Geochemical and 13C trends in sedimentary deposits of coastal Pondicherry region, East coast of India – Insights from a borehole study

Journal Pre-proof Geochemical and 13 C trends in sedimentary deposits of coastal Pondicherry region, East coast of India – insights from a borehole study K. Tirumalesh, S. Chidambaram, S. Pethaperumal, M. Sundararajan, R. Thilagavathi, C. Thivya, Diana Anoubam Sharma, U.K. Sinha

PII:

S0009-2819(19)30058-3

DOI:

https://doi.org/10.1016/j.chemer.2019.125553

Reference:

CHEMER 125553

To appear in:

Geochemistry

Received Date:

30 July 2019

Revised Date:

5 November 2019

Accepted Date:

6 November 2019

Please cite this article as: Tirumalesh K, Chidambaram S, Pethaperumal S, Sundararajan M, Thilagavathi R, Thivya C, Sharma DA, Sinha UK, Geochemical and 13 C trends in sedimentary deposits of coastal Pondicherry region, East coast of India – insights from a borehole study, Geochemistry (2019), doi: https://doi.org/10.1016/j.chemer.2019.125553

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Geochemical and 13C trends in sedimentary deposits of coastal Pondicherry region, East coast of India –insights from a borehole study K. Tirumalesh1,2, S. Chidambaram3,4, S. Pethaperumal5, M.Sundararajan6, R. Thilagavathi3, C. Thivya7, Diana Anoubam Sharma1, U.K. Sinha1 1

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Isotope and Radiation Application Division, Bhabha Atomic Research Centre, Mumbai, India 2 Homi Bhabha National Institute, Anushaktinagar, Mumbai, India – 400 094 3 Earth Sciences Department, Annamalai University, Chidambaram. Tamil Nadu, India- 608002, 4 Water Research Center, Kuwait Institute for Scientific Research, P.O. Box 24885 Safat, 13109 Kuwait 5 State Groundwater Unit and Soil Conservation, Department of Agriculture, Pondicherry, India. 6 National Institute for Interdisciplinary Science & Technology (NIIST), Thiruvananthapuram, Kerala, India- 695019 7 Department of Earth Science, Anna University, Tamil Nadu, India

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Dr. S. Chidambaram Professor, Department of Earth Sciences Annamalai University Chidambaram. Tamil Nadu, India - 608002,

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& Homi Bhabha National Institute Anushaktinagar, Mumbai, India – 400 094 Email: [email protected]; [email protected] Fax no: 91-22-25505345; Telephone no: 91-22-25593162

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Dr. K. Tirumalesh (corresponding author) Scientific Officer Isotope and Radiation Application Division Bhabha Atomic Research Centre, Mumbai, India – 400 085

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& Research Scientist, Water Resources Development and Management, Water Research Center,Kuwait Institute for Scientific Research, P.O. Box 24885 Safat, 13109 Kuwait Email: [email protected]

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Dr. S. Pethaperumal Scientist State Groundwater Unit and Soil Conservation Department of Agriculture Pondicherry, India -605001 Email: [email protected]

Dr.M.Sundararajan Scientist, National Institute for Interdisciplinary Science & Technology (NIIST), Thiruvananthapuram, Kerala, India- 695019 Email:[email protected]

Dr. R. Thilagavathi Post Doctoral Fellow Department of Earth Sciences, Annamalai University Chidambaram. - 608002, Tamil Nadu, India. Email:[email protected] Dr. C. Thivya Post Doctoral Fellow Department of Geology, University of Madras Guindy campus, Chennai, Tami Nadu 600085 Email:[email protected]

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Research Highlights

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Dr. U.K. Sinha Scientific Officer Isotope and Radiation Application Division Bhabha Atomic Research Centre, Mumbai, India – 400 085 Email: [email protected]

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Dr. Diana Sharma Post Doctoral Fellow Isotope and Radiation Application Division Bhabha Atomic Research Centre, Mumbai, India – 400 085 Email: [email protected]

Presence of multiple sources of sediment and its transport towards littoral zone through fluvial processes is

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inferred from micro-structural study 

Trace elemental ratios indicated felsic rocks as source rocks with contribution from Tonalites

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The observed positive Eu anomaly in the sediments points to the contribution of plagioclase feldspar

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Low Cr, Th and high REE contents are indicative of no/negligible impact of Deccan volcanic ash to the sediments

Marine nature of sediment deposition is confirmed by positive δ13C incursions

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Abstract Major, trace, rare earth elements and 13C isotope results of sediments collected up to the depth of 150 meter below ground level (m bgl) have been interpreted in relation to the provenance, weathering and deposition conditions of a multi layered

sedimentary formation of Pondicherry region located in East Coast of India. The samples fall in the coarse to medium grain size range (mean Mz: 0.29 – 1.32) and the sorting values (mean SD: 0.29 – 1.04) mostly infer very well sorted nature of sediments. Skewness (mean Ski: 0.09-0.99) shows the domination of very fine skew while the kurtosis (mean KG: 0.767.73) shows sediments from extremely lepto kurtic to platy kurtic nature. Micro-structural studies infer that sediments are derived from multiple sources and transported towards the littoral zone through the fluvial processes. Relatively depleted elemental concentrations with respect to upper continental crust (UCC) (elemental ratios < 1) are noticed in most of the sediments suggesting contribution of the weathered source rocks. Chondrite normalized distributions of the selected rare

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earth elements show uniform trends characterized by light rare earth element enrichment and heavy rare earth element depletion, which is a typical pattern of UCC exposed to weathering and erosion. Elemental ratios such as La/Sc (2.06-

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6.64), Th/Sc (0.66 – 4.13), Th/Cr (0.06-0.26) and Th/Co (0.46-1.54) and ternary plots (La-Th-Sc, Th-Hf-Co) indicate the contribution of felsic rocks that are inherently heterogeneous in nature. Observed positive Eu anomaly in Post Archean

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Australian Shale (PAAS) normalized patterns indicates contribution of plagioclase minerals. Th/U ratio (2.12-9.57) of the sediments reflects deposition under oxic conditions (shallow marine) whereas deeper sediments reveal anoxic condition

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(deep marine), which is further confirmed by δ13CTIC variations (-11.4 to +5.12 ‰ vs. VPDB) and Eu analmoly. Cr/Th ratio

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and total REE content indicate that there is no/negligible input of volcanic ash to these sediments.

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Keywords: granulometry; microstructure; carbon-13; REE; Eu-anomaly; Pondicherry

1. Introduction Major and trace element geochemistry has been used in many studies for deducing the nature of source rock (Nagarajan et al., 2017; Singh et al., 2001 and 2015; Madhavaraju et al., 2014) and reconstructing the paleogeography and paleotectonics of sedimentary basins (Roy et al., 2009). In recent times rare earth elements (REE) in the continental crust have received much attention, in specific to sedimentary formations, as their distribution provides reliable information on the origin of source rocks (Taylor and McLennan, 1985; Keesari et al., 2012; Singh et al., 2001 and 2015). There is a general consensus that the REEs are transferred virtually from source rocks to sediments and therefore the REE distributions reflect the nature

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of the exposed continental crust. REEs are more important than major and trace elements in deciphering the provenance since their concentrations are not affected during erosion, sedimentation and diagenesis. Researchers also regard REE and

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trace metals (Th, Sc and to some extent Cr and Co) as useful indicators for characterizing the sediment provenance. This is due to their low solubility and also ability to migrate along with the terrigenous component of sediment. In addition to

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geochemical parameters, environmental isotopes have also been used to provide information on stratigraphy on both local and global scales (Singh 2015; Duchamp-Alphonse et al., 2011). Isotope data of rocks/sediments, especially

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carbonates, were used to provide information on diagenesis (Madhavaraju et al., 2014).

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Geochemical studies in Cauvery basin were mostly concentrated on the surface or shallow sediments (Altrin et al., 2004; Madhavaraju et al., 2002; Bakkiaraj et al., 2010; Singh and Rajamani, 2001). A study by Altrin et al. (2004) pointed out that the detrital sediments present in the limestones were derived from felsic sources in Miocene formations and deposited

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under oxygen-rich environment. Another study by Bakkiaraj et al. (2010) found that the sediments from Upper Cretaceous formation of Cauvery basin were derived from felsic sources and showed signatures of Dharwar craton. Impact of Deccan volcanism in the sedimentary rocks of Late Cretaceous period in Cauvery basin was inferred by Madhavaraju and Lee (2010). Study by Keller et al. (2008) indicated the termination of Deccan volcanism near K-T boundary in Krishna-

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Godavari basin, SE India using lithological and biostratigraphical evidences. Another study by Keller et al. (2009) in intertrappean sediments in Central India also revealed that intertrappean depositions have occurred in predominantly terrestrial semi-humid to arid environments. The Deccan volcanism and its eruption during K-T boundary was studied by many researchers from different parts of the world (Jay and Widdowson, 2008; Chenet et al., 2008). Geochemistry of sedimentary rocks in Bhima basin suggested K-metasomatism and felsic igneous rocks as source rocks (Nagarajan et al., 2007). Study by Singh and Rajamani (2001) has reported that the recent clastic sediments from Cauvery floodplains were derived from high standing hills of Archean charnockites. Whilst there is abundant information on the shallow sediments of

Cauvery and its sub basins, there are still some gaps/uncertainties in the understanding of the source rock composition, weathering and deposition. In addition, very limited information is available for the deeper sedimentary formations of Cauvery and its sub basins, especially in Pondicherry region, which warrants a thorough study in view of the complex sedimentary successions prevailing in this region. In this paper, we report a new data set consisting of major (Na, K, Ca), trace element (Co, Sc, Cr, Zn, Hf, Th, U), REE (La, Ce, Eu, Yb and Lu) and

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C isotope data of the sediments collected from the Quaternary, Tertiary and Cretaceous

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formations of Pondicherry region. This study is significant as the sediments that were collected from the borehole cover both K/T and Q/T boundaries. The main objectives of the paper are to;

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 Evaluate the influence of Deccan volcanism on the sediments

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 Understand the provenance, weathering and deposition characteristics of the sediments from all the three

 Improve the current understanding of paleoclimatic conditions during the time of deposition of Cenozoic and

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Mesozoic sediments of Pondicherry sub basin of East Coast of India

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2. Materials and Methods

2.1 Geology

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The entire Pondicherry region is covered by the sediments ranging from the Cretaceous to Recent ages; the inboard sectors contain predominantly Cretaceous infill whereas the outboard ones contain a substantial Cenozoic section (Fig. 1a). The stratigraphy of this region is given in supplementary table (TS-1). The Cretaceous sediments of Mesozoic era are the oldest formations, which are further subdivided in to Ramanathapuram, Vanur, Ottai and Turuvai formations (Fig. 1b).The lower

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most formation namely Ramanathapuram, comprises alternate layers of sand, sandstone and calcareous claystone with thin seams of lignite and is not exposed anywhere in this region. This formation is unconformably overlaid by the Cuddalore formation at Ramanathapuram region and in other places by Vanur formation. There is a gradation of facies from Vanur to Ramanathapuram formations and no clear boundary exists between them. The Upper Cretaceous Vanur sandstone formation is exposed in the North of River Gingee. This formation consists of coarse grained, grayish white feldspethic sandstone and thin intercalations of dark grey shales, which is also present in the western part. Ottai claystone is exposed in a larger area compared to the Vanur sandstone and comprises black to greenish claystone, calcareous and micaceous

siltstone. Turuvai limestone forms the top most Cretaceous formation, which is highly fossiliferous with few bands of sandstone and outcrops in a thin strip in NE-SW direction. The Cretaceous formations are overlaid by sediments of Tertiary period, which are sub-divided into Kadapperikuppam, Manaveli and Cuddalore formations. Kadaperrikuppam formation falls under Paleocene epoch and comprises essentially the calcareous sandstones. Manaveli formation comprises yellowish brown calcareous sandy clay and shales with limestone. The Upper Tertiary sediments are represented by Cuddalore formation, which consists of coarse grained sandstones with minor clays and seams of lignite. The Quaternary formations of this region consist of laterites and alluvium. Most of this region shows large variations in the thickness and

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also lateral extent of different formations due to tectonic disturbances.

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2.2. Study site description

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The lithological data collected from CGWB (1993) and from the new boreholes (Andiarpalayam and Periakanganakuppam) was used to prepare a 2D cross section of the NW – SE transect. The names of the sites chosen for

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constructing 2D section are Andiarpalayam, Madagadipattu, Sattamangalam and Periakanganakuppam, shown in Fig. 2a. The 2D cross section is shown in fig. 2b. It can be noticed that from NW - SE the thickness of the Quaternary formation

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decreases and the thickness of Cretaceous formation increases from SW-NE. The thickness of Tertiary sediments remains more or less same. The semi-plastic to plastic nature of sediments indicates that sediments below the clay zone (90-100m bgl) represent Ramanathapuram formation. Lithological studies conducted at Madagadipattu and Sattamangalam sites also

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suggest the presence of Ramanathapuram formation (CGWB, 1993). Turuvai formation is not observed at this site. On the whole, this site comprises the major geological formations of the Pondicherry sub-basin.

2.3 Sampling of sediments

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A total of 46 sediments were sampled at an interval of 3m up to a depth of 150 m bgl from Andiarpalayam site (11°55′30′′N latitude; 79°37′14′′E longitude) situated in the west of Pondicherry. The physiography of the site is characterized by flat peneplain and is about 15 m above mean sea level. Twelve representative sediment samples (0-3 m, 912 m, 27-30 m, 36-39 m, 51-54 m, 60-63 m, 75-78 m, 105-108 m, 111-114 m, 129-132 m, 132-135 m and 138-141 m) were selected based on in situ nature for detailed chemical and isotopic analysis. A schematic map of litho units along with drill data is given in Fig. 3 (a&b). The drill data and field observations suggested that most of the litholog is comprised of

unconsolidated sediments and soft rock consisting clay, claystone, siltstone and mudstone. At certain depths (between 5558 and 80-86 m bgl) hard consolidated sedimentary rocks were encountered.

2.4 Analytical methods

2.4.1 Granulometric assay

The collected sediment samples from selected depths (12 representative samples) were separated by coning and quartering

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method. The samples were sieved at 0.50 ø intervals through ASTM sieve (from +18 to +230 mesh sizes) sets using a RoTap sieve shaker for 15 minutes. The sieved sediments were collected and weighed to compute weight percentage and

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cumulative weight percentage frequencies. The grain size parameters like Graphic Mean (Mz), Inclusive Graphic Standard

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Deviation (SD), Inclusive Graphic Skewness (Ski) and Graphic Kurtosis (KG) were determined using the software package.

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2.4.2 XRD studies and micro-structural analysis

The X-ray diffraction analyses (XRD) of the powdered sediment samples from selected depths were performed using Philips PW-1820 diffractometer consisting of a diffracted beam monochromator and multi-channel detector. The

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instrumental conditions set were; CuKα radiation (40kV, 30mA), step scanning at 0.02° /250s, 2θ range 3-70°. The PCPDF and XTAL softwares were used for mineral identification.

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Micro-structural studies were carried out for the samples from the selected depths and from that the coarser size fraction samples were chosen for mono-crystalline quartz grains study in order to examine their surface features. The fine sand fractions were also separately selected and treated by using the standard procedures to remove coating of iron oxide. After thorough cleaning, the dried grains were placed in rows upon aluminum specimen stub coated with double sided scotch

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tape. The stubs were positioned in a rotating vacuum evaporator for coating gold. Finally, the mounted grains were examined under Scanning Electron Microscope and photomicrographs were taken.

2.4.3 Instrumental Neutron Activation Analysis (INAA)

Several grams of these sediment samples from the selected depths were oven dried and ground using mortar and agar. The sediment samples (50 mg) were packed in aluminum foil and irradiated under a neutron flux of 10 13 cm-1 s-1 for 6hrs. A total of fifteen elements (Na, K, Ca, Co, Sc, Cr, Zn, Hf, Th, U, La, Ce, Eu, Yb and Lu) were determined. After appropriate

cooling, gamma-ray measurements were carried out by using coaxial and planar type Ge detectors coupled with multichannel analyser. The measured target nuclei and gamma energies are given in supplementary table (TS-2). Certified Reference Materials, CRM sl-1and sl-7 were used as calibration and check standards respectively. The deviations of the measured values for different elements in CRM sl-7 are given in supplementary table (TS-3) along with the errors due to counting statistics (2σ). In this study calcium was determined based on gamma ray activity of 47Sc since it is produced by 46

Ca (n, γ; β-) 47Sc, and have comparable half life (47Ca and 47Sc have 4.54 and 3.34 days respectively).

C isotope measurement was carried out by isotope ratio mass spectrometer (Europa, GEO 2020) from the 12 selected

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2.4.4 Carbon isotope (C-13) measurement

depths shown in Fig. 3a. 2 gm of dried sediment was acidified with concentrated H3PO4 and the generated CO2 gas was fed

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into mass analyzer. Na2CO3 salt that was calibrated against Vienna Pee Dee Belemnite (VPDB) standard was used for calibration. The results are expressed in δ values with a precision of ±0.02‰ (2σ). The precision was calculated by

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measuring 10-15 replicates of laboratory standard (Calcite) and calibrated against reference material NBS-18.

3.1 Granulometric Study

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3. Results

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Correlations among the sediment textural attributes have been used to infer the transport processes/depositional mechanisms of sediments in many modern and ancient sedimentary environments (Rajganapathi et al., 2013). The sediment textural attributes such as Mean (Mz), Sorting (SD), Skewness (Ski) and Kurtosis (K G) are used to reconstruct the depositional environment of sediments (Table 1). The samples show coarse (Mz: 0.29-0.69; SD: 0.29-0.76) to medium

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(Mz: 1.21-1.32; SD: 0.77-1.04) grain size range. The sediments belonging to depth range 30-60 m bgl is dominated by medium sand while the rest is characterized by coarse sands. Sorting values of sediments from all the depths show a narrow distribution and poorly sorted (50-60 m bgl) to very well sorted (rest of the depths) behavior. Skewness, a measure of the asymmetry frequency distribution, indicates very fine skew nature of sediments. Variation in the kurtosis values is a reflection of the flow characteristic of the depositing medium and the dominance of finer size. On the other hand the platy kurtic nature of sediments reflects the maturity of the sand. In the present case the kurtosis values (KG: 0.72-7.7) indicate

extremely lepto kurtic to platy kurtic nature of sediments. These sediment attributes collective indicate mixing of different size-range sediment populations in this region.

Linear Discriminate Function (LDF) is a statistical value used for estimating the variations in the energy and fluidity factors, which can be used to infer the different processes and environments under which sediment deposition occurred. The LDF of sediments was calculated using the equations by Sahu (1964). The process and environment of deposition deciphered by LDF are Y1 (Aeolian, Beach), Y2 (Beach, Shallow agitated water), Y3 (Shallow marine, Fluvial) and Y4

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(Turbidity, Fluvial). The computed LDF values are given in Table 2. The table indicated that all the sediment samples represent ‘beach’ environment based on Y1and Y2, 77% sediment samples represent ‘shallow marine’ environment

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followed by 33% sediment samples representing ‘beach’ environment. Y3 and Y4 reflect the fluvial condition followed by a few samples depicting ‘turbid’ environment during deposition. The LDF values indicate that all the sediment samples fall

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3.2 Mineralogy and microstructure of the sediments

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under rolling to bottom suspension condition.

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The dominant minerals identified at different depths are quartz, feldspar and micas followed by calcite, Mg-calcite, and aragonite. The analysis of 12 sediment samples from various depths indicated large variations in mineralogy (Fig. 3c), which can be attributed to the diverse nature of source rocks, deposition conditions of these sediments or alteration of

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minerals as a result of post depositional diagenesis. In most of the rock forming minerals REE are found to be dispersed as minor or trace constituents and exist as accessory minerals. The XRD patterns do not show any particular REE mineral suggesting that these elements either X-ray amorphous such as metal oxides or present in trace quantities (typically <5%). The surface textures of quartz grains can be utilized to achieve the understanding of the post depositional or diagenetic

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history of the sediments (Suresh Gandhi et. al. 2008; Ramamohanarao et.al 2003). During the processes of transportation and deposition, various micro-features are developed by mechanical and chemical processes and which in turn are influenced by physical and chemical properties of grains such as hardness, cleavage, solubility, tenacity, etc. The common features observed in the quartz grains of the studied sediments are cavities solution pitting and chemical etching ‘V’ marks indicating high- energy environment as well as the longer stay of sediments in the depositional environment as shown in Fig. 4 (slides 1-20). Mechanically produced irregular pits are quite common in these quartz grains spreading all over the grain surfaces (Fig. 4, slides 4, 5, 9, 10, 17 & 19) and these indicate differential relief. The pits are characterised by

elongated, circular or cresentric openings with uniform to irregular opening. A few pits are oriented, which might have been produced by impact during subaqueous collision in fluvial or near shore environment. V shaped indentations are also noticed on the raised surface of the grains as seen in Fig. 4 (slides 2, 3, 7, 8, 12 & 14). These are frequently found in the grains of subaqueous environment. Rounding of the edges due to grain transport is noticed. Impact V is usually formed in a high energy littoral environment. Groove features including elongate scratches, slightly curved troughs and arc-stepped furrows were found to be relatively uncommon (Fig. 4, slides 15, 17 & 18). These grooves appear in sets and oriented in a preferred direction with a conchoidal fracture.

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Etch V’s, the dominant microstructures formed by chemical activity in lagoonal or low energy subaqueous environments

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can be seen (Fig. 4, slides 13-15, 17-20). The degree of etching shows variation depending on the residence time. In some cases triangular etch pits are arranged in parallel line as shown in Fig. 4 (slide 7), which might have formed in a marine

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environment due to the rapid dissolution of silica at higher pH. Variable shape and size solution pits are noticed in the SEM. The common shapes being circular or semicircular or elongated (Fig. 4, slides 10-12). Precipitation features are

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characterized by authigenitic crystals or adhering particles (Fig. 4, slides 6 & 8), which are small convex projections with radial or circular configuration on the grain surface. The observed needle like or small globular deposits seem to have

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apparently deposited on the grains inferring their formation in the intertidal zone by deposition and periodic evaporation of inter-granular water. In conclusion, the micro-structural analysis of the studied sediments infer that the sub-angular, irregular stepped furrows and irregular curved grooves, impact ‘v’ markings indicate the impact of subaqueous collision,

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grinding collision and mutual colliding of grains in motion because of fluvial and near shore high energy fluvial energy condition. Sub-angular to sub-rounded grains, presence of deposits and solution pits indicate chemical action by tropical, low to high energy beach zone and chemical energy environments. Sub angular grains with irregular curved impact marks, solution pits indicate high energy fluvial near shore and high energy tropical environment.

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3.3 Major and trace element geochemistry

The major element (Na, K and Ca) and trace element concentrations (Co, Sc, Cr, Zn, Hf, Th and U) are given in Table 3 including literature values of the North American Shale Composite (NASC) and Upper Continental Crust (UCC). Depth profiles of major and trace elements are displayed in Fig. 5 (a & b). It is found that vertical profile of major elements show wide distribution. Na and K behave similarly all through the litho-section. Ca exhibits high variation between 105-132m bgl (Fig. 5a). On the other hand, trace elements show very similar pattern, with U being the least abundant (maximum up to

3 ppm) and Zn being the most (maximum up to 167 ppm) as shown in Fig. 5b. This similarity in trace element trends points to a common source for these elements dominants from felsic rocks, which is detailed in sections 4.1. The variation in each element across the litho section could be due to presence of varying amounts of Quartz and Plagioclase. A plot of major ions normalized to UCC averages is shown in Fig. 5c with NASC values for comparison. Most of the sediments show depleted values for all elements in comparison to UCC values (elemental ratios < 1). This depletion suggests that source rocks are weathered or diagenetically altered to remove feldspar and lithic fragments and thus increasing the

135 m and 132-141 m bgl with elemental ratios ranging up to 1.4 to 4 (Fig. 5c).

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3.4 Rare earth elements (REEs)

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proportion of quartz relative to source rock. Ca and Zn were found to be enriched compared to UCC values at depths 60-

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The REE data (La, Ce, Eu, Yb and Lu) of the selected sediments is given in Table 3. Literature values of Chondrite (CI), Post Archaean Australian Shale (PAAS), NASC and UCC are also listed in the table. Vertical profiles of the REEs are

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shown in Fig. 6a. It can be observed from the plot that the trends are similar for all the REEs indicating a common source, as observed in the case of trace element profiles (Fig. 5b). However it is noted that lighter REE (LREE: La and Ce) are

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more abundant compared to heavier ones (HREE: Yb and Lu). Chondrite normalized plot of REEs, Fig. 6b show remarkable uniformity of the sediments with enriched LREEs and depleted HREEs, which is a typical pattern of UCC exposed to weathering and erosion. The HREE depletion occurs in source rock if there is a preferential removal of HREE

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as carbonate complexes during chemical weathering (Cullers et al., 2002; Roy and Smykatz-Kloss, 2007). Granitic feldspars typically show a slight depletion in the HREE (Cullers et al., 2002). All the sediments in the present study show a lesser REE content compared to UCC, NASC and PAAS. Low REE concentrations reflect the dilution by Quartz with lesser amounts of K-feldspar, mica and trace amounts of calcite). Negative Eu anomalies are often due to presence of

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higher concentration of heavy minerals in the sediments. No Eu anomaly is observed in the REE patterns (Fig. 6 b), which is indicative of felsic nature of sediments. The Eu anomalies in the sediments are dependent on the ratios between feldspars and heavy minerals as quartz contains little or no REE (Taylor and McLennan, 1985). Absence of any particular heavy mineral in XRD profiles of the sediments further supports this finding (Fig. 3c). The REEs contents of shale composite (NASC) are also used to normalize the REE contents of sediments. A plot of NASC normalized REE pattern of the sediments indicates less steep or flat curve with pronounced positive Eu anomaly (Fig. 6 c). Although the REEs patterns follow similar trend, a difference in the position of the curves is noticed that can be attributed to total REE content. The

REE content in the sediments is mainly a function of quartz and clay mineral contributions. The positive Eu anomaly reflects the contribution of plagioclase minerals or secondary calcite deposits (Fig. 6 c).

3.5 Elemental correlations

In order to understand the inter-elemental correlations, a correlation matrix is constructed and given in Table 4. In general major elements are not correlated with other elements. Only moderate correlations (r2: 0.46-0.54) are noticed between Na – Sc and Na – Co elements. Similarly moderate correlation was observed between K – Zn (r2: 0.56). Hf showed moderate

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correlations with Sc and Cr (r2: 0.51-0.68) while Cr showed good correlations with Co and Sc (r2: 0.88-0.95). Th showed

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moderate correlations with Ca, Co, Sc, Cr, Zn (r 2: 0.46-0.63) while U showed moderate to good correlations K, Zn and Th (r2: 0.51 to 0.72). Calcium is not correlated with any other element. Majority of the trace elements show moderate to

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strong correlations (0.5 to 0.9) with REEs except Zn, Hf and U. All REEs show strong positive correlations among each other r2 typically between 0.7-0.9 indicating their coherent inter-element relationship. These positive correlations point to a

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common source for REEs as seen in the case of trace elemental and REE patterns (Fig. 5b & 6a).

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3.6 Carbon isotope (δ13C)

The 13C isotope values of the inorganic carbon expressed as permil values (‰) against VPDB are given in Table 3. Marine carbonates generally have positive δ13C values from 0.0 ±3‰ whereas soil gas on the other hand is much lighter

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isotopically and has δ13C value of about -26 ± 5‰ in temperate climate (Clark and Fritz, 1997). Precipitation of secondary calcite cement leads to δ13C of about -10 ± 5‰ (Fritz et al., 1989) and very negative values are found when organic compounds are mineralized (Fritz et al., 1989). It can be seen from the Table 3 that most of the studied sediments have δ13CTIC values in the range of -0.1 to -11.4‰ but the deep sediments show positive δ13CTIC values (+1.5‰ and +5‰). The

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complex geochemical environment of the sediments in this region is clearly reflected by the wide range of δ13CTIC values of sediment samples. Highly enriched δ13C values indicate marine sources whereas the depleted signatures normally reflect the terrestrial sources.

4. Discussion

4.1 Provenance studies

Elemental ratios (La/Sc, Th/Sc, Th /Cr and Th /Co) have been used to identify the nature of source rock (Wronkiewicz and Condie, 1987; Cullers, 2002). La and Th are more abundant in felsic rocks than in mafic rocks, while Sc and Co exhibit opposite trend. This is because, Th and La being incompatible elements preferentially get partitioned into melts and associated with felsic rocks (Wronkiewicz and Condie, 1987). So, the relative enrichment of incompatible over compatible elements indicates a felsic dominated provenance. Typical Th/Sc ratio for post Archean UCC is ~1 while felsic rocks have >1and mafic rocks show <1. Most of the analyzed sediments show Th/Sc ratio greater than or equal to unity (1 to 4.14) suggesting felsic rock sources like granite and granodiorite (Table 5). A few sediment samples show Th/Sc ratio slightly

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less than one (~ 0.9) and one sediment sample show lesser ratio (0.66) indicating some contribution from mafic sources (Table 5). Dominance of felsic source rocks is also demonstrated by the scatter plot of Th/Co versus La/Sc (after Cullers,

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2002). Sediment samples of this region plot near the felsic dominance as shown in Fig. 7a. Elemental ratio Th/Cr is also used to differentiate mafic and felsic rock contributions due to redox chemistry (Feng and Kerrich, 1990). Variations in

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Th/Co and Th/Cr ratios are 0.46-1.54 and 0.06-0.26 respectively and fall within the felsic source rock range (Table 5). These values also indicate that the nature of sediments is similar to the sediments belonging to nearby regions such as

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Rabanpalli and Sillakkudi formations (Nagarajan et al., 2007 and Bakkiraj et al. 2010) as shown in Table 5. High ratios are

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noted at 9-12m, 60-63m and 111-114m, which is due to low clay content in those depths and these depths also correspond to Quaternary, Tertiary and Cretaceous formations respectively.

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Hafnium in sedimentary rocks typically ranges from 2.6 to 6.5 ppm while intrusive masses such as Tonalite contain high concentrations (McLennan and Taylor, 1999). The studied sediments showed normal range of Hf concentrations (1.8 to 7.3 ppm) indicating the contribution of felsic rocks. Reasons for high Hf observed in topsoil (14.83ppm) need to be further investigated. Correlations between La/Th ratio and Hf concentration are also used to evaluate source rock composition (Floyd and Leveridge, 1987). As illustrated in Fig. 7 b, the relatively high Hf contents (1.8 – 7. 3 ppm) and low La/Th

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ratios (1.58 – 5.30) in these sediments suggest felsic source rocks. It is also observed that sediment data spread towards Andesite type indicating Andesite contribution. The elemental ratios of these sediments show similar ranges as that of sediments from sedimentary formations of nearby regions (Table 5), which are derived from felsic source rocks. A comparison of these elemental ratios with other sites such as Neogene sandstone of north-western Borneo Basin and Upper Tukau Formation (Borneo Island, East Malaysia) indicate a wider Th/Co ratios compared to study area sediments while La/Sc, Th/Sc and Th/Cr are found to be relatively narrower. However, sediments from Kachch basin (Gujarat, India) and

Cuddapah basin (Andhrapradesh, India) show similar ranges in these elemental ratios with that of the studied sediments. This clearly indicates that the studied sediments are influenced by both marine and non-marine deposition processes.

Felsic and mafic provenance of sediments can also be differentiated by ternary diagrams such as La-Th-Sc (Cullers, 2002) and Th-Hf-Co (Taylor and McLennan, 1985). The sediments data fall in a felsic rock dominant region in La-Th-Sc ternary plot (Fig. 8 a). Feldspar in these rocks is present as Plagioclase (typically Oligoclase or Andesine) with less alkali feldspar and more Quartz (>20%). This is further corroborated by Th-Hf-Co ternary diagram, where the sample data fall near

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Tonalite and Granitic sources indicating felsic provenance (Fig. 8 b). Most of the samples are plotted close to NASC and UCC (Fig. 8 b) also suggesting a provenance derived from felsic rocks. Contribution of Tonalite, which is an intrusive rock

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of felsic composition and phaneritic texture, can be inferred from Fig. 8 b.

The total REEs concentration (TREE: summation of La, Ce, Eu, Hf, Lu in ppm) varies with depth and ranges from 13.6

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ppm (132-135 m) to 93.5 ppm (51-54 m) as given in Table 5. Higher TREE values are observed at 51-54 m, 105-108 m

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and 138-141 m and lower values at 9-12 m, 60-75 m and 132-135 m. The lower of TREE matches with the potential aquifer sands of different ages; Quaternary, Tertiary and Cretaceous respectively, which is also observed in Th /Cr and Th

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/Co ratios (Table 5). Although the TREE contents are significantly different at different depths, it is interesting to note that the normalized distributions show fewer variations. Clay and fine sand fractions of the sediments contain high abundance of REEs (Cullers et al., 1988). Therefore variation in the TREE observed in these sediments can be attributed to the

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contribution of variable amounts of clay and fine sand. In general the amorphous metal oxides dispersed in the sediments account for the depletion of the REE compared to shale. Therefore, the difference between the REE values of PAAS and the studied sediments can be attributed to the component associated with amorphous phases. This is further corroborated by the absence of any REE specific mineral in XRD patterns of the bulk sediments (Fig. 3 c). Biogenic and authigenic phases

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of marine sediments formed directly from seawater tend to show lower NASC normalized HREE values (0.1 to 0.5) as shown in Fig. 6 c. The minerals that accommodate REE in sedimentary rocks as trace components and account for the deviation of the REE patterns include clay and ferromagnesium minerals. The finely dispersed amorphous metal hydroxides adsorbed on to the detrital particles in the sediments also deviate the REE from the normally observed patterns.

4.2 Weathering and Deposition conditions

The Th/U ratio is often used to infer the weathering under oxidizing conditions since both these elements exhibit redox sensitive nature ( Hurowitz and McLennan, 2005). The oxidation condition allows insoluble tetravalent U to become highly soluble hexavalent U hydroxides and UO22+ ionic complexes, on the contrary under reducing conditions both U and Th are insoluble in water and transported with detrital materials resulting in the formation of the sedimentary rocks with Th/U ratio close 3.8 (average UCC value) Table 5. Therefore, Th/U ratio of 3.8 indicates that the sediments are derived from a large homogenized continental provenance. But Th/U ratio increases significantly if weathering takes place under oxidizing conditions. Uranium concentrations in the studied sediments found to vary from negligible to 3ppm, and depths

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where U is not detected also show the low TREE values (Table 3 & 5). On the other hand, Th concentration in the sediments ranges from 1.5 to 7.5 ppm and high Th concentration is noted in sediments belonging to Late Cretaceous

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period. This could be due to the different geological events that occurred on the earth during this period (Madhavaraju et al., 2002). Th/U ratio in the studied sediments ranges from 2.12 to 9.57 indicating non homogeneity in the provenance

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(Table 5). Most of the sediments show high Th/U ratios (4.5 to 9.5) more than UCC (3.82) reflecting their origin from weathered source rocks. It is also noted that recent sediments showed higher ratios implying weathering under oxic

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environments. Lower Th/U ratios in older sediments (2.1 -2.3) less than UCC ratio (3.82) reflect anoxic environments.

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Study by Singh and Rajamani, 2001 showed that the mineralogical and geochemical features of sediments deposited by River Cauveri reflect low degree chemical weathering of the source rocks. From the plot of sediment REE patterns (Fig. 6 b & c) it is observed that sediments show similar patterns as that of PAAS

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indicating weathering has imparted enrichment of LREE over HREE. It is also reported that sediments derived from intense weathered sources have negative Eu anomaly whereas moderate weathered sources show positive Eu anomaly (Cullers et al., 1988). The Chondrite normalized values of (La/Lu)cn in the sediments of studied site range from 6.8 to 21.2 (Table 5) indicate moderate to high degree of source rocks weathering. This variation in (La/Lu)cn is ascribed to the

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preferential mobilization of HREE during weathering process (Nesbitt, 1996; Cullers, 2002) leading to higher (La/Lu)cn ratio (10.1 to 21.2) baring two depths 0 - 3 m and 60 - 63 m where the ratio is 6.8 and 9.5 respectively. A positive Eu anomaly in NASC normalized REE distribution (Fig.6 c) is indicated in all the sediments, but it is more prevalent in the case of sandstone formation though TREE is lesser compared to other sediments. During the weathering of source rocks, minerals rich in REEs break first and form secondary mineral phases wherein Eu enriched feldspars along with quartz are preferentially retained in coarser sediments leading to positive Eu anomaly. Similar positive Eu anomalies in sediments of

Cauvery basin are also reported by Singh and Rajamani (2001). Positive anomaly is also noticed by Singh et al. (2015) in sediments of ophiolitic complex in Indo-Myanmar Orogenic Belt of Northeast India.

Carbon isotope (13C) was also evaluated in selected sediments from different depths in order to assess the environment/climatic conditions during the time of deposition. Higher negative values of carbon isotopes were noted in 2730m, 75-78m and 135-138m depths, among these, first depth represents Tertiary and rest Cretaceous period. There were also positive values observed at 129-132m and 141-144m of the Cretaceous formation. A positive shift in δ13C is common

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phenomenon during increased surface productivity (typical of upwelling zones), which allows enhanced sequestration of C-rich organic carbon under anoxic–euxinic conditions (Gale et al., 1993). There were lesser variation of δ13CTIC in the

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sediments of Tertiary formations (-1.2‰ to -7.5‰) compared to extreme variations in Cretaceous formation (-11.4 ‰ to +5.11‰). These δ13CTIC trends suggest ‘warm and dry’ climatic conditions during Late Cretaceous period. Given the warm

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global climate which has been attributed to the Cretaceous Period in general, the sedimentary provenance suggests longstanding aridity in southern India during accumulation of the Cauvery Basin infill through the Mid and Late Cretaceous.

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These observations indicate that this region has undergone eustatic sea-level excursions, which are of global significance during the Mid to Late Cretaceous period (Hallam, 1992). A similar observation is reported by Madhavaraju et al (2002).

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Depths 27-30m and 75-78m comprising permeable sandstone zones show more negative values of δ13CTIC (-11.4‰ and 9‰), which could be due to the precipitation and recrystalization of carbonates from groundwater. It is observed from the

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Fig. 9 a & b that negative δ13CTICvalues correspond to low TREE values with pronounced positive Eu anomaly. These depths also belong to higher sand bearing formations. It is interesting to note that these depths, 27-30 m and 75 - 78m, fall in the zone of changing geological formation indicating Q/T and K/T boundaries respectively.

Comparisons are drawn between global sea-level curve and the mineralogical results obtained in this study by using

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Detrital Index (DI: detritus (phyllosilicates and quartz)/calcite ratio) in order to interpret the deposition conditions. A low DI generally reflects a more distant detrital source, decreased erosion and higher sea-level or deeper water conditions while a high DI indicates more proximal detrital source, increased erosion and lower sea-level or shallower water environment (Duchamp-Alphonse et al., 2011). The XRD patterns of the sediments from Tertiary and Quaternary formations show the presence of quartz to a greater extent than the Cretaceous formations leading to high DI. It is reasonable to assign this to lower sea level or shallow water environment. A similar observation of shallow marine character in Ariyalur region was established by Sundaram et al. (2001). The sedimentary deposits of Ariyalur region are well correlated with the deposits of

Pondicherry region. The micro-structural and granulometric inferences also support the shallow marine character of Pondicherry deposits. In addition, the positive Eu anomaly observed in the sediments also infers the influence of shallow marine conditions on sediment diagenesis. Similar observations were reported by Singh et al. (2015) in carbonates of northeast India. Sediment deposition in KG basin of SE India is also reported to have occurred in shallow marine environments that fluctuated between supratidal, estuarine, lagoonal and open marine conditions interrupted by periods of subaerial deposition marked by paleosols (Nagarajan et al. 2014). The calcite is dominant at 27-30m, 60-63m, 75-78m and 135-138m depths rendering a slight decrease in the DI, thus signifying comparatively higher sea-level or deeper water

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conditions at these depths. The DI also reflects fluctuations in terrigenous supply linked with changes in hydrolysis

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conditions.

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4.3 Influence of Deccan Volcanism

Influence of Deccan volcanism is noted in clastic rocks of Late Cretaceous and Early Tertiary sedimentary sections in some

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parts of Cauvery basin (Madhavaraju and Lee, 2010). These inferences were based on the high amount of Cr (38-622 ppm) and high Cr/Th ratio (3.73-76.73) present in the sediments. It was also reported by Keller et al. (2008) that most massive

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Deccan trap eruption occurred near the K–T mass extinction in SE India. In their study in SE part of India (KrishnaGodavari basin), they reported that volcanism may have played critical roles in both the K–T mass extinction and the delayed biotic recovery. These inferences were derived from the planktic foraminiferal based evidences. In this study we

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found Cr concentration between 12 and 115 ppm and Cr/Th ratio between 3.8 and 16.7 (Table 5), no anomalous high Cr was observed in any of the studied depth intervals indicating no/negligible input of volcanic ash in these sediments. It is reported that Deccan volcanism produced enormous amount of lava and large quantities of CO 2 which disturbed the ecosystem and led to greenhouse warming (McLean, 1985). This also induced acid leaching of many clay minerals leading

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to reduced TREE contents. Low TREE content reported in Rayambaram formation (Madhavaraju and Lee, 2010), and Anjar area of Deccan province (Shrivastava and Ahmad, 2008) was attributed to contribution of volcanic ash in the sediments. However, it is to be noted that sum of analyzed REEs in the studied sediments, even though only 5 out of 14 REE are accounted here, is more than that of Rayambaram formation (27-49 ppm) and the REE pattern resembles that of PAAS and UCC and not that of basalt pattern (Fig. 6). These findings clearly infer that the Deccan volcanism had no/negligible impact on the geochemical characteristics of studied sediments of th Pondicherry region. This observation is further supported by the study conducted by Madhavaraju et al. (2002), which concluded that no complete ash-blanketing

of the area took place preceding K/T event and nor is there any evidence for significant volcanogenic clay in the Tertiary section. 5. Conclusions

This study contributes to a deeper understanding of the source rock nature, weathering and deposition conditions in multisedimentary formations of the Pondicherry region.Textural analysis indicates the dominance of coarse to medium grained sediments in samples. LDF results show the dominance of shallow marine deposits in the beach while the influence of

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fluvial is minimal. The granulometric studies indicate that most of the grains form by rolling to bottom suspension rolling. Sub-angular, irregular stepped furrows and irregular curved grooves, impact ‘v’ markings were identified in the micro-

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structural studies. These observations infer subaqueous collision, grinding collision and mutual colliding of grains due to near shore high energy fluvial energy condition. The major and trace element patterns suggest that the source rocks are

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weathered and diagenetically altered to remove the lithic fragments leading a higher Quartz proportion in the sediments. The Th/U ratio infers oxic weathering in shallow sediments and anoxic in deeper sediments. The REE patterns show

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enriched LREE and depleted HREE, which is a typical of UCC exposed to weathering and erosion. Variable (La/Lu)cn values and low TREE content suggest moderate to intense weathering of source rocks. A positive Eu anomaly is observed

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in NASC normalized REE patterns which is in agreement with earlier studies carried out in Cauvery basin. δ13CTIC data infer the presence of shallow marine condition in Quaternary and Tertiary formations while deep marine condition in Cretaceous formation. Deccan volcanism on these sediments is not observed. The elemental and isotopic patterns suggest

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that depths 27-30 m and 75 - 78m represent Q/T and K/T boundaries respectively.

Acknowledgements

Authors sincerely acknowledge the support and encouragement by Dr. P.K. Pujari, Associate Director, RC & I Group,

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Bhabha Atomic Research Centre, Mumbai. Dr. Kallol Swain (Analytical Chemistry Division, BARC), Dr. Kathi Sudarshan and Dr. R. Acharya (Radio Chemistry Division, BARC) are duly acknowledged for their help in Neutron Activation Analysis and calculations. We sincerely acknowledge Dr. A.V. R. Reddy (former Head, Analytical Chemistry Division, BARC) for his valuable suggestions during the preparation of this manuscript. Authors thank Mr. Arzoo Ansari (IRAD, BARC) for his help in preparing 2D section and inset map.

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List of illustrations Fig.1 (a) Geological map of Cauvery basin (modified after Krishnan, 1982), (b) geological map of Pondicherry (after CGWB, 1993) Fig.2 (a) Location map of Pondicherry region and study site (Andiarpalayam), (b) 2D subsurface map of transect A-D with formations identified based on available stratigraphy (CGWB, 1993) Fig.3 (a) Schematic map of litho-section of study site based on in situ nature of sediments, (b) Vertical profile of rate of penetration data with studied depths marked and (c) X-Ray Diffraction patterns of the sediments at selected depths

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with major peaks identified (q=quartz, Kf=potash-feldspar, a = aragonite, c=calcite m-mica and Mg-cal = magnesium-calcite)

Fig.4 Slide nos. 1. Group photo of sub-angular Quartz grains, 2. Chemical Precipitation on the weathered surface, 3.

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Chemical Precipitation and etch v’s,4. Impact marks, stepped lines and chemical precipitation, 5. Chemical precipitation and irregular markings, 6.Group photo of sub-angular Quartz grains, 7. Step like scratched or eroded

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surface, 8. Weathered surface (seems to be Mud cracks), 9.Hackly fracture (like cleavage), 10. Chemical weathering and pit marks and precipitation, 11. Group photo of sub-angular Quartz grains, 12. Cuttings with plain surface by physical weathering, 13. Silica Precipitation (chemical weathering), 14. Curved impact marks with precipitation, 15.

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Scaly surface (onion peelings), 16.Group photo of sub-angular Quartz grains, 17. Curved impact marks with precipitation, 18. Curved Markings, 19.Curved scratch surface with some precipitations, 20. Etch v’s surface

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Fig.5 Depth wise profile of (a) major, (b) trace elements and (c) upper continental crust (UCC) normalized diagram for sediments. The plot for North American Shale Composite (NASC) is shown for comparison Fig.6 (a) Variation of Rare earth elements concentration (in ppm) with depth, (b) Chondrite normalized REE distributions, along with those of NASC, PAAS, UCC, (c) NASC normalized REE distributions

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Fig.7 Scatter plot of (a) Th/Co versus La/Sc showing source rock composition for the sediments (fields after Cullers, 2002) and (b) La/Th versus Hf of the sediments indicating felsic source rocks (fields after Floyd and Leveridge 1987) Fig.8 Ternary diagram of (a) La-Th-Sc, data for Granite, Andesite and Basalt from were taken from Condie (1993) and (b) Th-Hf-Co, data for Granite, Tonalite and Tholeiite is taken from Taylor and McLennan (1985)

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Fig.9 Depth wise variation of (a) δ13C and (b) total rare earth element concentration (TREE) in sediments of study site

Table 1 Granulometric parameters of sediments from Pondicherry region Depth (m, bgl)

1 2 3 4 5 6 7 8 9 10 11 12

0-3 9-12 27-30 36-39 51-54 60-63 75-78 105-108 111-114 129-132 132-135 138-141

Mean Mz 0.66 0.57 0.33 1.27 1.21 1.32 0.44 0.29 0.65 0.63 0.69 0.69

Coarse Coarse Coarse Medium Medium Medium Coarse Coarse Coarse Coarse Coarse Coarse

Sorting SD 0.65 0.76 0.57 0.77 0.88 1.04 0.44 0.29 0.65 0.66 0.58 0.56

M.Well sort Mod.Sort M.Well sort Mod.Sort Mod.Sort Poorly sort Well sort V.Well sort M.Well sort M.Well sort M.Well sort M.Well sort

Skewness Ski 0.47 0.09 0.74 0.15 0.09 0.19 0.63 0.50 0.39 0.41 0.31 0.19

V Fine Skew V Fine Skew V Fine Skew Fine Skew Near Symm Fine Skew V Fine Skew V Fine Skew V Fine Skew V Fine Skew V Fine Skew Fine Skew

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re

-p

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Note: bgl- below ground level

Kurtosis KG 1.00 1.14 7.73 0.92 0.76 0.85 0.72 4.68 0.93 1.21 0.85 1.19

Meso kurtic Lepto Kurtic Ex.Lepto Ku Meso kurtic Platy Kurtic Platy Kurtic Platy Kurtic Ex.Lepto Ku Meso kurtic Lepto Kurtic Platy Kurtic Lepto Kurtic

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S. No

Table 2 Linear discrimination Function of sediments from Pondicherry region

Beach Beach Beach Beach Beach Beach Beach Beach Beach Beach Beach Beach

65.11 85.89 182.95 78.58 85.52 110.90 44.34 105.72 62.21 68.30 54.25 56.87

Y3 Sh.Marine Sh.Marine Sh.Marine Sh.Marine Sh.Marine Sh.Marine Beach Sh.Marine Beach Sh.Marine Beach Beach

1.64 0.43 -0.31 4.87 6.73 8.96 -1.23 -1.40 2.02 2.05 1.67 2.07

Y4 Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial Fluvial

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lP

re

-p

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1 2 3 4 5 6 7 8 9 10 11 12 Note:

Y2

9.10 13.34 46.26 7.03 5.81 7.17 8.45 28.38 8.19 9.79 7.22 8.20

Fluvial Turbidity Turbidity Fluvial Fluvial Fluvial Fluvial Turbidity Fluvial Fluvial Fluvial Fluvial

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Depth (m, Y1 bgl) 0-3 1.35 9-12 1.59 27-30 22.56 36-39 0.22 51-54 0.73 60-63 1.54 75-78 0.08 105-108 12.81 111-114 1.33 129-132 2.28 132-135 0.78 138-141 2.01 bgl- below ground level

S.No

NASC UCC PAAS Chondrite

Cr mg kg-1 86.3 26.6 41.5 67.9 115.4 39.9 10.7 52.0 32.1 48.4 11.5 65.0 125 85

Zn mg kg-1 74.4 82.7 68.2 65.1 67.2 51.1 75.5 69.1 78.3 105.8 37.8 167.5 100 71

Hf mg kg-1 14.83 2.07 2.57 2.66 7.43 3.10 2.00 4.64 4.81 2.54 1.87 5.33 6.3 5.8

Th mg kg-1 5.60 6.99 4.03 5.02 6.75 4.52 1.70 7.51 7.14 6.98 1.55 6.80 12.3 10.7

U mg kg-1 0.73 0.80 0.73 0.73 1.47 0.73 0.73 1.65 3.09 0.73 0.73 2.99 2.7 2.8

Rare earth elements La Ce Eu mg kg-1 mg kg-1 mg kg-1 15.7 44.1 0.86 11.0 14.5 0.48 18.3 31.9 0.74 18.5 33.8 0.91 31.5 58.8 1.38 10.3 15.8 0.66 9.0 16.6 0.42 26.8 49.9 1.06 22.6 45.0 0.82 19.9 39.4 0.59 6.1 6.8 0.37 26.3 50.3 1.30 31 67 1.18 30 64 0.88 38.2 79.6 1.08 0.24 0.61 0.056

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Trace elements Co Sc mg kg-1 mg kg-1 8.69 5.61 4.85 1.69 5.57 3.78 10.14 5.85 14.72 10.23 5.92 3.43 3.43 1.43 11.73 5.71 4.64 3.40 7.94 4.49 2.11 1.74 12.04 6.41 26 15 17 13.6

-p

Ca % 0.050 0.070 1.079 0.050 2.478 3.477 0.850 3.775 9.256 12.345 0.290 2.011 2.4 2.99

re

0-3 9-12 27-30 36-39 51-54 60-63 75-78 105-108 111-114 129-132 132-135 138-141

Major elements Na K % % 0.117 0.757 0.528 0.807 1.232 1.942 1.061 1.256 2.067 1.958 1.771 2.220 0.291 2.096 0.701 2.918 0.404 2.535 0.331 1.701 0.306 2.452 0.680 4.749 0.75 3.2 2.89 2.8

lP

Depth m, bgl

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Table 3 Major, trace and rare earth element data of the sediments along with literature values of NASC, UCC, Chondrite-CI and PAAS

Yb mg kg-1 1.60 0.63 0.61 0.51 1.67 1.01 0.41 1.16 0.96 0.83 0.29 1.40 3.1 2.2 2.82 0.16

Lu mg kg-1 0.24 0.09 0.11 0.13 0.19 0.11 0.09 0.13 0.13 0.14 0.05 0.21 0.46 0.32 0.43 0.024

Isotope δ13C Permil (‰) nd -4.65 -7.83 nd -4.65 -5 -11.4 -0.1 nd 5.12 -9 1.5

-

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Note: North American Shale Composite (NASC), Upper Continental Crust (UCC), Post Archaean Australian Shale (PAAS), nd- not determined, bgl- below ground level, “-” data not available

Table 4 Correlation matrix of the measured chemical species in the sediments from Pondicherry region K 1.00

Ca 1.00

Co 0.46 1.00

Sc 0.54 0.95 1.00

Cr 0.88 0.95 1.00

Zn 0.56 1.00

Hf 0.51 0.68 1.00

Th 0.46 0.63 0.53 0.51 0.47 1.00

U 0.72 0.58 0.51 1.00

La 0.86 0.85 0.72 0.73 0.61 1.00

Ce 0.84 0.85 0.78 0.45 0.55 0.71 0.57 0.95 1.00

Eu 0.92 0.92 0.83 0.47 0.60 0.57 0.91 0.88 1.00

Yb 0.76 0.78 0.82 0.79 0.63 0.70 0.79 0.80 1.00

Lu 0.73 0.75 0.83 0.51 0.85 0.54 0.64 0.80 0.75 0.90 1.00

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Na 1.00

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Na K Ca Co Sc Cr Zn Hf Th U La Ce Eu Yb Lu

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-p

Note: Except δ13C all the measured parameters are included in elemental correlation matrix

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Table 5 Total rare earth element concentration (TREE) and other elemental ratios of the sediments from the study area, common parent rocks, nearby regions and elsewhere La/Co 1.80 2.28 3.30 1.82 2.14 1.74 2.62 2.29 4.86 2.51 2.91 2.18 1.19

Th/U 7.67 8.69 5.52 6.88 4.59 6.19 2.32 4.56 2.31 9.57 2.12 2.28 4.56

La/Th 2.80 1.58 4.55 3.68 4.66 2.28 5.30 3.57 3.16 2.85 3.96 3.87 2.52

La/Sc 2.80 6.53 4.86 3.16 3.08 3.00 6.30 4.70 6.64 4.44 3.53 4.10 2.07

Th/Sc 1.00 4.14 1.07 0.86 0.66 1.32 1.19 1.32 2.10 1.56 0.89 1.06 0.82

97.4

3.00

3.82

2.80

2.73

0.97

Sediments (this study

13.60 103

1.19 – 4.86

2.129.57

Th/Cr 0.07 0.26 0.10 0.07 0.06 0.11 0.16 0.14 0.22 0.14 0.14 0.11 0.10

(La/Lu)cn 6.8 13.1 17.9 15.3 16.8 9.5 10.1 21.2 17.4 14.4 11.7 13.1 7.0

1.07

0.31

9.7

-p

0.664.14

0.461.54 0.6719.4

0.060.26 0.132.7 0.0180.046

6.8-21.2

2.5-16.3

0.8-20.5

Basic Rock

(Cullers and Podkovyrov 2000)

0.430.86

0.050.22

0.04-1.4

Rabanpalli formation

(Nagarajan et al., 2007)

1.1-3.4

1.2-2.7

0.17-0.4

0.120.24

4.2-9.7

Sillakkudi formation

(Bakkiraj et al. 2010)

1.939.36

0.416.57

0.145.01

0.232.94

4.1-23.5

(Nagarajan et al. 2014)

-

0-2.6

0.3-6.5

0.0050.12

-

Tadpatri shale, Cuddapah Basin

(Mitra et al. 2017)

0.5-5.7

0.14-1.4

0.171.77

0.050.27

-

Chari Formation, Kachchh Basin, western India

(Ghaznavi et al. 2018)

-

0.71-5.0

0.350.95

0.20.91

-

(Nagarajan et al. 2017)

-

-

0.836.22

0.060.16

7.6-10.22

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Neogene sandstones, north-western Borneo Basin

re

(Cullers 2000)

lP

Granite

Typical values 1.58 – 2.075.30 6.65

Th/Co 0.65 1.44 0.72 0.50 0.46 0.76 0.49 0.64 1.54 0.88 0.73 0.57 0.47

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TREE 62.5 26.7 51.7 53.8 93.5 27.9 26.6 79.1 69.5 60.9 13.6 79.5 102.7

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Depth (m bgl) 0-3 9-12 27-30 36-39 51-54 60-63 75-78 105-108 111-114 129-132 132-135 138-141 NASC UCC (Taylor and McLennan 1985)

3-27 1.1-7

Upper Tukau Formation, Borneo Island, East Malaysia

Note- cn denote Chondrite normalized, “-” data not available

27