carbonate geochemistry

International Geology Review Vol 45 2003 p 16ndash26Copyright copy 2003 by V H Winston amp Son Inc All rights reserved

0020-68140364316-11 $1000 16

Geochemistry of Upper Miocene Kudankulam Limestones Southern India

J S ARMSTRONG-ALTRIN1 SURENDRA P VERMA Centro de Investigacioacuten en Energiacutea Universidad Nacional Autoacutenoma de Meacutexico (UNAM) Priv Xochicalco sn Col Centro

Apartado Postal 34 Temixco Mor 62580 Meacutexico

J MADHAVARAJUDepartment of Geology University of Madras Guindy Campus Chennai-600025 India

YONG IL LEE School of Earth and Environmental Sciences Seoul National University Seoul 151-742 South Korea

AND S RAMASAMY

Department of Geology University of Madras Guindy Campus Chennai-600025 India

Abstract

Concentrations of major trace and rare-earth elements (REE) were measured in shallow marinelimestone samples of the upper Miocene Kudankulam Formation southern India in order to inves-tigate the geochemical variations among various litho-units The CaCO3 content is higher in algallimestone (AL 92 plusmn 1 n = 3) and clastic limestone (CL 90 plusmn 2 n = 3) than sandy shell limestone(SSL 81 plusmn 1 n = 3) All trace elements exhibit lower concentrations than post-Archean AustralianShale (PAAS) values except one SSL sample Large variations in SREE content are observed amongCL SSL and AL (~14ndash142 ~68ndash124 and ~38ndash98 respectively) Almost all limestone samplesanalyzed from the Kudankulam Formation show a small negative cerium anomaly (CeCe ~08ndash09) except one AL sample which lacks this cerium anomaly (CeCe ~104) Variations in Ceanomalies and SREE contents in Kudankulam limestone samples are mainly controlled by theamount of terrigenous sediments and diagenetic behavior Shale-normalized REE patterns and (LaYb)s LaSc LaTh and ThSc ratios suggest that the detrital sediments present in the limestoneswere probably derived from felsic source rocks The observed low content of U (09 plusmn 05 n = 9) andUTh (02 plusmn 01 n = 9) ratio in these limestones are probably related to an oxygen-rich environment

Introduction

THE BEHAVIOR OF rare-earth elements (REE) inmarine waters sediments and carbonate rocks hasbeen studied in detail by many workers (Ronov etal 1967 Piper 1974 Klinkhammer et al 1983De Baar et al 1988 Elderfield et al 1990 Sholk-ovitz 1990) Dominant factors influencing the REEcontents of carbonate rocks are (1) the amount ofterrigenous input (Piper 1974 McLennan 1989Murray et al 1991b) (2) variations in the oxygenlevel in the water column (Liu et al 1988) and (3)biogenic sedimentation (Murphy and Raymond1984) The distribution of REE particularly the Ceanomaly in marine sediments and carbonate rockshas proved to be an excellent indicator of deposi-

tional environments such as widespread marineanoxia (Liu et al 1988 German and Elderfield1990 Murray et al 1991b) oceanic palaeo-redoxconditions (Liu et al 1988) proximity to sourcearea (Murray et al 1991b) surface productivityvariations (Toyoda et al 1990) lithology anddiagenesis (Nath et al 1992 Madhavaraju andRamasamy 1999)

It is important to study whether or not the redoxchanges observed in the water column are transmit-ted to the underlying sediments These types ofstudies should be carried out on modern sedimentswith known environmental settings which will helpin resolving uncertainties regarding depositionalenvironments of ancient sediments (Macfarlane etal 1994) From a detailed study of carbonate sedi-ments deposited from the oxygen minimum zone(OMZ) in the Arabian Sea Nath et al (1997) sug-1Corresponding author email jsaamazatlcieunammx

UPPER MIOCENE KUDANKULAM LIMESTONES 17

gested that there is no variation in Ce anomalydeposited between these carbonates and those out-side the OMZ

More recently Madhavaraju and Ramasamy(1999) studied shallow-marine Maastrichtian car-bonates of southern India to provide useful informa-tion regarding the geological environment such asterrigenous inputs and redox conditions at thetime and place of deposition They suggested that Uand UTh ratios are useful for paleoredox inter-pretations

No systematic geochemical work has yet beencarried out on the limestones of the upper MioceneKudankulam Formation We report new majortrace-element and REE data along with informa-tion on the depositional environment Our mainobjective is to gauge the usefulness of uraniumin predicting the paleoredox condit ions andthe probable reason for the variation in Ce con-centration and Ce anomalies in the Kudankulamlimestones

Geology and Stratigraphy

In the southeastern part of Peninsular India (Fig1) limestone deposits have been discovered thatindicate marine influence during the formation ofthe southern part of Tamil Nadu (Bruckner 1988)This deposit has been called Kudankulam Forma-tion which crops out 20 km NE of Kanniyakumarinear the village of Kudankulam Isolated exposuresare present near villages such as Navalady Mana-paud Tiruchendur and Sattankulam (Fig 2) Themaximum altitude of this bed is ~51 m nearKudankulam and +20 m above msl at TiruchendurSedimentary rocks of the Kudankulam Formationare dominated by clastic and carbonate rocks (Arm-strong Altrin Sam 1998) These strata are present inwell cuttings stream sections and in a number ofquarry sections The clastic and carbonate rockscontain numerous fossils such as bryozoans mol-luscs echinoderms algae and foraminifera Thethickness of the sedimentary unit is only 4 to 5 m

FIG 1 Simplified geological map of southern India showing the location of the study area (modified after Singhand Rajamani 2001) Abbreviations in inset G = Gujarat K = Kerala Kr = Karaikal beds S = Sri Lanka J = JaffnaFormation

18 ARMSTRONG-ALTRIN ET AL

Hence the area has not attracted many researchersBruckner (1988) has made an attempt to establishsea-level fluctuations based on the coastal carbon-ates of Tamil Nadu He selected the Kudankulamlimestones as the marker to reconstruct sea-levelchanges The facies build-up and petrological datasuggest that these limestones were deposited by ashallow sea and formed in a near-shore environ-ment (Bruckner 1988)

The Kudankulam Formation in southern India ismost probably the equivalent of the Jaffna Forma-tion of Sri Lanka The occurrence of index microfos-sils like Austroltrillina howchini sp and Taberinamalabarica sp places the age of the Jaffna Forma-tion in the upper part of the late Miocene specifi-cally in the Burdigalian stage (Sahni 1979 Cooray1984 Bruckner 1988) Hence the limestones of theKudankulam Formation are either of Burdigalian orof late MiocenendashPliocene age Detailed systematicwork on the stratigraphy and petrography wasreported by Ramasamy et al (1994) ArmstrongAltrin Sam and Ramasamy (1997) and Ramasamyand Armstrong Altrin Sam (1998) have carried outpetrography and major-element geochemistry onthis limestone formation Finally from a stable iso-tope study it has been concluded that these lime-stones were subjected to meteoric or fresh waterphreatic diagenesis (Armstrong Altrin Sam et al2001)

Analytical Methods

Samples were collected from surface outcropsand quarry sections Nine representative sampleswere analyzedmdashthree from clastic limestone (CL)three from sandy shell limestone (SSL) and threefrom algal limestone (AL) These samples werewashed with distilled water air dried and thenground in an agate mortar The analytical tech-niques proposed by Shapiro (1975) were adopted forthe preparation of solutions for major and trace ele-ments Si and Al were determined using a spectro-photometer Fe was analyzed by atomic absorptionspectrometer CaCO3 was determined by a titrationmethod using EDTA Trace-element (Ba Co Cr CuNi Sc Sr V Zn and Zr) concentrations were deter-mined using a Jobin Yvon 138 Ultrace inductivelycoupled plasma atomic emission spectrometer (ICP-AES) Rare-earth elements (REE) and additionaltrace elements (Cs Hf Nb Pb Rb Th U and Y)were analyzed by a VG Elemental PQII Plus induc-tively coupled plasma mass spectrometer (ICP-MS)(Jarvis 1988) United States Geological SurveyStandard MAG-1 was used for calibration All trace-and rare-earth elements were analyzed at the KoreaBasic Science Institute Three analyses were madefor each sample and averaged Analytical precisionfor both trace elements and REE is better than 5For preparing REE-normalized diagrams post-

FIG 2 Simplified geological map of the Kudankulam Formation showing sample locations


Archean Australian Shale (PAAS) values listed byTaylor and McLennan (1985) were used The ratio of[CeCe] (Ce anomaly) is defined using the calcu-lated value of [Ce] (CesampleCePAAS) and the pre-dicted value of [Ce] obtained by the interpolationfrom the PAAS-normalized values of La and Pr Thecalculation of Eu anomaly [EuEu] was done in asimilar way using the observed values of Sm Euand Gd

Results

Petrography

Clastic limestone (CL) The bioclasts are excep-tionally large Large foraminifers followed by bryo-zoan algal molluscan and crinoidal fragmentsdominate the bioclasts It also contains importantamounts of subrounded medium-sized quartz grainsand reworked bioclasts A few peloidal grains alsoare present Micritization of bioclasts is prevalentThe grains are cemented by sparry calcite

Sandy shell limestone (SSL) This litho-unit con-tains micritized molluscan grains along with bryo-zoan bioclasts They are highly fragmented Many ofthe bioclasts are subrounded suggesting depositionin a high-energy environment Scattered sub-rounded linear quartz grains also are present Micri-tization was accomplished by endolithic algae in anearly diagenetic environment The molluscan bio-clasts show lamellar shell wall structures

Algal limestone (AL) The lithology consists ofassorted bioclasts of bryozoa molluscs ostracodsforaminifers including miliolids echinoderms andalgal elements (Lithothamnium sp and Amphiroasp) Many molluscan shell fragments are com-pletely leached out and the voids are filled withsparry calcite reflecting vadose-fresh water diage-netic environments Several larger foraminifers andmiliolid smaller foraminifer also were identified

The association of bioclasts such as bryozoansmolluscs echinoderms algae and larger foramini-fers suggests that the depositional environment wasshallow marginal marine The fragmented androunded nature of most bioclasts reveals a moderateto highly agitated environment in a bank-like set-ting Considering the skeletal fabrics and the associ-ation of packstone with coated and worn bioclastsstandard microfacies (SMF) no 10 is suggested forthe dominant carbonate deposition of this areaFacies Zone-7 (Flugel 1982) may be appropriate todemonstrate the occurrence of dominant particlesfrom high-energy environments on shoals which

have moved down local slopes to be deposited inquiet water (Armstrong Altrin Sam and Ramasamy2000) The occurrence of clotted micrite and othercalcrete-related features reveal that these depositswere periodically subaerially exposed

Major elements

Concentrations of major elements in theKudankulam limestones are listed in Table 1 Smallvariations are found in Si and CaCO3 contents(~07ndash26 and ~88ndash91 respectively) in CL In SSLthe content of Si ranges from ~51 to 59 (Table 1)Like Si small variation is observed in CaCO3 con-tent for SSL (~80ndash82 Table 1) A low concentrationof Si is observed in AL which varies from ~07 to26 whereas their CaCO3 content is higher (~92ndash93) The Al content in CL SSL and AL varies from~01 to 08 ~06 to 09 and ~02 to 03 respec-tively (Table 1) The content of Fe is very low in theKudankulam limestones Geochemical composi-tions reveal the enrichment of terrigenous sedimentsin the CL and SSL relative to AL Si vs CaCO3shows a clear negative correlation (correlation coef-ficient r = ndash086 number of samples n = 9) whichprobably suggests that these two elements exhibitdifferent modes of origin The silica is derivedmainly from siliclastic sediments whereas theCaCO3 was derived from carbonate cements

Trace elements

Trace-element concentrations of the Kudanku-lam limestones are also listed in Table 1 The large-ion lithophile elements (LILE Sr Rb Cs and Ba)have low concentrations compared to PAAS (post-Archean Australian Shale Fig 3) One sample fromSSL (sample no 5) shows high concentrations of Srand Ba with respect to the average composition ofPAAS The ferromagnesian trace elements Co Crand V are depleted and Ni is somewhat enrichedparticularly in the SSL sample No 5 (Fig 3) Theenrichment of Ni particularly in the SSL is mainlydue to the high content of feldspars present in thislitho-unit

High-field-strength elements (HFSE) such as ZrY Nb Hf Th and U are resistant to weathering andalteration processes compared to other trace ele-ments (Taylor and McLennan 1985 Bhatia andCrook 1986 Feng and Kerrich 1990) These ele-ments also have lower concentrations in comparisonwith PAAS The variations in the elemental concen-trations in the CL SSL and AL are mainly due to


TABLE 1 Major (wt) Trace (ppm) and Rare-Earth Element (ppm) Data for the Kudankulam Limestones

Rock type Clastic limestone (CL) Sandy shell limestone (SSL) Algal limestone (AL)Sample 1 2 3 4 5 6 7 8 9

Si 263 067 236 586 512 517 161 262 074Al 075 014 071 087 056 057 027 021 027Fe 008 008 026 020 040 002 014 062 053Ba 72 62 60 124 822 59 41 96 91Co 114 168 727 190 173 184 161 221 753Cr 112 639 538 221 304 120 114 113 268Cs 042 004 026 012 009 009 007 025 022Cu 610 639 760 744 861 265 667 107 414Hf 088 054 076 123 069 055 044 055 056Nb 762 095 509 563 292 262 151 261 37Ni 85 63 66 119 801 64 37 113 96Pb 113 657 399 96 588 289 278 592 429Rb 158 101 990 164 231 99 616 146 119Sc 248 067 140 431 311 199 184 261 097Sr 47 59 40 43 584 122 139 84 45Th 156 145 970 101 387 520 261 514 490U 078 043 092 196 124 083 063 140 032V 666 113 174 320 294 118 905 186 115Y 790 259 583 168 729 840 508 157 418Zn 160 1115 144 164 837 409 596 143 731Zr 132 614 122 333 1172 770 524 681 609

Rare-earth elementsLa 343 345 252 305 163 162 866 193 150Ce 633 553 479 517 297 285 166 428 252Pr 747 069 564 609 326 351 187 458 295Nd 264 243 199 221 116 126 679 174 103Sm 381 043 282 351 227 196 112 335 151Eu 034 009 021 056 064 030 017 066 021Gd 296 047 213 321 178 184 110 347 126Tb 037 007 026 043 025 025 016 051 016Dy 179 041 125 238 140 142 085 292 081Ho 022 004 014 039 021 021 012 049 009Er 077 022 054 130 070 075 043 150 038Tm 009 003 006 016 009 009 005 019 004Yb 056 020 039 098 053 060 033 120 028Lu 007 002 005 014 008 008 004 017 004CaCO3 91 88 91 80 81 82 92 93 92

124 69 68 38 98 58EuEu 047 089 040 078 148 074 071 089 069CeCe 090 082 092 090 093 086 094 104 086(LaYb)s 449 129 481 229 226 200 192 118 396UTh 005 030 009 020 032 016 024 027 007ThSc 631 215 695 234 124 262 142 197 506LaSc 1384 512 1807 708 523 818 472 739 1547LaTh 220 238 260 303 420 313 332 380 306

SREE 142 14 106


differences in their lithologies as described in thepetrographic study

Rare-earth elementsThe results of REE concentrations are also pre-

sented in Table 1 The shale-normalized REE con-centrations are less than one for all Kudankulamlimestone samples (Fig 4) CL SSL and AL exhibitlarge variations in SREE content (~14ndash142 ~68ndash124 and ~38ndash98 respectively) Generally the REEcontents are lower in limestone samples than clasticsediments High contents of REE in clastic sedi-

ments are mainly due to the occurrence of silt andclay fractions because REE are readily accommo-dated in the clay structure (McLennan 1989) Thepresence of contrasting amounts of terrigenous sed-iments may cause the differences in the REE con-tents among Kudankulam limestones The lowcontent of REE in some samples could be due toREE dilution by carbonate minerals

The shale-normalized REE patterns of theselimestones (Fig 4) show a slight enrichment in lightREE relative to heavy REE In this diagram most ofthese samples show a small negative Ce anomaly

FIG 3 Multi-element diagram for the Kudankulam limestones normalized against average post-Archean AustralianShale (PAAS Taylor and McLennan 1985) These PAAS values are (in ppm) Co = 23 Ni = 55 Cr = 110 V = 150 Sr =200 Rb = 160 Cs = 15 Ba = 650 Pb = 20 Zr = 210 Y = 27 Nb = 19 Hf = 5 Th = 146 U = 31

FIG 4 Shale-normalized REE plots for the Kudankulam limestones with sample numbers PAAS normalizationvalues from Taylor and McLennan (1985) are (in ppm) La = 38 Ce = 80 Pr = 89 Nd = 32 Sm = 56 Eu = 11 Gd = 47Tb = 077 Dy = 44 Ho = 10 Er = 29 Tm = 040 Yb = 28 Lu = 043


(CeCe ~08ndash09) whereas one AL sample exhibitsno Ce anomaly (CeCe ~104 AL sample No 8Table 1) Similarly most of the Kudankulam lime-stone samples also show negative Eu anomalies (EuEu ~04ndash09) except for a single SSL sample whichshows a positive Eu anomaly (SSL sample No 5 EuEu ~15 Table 1) The presence of a positive Euanomaly particularly in this sample is consistentwith feldspar enrichment

Discussion

Source of REE and provenance characteristics

Average SREE contents of the Kudankulamlimestone samples (80 plusmn 40 n = 9 Table 2) is simi-lar to those of Upper Cretaceous shallow-marinecarbonates (Madhavaraju and Ramasamy 1999) aswell as modern carbonates of the Arabian Sea (Nathet al 1997 Table 2) For individual litho-unitsthere is a large variation in SREE content (CL 88 plusmn66 n = 3 SSL 87 plusmn 32 n = 3 AL 65 plusmn 31 n = 3)Differences in SREE content among individualsamples are mainly related to variations in theamount of terrigenous sediment included in theselimestone samples This seems to be supported bygenerally lower contents of Si and Al and highercontent of CaCO3 in AL than SSL and CL and fur-ther suggests that SREE contents are a function ofnon-carbonate impurities

In the Kudankulam limestones the average ratioof (LaYb)s (24 plusmn 14 n = 9) is somewhat higherthan the shallow-marine carbonates of southernIndia Arabian Sea carbonate sediments and IndianOcean carbonates (Table 2) Also the (LaYb)s ratiois higher than the postulated average value for ter-rigenous sediments [(LaYb)s = 13 Sholkovitz1990] For the individual litho-units the (LaYb)sratios for CL SSL and AL are 35 plusmn 20 22 plusmn 02and 24 plusmn 14 respectively (n = 3) Differences in(LaYb)s ratios among various litho-units may berelated to (1) changes in REE input from the sourceterrain and (2) diagenetic remobilization andexchange with interstitial water (Murray et al1991a) as well as to a decreasing trend of (LaYb)sratio with depth (Worash and Valera 2002) Suchdiagenetic processes have been documented inrecent shallow buried estuaries (Sholkovitz et al1989) Our study area reflects shallow-marine con-ditions where the fractionation of REE should havebeen low

The nature of the source rocks can be identifiedfrom REE patterns and (LaYb)s ratios Certaintrace-element ratios such as ThSc LaSc and LaTh also are useful to infer the nature of the sourcerocks because they are sensitive to average prove-nance compositions Th is a highly incompatibleelement whereas Sc is relatively compatible Bothof these elements are relatively uniformly trans-

TABLE 2 Average Values of Kudankulam Limestones in This Study Compared to Values of Shallow- and Deep-Marine Carbonate Sediments

Kudankulam carbonate1Shallow-marine

carbonate2Arabian Sea

carbonate sediments3Indian Ocean

carbonate sediments5

CeCe 090 plusmn 006 076 plusmn 016 084 plusmn 006 056

(LaYb)s 27 plusmn 14 18 plusmn 05 08 plusmn 02 103

SREE 80 plusmn 40 73 plusmn 20 78 plusmn 40 ndash

CaCO3 88 plusmn 5 75 plusmn 15 51 plusmn 22 653

EuEu 078 plusmn 031 058 plusmn 011 115 plusmn 008 ndash

U 09 plusmn 05 07 plusmn 05 6 plusmn 24 ndash

UTh 019 plusmn 010 022 plusmn 029 21 plusmn 054 ndash

1This study n = 92Madhavaraju and Ramasamy 1999 Late Cretaceous n = 83Nath et al 1997 n = 94Values from oxygen minimum zone n = 45Nath et al 1992


ferred into terrigenous sediments from the sourcethrough sedimentation (Taylor and McLennan1985) The Kudankulam limestone samples exhibitslightly LREE enriched and flat HREE patterns(Fig 4) with somewhat high average ratios of (LaYb)s ThSc LaSc and LaTh (27 plusmn 14 33 plusmn 2210 plusmn 5 and 31 plusmn 06 respectively n = 9 Table 1)implying that the terrigenous sediments present inthe shallow-marine Kudankulam limestones werederived mainly from felsic source rocks

Behavior of europium The EuEu ratio of the Kudankulam limestone

samples ranges from ~040 to 089 except for oneSSL sample which shows a remarkably high EuEu

ratio (EuEu ~15 SSL sample No 5 Table 1)Generally the absence of a negative Eu anomalyand the prevalence of a positive Eu anomaly inshale-normalized REE patterns are due to eithereolian input (Elderfield 1988) or hydrothermalsolutions (Michard et al 1983 Worash and Valera2002) Hydrothermal solutions originate in thedeep-sea environment but our study area is locatedalong a coastal belt Because only one Kudankulamlimestone sample (SSL sample No 5) lacks a nega-tive Eu anomaly (or has a positive Eu anomaly) itmay be due to local enrichment of feldspar ratherthan a regional effect such as eolian input or hydro-thermal solutions This interpretation is further sup-ported by the remarkable enrichment of Sr in thissample (Table 1 see the isolated sample in Fig 5)Finally the predominance of a negative Eu anomalyin the Kudankulam limestones reveals that the ter-rigenous part of these samples was probably derivedfrom felsic source rocks

Significance of uranium in the marine environmentUranium (U) is thought to be conservative in oxy-

genated seawater (Ku et al 1977) because of theformation of stable U+4 and soluble U+6 In oxic sea-water uranium is present in high concentrations asthe species uranyl tricarbonate [UO2(CO3)3

4ndash]whereas under reducing conditions the soluble U+6

is readily converted into insoluble U+4 which canbe removed from the solution onto sediment surfaces(Barnes and Cochran 1990) Uranium is mobilewhereas Th is relatively immobile in aqueous solu-tions (Anderson et al 1983 Nozaki et al 1981Wright et al 1984) In continental-margin environ-ments uranium is readily fractionated from Th justlike Ce which is fractionated from other REE(Whittaker and Kyser 1993)

In the Kudankulam limestones the U content isvery low (range ~032ndash196 mean 09 plusmn 05 n = 9Table 2) compared to sediments derived from theoxygen minimum zone (Nath et al 1997) HoweverU concentrations of the Kudankulam limestones aresimilar to the shallow-marine carbonates depositedunder oxic conditions (Madhavaraju and Ramasamy1999 Table 2) Therefore we propose that theobserved low content of U in the Kudankulam lime-stones is related to the oxygenation level in thewater column In an oxic environment U is easilyremoved from the sediments and transferred into thewater column In a reducing environment on theother hand U is removed from sea water and precip-itates onto the sediments In some cases lack of sig-nificant reduction of U+6 to U+4 has been observedin anoxic and suboxic waters (Anderson 1987Anderson et al 1989) In this context sedimentarygeochemists have made an attempt to employ the UTh ratio rather than the U concentration as a redoxindicator (Wright et al 1984 Jones and Manning1994) UTh ratios above 125 have been used toinfer suboxic and anoxic conditions The UTh ratiois high (gt125) in Arabian Sea sediments (Nath etal 1997) collected from the oxygen minimum zone(OMZ Table 2) The UTh ratio (~005ndash032 019 plusmn010 n = 9 Table 2) is low in the Kudankulam lime-stone samples compared to samples deposited underanoxic and suboxic conditions However UTh inthese limestones is comparable with shallow-marinecarbonates of southern India deposited under anoxic environment (Madhavaraju and Ramasamy1999 Table 2) which clearly suggests that theKudankulam limestones were deposited under oxicconditions Furthermore there is almost no remark-able variation in U contents and UTh ratios among

FIG 5 Bivariate plot of Sr ndash EuEu for the Kudankulamlimestones Note the enrichment of Sr in one sample (sampleNo 5) from SSL (sandy shell limestone) The samples fallingbelow the line (EuEu = 1) have by definition a negative Euanomaly


Kudankulam limestone samples suggesting a lackof significant variations in oxygen level in the watercolumn during deposition of these shallow-marinelimestones Thus U and UTh ratios could beconsidered as useful indicators for paleoredoxconditions

Variations in cerium contents and cerium anomalies

Numerous studies has been carried out on theapplication of Ce in the marine phases for inferringpaleoceanographic conditions (Grandjean et al1987 1988 Hu et al 1988 Liu et al 1988 Grand-jean and Albarede 1989 German and Elderfield1990 Nath et al 1997) The depletion of Ce in oce-anic water results from redox changes of cerium rel-ative to the rest of the REE (Elderfield 1988Piepgras and Jacobsen 1992 Nath et al 1994)

CeCe ratios in CL range from ~082ndash092 witha mean value of 088 plusmn 006 (n = 3) in SSL this ratioranges from ~086 to 093 with a mean value of 089plusmn 004 (n = 3) Thus there is no remarkable differ-ence in Ce anomalies between CL and SSL indicat-ing that there was not much fluctuation in bottom-water oxygen level Somewhat larger variations inCeCe ratios are present in AL (~086ndash104 095 plusmn009 n = 3) although the number of samples arevery limited The observed negative Ce anomalies inthe Kudankulam limestones (Table 2) are smallerthan those of deep-sea carbonates of the IndianOcean (Nath et al 1992) Arabian Sea sediments(Nath et al 1997) and shallow-marine Maastrich-tian carbonates of the Cauvery Basin southern India(Madhavaraju and Ramasamy 1999) Both Ce con-centrations and Ce anomalies can probably beexplained by variations in terrigenous sediments inthe Kudankulam limestones as well as some otherprocesses such as diagenesis

The absence of a negative Ce anomaly in AL(104 sample No 8) implies that apart from litho-logical input diagenesis may play a significant rolein incorporation of REE (particularly Ce) Pore-water nutrient studies (Nath and Mudholkar 1989)document Ce uptake and positive Ce anomaliesMollusk shell fragments exhibit either a positive Ceanomaly or no anomaly at all (Elderfield and Sholk-ovitz 1987 Sholkovitz and Elderfield 1988 Ger-man and Elderfield 1989 Sholkovitz et al 1989)Therefore the absence of a negative Ce anomaly inAL is probably unrelated to paleoredox conditionsbecause limestones from different litho-units of theKudankulam Formation deposited in the near-shoreshallow-marine environment show oxic conditions

where scavenging processes are negligible The ALexhibits numerous fossils such as mollusks and for-aminifera Apart from this these limestones seem tohave undergone some sort of diagenetic process(Armstrong Altrin Sam et al 2001) which mighthave played a major role in eliminating a negativeCe anomaly in this sample (AL sample No 8)Because the Kudankulam limestones were depos-ited in a shallow-marine oxic environment terrige-nous sediments from nearby crystalline source rockscould also have been deposited The Ce behaviorrecorded in the limestones suggests that REE frac-tionation in such sediments is not useful for paleore-dox reconstructions Hence observed Ce contentsand Ce anomalies in the shallow-marine Kudanku-lam limestones resulted from variations in terrige-nous sediment input as well as diageneticprocesses

Conclusions

REE patterns and LaSc LaTh ThSc and (LaYb)s ratios together with negative Eu anomaliesdemonstrate that terrigenous sediments present inthe Kudankulam limestones were mainly derivedfrom felsic source rocks In these limestones the(LaYb)s ratio is higher than the average values ofterrigenous sediments All but one Kudankulamlimestone sample exhibits negative Ce anomaliesVariations in (LaYb)s ratios and Ce anomalies mayhave resulted from differences in detrital sedimentsand diagenetic effects Furthermore the behavior ofCe in the Kudankulam limestones suggests thatREE fractionation in shallow-marine sediments isnot very useful for paleoredox studies Low but con-stant values of both U content and the UTh ratiosuggest the prevalence of oxic environments in thesedimentwater interface during deposition of theKudankulam limestones Finally our study revealsthat U can be considered as a useful indicator forpaleoredox conditions

Acknowledgments

We are grateful to Prof S P Mohan HeadDepartment of Geology University of Madras for hishelp and for providing laboratory facilities throughthe UGC SAP II and UGC COSIST programs Wethank Prof G Mongelli Italy and Prof P K Baner-jee Emeritus Scientist Jadavpur University Cal-cutta for their help during the study This work waspartly supported by PAPIIT grant IN-100596


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Anderson R F Bacon M P and Brewer P G 1983Removal of 230Th and 234Pa at ocean margins Earthand Planetary Science Letters v 66 p 73ndash90

Anderson R F Fleisher M Q and LeHurray A P1989 Concentration oxidation state and particulateflux of uranium in the Black Sea Geochimica et Cos-mochimica Acta v 53 p 2215ndash2224

Armstrong Altrin Sam J 1998 Microfabrics andgeochemistry of Kudankulam Formation Tamil NaduIndia Unpublished PhD thesis University ofMadras Tamil Nadu India 136 p

Armstrong Altrin Sam J and Ramasamy S 1997Petrography and major element geochemistry of bio-clastic rocks around Kudankulam Tamil Nadu Jour-nal of Indian Association of Sedimentologists v 16 p171ndash182

______ 2000 Stratigraphy and petrography of quarrysections around Kudankulam area Tamil Nadu Jour-nal of Indian Association of Sedimentologists v 19 p169ndash177

Armstrong Altrin Sam J Ramasamy S and MakhnachA 2001 Stable isotope geochemistry and evidencefor meteoric diagenesis in Kudankulam FormationTamil Nadu Journal of the Geological Society of Indiav 57 p 39ndash48

Barnes U C and Cochran J R 1990 Uranium removalin oceanic sediments and the oceanic U balance Earthand Planetary Science Letters v 97 p 94ndash101

Bhatia M R and Crook A W 1986 Trace elementcharacteristics of graywackes and tectonic setting dis-crimination of sedimentary basins Contributions toMineralogy and Petrology v 92 p 181ndash193

Bruckner H 1988 Indicators for formerly higher sea lev-els along the east coast of India and on the Andamanislands Hamburger Geographische Studien v 44 p47ndash72

Cooray P G 1984 Geology with special reference to thePrecambrian in Fernando CH ed Ecology and bio-geography of Sri Lanka The Hague Netherlands p1ndash34

De Baar H J W German C R Elderfield H and VanGaan P 1988 Rare earth element distributions inanoxic waters of the Cariaco Trench Geochimica etCosmochimica Acta v 52 p 1203ndash1219

Elderfield H 1988 The oceanic chemistry of the rareearth elements Philosophical Transactions of theRoyal Society of London v 325 p 105ndash126

Elderfield H and Sholkovitz E R 1987 Rare earthelements in the pore waters of reducing near shoresediments Earth and Planetary Science Letters v 82p 280ndash288

Elderfield H Upstill-Goddard R and Sholkovitz E R1990 The rare earth elements in rivers estuaries and

coastal seas and their significance to the compositionof ocean waters Geochimica et Cosmochimica Acta v54 p 971ndash991

Feng R and Kerrich R 1990 Geochemistry of fine-grained clastic sediments in the Archaean Abitibigreenstone belt Canada implications for provenanceand tectonic setting Geochimica et CosmochimicaActa v 54 p 1061ndash1081

Flugel E 1982 Microfacies analysis of limestones Ber-lin Germany Springer-Verlag 633 p

German C R and Elderfield H 1989 Rare earth ele-ments in the Saanich Inlet British Columbia a sea-sonally anoxic basin Geochimica et CosmochimicaActa v 53 p 2561ndash2572

______ 1990 Rare earth elements in the NW IndianOcean Geochimica et Cosmochimica Acta v 54 p1929ndash1940

Grandjean P and Albarede F 1989 Ion probe measure-ments of rare earth elements in biogenic phosphatesGeochimica et Cosmochimica Acta v 53 p 3179ndash3183

Grandjean P Cappetta P H and Albarede F 1988The REE and eNd of 40ndash70 Ma old fish debris fromthe West-African platform Geophysical Research Let-ters v 15 p 389ndash392

Grandjean P Cappetta P H Michard A and AlbaredeF 1987 The assessment of REE patterns and 143Nd144Nd ratios in fish remains Earth and Planetary Sci-ence Letters v 84 p 181ndash196

Hu X Wang Y L and Schmitt R A 1988 Geochem-istry of sediments on the Rio Grande Rise and theredox evolution of the South Atlantic Ocean Geochim-ica et Cosmochimica Acta v 52 p 201ndash208

Jarvis K E 1988 Inductively coupled plasma massspectrometry A new technique for the rapid or ultra-trace level determination of the rare-earth elements ingeological materials Geological Society of AmericaBulletin v 87 p 725ndash737

Jones B and Manning D A C 1994 Comparison ofgeochemical indices used for the interpretation ofpalaeoredox conditions in ancient mudstones Chemi-cal Geology v 111 p 111ndash129

Klinkhammer G Elderfield H and Hudson A 1983Rare earth elements in seawater near hydrothermalvents Nature v 305 p 185ndash188

Ku T L Knauss K G and Mathieu G G 1977 Ura-nium in open ocean Concentration and isotopic com-position Deep Sea Research v 24 p 1005ndash1017

Liu Y G Miah M R U and Schmitt R A 1988Cerium a chemical tracer for paleo-oceanic redoxconditions Geochimica et Cosmochimica Acta v 52p 1361ndash1371

Macfarlane A W Danielson A Holland H D andJacobsen S B 1994 REE chemistry and Sm-Nd sys-tematic of late Archaean weathering profiles in theFortescue Group Western Australia Geochimica etCosmochimica Acta v 58 p 1777ndash1794


Madhavaraju J and Ramasamy S 1999 Rare earth ele-ments in limestones of Kallankurichchi Formation ofAriyalur Group Tiruchirapal li Cretaceous TamilNadu Journal of the Geological Society of India v 54p 291ndash301

McLennan S M 1989 Rare earth elements in sedimen-tary rocks influence of provenance and sedimentaryprocesses in Lipin B R and McKay G A edsGeochemistry and mineralogy of the rare earth ele-ments Reviews in Mineralogy v 21 p 169ndash200

Michard A Albarede F Michard G Minister J F andCharlou J L 1983 Rare earth elements and uraniumin high temperature solutions from East-Pacific Risehydrothermal vent field (13degN) Nature v 303 p 795ndash797

Murphy K and Raymond J 1984 Rare earth elementfluxes and geochemical budget in the eastern equato-rial Pacific Nature v 307 p 444ndash447

Murray R W Buchholtz Ten Brink M R BrumsackH J Gerlach D C and Russ G P III 1991a Rareearth elements in Japan Sea sediments and diageneticbehavior of CeCe Results from ODP Leg 127Geochimica et Cosmochimica Acta v 55 p 2453ndash2466

Murray R W Buchholtz Ten Brink M R Gerlach D CRuss G P III and Jones D L 1991b Rare earthmajor and trace elements in chert from the Franciscancomplex and Monterey Group California AssessingREE sources to fine-gra ined marine sedim entsGeochimica et Cosmochimica Acta v 55 p 1875ndash1895

Nath B N Bau M Ramlingeswara Rao B and RaoCh M 1997 Trace and rare earth elemental variationin Arabian Sea sediments through a transect across theoxygen minimum zone Geochimica et CosmochimicaActa v 61 p 2375ndash2388

Nath B N and Mudholkar A V 1989 Early diageneticprocesses affecting nutrients in the pore waters of Cen-tral Indian Ocean cores Marine Geology v 86 p 57ndash65

Nath B N Roelandts I Sudhakar M and PluegerW L 1992 Rare earth element patterns of the CentralIndian Basin sediments related to their lithology Geo-physical Research Letters v 19 p 1197ndash1200

Nath B N Roelandts I Sudhakar M Plueger W Land Balaram V 1994 Cerium anomaly variations inferromanganese nodules and crusts from the IndianOcean Marine Geology v 120 p 385ndash400

Nozaki Y Horibe Y and Tsubota H 1981 The watercolumn distribution of thorium isotopes in the westernNorth Pacific Earth and Planetary Science Letters v66 p 73ndash90

Piepgras D J and Jacobsen S B 1992 The behavior ofrare earth elements in seawater Precise determinationof ferromanganese crusts Geochimica et Cosmochim-ica Acta v 56 p 1851ndash1862

Piper D Z 1974 Rare earth elements in the sedimentarycycle a summary Chemical Geology v 14 p 285ndash304

Ramasamy S Alex Johnson Paul B and MadhavarajuJ 1994 Stratigraphy petrography and sedimentationhistory of Kudankulam Formation along the southTamil Nadu coast India Bulletin of Pure and AppliedSciences v 13 p 43ndash58

Ramasamy S and Armstrong Altrin Sam J 1998 Infer-ences on rhodoids from Neogene carbona tes ofKudankulam Tamil Nadu Journal of the GeologicalSociety of India v 52 p 341ndash344

Ronov A B Balashov Y A and Migdisov A A 1967Geochemistry of the rare earths in the sedimentarycycle Geochemistry International v 4 p 1ndash18

Sahni A 1979 Miocene vertebrates from the coastal Ter-tiary rocks of Peninsular India and Sri Lanka Geolog-ical Survey of India Miscellaneous Publications v 45p 197ndash205

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Sholkovitz E R 1990 Rare earth elements in marinesediments and geochemic al standards ChemicalGeology v 88 p 333ndash347

Sholkovitz E R and Elderfield H 1988 Cycling of dis-solved rare earth elements in Chesapeake Bay GlobalBiogeochemistry Cycles v 2 p 157ndash176

Sholkovitz E R Piepgras D J and Jacobsen S B1989 The pore water chemistry of rare earth elementsin Buzzards Bay sediments Geochimica et Cosmo-chimica Acta v 53 p 2847ndash2856

Singh P and Rajamani V 2001 REE geochemistry ofrecent clastic sediments from the Kaveri floodplainssouthern India Implications to source area weatheringand sedimentary processes Geochimica et Cosmo-chimica Acta v 65 p 3093ndash3108

Taylor S R and McLennan S M 1985 The continentalcrust Its composition and evolution Oxford UKBlackwell 349 p

Toyoda K Nakamura Y and Masuda A 1990 Rareearth elements of Pacific pelagic sediments Geochim-ica et Cosmochimica Acta v 54 p 1093ndash1103

Whittaker S G and Kyser T K 1993 Variations in theneodymium and strontium isotopic composition andREE content of molluscan shells from the CretaceousWestern Interior seaway Geochimica et Cosmochim-ica Acta v 57 p 4003ndash4014

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gested that there is no variation in Ce anomalydeposited between these carbonates and those out-side the OMZ

More recently Madhavaraju and Ramasamy(1999) studied shallow-marine Maastrichtian car-bonates of southern India to provide useful informa-tion regarding the geological environment such asterrigenous inputs and redox conditions at thetime and place of deposition They suggested that Uand UTh ratios are useful for paleoredox inter-pretations

No systematic geochemical work has yet beencarried out on the limestones of the upper MioceneKudankulam Formation We report new majortrace-element and REE data along with informa-tion on the depositional environment Our mainobjective is to gauge the usefulness of uraniumin predicting the paleoredox condit ions andthe probable reason for the variation in Ce con-centration and Ce anomalies in the Kudankulamlimestones

Geology and Stratigraphy

In the southeastern part of Peninsular India (Fig1) limestone deposits have been discovered thatindicate marine influence during the formation ofthe southern part of Tamil Nadu (Bruckner 1988)This deposit has been called Kudankulam Forma-tion which crops out 20 km NE of Kanniyakumarinear the village of Kudankulam Isolated exposuresare present near villages such as Navalady Mana-paud Tiruchendur and Sattankulam (Fig 2) Themaximum altitude of this bed is ~51 m nearKudankulam and +20 m above msl at TiruchendurSedimentary rocks of the Kudankulam Formationare dominated by clastic and carbonate rocks (Arm-strong Altrin Sam 1998) These strata are present inwell cuttings stream sections and in a number ofquarry sections The clastic and carbonate rockscontain numerous fossils such as bryozoans mol-luscs echinoderms algae and foraminifera Thethickness of the sedimentary unit is only 4 to 5 m

FIG 1 Simplified geological map of southern India showing the location of the study area (modified after Singhand Rajamani 2001) Abbreviations in inset G = Gujarat K = Kerala Kr = Karaikal beds S = Sri Lanka J = JaffnaFormation




Analytical Methods





Results

Petrography






Major elements


Trace elements









SREE 142 14 106











Discussion




































Conclusions


Acknowledgments



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Analytical Methods





Results

Petrography






Major elements


Trace elements









SREE 142 14 106











Discussion




































Conclusions


Acknowledgments



REFERENCES





























































Results

Petrography






Major elements


Trace elements









SREE 142 14 106











Discussion




































Conclusions


Acknowledgments



REFERENCES

































































SREE 142 14 106











Discussion




































Conclusions


Acknowledgments



REFERENCES





































































Discussion




































Conclusions


Acknowledgments



REFERENCES













































































Conclusions


Acknowledgments



REFERENCES




























































REFERENCES



























































carbonate geochemistry

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