assessment of depositional environment using lithofacies association and petrophysical analysis

7/30/2019 assessment of depositional environment using lithofacies association and petrophysical analysis

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CHAPTER 1

1.0 IntroductionToday there are numerous description indices for clastic shape and size each

one trying to show the influence of dynamic conditions and clastic petrography

that are mobilised in certain transportation or depositional environment and

their shapes at certain moments. Particle morphometry or form (sieve analysis)

refers to the sum of the surface characteristics of sedimentary grains. Processes

of weathering, erosion, and transport may all leave distinctive imprints on

particles, in the form of fractures, worn surfaces, and particular surface textures

(Benn, 2010).

Resolving the stratigraphic patterns along the spread of a geographical area

entails an integrated approach of petrophysical analysis for the paleo-

enviromental events to be decrypted properly.

The facie characterisation of the outcrop section has a lot to do with the

deposition of sediments, the environment of deposition of the sediments and the

mineral contents to some extent.

1.1 Aims and objectives

The aim of this research is to describe the depositional environment of the

sediments in the study area which lies on Niger delta basin. The objective on the

other hand is to evaluate and analyse the petrophysical parameter of the


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sediments of the Benin formation, interpreting the identified and observed

patterns in other to evaluate and correlating them to some of the previously

devised models.

This is also aimed to give insight on the initial observation during this work.

1.2. Location and accessibility

The study area is a remote village of Ikot Amama which lays within the range

of longitude 0703050 and latitude 0501030 at Ibiono Ibom local government

area of Akwa Ibom state south-eastern Nigeria. Accessibility is highest when

most of the streams and marshy area are dried up. The high lands, elevations

and stream are highly dense with concentrated vegetation especially the under

growths causing limitation to accessibility of path connected area.

1.3 LIMITATIONS

The limitations encountered during this study include inaccessible roads

and uneasy walk paths. It was also quite difficult to get sample from the

outcrops or litho unit because of the height of some of the litho-section of

which some were about 8meters high and knowing that most exposed

surface s were weathered, the need of hammer to dig in for unexposed

unit to get un-3weathered deposits was required .the fear that some of

the lithosections might cave in and have one buried.


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1.4 Climate and Vegetation

Because of the effects of the Maritime and the Continental Tropical air masses,

the climate of this area is characterised by two seasons, namely, the wet or rainy

season and the dry season. The wet or rainy season lasts for about eight months

but towards the far north, it is slightly less. The rainy season begins about

March-April and lasts until mid-November. Relatively, this area which is

located in Akwa Ibom State receives relatively higher rainfall totals than most

other parts of southern Nigeria. The total annual rainfall varies from 4000mm

along the coast to 2000mm inland.

The dry season begins in mid-November and ends in March. During this brief

period, the whole Continental Tropical air mass and its accompanying north-

easterly winds and their associated dry and dusty harmattan haze. However, as a

result of the proximity of the area to the ocean, the harmattan dust haze, (locally

known as "ekarika") is not usually too severe as in the Sahelian zone of northern

Nigeria. Sometimes it lasts for only a few weeks between December and

January. The harmattan period is usually advantageous to the farmers because it

is congenial for harvesting and the storage of food crop. Temperature values are

relatively high in throughout the year, with the mean annual temperatures

varying between about 26C to 36C. The relative humidity of the study which

varies between about 75 per cent to 95 per cent, with the highest and lowest

values in July and January respectively. In January, areas which lie within 30 to

40 km from the coast experience mean relative humidities of more than 80 per


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cent, while values in areas further north vary between about 70 per cent a to 80

per cent Vegetation And Fauna. The existing climatic factors in this area would

have favoured luxuriant tropical rainforests with teeming populations of fauna

and extremely high terrestrial and aquatic biomass. The vegetation of the area is

still intact and concentrated with some of the native vegetation being almost

replaced by secondary forests of predominantly wild oil palms, woody shrubs

and various grass undergrowth. Mangroves cover extensive parts of the area.

1.5 Drainage, Topography and Soil

The area under study is drained by two rivers; the north-eastern and south-

eastern are drained by the Cross River while the north-western is drained by the

Kwa-Ibeo River. Most of other streams that are found in the area are seasonal

that is; the dry up during that dry season. The flow direction of these streams

and rivers are to the north-west and south. The streams are characterised by

igneous intrusion and laminated shale as the bedrocks. In general, the

topography of the area is flat with few steep and elevated areas.

Weathering and erosion constitutes the major soil forming agents in the area.

The debris derived from the weathering of the intrusive rocks are mainly

lateritic while the erosion and weathering of the shale bed provides excellent

humus due to incorporation of decayed organic materials. The soil in the area

has colour ranging from black to dark reddish and they have high clay content.


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Figure 1: Topographic map of study area


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CHAPTER TWO

2.1 Literature Review

With the general increasing interest of geologist to understand and describe the

lithological facies of the sedimentary deposits in the south eastern Nigeria, a lot

of works have been and is being done using different approaches.

Most recent works focuses on the use of geophysical analysis like the well log,

wire line logging, and electric soundings in combination with petrophysical

analysis to interpret the lithological sequence and facies. While others include

the use of paleo-environmental signatures analysed from the study area.

Previous investigation on the Paleoenvironmental Interpretation of the Nkporo

Formation Afikpo Sub-Basin, Nigeria by Okoro Anthony. U Onuigbo

Evangeline N., Akpunonu Eliseus O and Obiadi Ignatius I.

Department of Geological Sciences, Nnamdi Azikiwe University of Nigeria also employed

this same technique of lithofacies analysis and pebble morphormetry.

Pebble Morphometry and Particle Size Distribution as Signatures to

Depositional Environment of Maestrichtian Ajali Sandstone 1977; Banerjee,

1979; Ladipo, 1985; Amajor, 1986a, 1989; Reijers and Nwajide, 1996; Awalla

and Eze, 2004, and Nwajide, 2005). These studies which are now used as

models to understand the geological structure of the Niger delta basin

Wright, 1968; Murat, 1972; Olade, 1975; Whiteman, 1982 and Nwajide and

Reijers, 1996 all studied the evolution of the Niger delta basin as a result of the

regional folding and uplift of the Benue Trough during the Santonian to Early


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Campanian. Describing the formation of the Anticlinorium (Abakaliki

Anticlinorium) dislocated the depositional axis from the Benue Trough to the

Anambra Basin which was indicated to be a stable platform before the tectonic

event

2.2 Geologic study of the Area

The study area lays in the Niger delta basin underlain by the Benin

sedimentary formations of Late Tertiary and Holocene ages. Also, this area

consists of coastal plain sands, now weathered into lateritic layers. The latter

lithologies include the late abgada Formation at the base followed by akata

Formation. Upwards, the geologic succession passes imperceptibly into thick

sequences of clays, sands and gravel. Gravel beds and pebbly sands are

commonly exposed on hillsides, road-cuts and stream channels. Generally, the

sands in this area are mature, coarse and moderately sorted


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Figure 2: geologic map of study area

The Niger Delta is situated in the Gulf of Guinea and extends throughout the

Niger Delta Province as defined by Klett and others (1997). From the Eocene to

the present, the delta has prograded southwestward, forming depobelts that

represent the most active portion of the delta at each stage of its development


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(Doust and Omatsola, 1990). These depobelts form one of the largest regressive

deltas in the world with an area of some 300,000km2(Kulke, 1995), a sediment

volume of 500,000 km3

(Hospers, 1965), and a sediment thickness of over 10

km in the basin depocenter (Kaplan et al,1994).

Fig.3 Structural units of Niger Delta basin (Short and Stauble 1967)


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The formations of the study area are mainly:

1. Benin Formation (Youngest)

2. Agbada Formation and

3. Akata Formation (Oldest)

2.2.1. The Benin formation

This formation constitutes mainly of sand stones which make up of mainly 90%

of it and it stretches from the west through the Niger delta and extends up north

towards part of the Anambra basin where it transverses to the Mamu formation.

The sandstone of this formation is also intercolated with shale units and there is

poor sorting of the unit grains which include the fine sand, coarse sand, sub

angular to well-rounded pebbles, gravels and the angular cobbles units.

The presence of light streak and wood fragments suggests that they are mainly

of continental deposit of upper deltaic environment

The variability of the shallow water deposition is indicated basically by most structural units

that could be spoted within the benin formation. The thickness of this formation ranges from

about 6000ft and above. Just little collection of hydrocarbon could be found within this

formation. In addition to a surface formation the Benin Formation crops out

widely at surface across the delta province. Its limits shows below (figure 4)

based on Short and Stauble (1967) are much more extensive than those shown

by Dessauvagre (1974).


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The sequence encountered in Elele-1 contains more than 90% sand and a few

shaley intercalations. Shale content increases towards the base as shown in

(figure 4) below.The sand and sandstone are coarse to fine grained and

commonly granular in texture. The sand and sandstone are poorly sorted, and

partly unconsolidated. The sands and sandstones are white or yellowish brown

because of limonitic coats. Lignite occurs in thin streaks or a finely dispersed

fragment. Heamatite and feldspar grain are common. The members of the

formation shales are grayish brown, sandy and silty and contain plant remains

and dispersed lignite. Shales constitute only a very small part of the sequence.

2.2.2 Agbada formation

This formation is intermediate in age and position of the three formation found

in the study area (Use Ikot Amama) and is a sequence of sandstone and shale

Unit i.e. an interfingering of sandstone and shale at the bottom. The shale unit

that underlies the sand is quite thicker than the sand unit. It has high microfauna

content at the bottom which decreases upwards, indicating an increased rate of

deposition at the deltaic point.

The Agbada formation is not exposed in the Niger-delta region rather they occur

as subsurface rock between the Benin formation and the Akata formation. The

agbada formation is a replica of what is seen at ogwasi, Asaba and Ameki

formations which are Eocene and Oligocene the thickness of this rock unit

ranges from 1000ft (304.8 m) and above.


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The ages of this formation ranges from Eocene in the northern part to Pliocene/

Pleistocene in the south.

2.2.3 Akata Formation

This formation underlies the two formation mentioned above and its the oldest

amongst them in age. This formation is uniform clay with dark sandy, silt clay

with scanty plants remains occurring at the top especially close to the contact of

the overlying Agbada formation.

The Akata Formation is thought to be the main source rock for Niger Delta

complex oil and gas. The formation probably underlies the whole of the Niger

Delta complex south of the Imo shale outcrop which itself probably deposited

under similar condition of deposition and may be considered an up-dip

equivalent of Akatafacies The top of the Akata Formation is taken arbitrarily at

the deepest development of deltaic sandstone at 7810Ft in the type section. The

base of the formation was not reached at a depth of 11121Ft in Akata-1 but the

base has been penetrated in wells situated on the Delta Flanks.

The age of the formation ranges from Eocene to present day but conceptually

deep water Paleocene Imo shale and even late CetaceousNkporo Shale (Late

cretaceous) could be classed as AkataFacies.

The Akata Fauna is rich in planktonic foraminifera which indicate deposition on

a shallow marine shelf. Akatafacies extends into deep water and must contain

deep water assemblages. Akata also must be graded laterally and vertically into


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the deep water turbidities of the Avon-Mahin Fan, the Niger Fan, and the

Calabar Fan.

The arbitrary nature of the boundary between the Agbada and Akatafacies has

been commented upon. At the present day, Akatafacies are being deposited on

the continental shelf and slope and perhaps on the lower part of the pro-delta

slope, the present day outcrop of the Akata then is completely submarine. The

upper boundary is markedly time transgressive and has been deformed

structurally (synsedimentary) on large scale. The Imo Shale (Palaeocene)

represents up-dip subaerial outcrops of AkataFacies (Short &Stauble). We do

not have much data on the Akata Formation depth beneath the delta. Diapirs and

high pressure tones are developed on a grand scale but details are limited.


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Figure 4: extent of erosional truncation


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2.3 THE NIGER DELTA TECTONICS

Rapid sedimentation along the edge of the Niger delta resulted in faulting

contemporaneous with sedimentation, thus producing an abrupt thickness of

sediments across the fault line on the down thrown block. This is the well-

known growth fault line on the down thrown block. This is the well-known

growth fault structure. If sufficient movement occurs, an elongate anticline

(roll-over anticline) may form in front of the fault. Stoneley (1966) ascribed the

structures in the offshore areas to salt movement at depth. There appears to be

no doubt that the diapiric structures off the Niger delta are of the same origin as

those farther south and are possibly of AptianAlpian age.

The tectonic framework of the continental margin along the West Coast of

equatorial Africa is controlled by Cretaceous fracture zones expressed as

trenches and ridges in the deep Atlantic. The fracture zone ridges subdivide the

margin into individual basins, and, in Nigeria, form the boundary faults of the

Cretaceous Benue-Abakaliki trough, which cuts far into the West African

shield. The trough represents a failed arm of a rift triple junction associated with

the opening of the South Atlantic. In this region, rifting started in the Late

Jurassic and persisted into the Middle Cretaceous (Lehner and De Ruiter, 1977).

In the region of the Niger Delta, rifting diminished altogether in the Late

Cretaceous. Figure 3 shows the gross Paleogeography of the region as well as

the relative position of the African and South American plates since rifting


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began. After rifting ceased, gravity tectonism became the primary deformational

process. Shale mobility induced internal deformation and occurred in response

to two processes (Kulke, 1995). First, shale diapirs formed from loading of

poorly compacted, over-pressured, prodelta and delta-slope clays (Akata Fm.)

by the higher density delta-front sands (Agbada Fm.). Second, slope instability

occurred due to a lack of lateral, basinward, and support for the under-

compacted delta-slope clays (AkataFm). For any given depobelt, gravity

tectonics were completed before deposition of the Benin

Formation and are expressed in complex structures, including shale diapirs, roll-

over anticlines, collapsed growth fault crests, back-to-back features, and steeply

dipping, closely spaced flank faults (Evamy and others, 1978; Xiao and Suppe,

1992). These faults mostly offset different parts of the Agbada Formation and

flatten into detachment planes near the top of the Akata Formation.

2.3.1 Lithology

The Cretaceous section has not been penetrated beneath the Niger Delta Basin,

the youngest and southernmost sub-basin in the Benue-Abakaliki trough

(Reijers and others, 1997). Lithologies of Cretaceous rocks deposited in what is

now the Niger Delta basin can only be extrapolated from the exposed

Cretaceous section in the next basin to the northeast--the Anambra basin. From

the Campanian through the Paleocene, the shoreline was concave into the


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Anambra basin (Hospers, 1965) (see fig. 3 in this paper), resulting in

convergent longshore drift cells that produced tide-dominated deltaicn

sedimentation during transgressions and river-dominated sedimentation during

regressions (Reijers and others, 1997). Shallow marine clastics were deposited

farther offshore and, in the Anambra basin, are represented by the Albian-

CenomanianAsu River shale, Cenomanian-SantonianEze-Uku and Awgushales,

and Campanian/MaastrichtianNkporo shale, among others (Nwachukwu, 1972;

Reijers and others, 1997). The distribution of Late Cretaceous shale beneath the

Niger Delta is unknown in the Paleocene, a major transgression (referred to as

the Sokoto transgression by Reijers and others, 1997) began with the Imo shale

being deposited in the Anambra Basin to the northeast and the Akata shale in

the Niger Delta Basin area to the southwest.

Deposition of the three formations occurred in each of the five off lapping

siliciclastic sedimentation cycles that comprise the Niger Delta. These cycles

(depobelts) are 30-60 kilometers wide, prograde southwestward 250kilometers

over oceanic crust into the Gulf of Guinea (Stacher, 1995), and are defined by

synsedimentary faulting that occurred in response to variable rates of

subsidence3 and sediment supply (Doust and Omatsola, 1990). The interplay of

subsidence and supply rates resulted in deposition of discrete depobelts, when

further crustal subsidence of the basin could no longer be accommodated, the

focus of sediment deposition shifted seaward, forming a new depobelt (Doust


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and Omatsola, 1990). Each depobelt is a separate unit that corresponds to a

break in regional dip of the delta and is bounded landward by growth faults and

seaward by large counter-regional faults or the growth fault of the next seaward

belt (Evamy and others, 1978; Doust and Omatsola, 1990). Five major

depobelts are generally recognized, each with its own sedimentation,

deformation, and petroleum history. Doust and Omatsola (1990) describe three

depobelt provinces based on structure. The northern delta province, which

overlies relatively shallow basement, has the oldest growth faults that are

generally rotational, evenly spaced, and increases their steepness seaward. The

central delta province has depobelts with well-defined structures such as

successively deeper rollover crests that shift seaward for any given growth fault.

Last, the distal delta province is the most structurally complex due to internal

gravity tectonics on the modern continental slope.


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Figure 5: tectonic frame work of Niger delta


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CHAPTER THREE

3.1 Method of Study

The method of study applied in this work ranges from field-work which

involves working on the field to laboratory practical work and finally the data

analysis of which include the sieve and pebble morphometric analysis.

3.2Field work

This involves the study of the geology of the area and gathering information

from all observable geologic activities in the area. The data gathered in the field

depends on the following.

First is the scope of work which was predetermined before the field work. The

scope of work revolves around understanding the geologic as well as physical

processes of deposition in the area. Other points put in place included the

weathering activity, the relief, soil type, soil colour, soil texture, topography,

vegetation.

The data gathered also depended on the students level of involvement and

ability to see, visualise and take notes of the thing that he observes.

Finally is the materials used in the field observation.

The following materials were used for the field work

- Sample bags and small polythene bags for sample collection and storage

- The clinometers

- The GPS

- Steel tapes for mapping and analogue outcrop logging


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- Cameras for photography and digital logging

- Hammers for breaking rock and digging out rock sections.

- Pen, pencils and notes for recording observations

- Paper cello tapes for labelling the samples

- Field bags for carrying the samples.

3.3 Particle-Size analysis

Particle-size analysis comprises the measurement and analysis of the three

particle axes that define the three-dimensional shape of a particle. For many

applications, it is much more convenient to characterize particle size by only

one variable, such as the length of the intermediate particle axes or the size of

the sieve on which a particle was retained. Once the sizes of particles are

determined, they are statistically analysed, so that particle size distributions and

statistical parameters characterizing them can be compared between streams or

over time. The mean particle size on a streambed, a particular particle-size

percentile, a characteristic large particle size, as well as the entire spectrum of

particle sizes all affect the hydraulics of flow as well as bedload transport rates.

Studies concerned with the mechanics of particle entrainment, particle transport

and deposition need to include the description and comparison of particle

shapes.


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Pebble morphometric studies involves measurement (using vernier calliper) of

the long (L), intermediate (I), and short (S) axes of pebbles from pebbly

sandstones. The three mutually perpendicular axes of each pebble were

measured and the roundness estimate with the aid of a roundness image

set. Morphometric parameters such as size, flatness ratio, elongation

ratio, elongation ratio, maximum projection sphericity, form geometry and

oblate index were computed.

Figure 6: pebble geometric axis

The three mutually perpendicular axes (S, I and L) of each of the 90 pebbles

were measured using some set of instruments which include:

The venier callipers


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G cramp

The rulres

Table 3.1 Morphometric parametersIndices Formulae Author

elongation ratio

Sneed &Folk (1958)

Zingg (1935)

Zingg (1935)

Maximum projection sphericity

index (MPS) Sneed and Folk, 1958

Disc-Rod Index (DRI) Sneed & Folk (1958)

Oblate-Prolate Index (OPI)

[ ] Dobkins & Folk (1970)

Elongation index (IE) The percentage by weight of particles whose long

dimension is greater than 1.8 times the mean dimension measured with a

standard gauge. The elongation, n, is length divided by breadth and the

elongation ratio is 1/n

Roundness index The average radius of curvature of the corners of a particle,

divided by the radius of the maximum inscribed circle for a two-dimensional

image of the particle, i.e. (r/N)/R, where ris the average radius of curvature

at the corners,Nis the number of corners, andR is the radius of the largest

inscribed circle. In practice, it is used empirically and other techniques are also

used. For example, a pebble may be compared with a set of standard silhouettes.


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The resulting index figure allows inferences to be made about the nature of the

depositing process.

Sphericity An expression of how closely the shape of a grain resembles the

shape of a sphere. Sphericity can be determined by examining the relation

between the long (L), intermediate (I), and short (S) axes of the particle, the

maximum projection sphericity, , being given by the expression = 3(S2/LI).

For a perfect sphere, = 1. Values less than one relate to increasingly less

spherical shapes.

The bivariate plots of M.P.S. vs. OP Index,

The sphericity form diagrams were very useful in the environmental

discrimination of the pebbles.


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3.4 Sieving of particle size

The size of sand particles was measured manually by sieving. The different

equipment used in both approaches can affect the results. This makes it

necessary to compare different methods of particle-size

The primary purpose of sieve analysis is to determine particle size distribution

in sands which directly relates to;

Availability of different sizes of particles in parent material.

Processes operating where sediments are deposited, particularly

competency of the flow.

Concentration of particles in suspension and source rocks (Friedman,

1979; Lewis and McConchie, 1994).

Equipment

1. Sample splitters,

2. Plexiglas plate and 18 inch steel rulers,

3. shaker.

4. Miscellaneous pans, brushes, scoops, etc.

5. Sieves.

Eighteen samples from the exposure were analysed according to the technique

of Friedman (1979). The nests of sieve were arranged with the coarsest at the

top and the pan at the bottom. The disaggregated and weighed samples of each

of the sands were poured in to the uppermost sieve and shook for 15minutes.

The frequency curves of the samples were plotted and critical percentiles (5,


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16, 25, 50, 75, 84 and 95) were obtained and the t extural parameters of

the sands which include the graphic mean, median, graphic standard deviation,

inclusive graphic skewness and graphic kurtosis were calculated using the

following McManus(1995) statistical parameters

Table 3.2 McManus statistical parameters

Graphic mean Mcmanus, 1995

Median 50

Graphic standard deviation (1) + Inclusive graphic skewness (SKI) + Graphic kurtosis (KG)

The bivariate plots of

Skewness vs. standard deviation,

Mean vs. standard deviation,

Simple skewness vs. simple sorting (after Friedman, 1979) was used in

the environmental discrimination.

These results are plotted on graph of which the sieve scale is logarithmic. To

find the percentage of aggregate passing through each sieve, first the percentage

retained in each sieve was found using the following equation:

%retained =


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Where

= weight of aggregate in the sieve = total weight of aggregateThe next step was finding the cumulative percentage of aggregate retained in

each sieve which was done by adding the total amount of aggregate that is

retained in each sieve to the amount retained in the previous sieves.

The cumulative percentage passing was found by subtracting the percentage

retained from 100%

%cumulative passing = 100% - %cumulative retained

The values were plotted on a graph with cumulative percentage passing on the

y-axis and the logarithmic sieve size on the x axis (the semi-log graphic sheet).


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CHAPTER FOUR

4.1 Results and Interpretation

4.2 Field observations

The lithostratigraphic descriptions of the six outcrop sections studied are

presented in figures below. The lithofacies in most consists of repeated cyclic

deposition of fine sand, medium sand and pebbly sand. The fine sands are not

characterized by any form current ripples and parallel laminations or other

features associated with sand medium in the area.


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Table 4.1: Location 1 section 1

Three different facies (A-C) have been identified in the above chart. Also from

the stratigraphic sequence it can be seen that there is a sequence of repetition

(memory) of facie A and B until 1.6m were C come in and then at 2.0m the

memory sequence is continued.


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Table 4.2 Location1 section 2

Here, only two facies are identified and only little can be deduced form this

outcrop model.

Table 4.3 Location1 section3

Two different facies have been identified in the above chart. it can also be seen

that there is a sequence repetition of facies A.


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4.2.1 Facie association

Facie type A [para-conglomeratc bed]

is a matrix-supported rock that contains more than 15% of sand and restly

pebbles (para-conglomerates). This facie has colour ranging from white to light

brownish clast. This is the most prominent facie occurrences; it is a massive bed

with evidence of bioturbation. The poorly sorted pebbles (randomly packed

clast of different sizes) and sandstone showing that the pebbles and sandstone

were deposited by a highly flowing channel giving no time for the sediments to

properly settle in therefore indicative of a fluvial environment of deposition.

The members of this bed includes; L1S1U1, L1S1U3, L1S3U1, L1S3U3,

L3S1U2, L3S2U3. Represented as A in the lithologs above

Figure 7 Facie type A [para-conglomeratc bed]


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Facies type B massive sandstone

This facies is a massive brown medium to coarse grained sand. There are little

occurrences of fringinised sand in this facies sections as a result of the iron-III-

oxide content of the sand

Figure 8: Facies type B massive brown sandstone

Facies type c [massive sandstone]

This is a massive reddish brown sandstone facies. This is a fine sand bed with

no evidence of bioturbation. The members of this facies include; L1S1U2,

L1S3U2, L3S1U5, L3S3U2. This facie is indicated as B in the lithology.


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Figure 9: Facies type c [massive sandstone]

Facie type D [ ortho-conglomeratic beds]

It is a clast (pebble)-supported sedimentary bed with sand as matrix with 15%

or less in any mass of the bed. This is a massive brown colour bed with no

evidence of bioturbation or imbrication. The deficiency of the matrix was

probably caused by a fast flowing channel not giving in for the settlement of

debris of very less density. There is only a single occurrence of this facies in the

bed unit L3S3U1. This bed has an approximate thickness of about 2.5m

occurring from the 0m ground point. Represented as D in the litholog


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Figure 10: Facie type D [ ortho-conglomeratic beds]

Facies type E [massive intercalation of breccia debris]

This is a dark brown massive intercalation of breccia debris, pebble and fine

sand matrix with bioturbation. This bed has a thickness of approximately a

meter thick. The bed unit L1S2U2 falls into this type. The dark colour is as a

result of bio activities. Represented as E in the litholog

Figure 11: Facies type E [massive intercalation of breccia debris]


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4.3 Sieve Analysis Results

The sieve analysis for a select number of the sample recovered in the field was

carried out in other to assess the particle size distribution across each bed unit.

The picking of this sample was made base on the sections logged in the field.


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Table 4.7 Sample 1: Location 1, Section 1, Unit 1

W1 106.9g

grain size in

phisieve size wt. retained %retained

cumulative

%retained

cumulative

%passing

-1 2 22.7 21.23 21.23 78.77

0 1 25.8 24.13 45.37 54.63

1 0.5 29.8 27.88 73.25 26.75

2 0.25 15.9 14.87 88.12 11.88

3 0.125 8.6 8.04 96.16 3.84

4 0.063 3.4 3.18 99.35 0.65

PAN pan 0.2 0.19 99.53 0.47

106.4

Table 4.8 Sample: Location 1, Section 1, Unit 2

W1 74.8g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 5.4 7.22 7.22 92.78

0 1 11.7 15.64 22.86 77.14

1 0.5 27.6 36.90 59.76 40.24

2 0.25 17.6 23.53 83.29 16.71

30.125 7.5 10.03 93.32 6.68

4 0.063 2.9 3.88 97.19 2.81

PAN pan 1.7 2.27 99.47 0.53

74.4

Table 4.9 Sample: Location 1, Section 1, Unit 3

W1 66.7g

grain size in

phi sieve size wt. retained %retained

cumulative

%retained

cumulative

%passing

-1 2 16.4 24.59 24.59 75.41

0 1 13.4 20.09 44.68 55.32

1 0.5 16.4 24.59 69.27 30.73

2 0.25 13.7 20.54 89.81 10.19

3 0.125 4.3 6.45 96.25 3.75

4 0.063 1.7 2.55 98.80 1.20

PAN pan 0.6 0.90 99.70 0.30

66.5


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39

Chart 1

1.00

10.00

100.00

-1 0 1 2 3 4 PAN

cumulative%retained

Grain size in phi

L1S1U1

L1S1U2

L1S1U3


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40

Table 4.10 Location 1, Section 1, Unit 4

W1 97.8g

grain size inphi sieve size wt. retained %retainedcumulative%retained

-1 2 16.5 16.871 16.871 83.129

0 1 20 20.450 37.321 62.679

1 0.5 22.2 22.699 60.020 39.980

2 0.25 17.3 17.689 77.710 22.290

3 0.125 13.2 13.497 91.207 8.793

4 0.063 4.8 4.908 96.115 3.885

PAN pan 3.6 3.681 99.796 0.204

97.6


W1 89.5g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 24.3 27.15 27.15 72.85

0 1 29.9 33.41 60.56 39.44

1 0.5 19.6 21.90 82.46 17.542 0.25 8.6 9.61 92.07 7.93

3 0.125 3.7 4.13 96.20 3.80

4 0.063 1.7 1.90 98.10 1.90

PAN pan 1.3 1.45 99.55 0.45

89.1


W1 97.6g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 24.9 25.512 25.512 74.488

0 1 20.1 20.594 46.107 53.893

1 0.5 26.5 27.152 73.258 26.742

2 0.25 17.1 17.520 90.779 9.221

3 0.125 5.5 5.635 96.414 3.586

4 0.063 2.8 2.869 99.283 0.717

PANpan 0.4 0.410 99.693 0.307

97.3


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41

Chart 2

1.000

10.000

100.000

-1 0 1 2 3 4 PAN

cumulative%retained

grain size in phi

L1S1U4

L1S1U5

LIS1U6


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42


W1 114.9g

grain size inphi

sieve size wt. retained %retained cumulative%retained

cumulative%passing

-1 2 45 39.164 39.164 60.836

0 1 24.4 21.236 60.400 39.600

1 0.5 17.4 15.144 75.544 24.456

2 0.25 15.3 13.316 88.860 11.140

3 0.125 7.6 6.614 95.474 4.526

4 0.063 4.6 4.003 99.478 0.522

PAN pan 0.6 0.522 100.000 0.000

114.9


W1 92.6g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 12.6 13.607 13.607 86.393

0 1 19.7 21.274 34.881 65.119

1 0.5 23.4 25.270 60.151 39.849

2 0.25 20.7 22.354 82.505 17.495

3 0.125 9.5 10.259 92.765 7.2354 0.063 4.3 4.644 97.408 2.592

PAN pan 1.9 2.052 99.460 0.540

92.1


W1 65.8g

grain size in

phi

sieve size wt. retained %retainedcumulative

%retained

cumulative

%passing

-1 2 22.3 33.89 33.89 66.11

0 1 15.1 22.95 56.84 43.16

1 0.5 12.9 19.60 76.44 23.56

2 0.25 9.1 13.83 90.27 9.73

3 0.125 4.3 6.53 96.81 3.19

4 0.063 1.7 2.58 99.39 0.61

PAN pan 0.2 0.30 99.70 0.30

65.6


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43

Chart 3

1.000

10.000

100.000

-1 0 1 2 3 4 PAN

cumulatitive%retained

grain size in phi

L2S1U1

L2S1U2

L2S1U3


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44


W1 160.7g

grain size inphi


cumulative%passing

-1 2 73.1 45.49 45.49 54.51

0 1 32.8 20.41 65.90 34.10

1 0.5 28.4 17.67 83.57 16.43

2 0.25 15.2 9.46 93.03 6.97

3 0.125 6.8 4.23 97.26 2.74

4 0.063 3.3 2.05 99.32 0.68

PAN pan 0.3 0.19 99.50 0.50

159.9


W1 168.6g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 39.4 23.37 23.37 76.63

0 1 41.4 24.56 47.92 52.08

1 0.5 42.9 25.44 73.37 26.63

2 0.25 29.7 17.62 90.98 9.02

3 0.125 12.3 7.30 98.28 1.72

4 0.063 2.4 1.42 99.70 0.30

PAN pan 0.3 0.18 99.88 0.12

168.4


W1 92.4g

grain size inphi


cumulative%passing

-1 2 18.6 20.13 20.13 79.87

0 1 20.4 22.08 42.21 57.79

1 0.5 24.4 26.41 68.61 31.39

2 0.25 13.5 14.61 83.23 16.77

3 0.125 9.7 10.50 93.72 6.28

4 0.063 2.3 2.49 96.21 3.79

PAN pan 1 1.08 97.29 2.71

89.9


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45

Chart 4

1.00

10.00

100.00

-1 0 1 2 3 4 PAN

cumulative%retained

grain size in phi

L2S2U1

L2S2U2

L2S2U3


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46


W1 165.4g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 65.5 39.60 39.60 60.40

0 1 42.8 25.88 65.48 34.52

1 0.5 29.5 17.84 83.31 16.69

2 0.25 16.4 9.92 93.23 6.77

3 0.125 6.3 3.81 97.04 2.96

4 0.063 4 2.42 99.46 0.54

PAN pan 0.2 0.12 99.58 0.42

164.7


W1 92.9g

grain size in


cumulative

%retained

cumulative

%passing

-1 2 16.5 17.76 17.76 82.24

0 1 20 21.53 39.29 60.71

1 0.5 22.2 23.90 63.19 36.81

2 0.25 17.3 18.62 81.81 18.19

3 0.125 6.5 7.00 88.81 11.19

4 0.063 4.8 5.17 93.97 6.03

PAN pan 3.4 3.66 97.63 2.37

90.7


W1 70.0g

grain size in

phi sieve size wt. retained %retainedcumulative

%retained

cumulative

%passing

-1 2 16 22.86 22.86 77.14

0 1 14.7 21.00 43.86 56.14

1 0.5 14.8 21.14 65.00 35.00

2 0.25 13.9 19.86 84.86 15.14

3 0.125 5.9 8.43 93.29 6.71

4 0.063 3.6 5.14 98.43 1.57

PAN pan 1 1.43 99.86 0.14

69.9


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47

Chart 5

1.00

10.00

100.00

-1 0 1 2 3 4 PAN

cum

ulative%retained

grain size in phi

L2S3U1

L2S3U2

L2S3U3


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48

Table 4.22 summaries of various percentile values of the analysed samples.

UNITS 5 16 25 50 75 80 84 95

L1S1U1 0.00 0.00 -1.70 0.20 1.10 1.45 1.74 2.74

L1S1U2 0.00 -0.20 -1.75 0.30 1.50 1.27 2.00 3.00

L1S1U3 0.00 0.00 -1.63 0.28 1.25 1.10 1.74 2.75

L1SS1U4 0.00 0.00 -1.40 0.65 1.90 2.40 2.90 4.40

L1S1U5 0.00 0.00 0.00 -1.50 -0.70 0.90 1.25 2.68

L1s1u6 0.00 0.00 0.00 -0.30 -0.65 0.83 1.30 2.49

L2S1U1 0.00 0.00 0.00 -1.60 1.00 1.43 1.76 2.20

L2S1U2 0.00 -1.13 -1.68 0.70 1.75 1.90 2.20 3.30

L2S1U3 0.00 0.00 0.00 -0.40 0.60 0.80 1.00 3.70

L2S2U1 0.00 -1.20 -1.60 0.40 1.13 1.35 1.60 2.25

L2S2U2 0.00 0.00 -1.10 0.15 1.15 1.40 1.65 2.59

L2S2U3 0.00 0.00 -1.25 0.36 1.45 1.80 2.20 3.25

L2S3U1 0.00 0.00 0.00 -1.48 0.51 0.80 1.20 2.20

L2S3U2 0.00 0.00 -1.40 0.50 1.65 1.90 2.30 4.00

L2S3U3 0.00 0.00 -1.10 0.10 1.13 1.40 1.70 2.55


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49

Table 4.23 description of the various sieve analysis parameters

UNITS MEAN KURTOSIS SKEWNESS SORTING

standard

deviation REMARKS

L1S1U1 -0.08 0.40 0.81 0.87 0.85

poorly sorted, very

positively skewed,

Very platy kurtic, very

coarse sand

L1S1U2 -0.16 0.38 0.75 1.00 0.95

Very Poorly sorted, very

positively skewed,


coarse sand

L1S1U3 -0.18 0.39 0.74 0.87 0.85 Poorly sorted, very

positively skewed,


coarse sand

L1SS1U4 0.33 0.55 0.63 1.45 1.39

Very poorly sorted, very

positively skewed,

Very platy kurtic, coarse

sand

L1S1U5 0.30 -1.57 2.76 0.63 0.72

Moderately well sorted,

very positively skewed,


sand

L1s1u6 0.28 -1.57 1.35 0.65 0.70


positively skewed,


sand

L2S1U1 0.48 0.90 2.64 0.88 0.77

poorly sorted, very

positively skewed,

platy kurtic, coarse sand

L2S1U2 0.07 0.39 0.24 1.67 1.33 Very Poorly sorted,

positively skewed,


sand


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50

L2S1U3 0.27 2.53 1.51 0.50 0.81



Very lepto kurtic, coarse

sand

L2S2U1 -0.08 0.34 0.25 1.40 1.04

Very Poorly sorted,

positively skewed,


coarse sand

L2S2U2 0.10 0.47 0.85 0.83 0.80

Poorly sorted, positively

skewed,


sand

L2S2U3 0.18 0.49 0.73 1.10 1.04


positively skewed,


sand

L2S3U1 0.27 1.77 2.91 0.60 0.63



Very lepto kurtic, coarsesand

L2S3U2 0.17 0.54 0.66 1.15 1.18


positively skewed,


sand

L2S3U3 0.10 0.47 0.90 0.85 0.81 Poorly sorted sorted,


Very platy kurtic, coarsesand


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51

4.3.1 The bivariate plots of the sieve analysis parameters

Chart 6:bivariate plot of skewness vs. Standard deviation

After Friedman, (1961)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60

SKEWNESS

STANDARD DEVIATION

BEACH

RIVER


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52

Chart 7 bivariate plot of mean vs. Standard deviation

Chart 8:bivariate plot of skewness vs. simple sorting after friedman, (1979)

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60

MEAN

STANDARD DEVIATION

RIVER

BEACH

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80

SKEWNESS

SORTING

RIVER

BEACH


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53

4.3.2 Sieve analysis interpretation

The cumulative graph which is self-explanatory has pictorially shown using the

cumulative curves the grain size proportions. When trending along the

horizontal axis from Phi -1 to 2.0, the curve tend to have a very steep upward

Shows the high content of coarse to medium grained particles. But moving from

2.0 up to pan the curve slope becomes gentle indicating reduction in fine

particle contents.

The sieve analysis data for all sample has indicated that modal particle size

occurrence is the particle size of -1 having an average percentage retained

value of 25.9% which is the gravel sized particle followed by the 1coarse

grained particles of average percentage retained 21.56% while others are

0(21.56), 2(16.70), 3(7.74), 4(3.38) pan(1.21).

In the bivariate plot, most of the samples are located within the river sediment

zone( the upper right sections of the thre plots.


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54

4.4 Pebble morphometric results and interpretation

4.4.1 Results

The pebble morphometric also was carried out on a set of sample collected from

the initially mentioned lithology sections. The samples which include ten

pebbles used for the morphometric analysis were collected from pebble

containing units.


s/n L(cm) I(cm) S(cm) S/L I/L (L-I)/(L-S) 3S/LI 10[(L-1-0.5)]/(S/L)

1 4.0 2.6 1.8 0.450 0.650 0.636 0.825 3.030

2 3.4 2.2 1.8 0.529 0.647 0.750 0.920 4.722

3 3.3 1.8 0.9 0.273 0.545 0.625 0.497 4.583

4 3.1 1.7 0.9 0.290 0.548 0.636 0.517 4.697

5 2.5 2.0 1.2 0.480 0.800 0.385 0.702 -2.404

6 3.6 1.7 1.4 0.389 0.472 0.864 0.765 9.351

7 2.5 1.8 1.5 0.600 0.720 0.700 0.909 3.333

8 2.3 1.9 1.5 0.652 0.826 0.500 0.917 0.000

9 2.0 2.1 1.5 0.750 1.050 -0.200 0.930 -9.333

10 2.3 1.4 1.0 0.435 0.609 0.692 0.677 4.423



1 3.3 1.9 1.2 0.364 0.576 0.667 0.651 4.583

2 3.8 2.7 1.8 0.474 0.711 0.550 0.828 1.056

3 3.9 2.9 1.2 0.308 0.744 0.370 0.535 -4.213

4 3.0 2.2 1.2 0.400 0.733 0.444 0.640 -1.389

5 2.3 1.7 1.2 0.522 0.739 0.545 0.762 0.871

6 3.8 2.8 1.8 0.474 0.737 0.500 0.818 0.000

7 2.6 2.4 1.5 0.577 0.923 0.182 0.815 -5.515

8 2.7 2.2 1.4 0.519 0.815 0.385 0.773 -2.225

9 2.3 1.6 0.7 0.304 0.696 0.438 0.453 -2.054

10 1.8 1.4 1.0 0.556 0.7780.500

0.735 0.000


55/80

55



1 3.3 1.9 1.2 0.364 0.576 0.667 0.651 4.583

2 3.7 2.7 1.8 0.486 0.730 0.526 0.836 0.541

3 3.9 2.9 1.2 0.308 0.744 0.370 0.535 -4.213

4 3.0 2.2 1.2 0.400 0.733 0.444 0.640 -1.389

5 2.3 1.7 1.2 0.522 0.739 0.545 0.762 0.871

6 3.8 2.8 1.8 0.474 0.737 0.500 0.818 0.000

7 2.6 2.4 1.5 0.577 0.923 0.182 0.815 -5.515

8 2.7 2.2 1.4 0.519 0.8150.385

0.773 -2.225

9 2.3 1.6 0.7 0.304 0.696 0.438 0.453 -2.054

10 1.9 1.4 1.0 0.526 0.737 0.556 0.722 1.056



1 4.1 2.5 1.9 0.463 0.610 0.727 0.875 4.904

2 6.5 3.7 2.8 0.431 0.5690.757

0.970 5.960

3 5.3 2.7 1.6 0.302 0.5090.703

0.659 6.715

4 4.5 2.6 1.9 0.422 0.5780.731

0.837 5.466

5 3.1 2.5 2.0 0.645 0.8060.545

1.011 0.705

6 3.6 2.7 1.5 0.417 0.7500.429

0.703 -1.714

7 3.1 2.0 1.4 0.452 0.6450.647

0.762 3.256

8 2.6 2.1 1.6 0.615 0.8080.500

0.909 0.000

9 2.5 1.8 1.3 0.520 0.7200.583

0.787 1.603

10 2.1 1.7 1.3 0.619 0.8100.500

0.851 0.000


56/80

56



1 6.4 3.7 3.3 0.516 0.578 0.871 1.149 7.195

2 8.3 4.7 3.3 0.398 0.5660.720

0.973 5.533

3 4.0 2.7 2.5 0.625 0.675 0.867 1.131 5.867

4 4.7 3.7 3.0 0.638 0.787 0.588 1.158 1.382

5 4.2 2.0 1.7 0.405 0.476 0.880 0.836 9.388

6 5.2 4.4 2.5 0.481 0.846 0.296 0.881 -4.237

7 5.8 4.3 2.5 0.431 0.741 0.455 0.856 -1.055

8 4.1 2.7 1.6 0.390 0.659 0.560 0.718 1.538

9 5.7 2.9 2.0 0.351 0.509 0.757 0.785 7.318

10 5.3 3.5 2.5 0.472 0.660 0.643 0.944 3.029

Table 4.29 Sample 22: Location3, Section 3, Unit 1


1 3.0 2.4 1.8 0.600 0.800 0.500 0.932 0.000

2 4.5 2.8 2.6 0.578 0.622 0.895 1.117 6.829

3 3.3 1.4 1.5 0.455 0.424 0.778 0.538 6.105

4 3.9 2.0 1.4 0.359 0.513 0.737 0.706 7.242

5 2.5 2.0 1.4 0.560 0.800 0.455 0.8I9 -1.266

6 4.1 2.9 2.0 0.488 0.707 0.571 0.876 1.464

7 3.3 2.3 1.5 0.455 0.697 0.556 0.763 1.222

8 2.7 2.0 1.9 0.704 0.741 0.875 1.083 5.327

9 3.8 1.5 0.9 0.237 0.395 0.793 0.504 12.367

10 4.5 2.0 1.8 0.400 0.444 0.926 0.865 10.648


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57



1 5.6 3.7 3.1 0.554 0.661 0.760 1.129 4.697

2 3.2 2.3 1.9 0.594 0.719 0.692 0.977 3.239

3 3.4 2.8 2.0 0.588 0.824 0.429 0.944 -1.214

4 3.8 2.5 1.7 0.447 0.658 0.619 0.803 2.661

5 3.2 2.8 2.0 0.625 0.875 0.333 0.963 -2.667

6 5.2 3.9 2.5 0.481 0.750 0.481 0.917 -0.385

7 5.2 3.1 2.0 0.385 0.596 0.656 0.792 4.063

8 3.9 2.9 2.4 0.615 0.744 0.667 1.069 2.708

9 3.5 2.9 1.6 0.457 0.829 0.316 0.739 -4.030

10 3.2 1.8 11.0 3.438 0.563 -0.179 6.136 -1.977



1 8.6 5.1 4.1 0.477 0.5930.778

1.163 5.827

2 5.8 4.1 3.1 0.534 0.7070.630

1.078 2.425

3 4.6 3.1 2.2 0.478 0.6740.625

0.907 2.614

4 4.0 2.9 2.4 0.600 0.7250.688

1.060 3.125

5 4.7 2.8 2.3 0.489 0.5960.792

0.974 5.960

6 5.4 4.1 2.9 0.537 0.7590.520

1.033 0.372

7 7.0 4.3 3.4 0.486 0.6140.750

1.093 5.147

8 4.3 2.8 1.8 0.419 0.6510.600

0.785 2.389

9 4.4 3.3 2.7 0.614 0.7500.647

1.107 2.397

10 4.6 2.9 2.3 0.500 0.6300.739

0.970 4.783


58/80

58



1 3.9 2.9 1.5 0.385 0.7440.417

0.668 -2.167

2 3.5 1.9 1.3 0.371 0.5430.727

0.691 6.119

3 2.4 1.8 1.2 0.500 0.7500.500

0.737 0.000

4 3.5 2.3 2.0 0.571 0.6570.800

0.998 5.250

5 2.5 1.4 1.1 0.440 0.5600.786

0.724 6.494

6 2.5 1.8 1.3 0.520 0.7200.583

0.787 1.603

7 3.0 2.2 1.4 0.467 0.7330.500

0.746 0.000

8 2.7 1.8 1.6 0.593 0.6670.818

0.945 5.369

9 2.1 1.4 1.2 0.571 0.6670.778

0.838 4.861

10 2.6 1.5 1.0 0.385 0.5770.688

0.635 4.875

4.4.2 Pebble Morphometry Interpretation

In pebble morphometric interpretation, the dominant forms of the sample were

obtained from the available data. The mean value of 10 pebbles was taken from

the result obtained.

According to Hubert (1968), the elongation ratio values for fluvial

environments range from 0.6 to 0.9. most values gotten from the morphometric

data for ratio of elongation falls within this range. The maximum projection

sphericity of pebbles ( ) is generally high for fluvial environment than forbeaches.

From the result, the maximum value for the projection sphericity falls above

0.65 which indicates fluvial activity. In terms of geometric which describe the


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59

three dimensional aspects of a pebble proposed by folk,(1974) , which include

compact, compact bladed, compact elongated, compact platy, bladed elongated,

platy, very platy, very bladed and very elongated.

Since dominant forms for river pebbles are compact, bladed, compact bladed

and compact elongated, it can be deduced from the above data results that the

pebbles are of fluvial environmental deposits.

Table 4.33 total mean values for all pebbles.

Parameters mean count

Oblate-Prolate Index (OPI) 2.14

Maximum projection sphericity index (MPS) 1.04

Disc-Rod Index (DRI) 0.59

Flatness ratio 0.69

Elongation ratio 0.52


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60

4.4.3 Bivariate plots.

SCATTER PLOT OF MPSI VS OPI

Chart 9: scatter plot of maximum projection sphericity index versus oblate

index (dobkins and folk 1970)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

-15 -10 -5 0 5 10 15

RIVERRIVER

BEACH BEACH


61/80

61

Chart 10 sneed and folk form diagram

Table 4.34 sphericity form diagram counts all pebbles.

Sneed & Folk classes

Count Percent

Compact 7 7.78

Compact-Platy 3 3.33

Compact-Bladed 18 20.00

Compact-Elongate 13 14.44

Platy 1 1.11

Bladed 26 28.89

Elongate 19 21.11

Very-Platy 0 0.00

Very-Bladed 2 2.22

Very-Elongate 1 1.11

SLI

00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.90.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

1.0BLOCK

RODSLAB

C

VP VE

P B E

CBCP CE

VB


62/80

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4.5 Discussion

The area under study is a sedimentary terrain. While sedimentary environment

are parts of the earth surface physically, chemically and biologically distinct

from its adjacent areas. This work has emphasised thoroughly that a lot of

processes come into play in the sedimentary environment. The depositional

process is a product of the environment, which in turn is controlled by: Climate

Geography Tectonic setting Sediment supply. Although earlier works have

already modelled these processes categorizing them into three basically distinct

processes; physical chemical and biological.

Sedimentary grains are formed when the rocks at the Earth's surface are slowly

broken up physically by exposure to wind and frost, and decomposed

(chemically) by rainwater or biological action. These processes are collectively

termed weathering. Once a rock has been broken up by weathering, the small

rock fragments and individual mineral grains can be eroded from their place of

origin by water, wind or glaciers and transported to be deposited elsewhere as

roughly horizontal layers of sediment.

The resulting sediment reflects the original rock types that were weathered, the

efficiency of erosion and transport, the extents of chemical and physical

degradation of the sediment grains during transport, and the conditions under

which the grains were deposited from the transporting water, wind or ice. For

example, sand-sized grains of quartz are one of the main constituents of

sandstone, but those grains may have been transported by water in a river,


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carried by waves on a sea-shore, or blown around in hot desert sandstorms (to

give just three possibilities).

In this study work, we distinguish which of the many possibilities was the most

likely to have perpetuated the sedimentary deposit at Use Ikot Amama and the

Agali sandstone of the Benin formation not the less.

Some of the identified beds boosted intercalation of both fine and coarse

grained sandstone indicating either a deltaic or sudden change in the channel

velocity allowing for fine grained sediments to settle.

As earlier noted in the study that the coarse poorly sorted grains indicated a

fluvial environment and also that the particle are channel bed load, the presence

of the high occurrence of the pebbles in the study area conclude the fact that is a

fluvial environment. The observable paraconglomerates and the

orthoconglomerated in the field give the idea of the channel velocity. The

paraconglomerates with indicates high matrix shows a low stream velocity

allowing for the settlement of matrix.

The primary purpose of this study is to understand the facie characterisation of

various outcrop sections at Use Ikot Amama. This means, that the study

described each bed characteristics in terms of texture, geometry, grain to matrix

ratio, and lithological resemblance and repetition so as to track back to the

environment of deposition, the conditions under which the grains were

deposited from the transporting water.


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The field observation shows that the bed consists of fine grain sand, coarse

grain sand, paraconglomerats, orthoconlomerates, breccia and the lithological

sections shows some repetitive geological patterns.

The laboratory analysis revealed more in the characterisation most precisely the

pebble mophometry describing the pebble shape using the elongation ratio, the

oblate prolate index. The mean values of Flatness ratio for the pebbles is 0.69,

Elongation ratio is 0.52, M.P.S.I. is 1.04(river), Oblate Prolate index is

2.14(river). The bivariate plot of M.P.S.I. vs OP Index (Dobkins and Folk,

1970) is based on the proposition that the 0.66 sphericity (M.P.S.I) line best

separate beach and river pebbles while values less than 0.66 are typical of

beachs, higher values above 0.66 suggest fluvial origin. An OP index value

greater than -1.5 generally indicates fluvial conditions. The bivariate plot of

Roundness vs. Elongation ratio (after Same, 1966) show that roundness has the

greatest influence in determination of the depositional environment of the

pebbles i.e the lower the roundness, the higher the probability that the

depositional environment would be fluvial(Olugbemiro and Nwajide, 1997). It

is important to note that roundness alone is not particularly indicative of

depositional environment, rather the extent of abrasion that the grains or pebbles

have undergone, it reflect overall transport history(Lewis and McConchie,

1994) and does not necessarily reflect the distance grains have travelled from

their source. Sphericity is more reliable than roundness because it illustrates the

departure of the body from equidimensionality.


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OP index expresses the relationship of the change in form of pebbles ( platy,

elongate and compact) with environment. The plot of M.P.S.I vs OP index is

more diagnostic for environmental discrimination of pebbles than the plot of

same, 1966 (Roundness vs Elongation ratio). Moreover, with prolong transport,

sphericity and op index become increasingly divergent for fluvial and beaches

and thus provide better discrimination (Dobkins and Folk, 1970). The bivariate

plot of Coefficient of Flatness vs M.P.S.I. show that over 97% of the pebbles

are of fluvial origin.

According to Dobkins and Folk (1970) and Gale (1990), certain form classes

occur much more frequently in one environment than they do in another. Thus,

the three shape classes that are most diagnostic of beach action are platy, very

platy and very bladed. While bladed and platy predominate in high energy

beaches, bladed are most common on low energy beaches. On the other hand,

compact, compact bladed, and compact elongate are most indicative of fluvial

action. While beach pebbles plot toward the left and bottom parts of the

sphericity form diagram, fluvial pebbles plot near the upper part. The sphericity

form diagram of the pebbles sets from Sandstone also point to fluvial origin

(7.6% are compact, 14.4% compact elongate, 20.0% compact bladed, 21.11%

are elongate and 28.89% are bladed).

As for grain size distribution, the mean grain size in a deposit is largely a

function of energy of the processes controlling transport and deposition i.e

particles are segregated according to their hydrodynamic behaviour, which


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depends on size, specific gravity and shape. In contrast, the degree of sorting

grains in a deposit is a function of the persistence and stability of energy

condition except where constrained by availability of grains that can be

deposited in the environment (Olugbemiro and Nwajide, 1997).

From the sieve analysis various parameters were calculated with include the

mean, median, degree of sorting, skewness and kurtosis. Most of the sample

gave a result revealed poor sorted when correlated to the deduced observation

from the field it scores a pass mark. The approach used the size and shape of the

grains in the sediment or sedimentary rock sample acquired to reveal quite a lot

about the origin of the sediment.

Because a vigorous river transports much larger grains than a gentle current in a

lake, so the modal size of the grains which is the 1 grain size gives an

indication that strong currents could have transported and deposited the grains.

In other words, the grain size depends on the energy of the environment in

which the sediment was deposited. The general shape of the grains will tell you

about the nature of the transporting medium.

The degree of sorting in sediment is another useful method that was used in

distinguishing the different types of depositional situation. Sorting is a measure

of the range of grain sizes present in a sediment or sedimentary rock. Poorly-

sorted sediment as in the case of the studied sediments has a wide range of grain

sizes as a result of rapid deposition, such as occurs during a storm. On the other

hand, well-sorted sediment has a narrow range of grain sizes, and is the result of


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extensive reworking of sediment by wind action in deserts, or wave action on

beaches and in shallow shelf seas.

Also, the coarse grained particles show that the sediments were of bed load i.e.

they were carried along the channel beds.


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CHAPTER FIVE

5.1 summary and conclusions

Detailed sedimentological and lithofacies analyses show that the sediments

deposited at the study area Use Ikot Amama were likely deposited by two

sedimentary environment, the fluvial and the deltaic. A typical sequence begins

with accumulation of coarse fluvial channel and/or tidally influenced fluvial

channel deposits. The study of the pebble morphometry and grain size

distribution has shown that Sandstone is likely a product of fluvial deposition

though certain sieve analysis suggest near marine condition. This is in line with

the earlier conclusions of fluvial or fluvial deltaic.


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5.3 recommendations

The outcrop logging that was done is the field was able to provide a vague

model as a result of the analogue tools and methods. Further work should be

carried out using modern tool precisely the laser scanners and digital remote

photographic tools to get a clearer, more detail and information from any

lithology model.


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APPENDIX A

Abbreviations and symbols

B= bladedC= compact

CB= compact bladed

CE= compact elongated

CP= compact platy

E= elongated

L= location

S= section

U= unit

VB= very bladed

VE= very elongated

VP= very platy

MPS = Maximum projection sphericity index

DRI= Disc-Rod Index

OPI = Oblate-Prolate Index

IE = Elongation index = weight of aggregate in the sieve = total weight of aggregateL= long

I= intermediate

S= short


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APPENDIX B

Formula

Elongation ratio=

,

Flatness ratio =

Maximum projection sphericity index (MPS) = Disc-Rod Index (DRI) =

Oblate-Prolate Index (OPI) = []

Graphic mean =

Median = 50

Graphic standard deviation (1) = + Inclusive graphic skewness (SKI) =

+

Graphic kurtosis (KG) =

Degree of sorting =


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APPENDIX C

Verbal limits folk (1974)

SORTING INTERPRETATION

4.00

SKEWNESS INTERPRETAION

-1.0 Very Negatively skewed

-0.3 - (-0.1) Negatively skewed

-0.1 - 0.1 Symmetrical

0.1 - 0.3 Positively skewed

0.3-1.0 Very positively skewed

KURTOSIS INTERPRETAION

3.00 Extremely lepto kurtic


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MEAN INTERPRETAION

-1.00-0.00 Very coarse sand

0.00-1.00 Coarse sand

1.00-2.00 Medium sand

2.00-3.00 Fine sand

3.00-4.00 Very fine sand

4.00-5.00 Coarse silt


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APPENDIX D

Sand sorting classification based on standard deviation

Standard deviation sorting environment

4.00 Extremely poorly sorted Mainly geofluvial

settings


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Appendix E

The Sneed & Folk (1958) diagram

assessment of depositional environment using lithofacies association and petrophysical analysis

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