mineral chemistry of clays associated with the late cretaceousearly palaeogene succession of the...

0016-7622/2015-86-6-631/$ 1.00 © GEOL. SOC. INDIA

JOURNAL GEOLOGICAL SOCIETY OF INDIAVol.86, December 2015, pp.631-647

Mineral Chemistry of Clays Associated with the Late Cretaceous-Early Palaeogene Succession of the Um-Sohryngkew River

Section of Meghalaya, India: PalaeoenvironmentalInferences and K/Pg Transition

SUCHARITA PAL1, J. P. SHRIVASTAVA1* and SANJAY K. MUKHOPADHYAY2

1Department of Geology, University of Delhi, Delhi - 110 007, India2Ex-Palaentology Division, Geological Survey of India, 15, Kyd Street, Kolkata - 700 016, India

*Email: [email protected]

Abstract: A unique, continuous, shallow marine succession within the Langpar Formation in the Um-Sohryngkew riversection of Meghalaya contains late Maastrichtian through early Danian planktonic foraminiferal biozones (CF4-P1a)and the K/Pg boundary (between CF1 and P0). To resolve compositional overlap [in the three-fold clay mineral basedsub-divisions of the section (include 1-2 mm thick yellowish brown clay layer in biozone CF3)] and to understandpaleoenvironmental conditions prevalent at the time of K/Pg transition, micro-structural and compositional studies werecarried out. The paper discusses accurate compositional limits of solid solubility in smectite and illite. Clay morphologicalattributes distinctly vary with the changes in the biozonation. Major oxide data plots for the litho-units (samples JP1-16)over binary diagrams, show clustering of plots within the illite compositional field. Plots based on structural formulaeand layer charges of illite and kaolinite rich clays (from CF4 to Pla biozones), show closeness with the clay data fieldsof Agost, Caravaca, Petriccio and El-Kef K/T boundary sections as their charge occupancies at tetrahedral (Zt), octahedral(Zo) and interlayer (Zi) sites are similar. Thermodynamic data plots over ternary [AR2

3+Si3O10 (OH)2 - R23+SiO4O10(OH)2

- A3AlSi4O10(OH)2] diagram, clustered within the illite compositional fields. Majority of illites shows high K values.They represent occasionally higher Altet. and lower Aloct. layer charges. Calculated palaeotemperature values for illite(from the CF4 to Pla zones) vary from 68 - 232ºC. Sudden rise in the temperature (>140ºC) of illite formation noticed inthe upper part of the biozone CF3 (sample JP-12) is comparable to the K/T boundary layer of Caravaca section. Widevariation in the humid tropical to arid-semiarid climatic and thermal (diagenetic to low grade metamorphic) conditionsnoticed across the succession is possiby linked with the contemporaneous Abor / Deccan volcanic activities (at the timeof their deposition) as also reflected in their clay layer [Si (2.95-3.68)] and interlayer [K+Na (0.4-4.61)] charges.

Keywords: Um-Sohryngkew river section, K/Pg boundary, Structural formulae, Thermodynamic components, Claystratigraphy, Palaeoenvironment, Meghalaya.

INTRODUCTION

Late Cretaceous through early Paleogene continuousmarine successions (Fig. 1) are known from Egypt, Israel,Tunisia, Spain, Italy, France, Bulgaria, Kazakhatan, Texas,Alabama, and boreholes in the Pacific and Atlantic oceans(Yassini, 1979; Keller, 2004; Strong 2000; Arenillas et al.,2000;Arenillas and Arz, 2000; Hart et al., 2004, 2005; Galal,2006; Alegret and Thomas, 2007 and references therein).Most of the information on the K/Pg (Cretaceous/Paleogene)boundary events is from these sections which have fascinatedscientists on the cause-effect relationships. Despite thepresence of late Cretaceous and early Paleogene marinestrata (Nagappa 1959, Samanta 1974), Deccan Traps (with

intertrappeans), and mobile belts, the Indian sub-continentwas not known to have a K/Pg boundary section comparableto the international standards. Precise identification of theboundary events and their bearing on the paleogeographyand paleoclimate remained unknown for this region untilthe discovery of an uninterrupted finely resolved shallowmarine outcrop section (Fig. 1) from Meghalaya, easternIndia. Traditionally known as the Therriaghat section onthe west bank of the Um-Sohryngkew river, this lateMaastrichtian-early Danian sequence constitutes thelowermost part of a continuous marine section ranging fromlate Cretaceous through early Oligocene.

Medlicott (1871) recognized the Therriaghat section or

JOUR.GEOL.SOC.INDIA, VOL.86, DEC. 2015

632 SUCHARITA PAL AND OTHERS

Fig.1. Lithostratigraphy (modified after Mukhopadhyay, 2008) and sample locations on the Um-Sohryngkew river section. Insets:(a) Location of Meghalaya with respect to India, (b) Location of the Therriaghat section around Um-Sohryngkew river and(c) Lithological log at the K/T interval in the Um-Sohryngkew river. Note: Samples 1 - 16 collected from the section is referredto JP1 - JP16 in the text.


K/Pg INTERVAL CLAYS OF THE UM-SOHRYNGKEW RIVER SECTION, MEGHALAYA 633

the Um-Sohryngkew river section of Meghalaya (Fig. 1)that attracted attention of geologists and paleontologists asa reference section for the Bengal Basin (Dasgupta, 1977).Like any other K/Pg boundary sections, this section (citedFig 2; Shrivastava et al., 2013) also remained controversial(Biswas, 1962; Samanta, 1974; Dasgupta, 1977; Pandey,1981, 1990; Bhandari et al., 1987; Lahiri et al., 1988). Fineresolution stratigraphy based on planktonic foraminiferalzones revealed that Um-Sohryngkew river section iscontinuous across the boundary (Mukhopadhyay 2009,2011) which can be used to study paleoenvironment duringthe K/Pg transition. In this section, Pandey (1981, 1990)recognized an unconformity at the K/Pg boundary. Lateron, Bhandari et al. (1994) identified a 1.5 cm thick limoniticlayer enriched with Ir, Co, Ne, Os, Fe, Zn, Sb (by a factor of4 to ~1200) and rare earth elements (by a factor of 1.7 to~5), thus, considered the K/Pg boundary. Subsequentbiostratigraphic studies indicated that this clay layer lies inbiozone CF4, occurring below the actual K/Pg boundary(Mukhopadhyay, 2008). While accepting the presence ofthe Ir rich clay layer, Mukhopadhyay (2009) reported anotherbrown claystone layer (1-2cm thick) in biozone CF2 (justbelow the K/Pg boundary), showing significantly enrichedvalues of Au, Pt and Pd. Thus, in the Um-Sohryngkew riversection, high concentrations of platinum group metals occursat two stratigraphic levels corresponding to two successiveepisodes of Deccan volcanism. The first phase occurredduring biozone CF4 [Chron C30N; 66.5 - 67 Ma (Courtillotet al., 2000), 66.6 Ma (Keller, 2003), 66.2- 65.7 Ma (Ravizzaand Peucker- Ehrenbrink, 2003)], whereas, the second,the most vigorous phase of eruption occurred duringbiozone CF2 [Chron C29R; 65.4–65.2 Ma (Barrera, 1994;Courtillot et al., 1996; Hoffman et al., 2000; Keller, 2001)].This concurs with Ellwood et al., (2003) who discussedmore than one Ir anomaly in the Oman K/T (Cretaceous/Tertiary) boundary sections. Gertsch et al. (2011) studiedthe same interval which was earlier studied by Pandey (1990) and Bhandari et al. (1987, 1994) which includedlower part of the K/Pg interval from the same section ofMukhopadhyay (2008). Since Mukhopadhyay (2008)recovered planktonic foraminifera corresponding tobiozone CF4 from the samples of this interval, the K/Pgboundary transition of Gertsch et al. (2011) occurs withinthe biozone CF4 of Mukhopadhyay (2008), correlated thestudied interval of Pandey (1981, 1990) with his biozoneCF4. Based on well-established standard planktonicforaminiferal biozones which precisely identified a K/Pginterval in the Langpar Formation of the Therriaghat section.Mukhopadhyay (2008) yielded some diagnostic foraminiferaof the boundary which helped in the identification of

biostratigraphic continuity across the K/Pg boundary.Moreover, Mukhopadhyay (2012a) recorded few speciesof Guembelitria which is an essential biotic component ofthe K/Pg marine successions. Based on inferredpalaeoecology and palaeoenvironments, such species andtheir distribution provided crucial information related to theK/Pg boundary and transition strata. Biostratigraphicallywell-constrained shallow marine section along the river Um-Sohryngkew at Therriaghat in north-east India (Pandey,1990; Mukhopadhyay, 2008) records most of the attributesof a K/T boundary section including - two claystone layersof anomalous Platinum Group of Elements (PGE)concentration corresponding to biozones CF4 and CF2(Bhandari et al., 1987; Mukho-padhyay, 2009), cycles ofmarine transgression-regression, size reduction of planktonicforaminifera (as effects of Deccan eruption) and effects oftectonic pulses and micro-spherule rains on environmentand planktonic foraminifera (Mukhopadhyay, 2012a, b).Such unusual occurrence requires justification as planktonicforaminiferal extinction pattern in this section is gradualright from biozone CF4 to Pla (Mukhopadhyay, 2012a, b).Moreover, environmental conditions during basal Daniancould not be retrieved satisfactorily.

Based on clay mineral abundances (cited Figs. 3)Shrivastava et al., 2013 divided entire K/T boundarysuccession into lower, middle and upper parts. The spike inthe TOC content from the lower level (biozone CF3) of theupper part of the succession is characterized by negativeδCe anomaly which indicates suboxic/anoxic conditions.Clay mineralogical attributes, REE patterns and TOCcontents analogous to those of the known K/Pg boundariesappeared within 1-2 mm thick, yellowish brown clay layerin the biozone CF3 in the Um-Sohryngkew river section.Significant shift in the redox condition (cited Table 3;Shrivastava et al., 2013) occurred in the bottom seawaterand sediments (from Biozone CF4 to Pla) which largelycorresponds to changes in the planktonic foraminiferal(Mukhopadhyay, 2008) and Au, Pt, Pd anomalies ofMukhopadhyay (2009). The planktonic foraminifera basedboundary, however, occurs slightly above in the sectionbetween biozones CF1 and P0, developed in the coprolite-bearing shaly marlite within the calcareous shale (close tosample 14) layer. The early appearances of mimic attributesof clay minerals and REE patterns resemble to those of theboundary layers attributed to the initiation of tectonic eventsduring biozones CF3 (with attendant environmental changesthat affected the shelf area and the provenance).

Compositional overlap occurs among minerals such assmectites, illites, and mixed-layered I/S clays. Although, thisoverlap has been cited as evidence that smectite and illite



form a mutual solid solution, it is not necessarily indicativeof solid solution between them (Ransom and Helgeson,1989; Warren and Ransom, 1992). The purpose of thepresent communication is to determine accuratecompositional limits of solid solubility in smectite and illiteby critically analyzing compositional data in order togenerate sets of thermodynamic components that can be usedto describe the chemical interaction of illite and smectitewith their mineralogic and aquatic environments. It has beenfound that the clay proportions and their morphologicalattributes vary across the succession. In order to understandmicro-textural, micro-structural and compositional attributesof a single or multi-crystalline clays and non-clay phases inthe bulk clay matrix (<2µm fraction), high resolutionscanning electron microscope equipped with energydispersive spectrometer (SEM-EDX) was used in thepresent study. Microstructural elements include primaryclay particles, microaggregates and aggregates of particles.Clay fabric implies to the orientation and arrangement orspatial distribution of the solid particles as well as theparticle-to-particle relationships. Therefore, with thisunderstanding micro-structural and compositional studieson clays associated with Um-Sohryngkew river section ofMeghalaya area were carried out to resolvepaleoenvironment, paleo-temperatures and palaeo-depositional conditions during diagenesis as well ashydrothermal processes. Based on SEM-EDX study,hydrothermal clays were distinguished from the diageneticclays through their size, crystallinity, inter-stratification andflaky morphology.

MATERIAL AND METHODS

Field work was carried out under the aegis ofInternational Geological Correlation Programme (IGCP),Project-507.As per the sample-sites marked (with black solidcircles) in the mapped litho-log (Fig. 1c), samples (JP1-JP16) were collected from the middle part of the LangparFormation, covering the K/Pg boundary. Each sample of~500 gm was collected from 25 cm below the surface. Forfriable sediments, hollow steel pipes (3.5 cm diameter withone end pointed) were used as an auger to avoidcontaminations.

Prior to geochemical analysis, clay (0.2-2.0 µm) fractionswere separated out from each of the bulk samples usingprocedure discussed by Jha et al. (2012) which involvesdisaggregating each sample in the distilled water, then treatedwith 1N HCl (to dissolve and minimize carbonates) andthoroughly cleaned by centrifugation and finally suspensionwas removed. The clay fraction was separated out after

specified time intervals (based on the settling velocity ofparticles) following the dispersion-centrifugation-decantation procedure (Jackson, 1985; Larid and Nater,1993) and dried in the oven. Gold coated clay specimenswere prepared for scanning electron microscopic (SEM)study. These specimens were scanned (from 1000 X - 5000KX magnifications) under high resolution SEM (Carl-ZeissEVO-MA10, in-housed in the Department of Geology,University of Delhi). SEM images (Fig. 2) were obtained tounderstand morphological characters of the clay minerals.To determine major oxide compositions, clay minerals werecoated with a thin layer of carbon and analyses of thesespecimens were done using Energy Dispersive X-raySpectrometer [(EDX) (Oxford Make; Model-Inca X-Act)]in a window mode and data presented in Table 1.

SEM-EDX RESULTS

Clay samples (JP1 - JP16) represent complex assemblagesof clay matrix and other mineral phases. In general, SEMimages (Fig. 2a-p) show dominance of illite > kaolinite >montmorillonite. Morphological attributes of the clayminerals were recorded systematically and discussedbiozone-wise from older to younger rock-units. BiozoneCF4: SEM images (Fig. 2a) show platy kaolinite with longelongated illite particles in the light grey coloured earthylimestone unit (sample JP-1). Kaolinite- rich limestone layer(sample JP-2: Fig. 2b) shows dense aggregate of platy,smooth flakes of kaolinite. Silt layer (sample JP-3) rich inorganic matter, shows dense accumulation of kaolinite andillite grains (Fig. 2c). Grey calcareous shale sample (JP-4)comprising of kaolinite and illite, shows large, pseudo-hexagonal, platy laths of kaolinite, interstratified with tinygrains of elongated illite laths (Fig. 2d). The light coloured,hazy, sub-rounded, corn flake-like texture with wavy grainboundaries of smectite laths lie scattered in the groundmassmainly of kaolinite and quartz minerals (as shown in theinset picture of Fig. 2d). Silty layer (sample JP-5) is oftentraversed by quartz veins. SEM images show alteration ofsiliceous grains and pre-existing mud into smectite and otherphyllosilicates (Fig. 2e). In the inset picture (Fig. 2e),smectite grains (< 2µm) are adhered to massive quartz grainsand forms rosette-like structures (Fig. 2f). Successive layer(sample JP-6) in the Biozone CF4 with high organic mattercontent represents large number of kaolinite particles. Thekaolinite-rich silty mudstone (JP-7) shows denseaccumulation of platy, smooth flakes of kaolinite and smalllaths of illite. Scattered, massive quartz grains (inflated inappearance) occur alongwith micro-laths of flaky aggregatesstacked over quartz grains (Fig. 2g). Light coloured earthy



Fig.2. SEM microphotographs (specimens JP-1 to 8) show aggregate of kaolinite grains in sample JP-1, platy kaolinite grains insample JP-2, microaggregate of clay particles in sample JP-3, illite microaggregates in sample JP-4, parallel well developedstacks of illite particles and platy kaolinite particles in sample JP-5, platy kaolinite particles in sample JP-6, flakes of kaoliniteand small laths of illite in sample JP-7, platy hexagonal illite flakes in sample JP-8.



Fig.2 contd... SEM microphotographs (specimens JP-9 to 16) show needle shaped illite grains and platy kaolinite particles in sampleJP-9, needle-like parallel illite particles and tabular kaolinite particles in sample JP-10, criss-cross arrangement of illite lathsin sample JP-11, illite laths surrounding platy kaolinite particles in sample JP-12, matrix type structure with small illite lathsin samples JP13 and JP-14, or disaggregated kaolinite particles in sample JP-15 and well crystallized illite stacks in samplesJP-16.



limestone (JP-8) shows platy kaolinite and small flakes ofillite. The light coloured earthy limestone (JP-9) layercontains kaolinite and illite clays (Fig. 2h). The illite grainsare small, thin sheet-like structures (1-2µm) with irregulargrain margins, whereas, kaolinite grains are distinguishedby relatively thick flat sheet-like structure and smooth flakemargins. Clay matrix of fibrous-illite, lath-like illite andsmectite show alteration and conversion of lath-like illite tofibrous illite (Fig. 2i). Plates of kaolinite and illite laths,scattered over massive quartz grains, whereas, vermiformkaolinite particles stacked in the topmost silty layer (sampleJP-10) of the biozone CF4. Light grey coloured (sampleJP-10) clay consists of platy kaolinite and fibrous illite grains(Fig. 2j). In some parts of the section, platy kaolinite showsbook-like stacking. Small plates of kaolinite, rosette grainsof smectite, needle shape illite and massive grains of quartzare present (Fig. 2j). In the inset picture (Fig. 2j), pseudo-hexagonal, platy flakes of authigenic kaolinite lie overmassive silicate mineral grains. Biozone CF3: Greycalcareous shale (sample JP-11) chiefly consists of kaoliniteand illite. The SEM image (Fig. 2k) shows large, pseudo-hexagonal, platy laths of kaolinite inter-stratified with tinygrains of elongated illite laths. Abundance of kaolinite inthe upper part of the biozone CF3 (sample JP-12) occurs asaggregated and disaggregated particles alongwith illite. Illitegrains occur in different forms - rod shape (somewherepresent as tiny flakes) and they are scattered over massivequartz grains (Fig. 2l). Biozone CF2-CF1: Tiny illite flakesdominate Grey calcareous shale (sample JP-13) layer (Fig.2m). Sub-rounded, corn flake-like texture with wavy grainboundaries of kaolinite scattered in the groundmass chieflycomposed of quartz grains. Biozone P0: Palty kaolinite andsmall flakes of illite predominantly present in the silty layer(sample JP-14). Hazy, corn flakes-like texture with wavygrain boundaries of kaolinite particles scattered in thegroundmass of quartz (Fig. 2n). Biozone Pααααα: Shaly marllayer (sample JP-15) consists of scattered kaolinite particlesand few small laths of illite grains (Fig. 2o). Biozone Pla:Light coloured limestone layer (JP-16), rich in organicmatter, often traversed by quartz veins. SEM images showalteration of siliceous grains and pre-existing mud intosmectite and phyllosilicates (Fig. 2p). Inset picture (Fig. 2p)shows smectite grains (< 2µm) adhered to massive quartzgrains showing rosette-like structures.

Detrital kaolinites in association with the illite grainsdominate throughout the succession (Fig. 2a-p). The pseudo-hexagonal blocky kaolinite is of highly crystalline, occursin a wide range of grain sizes (maximum dimensions between0.5 and 10 mm) developed in the micro-fractures (withinrelatively fine-grained kaolinite). Platy kaolinite crystals are

of book-like and show vermiform character. These kaolinitegrains occur in the form of face-to-face stacks. Illite occursas sub-parallel flakes. The blocky kaolinite is found in bothprimary and secondary porosity, created by the dissolutionof feldspars. Sub-parallel arrays of platy illite developedduring crystal growth, thus, forming fibers and long laths(Hassouta et al., 1999). The anhedral platy crystals areperhaps of detrital origin, but, euhedral platy crystals developin a highly illitized sediments (e.g. as found in the EllonField and reported by Hassouta et al., 1999). Most of theareas with prolific occurrence of fibrous clays are suggestiveof their origin from weathering of the source rocks underwarm and humid climate with alternating periods ofevaporation.

Chemical composition of the mineral phases shows widerange of variation in the major oxide contents, such as SiO2,44.16 – 57.86%; Fe2O3, 0.26 – 3.87 % and Al2O3, 19.43 –37.68%. Data (Table 1) show that the SiO2 content rangesfrom 44.16 – 57.86% (average value = 53.79%), whereasAl2O3 content varies between 19.43 – 37.68% (average value= 27.38%). The SiO2 content of these clays is primarilyderived from the quartz in sand and silt size particles,whereas the main source of Al2O3 is clay minerals (inaddition to a few amount of Al2O3 derived from the feldsparminerals). In samples 1 and 12, low Al2O3 (11.1 and 9.29%,respectively) as well as low clay contents (6.68% and 4.8%,respectively) were noticed. To delineate clay compositionalfields' major oxide ratios were calculated from the majorelemental/ major oxide concentrations of the analyzedsamples (JP-1-16) and plotted over binary diagrams. Ratiosbetween MgO/Al2O3 vs. K2O/Al2O3, K2O/Al2O3 vs. FeO/Al2O3, Al2O3/SiO2 vs. MgO/Al2O3, Al2O3/SiO2 vs. K2O/Al2O3, MgO/Al2O3 vs. FeO/Al2O3 and MgO/Al2O3 vs. CaO/Al2O3 were plotted over standard compositional fields ofillite, kaolinite, smectite and chlorite. These fields weredelineated on the basis of their published (Weaver andPollard, 1973) major oxide data-sets. EDX data for thepresent samples when plotted over MgO/Al2O3 vs. K2O/Al2O3, Al2O3/SiO2 vs. K2O/Al2O3 and MgO/Al2O3 vs. K2O/Al2O3 diagrams (Fig. 3), it has been found that most of thedata plots cluster within the field of illite. But, in case ofK2O/Al2O3 vs. FeO/Al2O3 plots (Fig. 3), all the data plotscluster between smectite and chlorite fields. In case ofAl2O3/SiO2 vs. MgO/Al2O3 data plots (Fig. 3), samples JP-5, 8, 9, 14 and 15 fall within the field of chlorite. But, dataplots for the samples JP-1, 2, 3, 4, 7, 10, 12, 13, 16 fallsvery close to the compositional field of chlorite. Data plotsbetween MgO/Al2O3 vs. CaO/ Al2O3 (Fig. 3) show that thesamples (JP-1, 3, 13, 15 and 14) lie within the compositionalfield of illite, whereas, samples JP-2, 8 and 16 lie within the



limits of smectite field. Thus, they have significantcompositional differences.

STRUCTURAL FORMULAE ANDTHERMODYNAMIC COMPONENTS

Mineral chemistry data for individual clay (0.2-2.0 µm)minerals (Table 1) form the basis on which structuralformulae were calculated and presented in Table 2. (Weaverand Pollard, 1973). The weight percentages of the majoroxides after corrections were normalized to 100% forstructural formulae calculations. Using the procedurediscussed by Bain and Smith (1987), structural formulae ofclay minerals were calculated from the major oxide data onhalf unit cell basis, consisting of 22 negative charges (i.e.O10 (OH) 2). The FeO percentage required for structuralformulae calculations was calculated from the Fe2O3 usingthe conversion factor (Ragland, 1989). The total sum of theoctahedral cations of all the studied illite clays lies withinthe range of 2.02-2.55 (with an average of 2.26). Totaloctahedral occupancy is significantly higher than 2.0,especially in some illites of the Um-Sohryngkew riversection. It is most likely related to the presence of Fe, Aland Mg cations that occur externally on the illitic layers(e.g., Hower and Mowatt, 1966). Most illites generally showhigher K and occasionally higher Altet. and lower Aloct. layercharges. There are marked differences between differenttypes of illites. Illite and I/S mixed layers in the presentsuccession were resulted from diagenetic processes. Theseinclude authigenic crystallization, transformation of clayminerals and alteration of detrital feldspars. Amongst theseprocesses, the transformation of clay minerals is important

as it indicates P-T conditions at which rocks were formed.I/S mixed layers present only in one sample (i. e. JP-2) inthe lower part. The montmorillonite is present in very lowproportion, whereas, illite is present throughout thesuccession as one of the major clay minerals, indicates thatsome of the illite grains in this succession were probablyderived from the transformation of montmorillonite and I/Sclays.

The thermodynamic components accountable for theformation of illites in the samples were calculated from theirstructural formulae, following the procedure of Ransom andHelgeson (1993). This way, six generic thermodynamiccomponents responsible for illite solid solutions wererecast into actual thermodynamic components of illites inthe samples (Table 3). Illites form solid solutions withinthe compositional end members of Al- illite, Mg-illite andglauconite and the compositional plane of illite formed ofthese end members is defined by the equation: 565.5 =4.5ZO+ 30.0ZT –31.5 OOC (1), where, Zo = octahedralcharge, Zt = tetrahedral charge and Ooc = total number ofcations in the octahedral region. The sum of total chargesand cation occupancies is less than 565.5 for allthe samples, thus satisfy above equation, indicating thatthe sample compositions are well within the compositionallimits of the illite solid solution. Present study shows thatthe data plots for the illite predominant clay samples liewithin the illite field, when plotted over ternary AR2

3+

AlSi3O10(OH)2 - R23+Si4O10(OH)2 – AR3

2+AlSi3O10(OH)2diagram (Fig. 4.) of Ransom and Helgeson (1993), attributedto the presence of other minerals with kaolinite,montmorillonite.

Illites formed from kaolinite precursors are normally

Table 1. Major oxide analyses (Wt %) of clays and their calculated parameters for the samples JP1-16 of the K/Pg boundary succession of the Um-Sohryngkew river section

Samples JP-1 JP-2 JP-3 JP-4 JP-5 JP-6 JP-7 JP-8 JP-9 JP-10 JP-11 JP-12 JP-13 JP-14 JP-15 JP-16

Major oxides (in Wt%)

SiO2 55.32 49.01 56.46 55.61 55.76 53.60 57.86 54.39 58.18 53.18 57.01 53.12 44.16 44.85 56.24 55.87Al2O3 27.67 19.43 22.04 27.74 26.47 37.68 26.42 24.03 27.57 30.41 27.41 29.71 24.77 31.42 26.08 29.22FeO 6.09 19.75 7.19 8.01 6.09 1.31 5.63 8.32 5.13 3.71 8.39 8.12 16.49 8.58 6.72 6.26Fe2O3 1.20 3.87 1.41 1.57 1.19 0.26 1.10 1.63 1.01 0.73 1.65 1.59 3.23 1.68 1.32 1.23TiO2 0.00 0.00 2.75 1.15 0.00 0.00 0.56 2.34 0.60 2.21 0.00 0.00 1.33 1.60 1.07 0.00MgO 2.24 1.69 1.94 1.57 2.68 0.00 2.48 3.99 2.55 1.36 0.00 2.67 1.55 6.16 2.74 2.25CaO 1.36 0.00 3.32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.21 0.57 1.15 0.00Na2O 0.82 0.18 0.87 0.30 0.47 0.37 0.91 0.20 0.32 0.63 1.81 0.86 1.81 0.37 0.00 0.50K2O 4.38 6.42 4.12 4.17 4.34 6.78 5.12 5.23 4.71 7.82 3.88 4.06 5.76 4.90 4.81 4.75

Calculated parameters (in Wt %)

CIA 80.78 15.41 72.58 86.08 84.60 26.01 81.40 18.56 84.55 78.25 82.78 85.77 73.83 84.29 81.39 21.72PIA 67.96 10.32 59.00 73.14 70.72 21.33 65.61 14.51 70.11 58.12 71.05 74.03 56.66 71.14 66.38 18.19CIW 92.65 16.24 83.99 98.89 98.24 27.29 96.66 19.34 98.82 97.96 93.77 97.18 89.13 97.05 95.77 22.52WIP 512.72 301.89 538.87 212.22 307.99 411.34 564.65 305.88 227.17 424.53 1070.42 526.57 1083.81 263.63 43.16 474.55STI 3084.67 352.21 1157.67 2698.66 337.13 242.24 4977.90 1349.77 4902.23 1645.96 307.94 278.74 2140.68 2194.97 2753.02 291.21V 7.21 0.25 4.25 16.97 9.77 0.44 9.29 0.28 11.22 19.14 17.20 9.55 6.68 5.10 7.94 0.33An.ppt.mm/Yr) 1113.39 180.37 996.52 1189.17 1167.99 332.07 1122.04 225.59 1167.13 1076.27 1142.05 1162.32 1013.81 1163.37 1122.06 270.89



characterized by low octahedral Mg and Fe (Srodon & Eberl,1984), and the same is true for hydrothermal illites. Nocompositional trends have been demonstrated for these illitesin the diagenetic regime, although Cathelineau et al. (1987)has used the compositions of hydrothermal illites asgeothermometers. The crystal chemistry of illite was usedin the estimation of crystallization temperatures. Although,illite geothermometers are not accurate temperature markers,nevertheless their crystal structure is considered as goodindicator for thermal range in which they have been formed

(Merriman and Peacor, 1999). Clay geothermometry hasbeen applied to a variety of rock types to determine theirformation conditions (Cathelineau and Niveau, 1985;Kranidiotis and MacLean, 1987; Cathelineau, 1988; Jowett,1991; Zang and Fyfe, 1995; Zhang et al., 1997). Tetrahedralsite occupancy was used (Cathelineau and Izquierdo, 1988)in the illite geothermometry. Five different geothermometrytechniques were employed in order to estimate thetemperatures (in °C) - T1 = 213.3 Aliv + 17.5 (Cathelineauand Nieva, 1985), T2 = -61.92 + 321.98 Aliv (Cathelineau,

Fig.3. Major oxide data plotted alongwith the standard clay compositions to delineate clay compositional fields for lower, middle andupper parts of the Um-Sohryngkew river succession [Data source: Weaver and Pollard (1973), Alexandre, et al. (2005), Polito, etal. (2005), Beaufort, et al. (2005) for Illite (n=159); Nutt (1989), Komninou and Sverjensky (1995), Polito, et al. (2005),Alexandre, et al. (2005) for Chlorite (n=92), Ross and Hendricks (1945), Weaver and Pollard (1973) for Smectite (n=4) and forKaolinite (n=4)].



1988), T3 = 106 Aliv + 18, where Aliv = Aliv + 0.7(Fe/Fe +Mg) Kranidiotis and MacLean (1987), T4 = 319 Aliv-69,where Aliv = Aliv + 0.1(Fe/Fe + Mg), Jowett (1991), T5 =17.5 + 106.2 [2 Aliv - 0.88 (Fe - 0.34)] Zang and Fyfe (1995)for the formation of illite from various rock units in the studyarea. Temperature constraints on compositional variationsare also given along with their structural formulae (Table4). The calculations used by Kranidiotis and MacLean(1987) and Jowett (1991) have taken into account thevariation between Fe and Aliv contents, whereas thecalculation used by Cathelineau (1988) suggested that thereis no relationship between these two parameters. Estimatedtemperature range demonstrates temperature discrepanciesthat occurred with respect to T1, T2, T4 and T5 methods,however, T3 geothermometric (Kranidiotis and MacLean,1987) estimates seem to be quite reliable amongst the alltemperature estimations. It is generally possible thatestimated temperature discrepancies may occur when fourmethods are employed. The average temperature (T1-T5)ranges (Table 4) were calculated for illite separated outfrom the rock-unit of the Um-Sohryngkew river section,Meghalaya.Average range of temperatures for illite (Ri) wererecalculated to minimize discrepancies arising due to widerange of temperature variations (Table 4). Weaver et al.(1984) have suggested temperature ranges for early (90°-140°C), middle (~ 200°C) and late (250°-280°C) stages ofdiagenesis. Shale, siltstone and limestone layers of Um-Sohryngkew river succession represent temperature rangefor illite formation (Ri = 68-232ºC) with an average

temperature value of 129.32°C (Table 4). The temperaturerange of illite (Ri = 94° - 232°C) from the upper part (CF3-Pla zone) indicates that these clays were formed at averagehigh temperature of about 154°C (Table 4). Underdiagenesis, high temperature possibly has raised basin fluidactivity or fluid-rock interaction. The temperature rangesof illite (Ri = 68° - 158°C) from the lower part of thesuccession show low temperatures 110.66°C, indicatingearly stage of diagenesis (Table 4). The temperature range

Table 2. Structural formulae and layer charges of clay minerals calculated on the basis of half unit cell [O10(OH)2] from Um-Sohryngkew riversection

Samples JP-1 JP-2 JP-3 JP-4 JP-5 JP-6 JP-7 JP-8 JP-9 JP-10 JP-11 JP-12 JP-13 JP-14 JP-15 JP-16

Tetrahedral

Si 3.50 3.38 3.68 3.54 3.52 3.30 3.62 3.54 3.61 3.41 3.58 3.35 3.11 2.95 3.56 3.48Al(iv) 0.50 0.62 0.32 0.47 0.48 0.70 0.38 0.46 0.39 0.58 0.41 0.64 0.88 1.04 0.43 0.51Net charge 15.50 15.38 15.68 15.53 15.52 15.30 15.62 15.54 15.61 15.41 15.58 15.35 15.11 14.95 15.56 15.48Layer charge 0.50 0.62 0.32 0.47 0.48 0.70 0.38 0.46 0.39 0.58 0.41 0.64 0.88 1.04 0.43 0.51

Octahedral

Al(vi) 1.56 0.96 1.37 1.60 1.49 2.04 1.57 1.39 1.63 1.71 1.61 1.56 1.16 1.39 1.51 1.62Fe2+ 0.38 1.34 0.46 0.50 0.54 0.08 0.35 0.53 0.31 0.23 0.51 0.50 1.14 0.55 0.41 0.38Fe3+ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Mg 0.21 0.23 0.19 0.15 0.25 0.21 0.23 0.39 0.24 0.13 0.00 0.25 0.16 0.60 0.25 0.20SUM 2.15 2.53 2.02 2.25 2.29 2.32 2.15 2.31 3.30 2.07 2.13 2.32 2.47 2.55 2.18 2.22Net Charge 5.86 6.03 5.41 6.10 6.07 6.68 5.86 6.00 9.34 5.86 5.88 6.21 6.12 6.50 5.89 6.07Layer charge -0.14 0.03 -0.59 0.10 0.07 0.68 -0.14 0.00 3.34 -0.13 -0.11 0.21 0.12 0.50 -0.10 0.07Net layer charge 0.87 1.04 0.42 1.11 1.08 1.69 0.87 1.01 2.99 0.87 0.89 1.22 1.13 1.51 0.90 1.08

Interlayer

Ca 0.09 0.00 0.23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.04 0.07 0.00Na 0.10 0.02 0.11 0.04 0.06 0.06 0.11 0.03 1.86 0.07 0.10 4.34 0.24 0.04 0.00 0.06K 0.35 0.57 0.34 0.34 0.35 0.37 0.41 0.44 0.46 0.64 0.32 0.26 0.51 0.41 0.38 0.37Layer charge 0.64 0.59 0.92 0.38 0.41 0.43 0.52 0.46 2.32 0.71 0.43 4.61 0.94 0.54 0.54 0.43

Fig.4. Showing compositional field for smectite and illiteceladonite and mixed layer clays (after Weaver and Polard,1973), where data plots lie within the illite field. Thechemical formula groups at the apices of the trianglecorrespond to generic formula in which A = monovalentcations or divalent cations expressed as their monovalentequivalent, R2+ = the divalent cations and R3+ = trivalentcations.



of illite (Ri = 82° - 133°C) from the middle part (upper CF4and lower CF3 biozones) shows comparatively very lowvalue of 98.17°C temperature representing early stage ofdiagenesis. These illites were formed at low temperatures,

indicating low pH and low Eh conditions at the time of theirformation. The wide compositional variations occur withthe temperature ranging from 68-232ºC for illite clays ofthe Um-sohryngkew river section (Table 4). It has been found

Table 3. Thermodynamic components (in mole fraction) accountable for the half unit cell of illites in the Um-Sohryngkew river section

S. Thermodynamic JP-1 JP-2 JP-3 JP-4 JP-5 JP-6 JP-7 JP-8 JP-9 JP-10 JP-11 JP-12 JP-13 JP-14 JP-15 JP-16No. components (Illite)

1 KMg3AlSi3O10(OH)2 0.07 0.07 0.06 0.04 0 0.06 0.07 0.12 0.07 0.04 0 0.08 0.05 0.20 0.08 0.06

2 KFe3AlSi3O10(OH)2 0.12 0.44 0.15 0.16 0.17 0.02 0.11 0.17 0.10 0.07 0.17 0.16 0.38 0.18 0.13 0.12

3 KFe2AlSi3O10(OH)2 -0.06 -0.37 -0.13 -0.09 -0.06 0.09 -0.09 -0.19 -0.08 0.03 -0.06 -0.08 -0.22 -0.12 -0.11 -0.05

4 KAl3Si3O10(OH)2 0.18 0.17 0.17 0.15 0.15 0.25 0.25 0.19 0.22 0.50 0.15 0.10 0.15 0.06 0.2 0.20

6 Al2Si4O10(OH)2 0.68 0.49 0.73 0.69 0.72 0.64 0.70 0.63 0.71 0.58 0.72 0.63 0.45 0.45 0.68 0.67

Table 4. Calculated palaeo-temperatures (T1-T5), octahedral vacancies (Vac), thermo-parameters and structural formulae of illites of the Um-Sohryngkewriver succession

Bio- Sample Clays Thermo- Calculated Average Structural formulaeZones No. parameters Temperatures in °C Temp.

Vac Fe/ R2+ T1 T2 T3 T4 T5 T1 to T5ΣR2+

Pla JP-16 Illite 3.78 0.64 0.59 127.79 104.57 120.86 95.95 122.60 114.36 [Al1.62 Fe0.38Mg0.20][Si3.48Al0.51]O10(OH)8.Na0.06 K0.37

Pα JP-15 Illite 3.81 0.61 0.68 110.54 78.53 110.11 70.15 101.74 94.22 [Al1.51 Fe0.41Mg0.25][Si3.56Al0.43]O10(OH)8.Ca0.07 K0.38

P0 JP-14 Illite 3.44 0.47 1.16 240.53 274.75 164.38 264.56 216.62 232.17 [Al1.39 Fe0.55Mg0.60][Si2.95Al1.04]O10(OH)8.Ca0.04 Na0.04 K0.41

CF1JP-13 Illite 3.52 0.87 1.31 206.85 223.91 177.04 214.18 120.72 188.54 [Al1.16Fe1.14Mg0.16][Si3.11Al0.88]

CF2 O10(OH)8.Ca0.09 Na0.24 K0.51

JP-12 Illite 3.68 0.66 0.76 155.19 145.93 135.90 136.92 137.14 142.22 [Al1.56 Fe0.50Mg0.25][Si3.35Al0.64]CF3 O10(OH)8. Na4.34 K0.26

JP-11 Illite 3.87 1 0.52 106.29 72.11 136.32 63.79 86.91 93.09 [Al1.61 Fe0.51][Si3.58 Al0.41]O10(OH)8. Na0.10K0.32

JP-10 Illite 3.92 0.64 0.36 142.77 127.18 127.87 118.35 153.49 133.94 [Al1.71 Fe0.23Mg0.13][Si3.41Al0.58]O10(OH)8.Na0.07 K0.64




JP-6 Illite 3.68 0.27 0.29 166.74 163.36 112.83 154.19 193.74 158.17 [Al2.04Fe0.08 Mg0.21][Si3.30Al0.70]O10(OH)8. Na0.06 K0.37

CF4 JP-5 Illite 3.71 0.68 0.79 119.33 91.79 119.23 83.29 97.43 102.22 [Al1.49 Fe0.54Mg0.25][Si3.52Al0.48]O10(OH)8. Na0.06 K0.35

JP-4 Illite 3.75 0.77 0.65 118.45 90.47 125.37 81.98 101.08 103.48 [Al-1.60 Fe0.50Mg0.15][Si3.54Al0.47]O10(OH)8. Na0.04 K0.34

JP-3 Illite 3.98 0.70 0.65 86.49 42.22 104.95 34.18 73.32 68.23 [Al1.37 Fe0.46Mg0.19][Si3.68Al0.32]O10(OH)8.Ca0.23 Na0.11 K0.34

JP-2 Illite 3.47 0.85 1.57 149.51 137.35 146.87 128.42 42.64 120.96 [Al0.96 Fe1.34Mg0.23][Si3.38Al0.62]O10(OH)8. Na0.02 K0.57

JP-1 Illite 3.85 0.64 0.59 124.63 99.80 118.84 99.22 119.99 110.90 [Al1.56 Fe0.38Mg0.21][Si3.50Al0.50]O10(OH)8.Ca0.09 Na0.10 K0.35



that these illites are formed through early stages of diagenesisto low-grade metamorphic alterations under hydrothermalconditions. Vidal et al. (2001) proposed for tetrahedral AlIV

and octahedral vacancies as a function of measuredtemperatures in active geothermal systems. These variationsin the tetrahedral AlIV and the octahedral [VAC = 6 - AlVI -(Mg + Fe)] site occupancies are mainly temperaturedependent and considered in this work.

DISCUSSION

Calculated average temperature vs. chemical properties(Fe2+, K2+, interlayer charges and octahedral vacancies) ofillites data from all the biozones of the Um-Sohryngkewriver section along with the well known Danian,Maastrichtian and Cretaceous-Tertiary boundary layers ofAgost, Caravaca, Petriccio and El Kef were plotted (Fig.5). Three stages of temperature (<70oC, 80o-140 oC and>140oC) of formation for illite were distinguished by their

chemical attributes for various rock units of the area (Fig.5). Temperature < 70oC is associated with 0.46 amu ofoctahedral Fe of sample JP-3, indicating early stages ofdiagenesis (Fig. 5). Some of the illites (CF4 zone exceptJP-6 and lower part of CF3 zone) with Fe2+ content 0.08 to1.34 are associated with the temperature of the layers rangingfrom 80 -140 oC. It indicates progressive alteration and claycrystallinity under early to middle stages of diagenesis(Fig. 5). Few illites characterized by Fe (0.38-1.14) are fromupper zones, formed at >140 oC, indicating highly crystallineillite under late stages of diagenesis (Fig. 5). The high Kcontent corresponds to a high temperature of formation(Cathelineau, 1988). Most of the illites from various rockunits contain high amount of K (0.3-0.6 amu) and showinverse correlation with the temperature of formation (below140 oC), whereas, low K containing illite corresponds tohigh temperatures (Fig. 5). Octahedral vac shows significantinverse correlation with the temperature of formation ofillites. Most of the illites are characterized by high octahedral

Fig.5. Data plots between average temperature (oC) values (using geothermometers of Cathelineau and Nieva, 1985; Cathelineau, 1988;Kranidiotis and MacLean, 1987; Jowett, 1991; Zang and Fyfe, 1995) for illite clays from Um-Sohryngkew river section (Presentdata: Table 2) and their comparison with published (Cited Table 1: Ortega et al., 1998) values of Maastrichtian, K/T boundaryand Danian layers from Agost, Caravaca, Petriccio and El-Kef sections and their (a) Fe2+, (b) K2+, (c) interlayer charges and(d) Octahedral vacancy represent changes in the site vacancies/charges and interlayer charges with respect to temperature.



vac (from 3.8 to 3.9), formed at comparatively lowtemperatures (from 68°C to 94°C), whereas, low octahedralvac (3.4-3.6) of illites were formed at 158 - 232°C (Fig. 5).Fields for the K/T boundary layer clays from well-knownlocalities across the world show that these layers wereformed between 80o-140C temperatures, but K/T boundarylayer of Caravaca section shows high temperature of itsformation (>140oC). The relationship between K andoctahedral Al, Fe, Mg, Mn and Ti cations is plotted for illitedata from Um-Sohryngkew river section and used in thedetermination of transformation and alteration effects onclay physils during hydrothermal alteration (Fig. 6). K-fixation into inter-layers has enhanced the layer chargeswhich is concomitant with the illitization process duringhydrothermal alteration. Low to moderate degree of K-fixation achieved by pre-existing clays illite, smectite andI/S mixed layer complexes in the study area (0.32 to 0.64K+

ion substitution), indicative of minor hydrothermal effectson these rock units. Mg ions are always one of thepredominant divalent components within the octahedrallayer of the hydrothermal illite, but, the amount variessignificantly. Illite with the highest degree of octahedral Mg(>0.30) occupancies were found at P0 zone. Hydrothermalillite represents composition with low interlayer andoctahedral layer charges due to significant substitution ofSi, Al(iii), K, Al(iv) and Mg ions. Illites characterized by its Si(2.95-3.68) and interlayer K+Na (0.4-4.61) contents,indicate wide variation in the paleoenvironmental (humidtropical to arid-semiarid) and thermal conditions (diageneticto low grade metamorphism) during deposition and volcanicactivity.

Sediments at the K/T boundary contain relativelycommon clay minerals, perhaps formed by alteration ofglassy volcanic ash from episodes of intense volcanism inthe latest Cretaceous time (Rampino and Reynolds, 1983;Alvarez et al., 1980; Smit and Hertogen, 1980). Presenceof fibrous illite is favoured by high silica activity in thesolution (Huang, 1990 and Small et al., 1992). Assumingthat the source region largely consists of low grademetamorphic rocks and their weathering occurred underseasonal climate changes - warm and humid, alternating withperiods of evaporation - producing fibrous clays. Structuralformulae (on 22 oxygen basis) and layer charges calculatedfor illite and kaolinite rich clays (JP-1-16) from biozonesCF4 to Pla when plotted over binary diagrams, they showthat their data disposition is very close to the clay data fieldof well known Agost, Caravaca, Petriccio and El-Kef K/Tboundary sections, but, samples JP-3, JP-13 and JP-14 falldistinctively much away from the clay data fields of K/Tboundary clays as they possess relatively high octahedral(Zo) and interlayer (Zi) charges. Thermodynamic data forclays associated with the Um-Sohryngkew river section,Meghalaya when plotted over ternary [AR2

3+Si3O10(OH)2 -R2

3+SiO4O10(OH)2 - A3AlSi4O10(OH)2] diagram (Ransomand Helgeson, 1993) lie within illite fields (Fig. 4). It hasbeen found that the clays associated with the Um-Sohryngkew river section confine to compositionalfields represented by Al and Mg illite, and glauconite endmembers. It is therefore pointed out that the commonassociation of montmorillonite served as a source of Al.Most of the clay minerals are of dioctahedral composition.Data plots closeness for Um-Sohryngkew river sampleclays is due to their similar charge occupancies attetrahedral (Zt) octahedral (Zo) and interlayer (Zi) sites.Most of the illites present in this succession showhigher K contents and represent occasionally higher Altet.and lower Aloct. layer charges. The montmorillonite ispresent in very low proportion, whereas, illite is presentthroughout the succession as one of the major clayminerals, indicating that the illite grains in this successionwere possibly derived from the transformation ofmontmorillonite and I/S clays. On the basis of theirtetrahedral site occupancies, average palaeotemperatureswere calculated (Table 4) for illite clays from the CF4 toPla zones of the Um-Sohryngkew river section, representingtemperature (Ri) range 68-232ºC for illite formation withan average temperature value of 129.32°C (Table 4). Mostof the illites show high octahedral vac (from 3.8 to 3.9),formed at comparatively low temperatures (from 68°C to94°C), whereas, low octahedral vac (3.4-3.6) of illites wereformed at 158 - 232°C (Fig. 5). Illite temperature range (Ri)

Fig.6. Relationship between K and octahedral Al, Fe, Mg, Mnand Ti cations in the illite from Um-Sohryngkew riversection, indicate low degree of hydrothermal transformationof smectite into illite (cations calculated on 22 oxygenbases).



is 94° - 232°C. It is characterized by its Fe values (0.38-1.14) and high K content from the upper part (CF3-Pla zone).These clays were formed at average high temperature~154°C (Table 4) as represented by highly crystallineillites, formed under late stages of diagenesis (Fig. 5).High temperature attained during diagenesis possiblyraised basin fluid activity or fluid-rock interaction. Well-known K/T boundary layer across the world and theirclays data disposition fields show temperatures of 80-140o

C for the formation of K/T boundary layers, but K/Tboundary layer of Caravaca section shows high (>140oC)temperature of its formation which is comparable to thesudden temperature (>140ºC) increase found in theupper part of the biozone CF3 (sample JP-12). Hydro-thermal illites represent distinct compositions havinglow inter-layer and octahedral layer charges, possiblydue to significant amount of Si, Al(iii), K, Al(iv) and Mgion substitutions in these illites. Wide variation inpaleoenvironmental (humid tropical to arid-semiarid) andthermal conditions due to volcanic activity varyingfrom diagenetic to low grade metamorphism occurredduring their deposition is reflected in the Si (2.95-3.68)

and interlayer K+Na (0.4-4.61) contents of the illites.Data between octahedral (Zo) vs. interlayer (Zt) charges,

tetrahedral (Zt) vs. octahedral (Zo) charges and tetrahedral(Zt) vs. interlayer (Zi) charges for Biozone CF4 to Plasamples from Um-Sohryngkew river section, Meghalayaalongwith illite and kaolinite rich clays (JP-1-16) whenplotted over binary diagrams (Fig. 7), they show that theirdata dispositions are very close to the clays from well knownK/T boundary sections, except for samples JP-3, JP-13 andJP-14 which lie distinctively much away from the data fieldsof the well known K/T boundary clays as they possessrelatively high octahedral (Zo) and interlayer (Zi) charges.The closeness in the data plots for the clays from Um-Sohryngkew river samples is due to their similar chargeoccupancies at different sites. The average palaeo-temperatures were calculated from illite clays on the basisof their tetrahedral site occupancies from the CF4 to Plazones of the Um-Sohryngkew river section. Hightemperature range was noticed for the upper CF3 to P0biozones. Sudden increase in the temperature (>140ºC) inupper CF3 biozone (sample JP-12) is perceived. Such anincrease in the temperature to a certain extent is possibly

Fig. 7. Bivariate data plots for (a) octahedral (Zo) vs interlayer (Zi), (b) tetrahedral (Zt) vs octahedral (Zo) and (c) tetrahedral (Zt) vsinterlayer (Zi) charges in illite clays from Um-Sohryngkew river section (Present data: Table 2) and their comparison with thepublished (cited Table 1: Ortega et al., 1998) values of Maastrichtian, K/T boundary and Danian layers from Agost, Caravaca,Petriccio and El-Kef sections, respectively.



linked with the volcanic activity associated with the Abor /Deccan volcanism (Pal et al., 2015; Pal et al., 2015, in press).Abor volcanics as being sandwiched between fossiliferousPaleocene-lower Eocene quartzites and foraminifera-bearinguppermost lower Eocene to middle Eocene argillaceoussediments of Yinkiong Formation. The Yinkiong Formationcontains foraminifers’ assemblage indicating early to midEocene age. Late Paleocene to early Eocene age of Aborvolcanic is coeval to early stages of India - Asia collisionsuggesting them to be Himalayan foreland basin volcanicrocks (Sengupta et al. 1996). Deccan volcanic activitywitnessed immense accumulation of tholeiitic magma in thePeninsular India at the Cretaceous-Paleogene boundary (66Ma; Gradstein et. al. 2012). Its activity started earlier to theCretaceous-Paleogene boundary (KPB), but, major episodeof volcanism occurred either ~ 300 ky before the KPB orthe KPB itself (Paul et al., 2013).

CONCLUSION

Um-Sohryngkew river section at Therriaghat representsuninterrupted, shallow marine succession across theCretaceous-Paleocene boundary, where significant increasein the kaolinite contents as well as layer and inter-layercharges in illites associated with the yellowish brown claylayer (sample JP-12) is comparable to the clays associatedwith the well-established K/T boundary layers of Agost,Caravaca, Petriccio and El-Kef sections. These attributesof the 1 to 2 mm thick, yellowish brown clay layer which liebetween silty mudstone (20-25 cm thick) and grey calcareousshale layer (sample JP-12) located in the biozone CF3

together with the sudden increase in the temperature(>140ºC) perceived in the upper part of the biozone CF3(sample JP-12) are analogous to the attributes of the claysassociated with the K/T boundary layer of the Caravacasection as it also shows high temperature of its formation(>140oC). When these spikes found in biozone CF3correlated with the time sequence, it has been found thatthese changes are possibly due to multiple K/T boundarytransition events, occurred in the late Maastrichtian period.On the basis of planktonic foraminiferal study,Mukhopadhay (2008) marked the K/T boundary layer onthe contact between biozones CF1 and P0, developed in thecoprolite-bearing shaly marlite in the Therriaghat sectionand within the calcareous shale. It is marked by the extinctionof Plummerita hantkeninoides, an index fossil for at last300 ky of the Cetaceous (Pardo et al. 1996). It lies at least ~30 m above the base of the Langpar Formation in theMahadeo-Cherrapunji road section. Warm water species hasnot been recovered from the transgressive phase of biozoneCF3 at Therriaghat and Andaman Island sections, possiblyattributed to tectonic movements related to the collision ofthe Indian plate with the Burmese plate along the ArakanYoma-Andaman mobile belt.

Acknowledgements: To carry out field work in the Um-Sohryngkew River section, JPS and SKM acknowledgeIGCP-507 Project Grant for financial and logistic supportas received through the Geological Survey of India, Kolkata.SP and JPS acknowledge Council of Scientific and IndustrialResearch (CSIR), New Delhi for financial support in theform of a project [Grant No.24 (0315)/11/EMR-II].

ReferencesACHARYA, S.K. and PUSPENDU, S. (2013) Age and tectono-magmatic

setting of abor volcanics, siang window, eastern himalayansyntaxial area, India. Jour. Applied. Geochem., v.15, pp.170-192.

ALEGRET, L. and THOMAS, E. (2007) Deep sea environments acrossthe Cretaceous/Paleocene boundary in the eastern SouthAtlantic Ocean (ODP Leg 208, Walvis Ridge). MarineMicropal., v.64, pp.1–17.

ALEXANDRE, P., KYSER, K., POLITO, P. and THOMAS, D. (2005)Alteration mineralogy and stable isotope geochemistry ofPaleoproterozoic basement-hosted unconformity-type uraniumdeposits in the Athabasca Basin, Canada. Econ. Geol., v.100,pp.1547-1563.

ALVAREZ, L. W., ALVAREZ, W., ASARO, F. and MICHEL, H. V. (1980)Extraterrestrial cause for the Cretaceous-Tertiary extinction.Science., v.208, pp.1095-1108.

ARENILLAS, I. and ARZ, J.A. (2000) Parvularugoglobigerinaeugubina type-sample at Ceselli (Italy): planktonicforaminiferal assemblage and lowermost Danianbiostratigraphic implications. Rivista Italiana di Paleontologiae

Stratigrafia. v.106, pp. 379-390.ARENILLAS, I., JOSE,A., ARZ, J. A., MOLINA, E. and DUPUIS, C. (2000)

The Cretaceous/Paleogene boundary at Ain Settara, Tunisia:sudden catastrophic mass extinction in planktonic foraminifera.Jour. Foram. Res., v.30, pp.202–218.

BAIN, D.C. and SMITH, B.E.L. (1987) Chemical analysis. In: M.J.Wilson, (Ed.), A Handbook of Determinative Methods in ClayMineralogy. Blackie, Glasgow, pp.248-274.

BARRERA, E. (1994) Global environmental changes preceding theCretaceous-Tertiary boundary: Early-upper Maastrichtiantransition. Geology, v.22, pp.877-880.

BEAUFORT, D., PATRIER, P., LAVERRET, E., BRUNETON, P. and MONDY,J. (2005) Clay alteration associated with Proterozoicunconformity-type uranium deposits in the East AlligatorRivers Uranium Field (Northern Territory, Australia). Econ.Geol., v.100, pp.515-536.

BHANDARI, M., SHUKLA, P.M. and PANDEY, J. (1987) Iridiumenrichment at Cretaceous-Tertiary boundary in Meghalaya.Curr. Sci., v.56, pp.1003-1005.

BHANDARI, M., GUPTA, M., PANDEY, J. and SHUKLA, P.M. (1994)



Chemical profiles in K/T boundary section of Meghalaya,India: cometary, asteroidalor volcanic. Chemical Geol., v. 113,pp. 45-60.

BISWAS, B. (1962) Stratigraphy of the Mahadeo, Langpar, Cherraand Tura formations, Assam, India. Geol. Mining Metall. Soc.India Bull., v.25, pp.1-25.

CATHELINEAU, M. and NIEVA, D. (1985) A chlorite solid solutiongeothermometer. The Los Azufres (Mexico) geothermalsystem: Contrib. Mineral Petrol., v.91, pp.235-244.

CATHELINEAU, M., OLIVER, R. and NIEVA, D. (1987) Quaternaryvolcanic series of the Los Azufres geothermal field (Mexico).Geofis Int., v.26, pp.273-290.

CATHELINEAU, M. (1988) Cation site occupancy in chlorites andillites as a function of temperature. Clay Mineral. v.23, pp.471-485.

CATHELINEAU, M. and IZQUIERDO, G. (1988) Temperature -composition relationships of authigenic micaceous mineralsin the Los Azufres geothermal system. Contrib. Mineral.Petrol., v.100, pp.418-428.

COURTILLOT, V., JAEGER, J. J., YANG, Z., FERAUD, G. and HOFFMAN,C. (1996) The influence of continental flood basalts on massextinction: where do we stand? Geol. Soc. Ame. Spec. Paper,v.307, pp.513-526.

COURTILLOT, V., GALLET, Y., ROCCHIA, R., FERAUD, G., ROBIN, E.,HOFFMAN, C., BHANDARI, N. and GHEVARIA, Z.G. (2000) Cosmicmarkers, 40Ar/39Ar dating and palaomagnetism of the KTsections in the AnjarArea of the Deccan large igneous province.Earth Planet. Sci. Lett., v.182, pp.137-156.

Dasgupta, A. B. (1977). Geology of Assam-Arakan Region. Quat.Jour. Geol. Mining Metall. Soc. India, v.49, pp.1-54.

ELLWOOD, B.B., MACDONALD, W.D., WHEELER, C. and BENOIST, S.L.(2003) The K/T boundary in Oman: identified using magneticsusceptibility and measurements with geochemicalconfirmation. Earth Planet. Sci. Lett., v.106, pp.529–540.

GALAL, G. (2006) Late Maastrichtian-Early Danian serial planktonicforaminifera as indicators of paleoecology at West CentralSinai, Egypt. Revue de Paleobiologie. v.25, pp.439-436.

GERTSCH , B., KELLER, G., ADATTE, T., GARG , R., PRASAD, V.,BERNER, Z. and FLEITMANN, D. (2011) Environmental effectsof Deccan volcanism across the Cretaceous–Tertiary transitionin Meghalaya, India. Earth Planet. Sci. Lett., v.310, pp.272-285.

GRADSTEIN, F.M., OGG, J.G. and SCHMITZ, M. D. (2012) TheGeologic Time Scale. Boston, USA, Elsevier, DOI: 10.1016/B978-0-444-59425-9.00004-4.

HART, M.B., FEIST, S.E., PRICE, G.D. and LENG, M.J. (2004)Reappraisal of the K-T boundary succession at Stevns Klint,Denmark. Jour. Geol. Soc. London, v.161, pp.885-892.

HART, M.B., FEIST, S.E., HAKANSSON, E., HEINBERG, C., PRICE, G.D.,LENG, M.J. and WATKINSON, M.P. (2005) The Cretaceous-Paleogene boundary succession at Stevns Klint, Denmark;Foraminifers and stable isotope stratigraphy. Palaeogeo.Paleoclimat. Paleoeco., v.224, pp.6-26.

HASSOUTA, L., BUATIER, M.D., POTDEVIN, J.L. and LIEWIG, N. (1999)Clay diagenesis in the sandstone reservoir of the Ellon Field(Alwyn, North Sea). Clay Mineral., v.47, pp.269–285.

HOFFMAN, C., FERAUD, G. and COURTILLOT, V. (2000) 40Ar/39Ardating of mineral separates and whole rock from the westernGhat lava pile: further constraints on duration and age ofDeccan Traps. Earth Planet. Sci. Lett., v.180, pp.13-27.

HOWER, J. and MOWATT, T. C. (1966) Mineralogy of the illite-illite/montmorillonite group. Amer. Mineral., v.51, pp.821-854.

HUANG, P.M. (1990) Role of soil minerals in transformations ofnatural organics and xenobiotics in soil. In: J.M. Bollag andG. Stotzky (Eds.), Soil Biochemistry. Marcel Dekker Inc., NewYork, v.6, pp.29-115.

JACKSON, M.L. (Ed.) (1985) Soil Chemical Analysis AdvanceCourse: 2nd edition, Madison, Wisconsin, pp.100-166.

JHA, S. K., SHRIVASTAVA, J.P. and BHAIRAM, C. L. (2012) Claymineralogical studies on Bijawars of the Sonrai Basin: Palaeo-environmental implications and inferences on the uraniummineralization. Jour. Geol. Soc. India, v.79, pp.117-134.

JOWETT, E.C. (1991) Fitting iron and magnesium into thehydrothermal chlorite geothermometer: GAC/MAC/SEG JointAnnual Meeting (Toronto, May 27-29, 1991), Program withAbstracts 16, A62.

KELLER, W.D. (1985) The nascence of clay minerals. Clays andClay Minerals, v.33, pp.161-172.

KELLER, W.D., REYNOLDS, R.C. and INOUE, A. (1986) Morphologyof clay minerals in the smectite-to-illite conversion series byscanning electron microscopy: Clays and Clay Minerals., v.34,pp.187-197.

KELLER, G. (2001) The end-Cretaceous mass extinction in themarine realm: year 2000 assessment. Planet. Space Sci., v.49,pp.817-830.

KELLER, G. (2003) Biotic effects of impact and volcanism. EarthPlanet. Sci. Lett., v.215, pp.249-264.

KELLER, G. (2004) Low-diversity, late Maastrichtian and earlyDanian planktonic foraminiferal assemblages of the easternTethys. Jour. Foram. Res., v.34, pp.49-73.

KOMNINOU, A. and SVERJENSKY, D.A. (1995) Pre-ore hydrothermalalteration in an unconformity-type uranium deposit. Contrib.Mineral. Petrol., v.121, pp.99-114.

KRANIDIOTIS, P. and MACLEAN, W. H. (1987) Systematics of chloritealteration at the Phelps Dodge massive sulfide deposit,Matagami, Quebec. Econ. Geol., v.82, pp.1898-1911.

LAHIRI, T.C., SEN, M.K., RAYCHAUDHURI,A.K. and ACHARYYA, S.K.(1988). Observations on Cretaceous/Tertiary boundary andreported iridium enrichment, Khasi Hills, Meghalaya. Curr.Sci., v.57, pp.1335-1336.

LAIRD, D.A. and NATER, E.A. (1993) Nature of the illitic phaseassociated with randomly interstratified smectite/illite in soils.Clays and Clay Minerals, v.41, pp.280-287.

MEDLICOTT, H.B. (1871) Geological sketch of Shillong Plateau.Geol. Surv. India Mem., v.7, pp.151-207.

MERRIMAN, R.J. and PEACOR, D.R. (1999) Very low- grademetapelites:mineralogy, microfabrics and measuring reactionprogress. In: M. Frey and D. Robinson (Eds.), Low grademetamorphism. Blackwell.

MUKHOPADHYAY, S.K. (2008) Planktonic for aminiferal successionin late Cretaceous to early Palaeocene strata in Meghalaya,India. Lethaia., v.41, pp.71-84.

MUKHOPADHYAY, S.K. (2009) Convener’s report for 2008 on theprogress of work in the IGCP Project 507, on ‘Palaeoclimatein Asia during the Cretaceous: their variations, causes, andbiotic and environmental responses’. IGCP Ind. Newslett.,v.29, pp.11-13.

MUKHOPADHYAY, S.K. (2011) Can late Maastrichian planktonicforaminifera and palaeoclimatic help understand the problemsof Present Day global warming? Ch. 22, Earth Resource and



Environment (Ed. R. Venkatchalapathy), Research Publishing,Singapore.

MUKHOPADHYAY, S.K. (2012a) Guembelitria (Foraminifera) in theUpper Cretaceous-Lower Paleocene succession of the LangparFormation, India, and its paleoenvironmental implication. Jour.Geol. Soc. India, v.79, pp.627-651.

MUKHOPADHYAY, S.K. (2012b) Morphogroups and small sized testsin Pseudotextularia elegans (Rzehak) from the LateMaastrichtian succession of Meghalaya, India as indicators ofbiotic response to paleoenvironmental stress. Jour.Asian EarthSci., v.48, pp.111-124.

NAGAPPA, Y. (1959) Foraminiferal biostratigraphy of theCretaceous-Eocene succession in the India-Pakistan-Burmaregion. Micropaleontology, v.5, pp.145-192.

NUTT, C.J. (1989) Chloritization and associated alteration at theJabiluka unconformity-type uranium deposit, NorthernTerritory, Australia. Canadian Mineralogist, v.27, pp.41-58.

ORTEGA-HUERTAS, M., PALOMO, I., MARTI´NEZ-RUIZ, F. andGONZALEZ I. (1998) Geological factors controlling clay mineralpatterns across the Cretaceous-Tertiary boundary inMediterranean and Atlantic sections. Clay Minerals, v.33,pp.483-500.

PAL, S., SHRIVASTAVA, J.P. and MUKHOPADHYAY, S.K. (2015)Polycyclic Aromatic Hydrocarbon compound excursions andK/Pg transition in the late Cretaceous-early Paleogenesuccession of the Um-Sohryngkew river section, Meghalaya.Curr. Sci., v.109, pp.1140-1150.

PAL, S., SHRIVASTAVA, J.P. and MUKHOPADHYAY, S.K. (in press)Physils and organic matter-base palaeoenvironmental recordsof the K/Pg boundary transition from the late Cretaceous-earlyPalaeogene succession of the Um Sohryngkew river sectionof Meghalaya, India. Chemie der Erde-Geochemistry, http://dx.doi.org/10.1016/j.chemer.2015.09.004

PANDEY, J. (1981) Cretaceous foraminifera of Um SohryngkewRiver section, Meghalaya. Jour. Palaeo. Soc. India, v.25, pp.53-74.

PANDEY, J. (1990). Cretaceous/Tertiary boundary, iridium anomalyand foraminifer breaks in the Um Sohryngkew River section.Curr. Sci., v.59, pp.570–575.

PARDO, A., ORTIZ, N. and KELLER, G. (1996) Latest Maastrichtianand K/T boundary foraminiferal turnover and environmentalchanges at Agost, Spain. In: N. McLeod and G. Keller (Eds.),Biotic and Environmental Events across the Cretaceous/Tertiary Boundary. Norton, New York, NY, pp.139–171.

PAUL, R.R., ALLEN, L.D., FREDERIK, J.H., KLAUDIA, F.K., DARREN,F.M., WILLIAM, S.M., LEAH, E.M., RONALD, M. and JAN, S.(2013) Time scale of critical events around Cretaceous-Paleogene boundary. Science, v.339, pp.684-687

POLITO, P.A., KYSER, T.K., THOMAS, D., MARLATT, J. and DREVER,G. (2005) Re-evaluation of the petrogenesis of the ProterozoicJabiluka unconformity-related uranium deposit, NorthernTerritory, Australia. Mineralium Deposita, v.40, pp.238-257.

RAGLAND, P.C. (1989) Basic analytical petrology. 369p.RAMPINO, M.R. and REYNOLDS R.C. (1983) Clay mineralogy of the

Cretaceous-Tertiary Boundary Clay. Science, v.219, pp.495-498.

RANSOM, B. and HELGESON, H.C. (1989). On the correlation ofexpandability with mineralogy and layering in mixed-layer

clays. Clays and Clay Minerals, v.37, pp.189-191.RANSOM, B. and HELGESON, H.C. (1993). Compositional end

member and thermodynamic components of illite anddioctahedral aluminous smectite solid solutions. Clays & ClayMinerals, v.41, pp.537-550.

ROSS, C.S. and HENDRICKS, S.B. (1945) Minerals of themontmorillonite group. USGS Prof. Paper, 205B, pp.23-47.

SAMANTA, B.K. (1974) The limits and subdivisions of Palaeocenewith remarks on the marine occurrences recorded in the India-Pakistan region. Geol. Mining Metall. Soc. India, GoldenJubilee Volume, pp.183-205.

SENGUPTA, S., ACHARYA, S.K. and DE SMETH, J.B. (1996)Geochemical characteristics of the Abor volcanic rocks, NEHimalaya, India: nature and early Eocene magmatism. Jour.Geol. Soc. London, v.153, pp.695-704.

SHRIVASTAVA, J.P., MUKHOPADHYAY, S.K. and PAL, S. (2013)Chemico-mineralogical attributes of clays from the lateCretaceouseearly Palaeogene succession of the UmSohryngkew river section of Meghalaya, India: palaeo-environmental inferences and the K/Pg boundary. CretaceousRes., v.45, pp.247-257.

SMALL, J.S., HAMILTON D.L. and HABESCH, S. (1992) ExperimentalSimulation of Clay Precipitation within Reservoir Sandstones2: Mechanism of Illite Formation and Controls on Morphology.Jour. Sed. Petrol., v.62(3), pp.520-529.

SMIT, J. and HERTOGEN, J. (1980) An extraterrestrial event at theCretaceous-Tertiary boundary. Nature., v.285, pp.198-200.

SORDON, J. and EBREL, D.D. (1984) Illite. In: S.W. Bailey, (Ed.),Micas. Reviews in Mineralogy 13, Min. Soc. Amer.,Washington, D.C., pp.495-544.

STRONG, C.P. (2000) Cretaceous-Tertiary foraminiferal successionat Flaxbourne River, Marlborough, New Zealand. Jour. Geol.Geophys., v.43, pp.1-20.

VIDAL, O., PARRA, T. and TROTET, F. (2001) A thermodynamic modelfor Fe-Mg aluminous chlorite using data from phaseequilibrium experiments and natural pelitic assemblages inthe100º to 600ºC, 1 to 25 kb range. Amer. Jour. Sci., v.301,pp.557-592.

WARREN, E.A. and RANSOM, B. (1992) The influence of analyticalerror upon the interpretation of chemical variations in clayminerals on standard clay diagrams AEM and XRD. ClayMiner., v.6, pp.17-22.

WEAVER, C.E. and POLLARD, L.D. (1973) The chemistry of clayminerals, Elsevier, 213p.

WEAVER, C.E., HIGHSMITH, P.B. and WAMPLER, J.M. (1984) Chlorite(Chapter 5). In: C.A. Weaver et al. (Eds.), Shale-SlateMetamorphism in Southern Appalachians. Developments inPetrology, Elsevier, Amsterdam., v.10, pp.99-139.

YASSINI, I. (1979) Maastrichtian-Lower Eocene biostratigraphy andthe planktonic foraminiferal biozonation in Jordan. RevistaEspanola de Micropal., v.11, pp.5–57.

ZANG, W. and FYFE, W.S. (1995) Chloritization of thehydrothermally altered bedrocks at the Igarapé Bahia golddeposit, Carajás, Brazil. Miner. Depos., v.30, pp.30-38.

ZHANG, X.Y., ARIMOTO, R. and AN, Z.S. (1997) Dust emission fromChinese desert sources linked to variations in atmosphericcirculation. Jour. Geophy. Res., v.102(D23), pp.28041-28047.

(Received: 12 June 2014; Revised form accepted: 29 December 2014)

mineral chemistry of clays associated with the late cretaceousearly palaeogene succession of the...

Documents