea tar pits in Los Angeles, in which the remains of prehistoric flora and fauna have been found. A natural asphalt pool is Pitch Lake, Trinidad. Deposits of asphalt-impregnated rock, called rock asphalt, are found throughout the world. An asphalt deposit of some commercial importance is Gilsonite, also called uintaite, found in the Uinta River Basin of Utah in the southwestern United States and used in the manufacture of paints and lacquers. Bitumen Bitumen, any of various naturally occurring mixtures of hydrocarbons with their non-metallic derivatives. Crude petroleum, asphalt, and tar are bitumens, which are characteristically dark brown or black and which contain little nitrogen, oxygen, or sulphur. Commercially the term bitumen refers chiefly to hydrocarbons in a solid or semi-solid state, but in a wider sense it refers to all natural hydrocarbons, which may also occur in a liquid or gaseous state. Bitumen, distributed in various locations throughout the world, is found in all geological strata formed from the Precambrian to the Quaternary period. In antiquity bitumen was the Roman name for an asphalt used as a cement and mortar. Naphtha Naphtha, term applied to several volatile, flammable liquids, obtained by distillation of various organic materials and used as a solvent for fats, gums, and resins, particularly in the manufacture of varnishes and waxes and in the dry cleaning of textiles. Petroleum naphtha, or mineral naphtha, is obtained from petroleum as a crude distillate that is lighter than kerosene and has a lower boiling point. It contains a mixture of methane-type hydrocarbons. The distillates with lower boiling points than petroleum naphtha are called ligroin. Other forms of naphtha are crude naphtha, obtained from coal tar; shale naphtha, obtained from shale; and wood naphtha, obtained from wood. Solvent naphtha, used for dissolving rubber, is a high-boiling-point fraction distilled from coal tar. Wax Paraffin wax is a mixture of saturated hydrocarbons of high molecular mass, produced during the refining of petroleum. Most commercial waxes now come from petroleum.
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Fossils of the United Arab Emirates Overview The work so far undertaken by palaeontologists in the United Arab Emirates has shown the Emirates to have - for its geographical size - the most diverse palaeontological heritage of any country in the Arabian Peninsula. Fossils can be found ranging in time from nearly 300 million years ago to 8 million years. In addition, modern sedimentological processes such as the development of sabkha and carbonate environments with their associated fauna and flora found along the Arabian Gulf and Indian Ocean coastlines of the United Arab Emirates are now being re-studied to provide an important example of a modern environment that, in turn, can be compared with a similar environment in the geological past. Such studies can be of importance to future hydrocarbon exploration in the United Arab Emirates. Research Background Since 1979 an international team of palaeontologists and geologists have taken part in a research project, supported by the Abu Dhabi Company for Onshore Oil Operations (ADCO) and the UAE Ministry for Higher Education and Scientific Research, led by The Natural History Museum, London. Their work embraces three themes:
1. The geology and palaeontology of the Miocene (23 million to 5 million years ago) rocks found in the Western Region of Abu Dhabi.
2. The Eocene to Oligocene (30 to 50 million years ago) environment and fossils found at Jebel Hafit
3. The geology and palaeontology of the Cretaceous rocks (about 70 million years old) found in the Eastern Region of the UAE, bordering the foothills of the Hajar Mountains.
In addition, preliminary studies have been carried out on the 150 million year old fossils found in the Musandam region of the United Arab Emirates. The Jurassic/Cretaceous Sea - 150 million years ago Hidden in deep wadis in the Emirate of Fujairah lie outcrops of marine rocks deposited at the time that dinosaurs flourished - 150 million years ago. These limestones belong to the Musandam Group of rocks that range in time from 200 to about 97 million years. In the northern part of Musandam these limestones were deposited in a deep-water sea that shallowed towards the south. These beds are now exposed in the vicinity of Ras al-Khaimah. Later, perhaps 70 million years ago, these limestones suffered severe tectonic events associated with mountain building in the Musandam area and were broken up into huge pieces. These pieces, some forming blocks as large as 30 meters in diameter, were incorporated into sediments of a younger age to constitute a mix of Musandam Group rocks of varying Cretaceous ages. Jurassic/Cretaceous Fossils Various fragments of corals can be found but most are too poorly preserved to be identified. Other fossils are fragments of sponges, algae and bivalves. Overall, this geological time period in the United Arab Emirates requires further exploration and study.
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The following topic is good to go through and get a good picture of the microfossils of the Lower Cretaceous. It is taken from a study carried out on the Shuaiba in Shaybah (Saudi Arabia) Microfossils of the Shuaiba formation of Saudi Arabia.
Figure 72- Biostratigraphy of the Shuaiba formation in the Shaybah field (Late Aptian nannofossil evidence is confined to localities off the eastern flank of the Shaybah
Carbonate platform (const.) = consistent presence up succession; (inc.) = increase in abundance)
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Rudist Species from Shuaiba Formation
Figure 73- Plate 1 Rudist species from the Shuaiba formation of the Shaybah field
(1) Agriopleura cf. marticensis (length 52 mm) (2) Agriopleura cf. blumenbachi, elongated right valve, with trace of small, concave left valve (length 90 mm) (3) Glossomyophorus costatus showing sharply coiled left valve and almost rectilinear, elongated right valve (length 76 mm) (4) Oblique transverse sections of Glossomyophorus costatus left valves (max. width 40 mm) (5) Vertical section through Agriopleura cf. marticensis (6) Vertical sections of right and left valves of Glossomyophorus costatus in growth position (length 90 mm)
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Figure 74 - Plate 2 Rudist species from the Shuaiba forma
(1) Horiopleura cf. distefanoi, note distinctive invagination of conical Right valve and fragments of teeth (length 93 mm)
(2) Horiopleura cf. distefanoi, note the conical right valve and Dome-like left valve (length 70 mm)
(3) New genus, new species (Skeleton, in press) aff. Retha, note Strongly coiled left valve and rectilinear finely ribbed right Valve (max. width 37.5 mm)
tion of the Shaybah field
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Figure 75- Plate 3 Rudist species from the Shuaiba formation of the Shaybah field
(1) Offneria nicolinae, right valve (length 80 mm) (2) Offneria nicolinae, transverse sections of right and possibly left valves (max. width 15 mm) (3) Offneria murgensis, vertical sections of right valve showing septulae (length 60 mm) (4) Offneria murgensis, transverse section of left valve showing pallial canals (Max. diam. 42 mm) (5) Offneria murgensis, transverse thin-section of right valve showing pallial canals (Max. wall width 9 mm)
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Figure 76- Plate 4 (1) Lithocodium aggregatum (maximum fragment dimension 50 mm) (2) Palorbitolina lenticularis (diam. 2.5 mm) (3) Undifferentiated textularid (length 0.3 mm) (4) Praechrysalidina subcretacea (length 1.2mm) (5) Debarina hahounerensis (diam. 0.8 mm) (6) Lenticulina sp. (diam. 0.8 mm) (7) Vercorsella arenata (length 0.4 mm) (8) Hedbergella delrioensis (diam. 0.3 mm) (9) Hedbergella delrioensis (diam. 0.3 mm) (10) Finely structured echinoid spine (diam. 0.2 mm) (11) Highly ribbed echninoid spine (diam. 0.4 mm)
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Figure 77- Plate 4. (Cont) (12) Choffatella decipiens (diam. 1.2 mm) (13) Costate rotalid (diam. 0.8 mm) (14) Undifferentiated polymorphinid (length 0.7 mm) (15) Microsolenid coral (max. fragment width 80 mm) Plate 5. (next page) (1) Platy coral (max. fragment dimension 45 mm) (2) Lithocodium aggregatum (3) Salpingoporella dinarica (lumen diam. 0.3 mm) (4) Trocholina alpina (diam. 0.5 mm) (5) Palorbitolina lenticularis (diam. 2.5 mm) (6) Reophax sp. A (length 1.2 mm) (7) Reophax sp. B (length 0.4 mm) (8) Bigenerina sp. (length 0.3 mm) (9) Stilostomella sp. (length 0.4 mm) (bivalve width .2 mm) (10) Textularia sp. A (length 0.6 mm) (11) Ammobaculites sp. (12) Nodosaria sp. (length 0.4 mm) (13) Ovalveolina reicheli (diam. 0.5 mm) (max. fragment dimension 50 mm) (14) Bivalve within bored hole in coral; note geopetal sediment
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Figure 78- Plate 5 Various Shuaiba formation fossils typical of the “middle Shuaiba” lagoonal sediments in the Shaybah field (see previous page)
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Figure 79- Plate 6 Various Shuaiba formation fossils typical of the “upper Shuaiba” in the Shaybah field (see next page)
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Plate 6. (Previous page) (1) Agriopleura cf. marticensis (length 52 mm) (2) Palorbitolina lenticularis (diam. 2.5 mm) (3) Debarina hahounerensis (diam. 0.8 mm) (4) Cribellopsis neoelongata, vertical section (max. dimension 0.7 mm) (5) Cribellopsis neoelongata, transverse section (diam. 0.3 mm) (6) Praechrysalidina subcretacea (length 1.2 mm) (7) Nautiloculina sp. (diam. 0.5 mm) (8) cf. Pfenderina sp. (diam. 0.4 mm) (9) Undifferentiated rotalid (diam. 0.4 mm) (10) Vercorsella arenata (length 0.4 mm) (11) Coptocampylodon lineolatus (diam. 0.7 mm) (12) Salpingoporella dinarica (lumen diam. 0.3 mm) (13) Indeterminate dasyclad algae (length 1.2 mm) (14) Mesorbitolina texana (max. diam. 1.3 mm; from Nahr ’Umr formation) Note - Read more about it in Bio Facies of Shuaiba.
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Cretaceous Fossils of the Simsima Limestone Formation Much of this ancient marine fauna of crabs, sea-urchins, bivalve shells, corals and sea worms would be easily recognizable to us today. However, there are also fossils from some groups of animals that have completely disappeared, having become extinct at the end of the Cretaceous period. These include the ammonites, free-swimming relatives of bivalves and sea snails that possessed a spirally coiled chambered shell. Another group of marine animals that no longer exists today are the rudists, a highly specialized kind of bivalve with a large, horn-shaped lower valve that rested on or in the sediment. A rudist found by Natural History Museum palaeontologists from Jebel Rawdah has been given the new scientific name of Glabrobournonia arabica.
Figure 80- Cretaceous Fossils of the Simsima Limestone Formation
Corals were common in these waters, sometimes forming dense bush-like thickets or patch reefs and sometimes occurring as button-like individuals (some rudists resemble these corals) scattered across the ocean floor. On the edges of the shoals, massive brain corals are to be found. Probably the most unusual of all the corals is the fan-shaped and solitary Diploctenium, which attached itself to the sea floor by a thin stalk. Rather delicate for potential preservation as a fossil, it is only found in rocks deposited in the more sheltered environments. Of the 45 sea-urchins now known from the Simsima Formation, 14 species are new to science and some of them have been named after places where they were found or, in one instance, after a person who has helped the Natural History Museum team - Codiopsis lehmannae. Specimens named after places in the Emirates are Prionocidaris? Emiratus, Heterodiadema buhaysensis, Goniopygus arabicus, Circopeltis? Emiratus, and Petalabrissus rawdahensis.
UAE's Miocene rocks and their fossil record The Miocene rocks have been divided into two formations - the Baynunah and the Shuwaihat Formations named after the places where they are best exposed. The Shuwaihat Formation outcrops at sea level in some of the coastal exposures and mainly consists of fossilized Aeolian sands. These rocks seem to lack any fossils that can be used for dating purposes, but by careful Stratigraphic work it is believed that rocks of the Shuwaihat Formation might be of the same age as similar rocks found in Saudi Arabia. Thus, their age might be about 14 million years old. Confirming evidence for this date, plus or minus a few million years, comes from detailed analysis of the imprint of the earth's magnetic field on the iron minerals in the sandstone: magneto chronology.
Figure 81- Micene fossil
Vertebrate Fossils from the M In 1979 a palaeontologists from the Natur
Museum, London, visited Jebel Dhanna inWestern Region and discovered some fossweathering out of soft sandstones. These tbelonging to the first known fossil horses were from an extinct animal called Hippathe size of a small pony that had three toeits feet. Hipparion is unknown in the Old 11 million years but geological maps of thRegion indicated that the rocks were equito rocks previously described from Saudi dated at about 16 million years old. The hdisproved the evidence detailed on the geoand showed that the Emirate of Abu Dhabknown record of fossiliferous late Miocenthe whole of the Arabian Peninsula.
After the Aeolian sands of the Shuwaihat Formation had become rock, a regional river system evolved. The sands, gravels and clays deposited by this river form the Baynunah Formation that overlies the Shuwaihat Formation in the Western Region. The Baynunah Formation contains fossils and, so far, four species of invertebrates; two species of plants; three species of fish; eight species of reptiles; two species of birds and 31 species of mammals have been identified. Of these one species of fish and two mammal species are new to science. It is likely that the fossils from Abu Dhabi represent animals that lived during a time period of between 6 and 8 million years ago.
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Figure 82- Vertebrate fossil of Miocene
al History Abu Dhabi's il horse teeth eeth, from Arabia, rion, about s to each of World before e Western
valent in time Arabia and orse fossils logical maps i had the only e rocks from
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The Jebel Hafit Sea - 30 million years ago Jebel Hafit rocks are of lower Eocene to middle Oligocene age - 50 to 30 million years old. The Tethys seaway stretched across this part of the Emirates linking the Indian Ocean with the Mediterranean and the sea covered most of northern Africa, Jordan, Syria and Iraq. At this time most of the northern Emirates, Dubai and the Hajar Mountains were an island and marine life flourished in the shallow tropical Tethyan Sea around shoals and in lagoons. Microscopic animals make up the bulk of the marine fossils to be found at Jebel Hafit. These fossils are important to oil exploration as their presence in various time horizons in a bore hole core can tell the oil geologist the age of the rocks in which they are found. Distribution across the Middle East of one such microfossil found at Jebel Hafit, Nummulites, is important to the oil industry as the Asmari Limestone in which Nummulites species are found, is a key geological horizon. Jebel Hafit fossils
Figure 83- Nummulite of Jebel Hafit
Continental Movement and Ancient Arabian Fauna Just before the dinosaurs became extinct, 70 million years ago, the oceanic crust in what are now the foothills of the Hajar Mountains emerged above sea level. Around the islands formed by this event shallow water, marine carbonates were deposited. This habitat supported a unique and diverse assemblage of invertebrate animals ranging from echinoids and corals to bizarre molluscs called rudists. Their fossilized remains can now be found at Jebel Huwayyah, Jebel Rawdah and Jebel Buhays. About 23 million years ago, a land bridge, possibly located between Qatar and the coastal Fars region of Iran was formed. Land animals from both Africa and Asia had the opportunity for intercontinental dispersal via Arabia and it is probable that these changes to Middle East geography also changed the flow of river systems in northwestern Africa and in Mesopotamia allowing animals in freshwater habitats, such as fish, turtles, crocodiles and aquatic mammals, to disperse into new ecosystems. The remains of these animals can be found, but rarely, in the Western Region of the Emirate of Abu Dhabi. Consequently, the United Arab Emirates is palaeontologically unique for it has the finest locations for discovering Middle East Cretaceous marine invertebrates and late Miocene Arabian continental vertebrate fossils.
At the foot of Jebel Hafit, near where the road from the cement Works passes through a man-made gorge, numerous fossils of Nummulites, almost the size of a bottle-top, can be found. With Them, lying loose on the scree slopes, are fragments of branchingcorals, oysters and gastropods, rare sea urchins and, even rarer, remains of barnacles and crab claws. At the northern part of the Jebel north towards Al Ain, south of the Khalid bin Sultan road, eroded flanks of the anticline are exposed in the wadi. Here very Hard, massive limestones are preserved with their beds in a near vertical position. Numerous coral "heads" are found here, some Quite large about 60 centimeters in diameter.
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Desert of the United Arab Emirates The Desert Most of the surface of the present day UAE is a sand desert, stretching from the Arabian Gulf coast south to the unbroken and uninhabited sands of the Empty Quarter, and east to the gravel plains bordering the Hajar Mountains. The desert is a geologically recent feature, the result of prolonged sub aerial erosion and deposition in an arid environment. The sands overlie the thick, oil-rich sedimentary strata of the Arabian Platform, which constitutes the bedrock of most of the UAE, but the oil producing rocks, are nowhere exposed at the surface, and are known only from drilling.
Figure 84- Desert of UAE
Dune Patterns Sand dune formation is controlled by a combination of wind strength and direction, and sediment supply. In detail, however, the formation of dune patterns is complex and remains poorly understood. Within a given area the dune pattern may be quite regular, but also very intricate. Physical features are typically created on several different scales: giant sand ridges on a scale of hundreds of meters to a few kilometers, sand dunes measured in meters to tens of meters, and ripples on a scale of centimeters to a meter or more. This hierarchy can be readily observed in the deserts of the UAE. Since dune patterns vary with wind direction, seasonal or occasional variations in wind direction introduce new elements into the overall pattern. These elements may reinforce or cancel each other, in the same manner as ocean waves. In addition, because sand dunes cannot move or change as quickly as ocean waves, past history may play a significant part in what we see today. Despite relatively consistent prevailing wind directions in the present day UAE, dune patterns and alignment vary considerably from area to area. The Effects of Climatic Change The largest dune features of the present day UAE, including the major transverse dunes of Liwa and Manadir, the smaller eroded dune ridges of the Northern Emirates, and the longitudinal dunes of the southwest, are believed to date from the most recent glacial period, more than 10,000 years ago. A glacial origin for these major features is consistent with the fact that they do not seem to be aligned with today's prevailing winds.
In many areas near the coast, the sand is stabilized by vegetation, although the natural flora has been altered in recent times by extensive grazing of domesticated animals. Further inland the sands may be quite barren, as few plants can successfully colonize the mobile dunes.
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The present day wind regime appears to be transporting material from the coast inland and reworking the surface of the major earlier structures without, so far, removing or reorienting them. For example, one may observe between Abu Dhabi and the Liwa oasis that extensive tongues of pale sand resembling a choppy sea of dunes (aligned NE-SW) are filling in broad troughs between higher, flatter ridges of red sand (aligned WNW-ESE). The latter are known as suruq, or easy travel zones, and are interpreted as the eroded cores of older, larger ridges. Further inland, however, the major transverse dune ridges of Liwa and Manadir are neither in motion nor are they being eroded at the present time, although the smaller dunes on their surfaces conform to present day winds. Rainfall effects In addition to changes in wind regime, the UAE deserts have experienced changes in rainfall at various times in the past. This is indicated by the widespread occurrence of outcrops of lightly cemented, cross-bedded dune sands. These were cemented by the precipitation of calcium carbonate and other salts from ground water at a time when the water table was higher than it is today. Other evidence of higher rainfall in the past includes playa lake sediments, horizons containing abundant fossil roots and burrows, fossil reeds, crocodile bone, freshwater mollusc shells and trails, and fragments of ostrich eggshell. Occasional gravel deposits, often preserved as low, flat-topped hills or mesas, testify to the presence of rivers. Some of these features may be attributable to the alternation of so-called pluvial (wet) and inter-pluvial (dry) periods recognized elsewhere and believed to correlate with the stages of Pleistocene glaciations. Arid conditions in the UAE predated the Pleistocene, however. The widespread Miocene deposits of the Baynunah Formation (c.6-7 million years old) in the west of Abu Dhabi are interpreted as a major river system that watered a semi-arid, subtropical savannah. The Baynunah formation contains the fossilized remains of early relatives of elephants, hippopotamus, horses, cows, crocodiles, turtles and other animals. The intervening Pliocene is not known from the UAE, but was a period of drought in both East Africa and the Mediterranean. Sabkha Environments Sabkha is the Arabic term for low-lying saline flats subject to periodic inundation. Three types are recognized, based on their environment of formation. All are found in the UAE. Coastal sabkha, as the name implies, forms at or near the marine shoreline. Fluvio-lacustrine (i.e. river-lake) sabkha is formed in association with riverine drainage patterns in arid areas. Inland or interdune sabkha is found in low-lying basins within the sand desert. All sabkhas share certain characteristics. Although they are restricted to hot, arid regions, the sabkha surface is always very close to the local water table, usually within about a meter. Groundwater is drawn towards the surface by capillary action and evaporates in the upper subsurface in response to the high temperatures. There it deposits dissolved salts, including calcium carbonate, gypsum (CaSO4-2H2O), anhydrite (CaSO4) and sodium chloride or halite (NaCl), which precipitate in that order. These salts create a hard, impermeable crust in a zone about half a meter below the surface. This crust, along with high salinity, discourages all plant growth. The crust also impedes the drainage of surface water, so that after rains the sabkhas flood. The surface water then evaporates over time, often leaving behind a dazzling white crust of salt.
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Descriptive Glossary Evaporite A natural salt or mineral deposit formed by evaporation of water. A Sedimentary rock formed over geologic time from the residues left as salty waters of ancient seas or lakes evaporated in arid locations. Limestone, dolomite, gypsum, halite, and many other minerals are common constituents of evaporites, which occur on all continents and are often associated with deposits of gas and oil. Sabkha Sabkha is an arabic name for a salt-flat that has come into general use in sedimentology following classic research in the United Arab Emirates of the Arabian Gulf in the 1960s and later. They are flat and very saline areas of sand or silt lying just above the water table and often containing soft nodules and enterolithic veins of gypsum or anhydrite. A thin crust of halite and gypsum may be present in some parts. Many ancient evaporites show sedimentary feature of sabkhas, such as gypsum nodules.
Figure 85- Sabkha
Fossil The remains or impression of a prehistoric plant or animal, usu. petrified while Embedded in rock, amber, etc. Macroscopic organisms 1. Visible to the naked eye. 2. Regarded in terms of large units.
Floras The plants of a particular region, geological period, or environment.
Fauna The animal life of a region or geological period.
A supratidal part of a large coastal sabkha at Umm Said in Qatar. This particular area is the remains of a lagoon indirectly filled with Siliciclastic sand of Aeolian origin, originating from some large barchan sand dunes. The flatness is controlled by the content of capillary moisture from the water-table, which is only about half a meter (one and a half feet) down, keeping the sand damp and firm and preventing it from being blown away.
A lower part of the same sabkha where a thin halite crustes is developed. The halite is empheral and easily dissolved by a rare flood of rain.
Oolite Limestone made up of small spherical particles of calcium carbonate, resembling eggs (Greek, oon, an egg). Each particle has been called an oolith or ooid; the rock is sometimes known as oolith and the individual particles as oolites. Individual grains vary from 0.25-2.0 mm but are commonly 0.5-1.0 mm in diameter Mollusc Any invertebrate of the phylum Mollusca .
Figure 86- Bivalve Mollusc
Dinosaurs An extinct reptile of the Mesozoic era, ofte
Figure 87- Dinosaur Shapes and SizesDinosaurs varied greatly in size and shapto a length of 24 m (80 ft), to the Compsoabout the same size as a modern-day go
Bivalve Mollusc Clams have long been one of the most popular of the edible shellfish. Referred to as bivalve molluscs because of the two valves, or shell-halves, that enclose the body, these small filter-feeding animals are commonly found in intertidal areas throughout the world. Strong internal muscles, a hinge ligament, and a calcified hinge at the apex of the shell allow the clam to protect itself against many types of predator by keeping the shell tightly closed. The prominent growth rings found on the outer surface of the clamshell are useful in determining the clam’s age.
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n of enormous size.
e, ranging from the giant Apatosaurus, which grew gnathus, a small predator about 60 cm (2 ft) tall, or ose.
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Terrestrial vegetation 1. Of or on or relating to the earth; earthly. 2. A) of or on dry land. B) Zool. living on or in the ground; not aquatic, arboreal, or aerial. C) Bot. growing in the soil; not aquatic or epiphytic.
Ferns Common name for any of a group of cryptogamous (spore-producing) vascular plants. The fern group (class) contains about 350 genera; estimates of the number of species range from 9,000 to 12,000. Ferns are found throughout the world
Figure 88- Ferns
Cycads Common name for any of a group of three families of slow-growing palm-like plants. Today only ten genera and 106 species of cycads occur, but during the Age of the Dinosaurs, the Jurassic period, some 200 million years ago, they were the dominant plant life. Cycads are primitive gymnosperms (“naked seed” plants) with motile sperm cells, producing exposed seeds in cone-like clusters at the apex of the plants.
Figure 89- Cycads
Ginkgophytes Ginkgo, genus of deciduous trees; the maidenhair tree is the only living representative of its family and order, although other plants of this order were abundant in the Mesozoic era (about 245 million to 65 million years ago)
Cycad The palm-like cycads are not palms at all, but very primitive plants that were the dominant form of vegetation during the age of dinosaurs. They now appear in tropical, subtropical, and warm temperate areas. The plants’ attractive frond-like leaves have made them an important horticultural species.
Fern Ferns are considered some of the oldest land plants on earth, dating from 200 million years ago. Ferns are cryptogamous, or spore-producing, plants. Found worldwide, ferns are capable of growing in soil, water, on rocks, or on other plants. They range in size from a few centimeters to nearly 24 m (80 ft) in height. The underground stems and the fronds, or leaves, of some fern plants are edible.
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Figure 90- Ginkgo
Bennettitaleans 1. A) any stiff grass of the genus Agrostis. B) Any of various grass like reeds, rushes, or sedges.2. A stiff stalk of a grass usu. with a flexible base.
Gymnosperms Gymnosperm (Greek gumnos, “naked”; sperma, “seed”), common name for any seed-bearing vascular plant without flowers. There are several types: the cycad, ginkgo, conifer, yew, and gnetophyte. The gymnosperms include the most ancient of the living seed plants; they appear to have arisen from fern-like ancestors in the Devonian period (about 408.5 million to 362.5 million years ago). Scientific classification: Gymnosperms are contained in four divisions: Cycadophyta, Ginkgophyta, Pinophyta, and Gnetophyta.
Angiosperms (Greek aggeion, "vessel"; sperma, "seed"), common name for the division comprising the flowering plants, the dominant form of plant life. Members of the division are the source of most of the food on which human beings and other mammals rely and of many raw materials and natural products. Included in the division are most shrubs and herbs, most familiar trees except pines and other conifers, and specialized plants such as succulents, epiphytes, and aquatic types.
Pangaea (Greek, “All Land”), the name today given to the supercontinent that existed during the late Palaeozoic and early Mesozoic eras (about 300 million to 200 million years ago), and which comprised two large continental masses: Gondwanaland to the south and Laurasia to the north. In 1912 the German meteorologist Alfred Wegener developed the theory of continental drift: that the continents as we know them emerged from the breaking up of one supercontinent—Pangaea Lycophytes Lycopsid, common name for any moss-like vascular plant in the division (class) that contains the clubmosses, spike mosses, quillworts, and many extinct orders. Lycopsids are vascular plants with small, simple leaves. Spore-producing bodies (sporangia), when present, are borne at the base of the upper side of the leaf. Tree-sized lycopsids made up much of the forests of the Carboniferous period, but present-day species are small plants often mistaken for unrelated mosses and seedling conifers.
Ginkgo The ginkgo, or maidenhair tree, is believed to be one of the most primitive living plants. Characterized by bright green, two-lobed leaves, this deciduous gymnosperm grows to a height of 30 m (100 ft). The female ginkgo produces a foul-smelling fruit with an edible kernel during the late summer or early autumn.
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Scientific classification: Lycopsids make up the class Lycopodiatae.
Figure 91- Club Moss Glossopterids The Glossopteridales are an extinct group of seed plants that arose during the Permian on the great southern continent of Gondwana. These plants went on to become a dominant part of the southern flora through the rest of the Permian, though they dwindled to extinction by the end of the Triassic Period.
Figure 92- Fossilized Glossopterid leaf
The most frustrating aspect of glossopterid paleobiology is that no one is really certain what these plants looked like. Large portions of plants have never been preserved intact, and so reconstructing them has been done from rather tiny pieces. Our best guess is that they were large shrubs or small trees, perhaps a bit like a magnolia or Gingko. Dicynodonts An extinct group of mammal-like reptiles.
Figure 93- Dicynodonts
Club moss The club moss is one of approximately 200 species of clubmosses ranging from arctic regions to the Tropics. The club moss is common to open, dry woodland areas and open, rocky spaces. Although some of the temperate woodland species form large mats on the ground, most of the tropical species grow on trees.
These animals lived from approximately 260 million years ago until 225 million years. The most distinctive feature of dicynodonts organization was that they were herbivorous animals, feeding on the various kinds of plants that were available in the Late Permian and Triassic. The skull usually bears no teeth, but is equipped with a horny beak for cropping vegetation.
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Ammonites Ammonite, common name for an extinct group of cephalopods that usually had a tightly coiled, spiral-shaped shell. These squid-like animals appeared during the Devonian period approximately 400 million years ago and died out along with the dinosaur lineages at the end of the Cretaceous period 65 million years ago. Scientific classification: Ammonites belong to the phylum Mollusca, the class Cephalopoda, and the subclass Ammonoidea.
Figure 94- Ammonite
Feldspar Feldspar is the most abundant mineral in the world, making upearth’s crust. This specimen contains two different forms of fel
Amazon stone) and white orthoclase.
Figure 95- Feldspar
Jurassic Ammonite Now extinct, ammonites were chambered molluscs common in the Jurassic era (about 208 million years ago). Many had hard, coiled shells. The animal added chambers to the shell as it grew, actually living only in the chamber closest to the opening. This well-preserved fossil shows the layer of mother-of-pearl that coated the shell. Historically, ammonites have been used for decoration. Palaeontologists use certain ammonites to date rock formations.
nearly half of the volume of the dspar: green microcline (also called
Feldspar Feldspar is the most abundant mineral in the world, making up nearly half of the volume of the earth’s crust. This specimen contains two different forms of feldspar: green microcline (also called Amazon stone) and white orthoclase.
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Ceratopsian Group of herbivorous (plant-eating) dinosaurs that lived during the Cretaceous period, more than 65 million years ago. In all but the earliest species of the ceratopsian group—to which Triceratops belonged—one or more horns protruded from the front of the skull, and all ceratopsian had a parrot-like beak formed by a unique bone, the rostra. The ceratopsian appear to have migrated east to North America, where they became extinct at the close of the Cretaceous period.
Scientific classification: genus Triceratops, an ornithischian (bird-hipped) dinosaur of the suborder Ceratopsia.
Pachycepalosaurid Dinosaur of the cretaceous period. Plate tectonics Theory of global tectonics (geological structural deformations) that has served as a master key, in modern geology, for understanding the structure, history, and dynamics of the Earth’s lithosphere, which includes the crust. The theory is based on the observation that the solid layer of the Earth’s lithosphere is broken up into about a dozen semi-rigid plates. The boundaries of these plates are zones of tectonic activity, where earthquakes and volcanic eruptions tend to occur.
Subduction zone The sideways and downward movement of the edge of a plate of the earth's crust into the mantle beneath another plate. The ultimate cause of plate tectonic quakes is stresses set up by movements of the dozen or so major and minor plates that make up the Earth's crust. Most tectonic quakes occur at the boundaries of these plates, in zones where one plate slides past another—as at the Pacific Rim and at the San Andreas Fault in California—or is subducted (slides beneath the other plate). Subduction-zone quakes account for nearly half of the world's destructive seismic events and 75 per cent of the Earth's seismic energy
Plutonic igneous rocks Plutonic rocks, such as granite and syenite, were formed from a magma buried deep within the crust of the Earth. The rocks cooled very slowly, thus permitting large crystals of individual minerals to form.
Volcanic rocks Typified by basalt and rhyolite, were formed when the molten magma rose from a depth and filled cracks close to the surface, or when the magma was extruded upon the surface of the Earth through a volcano. Subsequent cooling and solidification of the magma were very rapid, resulting in the formation of fine-grain minerals or glass-like rocks.
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Pyroclastic rocks Of or formed from fragments of rock from a volcanic eruption.
Pyroclastic flow A dense mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and often flowing at great speed. Protolith The unmetamorphosed rock from which a given metamorphic rock was formed. For example, sandstone is the protolith of quartzite. Rocks in the Cuyuna range today have all been metamorphosed from other pre-existing rock types. Allogenic Descriptive of detrital rock constituents and minerals derived elsewhere from older formations and redeposited. Compare to Authigenic. Detrital orthoclase Orthoclase, monoclinic feldspar with the formula KAlSi3O8, is one of the most common of all minerals. It is often white, gray, or flesh-red in color and sometimes occurs as colorless crystals. Natural continuum Anything seen as having a continuous, not discrete, structure. The following paragraph contains the word: Ecosystem Diversity
This is certainly the most ill defined of the subjects covered by the term biodiversity. Evaluation of ecosystem diversity, or diversity at the habitat or community level remains problematic. There is no single way to classify ecosystems and habitats. The main units that can be recognized actually represent different parts of a highly variable natural continuum.
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Scanning electron microscope An electron microscope in which the surface of a specimen is scanned by a beam of electrons, which are reflected to form an image (abbr.: SEM).
Figure 96- Scanning Electron Microscope This scanning electron microscope (SEM) is to the left of the operator, with the computer images of the specimen on the screens to the right. Although the SEM cannot ”see“ objects as small as those that a transmission electron microscope can resolve, the images it produces are more useful for seeing the three-dimensional surface structure of small objects.
Greenhouse effect Term for the role the atmosphere plays in helping warm the Earth's surface. The atmosphere is largely transparent to incoming short-wave solar radiation, which is absorbed by the Earth's surface. Much of this radiation is then reemitted at infrared wavelengths, but it is reflected back by gases such as carbon dioxide, methane, nitrous oxide, halocarbons, and ozone in the atmosphere. This heating effect is at the root of the theories concerning global warming.
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Plankton The small and microscopic organisms drifting or floating in the sea or fresh water.
Figure 97- Plankton in a Drop of Water As pictured here, a variety of plankton can exist in a single drop of ocean water. In fact, plankton can become dense enough to color the water. The red tides that occur in coastal waters around the world are caused by billions of plankton of various species.
Types of plankton Foraminifera - CaCO3, animal-like (such as Globigerina ooze) Coccolithophores - CaCO3, plant-like (forms chalk) Diatoms - SiO2, plant-like (forms diatomaceous earth - diatomite) Radiolarians - SiO2, animal-like Coccoliths (Planktonic) Coccolithophorids are members of the Haptophyta (or Prymnesiophyta) that have intricate, calcified scales called coccoliths attached to their cell bodies. Some bloom-forming coccoliths are implicated in the production of dimethyl sulphide, a contributor to acid rain. Fossilized coccoliths, which form the white cliffs of Dover, are important in the geological study of strata (layers of sedimentary rock)
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Forams (Planktonic) Any protozoan of the mainly marine order Foraminifera.
Foraminifera Order of single-celled amoeba-like marine organisms of the phylum (or super class) Sarcodina in the kingdom Protoctista. Foraminifera, also called foraminifers or Forams, extrude shells, called tests, that may be either wholly organic, mixed with sand grains, or composed of a thin organic inner layer and a thick calcareous outer layer. Although many tests are solid, the most common type is calcareous and porous. He living species occur on the bottom of shallow seas or float as plankton in the upper levels of the oceans. Their food consists mainly of bacteria and diatoms. When the Planktonic species die, their tests sink to the bottom, forming a thick deposit known as the Globigerina ooze, named after the abundant family Globigerinidae. In past ages, chalk rocks were formed by the compression of similar foraminiferal oozes, and the pyramids of Egypt were built of foraminiferal limestone capped with granite. Geologists study deposits of foraminifer’s shells for clues to the location of petroleum. Different Foraminifers are Dictyoconus arabicus, Valvulinella, Paravalvulina arabica, Pseudocyclammina lituus, Pseudocyclammina, Chrysalidina, Palorbitolina lenticularis, Choffatella decipiens (See fossils of UAE) Benthonic The flora and fauna found at the bottom of a sea or lake. Benthic plants and animals inhabit distinct seafloor habitats. The shallow-bottom habitat that extends from the shore to the edge of the continental shelf supports molluscs, polychaete worms, and attached algae and sponges. The continental slope and beyond make up the benthic zone, which includes the deepest part of the ocean floor. It is sparsely populated with deposit feeders and filter feeders such as the pycnogonid sea spiders and stalked crinoids (sea lilies). Green algae
Figure 98- Green Algae
Green Algae These green algae, shown here exposed at low tide, belong to one of some 6,000 to 7,000 species of plants that make up the phylum Chlorophyta. Organisms in this phylum may appear as single cells, amorphous sheets, or collections of long filamentous strands. Although able to survive in marine and fresh waters, damp soil, or snow and ice, most species are found in freshwater habitats.
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Coralline red algae (Rhodophyta) Coralline algae are important in the formation of coral reefs, producing new material and cementing together other organisms. Hey lack chlorophyll b and have special blue and red pigments.
Figure 99- Red Coralline Algae Bivalves Common name for any mollusc characterized by a shell divided intoside, gills specialized for feeding, and a reduced head. Bivalves formMollusc. The main fossil-microfossil groups present in the Cenozoic were the
Gastropods Any mollusc of the class Gastropoda, which includes snails and slugaster, “stomach”; pous, “foot”) are generally characterized by a singbody. They form the second-largest class in the animal kingdom, ouThe term “bivalve” is also applied to some gastropods
Figure 100- Gastropods
Red Coralline Algae The red coralline algae belong to the phylum Rhodophyta. They can incorporate calcium carbonate into their cell walls, giving the body a rigid, segmented appearance and texture. Most of the red algae have the ability to carry on photosynthesis at much greater depths than other types of algae. Some species from the Bahamas grow at depths of nearly 270 m (880 ft).
two halves hinged at one the class Bivalvia. See
lamellibranches, or bivalves.
gs. The Gastropoda (Greek, le shell and an asymmetric
tnumbered only by insects.
Gastropods Gastropod molluscs range in size from the smallest snail, barely visible, to a sea slug three to four times the weight of an average domestic cat. Basic gastropod structure includes a single shell enclosing a twisted, asymmetric body, as seen in the snail. In the slug, both of these features have been lost. Some gastropods show further modification: the gills with which most molluscs breathe have been replaced by lungs in terrestrial snails and by featherlike projections called cerata in some slugs.
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Corals Common name for members of a large class of marine invertebrates characterized by a protective calcium carbonate or horny skeleton. This protective skeleton is also called coral.
Figure 101- Corals
Brachiopods A marine invertebrate of the phylum Brachiopoda Also called lamp shell. Lampshell, common name for members of a phylum of small marine animals with two shells. Formerly classified in the same phylum as mollusks. Lampshells were a dominant form of life in the earliest geological times, but since the close of the Palaeozoic Era they have been steadily decreasing. Scientific classification: Lampshells belong to the phylum Brachiopoda. Lampshells having hinges make up the class Articulata that without hinges the class Inarticulata.
Branching Coral Colonies Branching coral is actually a colony of very small individual animals called coral polyps. Branching corals are considered hard corals, since they have a hard calcium carbonate skeleton. Their bright colors result from the presence of symbiotic algae that live in their body tissues and produce most of the food that the coral needs to survive.
Orange Tube-Coral Orange tube-coral does not grow in areas of dense coral development. Instead it thrives on the sides of boulders, under hangings, and drop-offs. This type of coral can also be seen in tide pools.
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Bryozoans Any aquatic invertebrate animal of the phylum Bryozoa Also called polyzoan. Moss Animals, common name for two phyla of small, simple aquatic animals that feed with a crown of tentacles called a lophophore, and usually form attached, mossy colonies.
Figure 102- Bryozoans Trilobites Common name for a class of extinct marine arthropods. Trilobites ranged in length from a few millimeters up to about 65 cm (26 in), although most species were between 3 and 7 cm (1 and 3 in) long. Trilobites lived during the Palaeozoic era (570 million to 245 million years ago) and were common in the early part of that era. The trilobites were named after the arrangement of their exoskeleton, or outer shell, into three lobes. The exoskeleton, the part of the organism that is most commonly preserved, was made of calcium carbonate and covered the back of the animal.
Figure 103- Trilobites fossilized Trilobites had a pair of compound eyes. In some trilobites, the eyes had densely packed lenses and may have served merely as a light-sensitive warning device to detect movement. In other trilobites, the eyes had fewer and more complex lenses and may have been capable of forming images and perceiving depth.
Fossilized Trilobite Large numbers of trilobites, primitive arthropods that became extinct more than 200 million years ago, have been preserved as fossils. Because these marine animals were typical of the Palaeozoic era, palaeontologists often use them in determining the relative age of the rock strata.
Moss Animals Comprising 4,000 to 5,000 species, moss animals appear more like plants than animals. They are aquatic, and usually colonial and sessile, with globular stalked bodies. Individual colonies grow from less than 1 mm (.04 in) to several cm (about 1 in) in diameter. Most species are marine. Moss animals lack circulatory, respiratory, and excretory systems, and feed primarily on phytoplankton.
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Trilobites lived in shelf and slope environments around continental margins and in the shallow continental seas that covered areas of the Earth that today are landmasses. Most trilobites were bottom-dwellers, although some may have been swimmers or floaters. Some that possessed exceptionally large eyes and a large field of vision, such as Carolinites, are thought to have been swimmers that inhabited surface waters. Others, with reduced eyes or no eyes at all, preferred deeper, darker waters. Many trilobites burrowed into the sea bottom for protection and to seek food.
Trilobites employed a variety of feeding strategies. Many ploughed through mud at the bottom of oceans and seas, ingesting the sediment to sift out organic matter. Others were scavengers or predators. Most trilobites could roll themselves up into a defensive position so that only the exoskeleton was exposed.
The fossilized remains of trilobites are useful because they help scientists develop relative timescales for the ancient marine environment. Because trilobites evolved quickly and were widely distributed, comparing the trilobite fossils found in rock layers in different regions of the Earth can indicate which rock layer is older than the other. Trilobite fossils are particularly helpful in developing timescales for the Early Palaeozoic era.
Scientific classification: Trilobites belong to the phylum Arthropoda and the subphylum Trilobita.
Crinoids Any echinoderm of the class Crinoidea. Sea Lily, common name for an echinoderm native mainly to tropical seas, having a disc-shaped body covered with bony plates, and feathery arms that extend upwards from the body to form a cup. Sea lilies are generally recognized as the most primitive form of echinoderm. Only a few hundred species are now extant, but thousands of extinct species have been found in fossil form, particularly in limestones that originated in the Palaeozoic era.
Figure 104- Sea Lily, or Crinoid
Sea Lily, or Crinoid Most sea lilies live attached to the deep-sea floor, although some are capable of movement. The sea liliesrepresent an ancient group of marine invertebrates that flourished during the Palaeozoic era, between 230 and 600 million years ago.
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Echinoids Sea Urchin, common name for approximately 950 species of echinoderms having rigid, spherical shells, or tests, made up of closely fitting bony plates. Scientific classification: Sea urchins belong to the class Echinoidea. Sea urchins without gills make up the order Cidaroida.
Figure 105- Sea Urchin The sea urchin is included within the phylum Echinodermata, the spiny-skinned animals. The round body, called the test, is covered with movable protective spines, the length of which varies from less than 1 cm (0.5 in) to over 30 cm (12 in). The mouth is on the lower surface, while the anus is located on the top. The five-sided jaw apparatus, called Aristotle’s lantern, is used for scraping algae off rocks.
Bioherms Include the sponges and Corals. See Pic below.
Pic - Sponge coral coral coral
Figure 106- Bioherms
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Rudist bivalve Group of marine animals that no longer exists today. A highly specialized kind of bivalve with a large, horn-shaped lower valve that rested on or in the sediment. A rudist found by Natural History Museum palaeontologists from Jebel Rawdah has been given the new scientific name of Glabrobournonia arabica. Tidal flat In the sheltered waters of lagoons and estuaries tidal currents are the dominant process. Their action sorts the available sediment, depositing mud nearest to the shore, in the intertidal zone, to develop mudflats. Breccias Coarse-grained rock of solidified rubble formed from fragments larger than 2 mm set in a finer matrix. The rock is similar to a conglomerate except that the large clasts are angular. As with conglomerate, in principle the large fragments should form the major component before the rock is called a breccia, but since they are most conspicuous, rocks with a small proportion of large angular blocks may be so called. Many breccias are sedimentary and accumulate, after very little transportation, as screes at the foot of cliffs in mountainous regions or on bold shorelines. Frost shattering in highland areas is particularly efficient at producing angular debris, as is wave battering by the sea.
Escarpment A long steep slope at the edge of a plateau. A high vertical, near vertical, or overhanging face of rock, earth, or ice, associated with cliffs. Talus Concave sections of slope are characterized by creep and soil erosion, and by the accumulation of scree (talus) and colluviums (weathered rock debris) at the slope base. Concave slopes may be features created by the transport and deposition of debris
1. The slope of a wall that tapers to the top or rests against a bank. 2. Geol. a sloping mass of fragments at the foot of a cliff.
Figure 107- Profile of a Slope
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Twinning Two or more intergrown crystals of the same mineral, which are related by an element of symmetry that was not present in the untwinned crystal
Figure 108- Twinning
Polarized light The atoms in an ordinary light source emit pulses of radiation of extremely short duration. Each pulse from a single atom is a nearly monochromatic (single-wavelength) wave train. The electric vector corresponding to the wave does not rotate about the wave’s direction of travel, but keeps the same angle, or azimuth, with respect to it. The initial azimuth can have any value. When a large number of atoms are emitting light, these azimuths are randomly distributed, the properties of the light beam are the same in all directions, and the light is said to be unpolarized. If the electric vectors for each wave all have the same azimuth angle (that is, all the transverse waves lie in the same plane), the light is plane, or linearly, polarized.
Figure 109- Polarized Light Polarized light consists of individual photons whose electric field vectors are all aligned in the same direction. Ordinary light is unpolarized because the photons are emitted in a random manner, while laser light is polarized because the photons are emitted coherently. When light passes through a polarizing filter, the electric field interacts more strongly with molecules having certain orientations. This causes the incident beam to separate into two beams, whose electric vectors are perpendicular to each other. A horizontal filter absorbs photons whose electric vectors are vertical (above). A second filter turned 90° to the first absorbs the remaining photons.
The presence of Twinning can be an important identification feature, which can, in some minerals, be used as a guide to chemical composition.
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At other angles the intensity of transmitted light is proportional to the square of the cosine of the angle between the two filters. In the language of quantum mechanics, polarization is called state selection. Because photons have only two states, light passing through the filter separates into only two beams. The petrographic microscope is used to identify and quantitatively estimate the mineral components of igneous rock and metamorphic rock. It is equipped with a Nicol prism or other polarizing device to polarize the light that passes through the specimen being examined. Another Nicol prism or analyzer determines the polarization of the light after it has passed through the specimen. The microscope also has a rotating stage that, by suitable adjustment, indicates the change in polarization caused by the specimen.
Euhedral A morphological term referring to grains in igneous rocks which have a regular crystallographic shape. Euhedral forms are developed when a crystal grows freely in a melt and is uninhibited by the presence of any surrounding crystals. Their own natural crystallographic form will thus control the shape of the growing crystals.
Figure 110- Euhedral Crystals Marble Limestone in a metamorphic crystalline (or granular) state, and capable of taking a polish, used in sculpture and architecture.
Pic1- these are well shaped grains in igneous rocks. All crystal edges are distinct. The mineral has formed early and has been free to grow unhindered by surrounding minerals
Pic2- Euhedral crystal of Quartz
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Gypsum A hydrated form of calcium sulphate occurring naturally and used to make plaster of Paris and in the building industry.
Figure 111- Gypsum and Crystal Structure A common sedimentary mineral, gypsum is soft enough to be scratched by a fingernail. The crystals are formed by the evaporation of saline waters. Therefore, rich deposits of gypsum are frequently found near the sea. Gypsum has a monoclinic crystal structure, which means it has three axes of unequal length, two of which are perpendicular to the third axis, but not to each other.
Halite Mineral form of common salt, with the chemical composition sodium chloride, NaCl. Halite, also called rock salt, is a common mineral, formed by the drying of enclosed bodies of salt water; subsequently rock strata formed from other sedimentary deposits have often buried the beds so formed. Beds of halite range in thickness from a few meters to 30 m (100 ft) and have been found at great depths beneath the surface of the Earth. This mineral is often found associated with gypsum, sylvite, anhydrite, calcite, clay, and sand. Halite is widely disseminated over the world; in Europe there are deposits in Cheshire, England. Halite crystallizes in the isometric system, usually in the form of cubes, and shows perfect cubic cleavage. It is colorless and transparent when pure but is often tinted yellow, red, blue, or purple by impurities. It has a hardness of 2.5 and a relative density of 2.16. Rhombohedral The Hexagonal system comprises crystals with four axes. Three of these axes are in a single plane, symmetrically spaced, and of equal length. The fourth axis is perpendicular to the other three. Some crystallographers split the hexagonal system in two, calling the seventh system thus formed trigonal or rhombohedral. Quartz, Siderite, Magnesite, Ilmenite, Haematite occurs in rhombohedral crystals.
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Cleavage The splitting of rocks, crystals, etc., in a preferred direction.e.g Slate The physical properties of minerals are important aids in identifying and characterizing them. Most of the physical properties can be recognized at sight or determined by simple tests. The most important properties include powder (streak), color, cleavage, fracture, hardness, lustre, relative density, and fluorescence or phosphorescence. Vitreous 1. Of, or of the nature of, glass. 2. Like glass in hardness, brittleness, transparency, structure, etc. (vitreous enamel). Glass is called amorphous because it is neither a solid nor a liquid but exists in a vitreous, or glassy, state Lustre 1 gloss, brilliance, or sheen. 2. A shiny or reflective surface. 3. Property of describing minerals.
Effervesces 1. Give off bubbles of gas. 2. Carbonates undergo effervescence when treated with hydrochloric acid. 3. Dissolved under a pressure of two to five atmospheres, carbon dioxide causes the effervescence in carbonated beverages. Polymorph The occurrence of something in several different forms.
Figure 112- Halimeda
Halimeda - Much lime mud forms from the disintegration of calcareous algae such as Halimeda and Penicillus. When the calcareous algae die, their skeletons break down and disintegrate producing aragonite needle muds. The lime mud lithifies to form micrite or calcilutite (fine-grained limestone).
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Coccolithophorids Coccolithophorids are members of the Haptophyta (or Prymnesiophyta) that have intricate, calcified scales called coccoliths attached to their cell bodies. Cyanobacteria Members of the phylum comprising photosynthetic single-celled organisms that lack an enclosed nucleus or other specialized cell structures. In some classification systems they are classified as algae and called blue-green algae. In shallow tropical waters, mats of cyanobacteria grow into humps called stromatolites. Fossil stromatolites are found in rocks formed more than 3 billion years ago, during the Precambrian. They suggest the role played by cyanobacteria in changing the ancient carbon-dioxide-rich atmosphere into the oxygenated mixture that exists today. Scientific classification: Cyanobacteria make up the phylum Cyanophyta, in the kingdom Prokaryota.
Sequence boundary Boundary between rocks of two different ages e.g. Permian-Triassic boundary Transgressive surface Geol. (of the sea) spread over (the land). An advance of the sea across the land, due to subsidence of the land, or a eustatic rise in sea level. Opposite of Regression Melting of ice caps leads to sea level rise (transgression) - it has been calculated that complete melting of the Antarctic Ice Sheet would cause a sea level rise of 60 - 70 meters (200 feet). Regression A withdrawal of the sea from the land, due to uplift or a eustatic drop in sea level. See transgression. Growth of ice caps leads to drop in sea level (regression) - calculations show that sea level was as much as 100 meters (300 feet) lower than at present at the height of the last Ice Age glaciations. Much of the Continental Shelf area would have been exposed and dry. Karst A limestone region with underground drainage and many cavities and passages caused by the dissolution of the rock. Eastern Slovenia, characterized by typical limestone topography, is one of the world’s best-known areas of karst, and is where the term originated; “Karst” is the German form of the Slovene word “Kras”, meaning barren, stony ground. Orbitolina In the Cretaceous sediments of the Middle East, including key reservoir intervals, the larger foraminifera belonging to the Orbitolinidae (e.g., Orbitolina) are often common. However, uncertainty in the taxonomy of this group as applied to the Middle East has resulted in much material being referred to "dustbin taxa," such as Orbitolina discoidea and Orbitolina lenticularis.
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Heteraster musandamensis Genus Heteraster. Very common in a rubbly limestone in the upper beds of the Musandam Limestone, east of Khassab village, Elphinstone Inlet
Figure 113- Heteraster Musandamensis
Globigerinids Planktonic marine foraminifera of the genus Globigerina, having a calcareous shell, which collects as a deposit (ooze) over much of the ocean floor. See Foraminifera Argillaceous Clay, esp. that used in pottery. Clay minerals are the main constituent of most argillaceous rocks—the siltstones, mudstones, shales, and marls that make up more than half of all sedimentary rocks.
Ancyloceratinid Hookworms Pseudohaploceras Gastropod, bivalve, fragment of plant, Radiolarian cherts Radiolaria, subclass of protoctistan life forms in the class Sarcodina, which also includes the amoebas. Like the amoebas, radiolarians are single-celled, but they are distinguished by the intricate exoskeletons, called tests, that almost all of them secrete. The test, generally spherically symmetrical and sometimes several millimeters wide, is usually made of silica and often has many spines extending outward. When radiolarians die, their shells sink, forming the so-called radiolarian ooze of deep ocean floors that has formed much sedimentary rock in the course of geological time.
Calpionella The Jurassic/Cretaceous boundary sees Habshan Unconformities 1. A large break in the chronological sequence of layers of rock. 2. The surface of contact between two groups of unconformable strata. Facies Geol. the character of rock etc. expressed by its composition, fossil content, etc. The term facies refers to all of the characteristics of a particular rock unit. For example, you might refer to a "tan, cross-bedded oolitic limestone facies". The characteristics of the rock unit come from the depositional environment. Every depositional environment puts its own distinctive imprint on the sediment, making a particular facies. Thus, a facies is a distinct kind of rock for that area or environment.
Figure 114- Facies
Each depositional environmechange when dealing with the Brackish Estuaries are very rarely in a estuarine mixing, but wind, wwater and freshwater mix to foscillations in river flow, the can shift seasonally and varyThe brackish zone might havwater of about 35 ppm.
Charophytes Stonewort, common name foCharophyceae of the plant kof calcium carbonate usually phylum, the Charophyta. Soperiod (408.5 million to 362.
Salpingoporella (HeSee Fossils of UAE
A = Sandstone facies (beach environment) B = Shale facies (offshore marine environment) C = Limestone facies (far from sources of terrigeneous input)
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nt grades laterally into other environments. We call this facies rock record.
static condition. Tides are the principal energy source causing ave motions, and river run-off can also be important locally. Salt orm what is generally called brackish water. Due mostly to three main estuarine zones—salt water, brackish, and freshwater— greatly between different areas. e a salinity of 2 to 10 parts per million (ppm), compared with salt
r about 440 species of green algae belonging to the class ingdom. Stoneworts are so called because a thick, brittle, limy crust covers the plant surface. They are sometimes regarded as a separate me genera are known only as fossils and date from the Devonian 5 million years ago). See Green algae.
nsonella) – Calcareous algae
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Dinarica Radoicic – calcareous algae See Fossils of UAE Mica Is a term applied to a group of rock-forming minerals, which forms crystals in the monoclinic system, and is characterized by a perfect basal cleavage that causes them to separate into very thin, somewhat elastic leaves? The micas are complex aluminum silicates, the color varying with the composition. They range in hardness from 2 to 4 and in relative density from 2.7 to 3.2. The most important micas are muscovite, phlogopite, lepidolite, and biotite. Muscovite, also called white mica or common mica, which contains potassium and aluminum, is transparent in thin sheets and translucent in thicker blocks; it is colored in light shades of yellow, brown, green, or red. Phlogopite, which contains potassium, magnesium, and aluminum, is transparent in thin sheets, vitreous or pearly in thick blocks, and is yellowish-brown, green, or white in color. Lepidolite, or Lithia mica, which contains potassium, lithium, and aluminum, is usually lilac or pink in color. Biotite, which contains potassium, magnesium, iron, and aluminum, has a splendent lustre and is usually dark green, brown, or black in color but is sometimes light yellow. Muscovite and phlogopite are used as insulating material in the manufacture of electrical apparatus, particularly vacuum tubes. Scrap mica, obtained as waste material in the manufacture of sheet mica, is used as a lubricant when mixed with oils and as a fireproofing material. Weathering Weathering, in geology, processes of physical disintegration and chemical decomposition of solid rock materials at or near the Earth's surface. Physical weathering breaks up rock without altering its composition, and chemical weathering decomposes rock by slowly altering its constituent minerals. Both processes work together continuously to produce debris that is then transported away mechanically or in solution, as in erosion. Weathering processes also aid in the formation of soil.
• Physical weathering results primarily from temperature changes, such as intense heat, the action of water freezing in rock crevices, and living organisms, such as tree roots and burrowing animals. Temperature changes alternately expand and contract rocks, causing granulation, flaking, and massive sheeting of the outer layers. Frost action and organisms widen cracks, exposing deeper layers to chemical weathering.
• Chemical weathering alters the original mineral composition of rock in a number of ways, such as by dissolving minerals by water and weak soil acids; by oxidation; by producing a chemical reaction with carbon dioxide; and by hydration, which is a process in which water chemically combines and reacts with minerals. Plants, such as lichens, also decompose certain rocks by extracting soluble nutrients and iron from the original minerals. Geomorphology, the study of landforms, investigates how weathering and erosion, and other processes have created the visible landscape.
Granite Igneous rock of visible crystalline formation and texture. It is composed of feldspar (usually potash feldspar and oligoclase) and quartz, with a small amount of mica (biotite or muscovite) and minor accessory minerals, such as zircon, Apatite, magnetite, Ilmenite, and sphene. Granite is usually whitish or gray with a speckled appearance caused by the darker crystals. Potash feldspar imparts a red or flesh color to the rock. Granite crystallizes from magma that cools slowly, deep below the Earth's surface. Exceptionally slow rates of cooling give rise to a very coarse-grained variety called pegmatite. Granite, along with other crystalline rocks, constitutes the foundation of the continental masses, and it is the most common intrusive rock exposed at the Earth's surface.
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The relative density of granite ranges from 2.63 to 2.75. Its crushing strength is from 1,050 to 14,000 kg per sq cm (15,000 to 20,000 lb per sq in). Granite has greater strength than sandstone, limestone, and marble and is correspondingly more difficult to quarry. It is an important building stone, the best grades being extremely resistant to weathering.