Geosciences Journal Vol. 19, No. 2, p. 237  256, June 2015 DOI 10.1007/s12303-014-0039-1 ⓒ The Association of Korean Geoscience Societies and Springer 2015

Carbon, oxygen and strontium isotopic signatures in -Danian of the Cauvery Basin, South India

Jayagopal Madhavaraju* Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de México, Apartado Postal 1039 Hermosillo, Sonora 83000, México Alcides N. Sial Nucleo de Estudos Geoquímicos e Laboratório de Isótopos Estáveis (NEG-LABISE) Departmento de Geologia, Universidade Federal de Pernambuco, Caixa Posta 7852, 50670-000 Recife, PE, Brazil Reghunathan Rakhinath Sooriamuthu Ramasamy } Department of Geology, University of Madras, Chennai 600025, India Yong IL Lee School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Republic of Korea Ariputhiran Ramachandran Department of Geology, University of Madras, Chennai 600025, India

ABSTRACT: A petrographic, carbon, oxygen and strontium study studies have proven that the carbon and oxygen isotopic of the carbonate succession of the shallow marine Kallankurichchi composition of carbonate rocks offer valuable information and Niniyur formations of the Cauvery Basin, Tamil Nadu, India was about the temperatures of formations (Ali, 1995; Coniglio et conducted to understand the isotopic variations in seawater during Maastrichtian-Danian. The limestones from both the Kallankurichchi al., 2000), sources of carbonate (Hudson, 1977; Gao et al., and Niniyur formations show large variations in Mn and Sr con- 1996; Kumar et al., 2002; Poulson and John, 2003), and/or centrations and high Mn/Sr ratios indicate alterations of primary palaeoclimate (Quade and Cerling, 1995; Srivastava, 2001; isotopic signatures during shallow burial diagenesis. The limestones of Scott, 2002). both the Kallankurichchi and Niniyur formations show negative Stable isotope compositions, along with petrography of 13  C (‒4.73 to ‒0.49‰ VPDB; ‒5.63 to ‒1.87‰ VPDB; respectively) carbonate rocks, may prove to be important tools to trace and 18O values (‒8.89 to ‒3.66‰ VPDB; ‒8.56 to ‒5.41‰ VPDB; respectively). The carbon and oxygen isotope composition, 13C vs. fluid origin and to reconstruct large-scale movements and 18O plot and Mn/Sr ratio suggest that the measured 13C and 18O evolution of fluids (Allan and Matthews, 1982). The diagenesis values have been significantly altered during diagenesis. The lime- of carbonate rocks encompasses all the processes that affect stones from both the Kallankurichchi and Niniyur formations show the sediments after deposition and up to the processes of large variations in 87Sr/86Sr values (0.709310 to 0.711962; 0.708280 metamorphism at high temperatures and pressures (Moore, 87 86 to 0.708398, respectively) which are higher than Sr/ Sr ratios of the 2001). Carbonate rocks deposited in marine environments contemporary Lower Maastrichtian (87Sr/86Sr: 0.707760) and Danian (0.707819 to 0.707833) seawaters. The elevated 87Sr/86Sr ratios in the mainly record the carbon isotopic composition of the ocean limestones of the Kallankurichchi Formation suggest that these water (Scholle and Arthur, 1980). limestones were significantly modified by pore fluids during mete- The stratigraphic correlation of marine carbonates using oric diagenesis. The observed large fluctuations in 87Sr/86Sr ratios in carbon isotope signatures has been successfully applied to the Niniyur Formation resulted from variations in riverine input. One marine carbonate sediments (Jenkyns, 1995; Weis- 87 86 sample from the Niniyur Formation exhibits an unaltered Sr/ Sr ratio sert et al., 1998; Moullade et al., 1998). Initially it was applied (0.707828) which is interpreted to indicate an age of 65.02 Ma. to pelagic succession, but has since been applied to shallow Key words: stable isotopes, strontium isotopes, diagenesis, Maastrichtian- marine carbonates (Jenkyns, 1995; Ferreri et al., 1997; Grotsch Danian age, South India et al., 1998; Madhavaraju et al., 2013a, b), with promising results, when compared to magnetostratigraphic (Lini et al., 1. INTRODUCTION 1992; Henning et al., 1999) and biostratigraphic (Masse et al., 1999; Erba et al., 1999) data. The carbon and oxygen isotopic compositions of carbon- The 87Sr/86Sr ratio of seawater is nearly constant at any ate sediments/rocks reflect the physicochemical properties of particular period in geologic time in the entire ocean because the waters in which the organisms grew (Morrison and Brand, of the long residence time of strontium in the ocean (Burke 1986) and provide information regarding the diagenetic pro- et al., 1982; Hodell et al., 1989). The strontium isotopic cesses and environments that initiate the conversion of skel- composition of ancient seawater is identified by measuring etal carbonates into limestones (Jenkyns et al., 1994). Many the composition of carbonate shells and rocks, which serve as a reliable proxy to understand the tectonic evolution of the *Corresponding author: [email protected] Earth System. The variations in 87Sr/86Sr ratios indicate the 238 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran waxing and waning of Sr input from continental flux vs. the ment is characterised by structural highs and lows, these being input from the mantle flux (hydrothermal systems) (Faure, evidenced of strong tectonic activity affecting the basin since 1986; Taylor and Lasaga, 1999). The strontium isotopic study its inception. The sedimentary rocks of the Cauvery Basin provides possible constraints on the importance of various were deposited in an elongate, narrow strait extending in a factors that can affect global weathering rates, such as oro- NNE–SSW direction, its margins delineated by faults except genic events (Edmond, 1992) and glacial activity (Hodell et al., in the north where the basin was connected to the open ocean 1989), and the relative consequence of significant changes in (Sundaram and Rao, 1986). These sedimentary rocks are well mid-ocean ridge hydrothermal output (Rea, 1992). exposed in five geographic areas: Pondicherry, Vridhacha- Several studies on stratigraphy, sequence stratigraphy, palaeon- lam, Ariyalur, Tanjore and Sivaganga (Fig. 1). These geo- tology, clay mineralogy, depositional environments and tec- graphic areas currently have no interconnection, but there is tonic settings of the Cauvery Basin have been under taken no doubt that they were once connected (Blanford, 1862). by numerous researchers (Sastry et al., 1972; Sundaram and Kailasam and Bhanumurthy (1962) carried out detailed geo- Rao, 1986; Ramasamy and Banerji, 1991; Govindan et al., physical studies in the sedimentary rocks of the five geographic 1996; Madhavaraju and Ramasamy, 1999a, b, 2001, 2002; areas that suggest that the sediments of these five regions were Sundaram et al., 2001; Nagendra et al., 2002; Madhavaraju deposited in a single basin. Of the five geographic areas, the et al., 2002, 2004, 2006). Madhavaraju and Lee (2009) have Ariyalur area has the largest exposures of sedimentary rocks undertaken geochemical studies on the carbonate rocks of (Fig. 2). Studies carried out by the Oil and Natural Gas Cor- the Dalmiapuram Formation to understand the provenance poration (ONGC) in various parts of the basin reveal that the and paleo-redox conditions. They carried out subsequent geo- thickness of sedimentary rocks is 4 to 6 km, ranging from chemical studies on the clastic rocks of Maastrichtian-Danian Early Cretaceous to Recent age (Govindan et al., 1996). age to infer the influence of Deccan volcanism in the sed- Blanford (1862) was the first to carry out detailed strati- imentary sequences of the Cauvery Basin (Madhavaraju and graphic studies on these sedimentary rocks and he named Lee, 2010). Ramkumar et al. (2010) have undertaken a strontium three groups: the Uttatur, the Trichinopoly and the Ariyalur. isotopic study across the K/T boundary in the Cauvery Basin. In These three groups are disconformable and at places the addition, Ramkumar et al. (2011) described the chemostratigraphic unconformable relationship represents successive stages of variations of the sedimentary rocks of the Cauvery Basin marine transgression. Later, detailed and extensive studies using major and trace elemental data. Zakharov et al. (2011) were undertaken by Sundaram and Rao (1986) and Sunda- have undertaken isotopic studies on bivalve and belemnite ram et al. (2001) on the Cretaceous-Paleocene rocks. They shells to infer the palaeotemperature and Cretaceous climatic followed the general classification proposed by Blanford conditions in the Cauvery Basin. Most of the studies were (1862), and they divided the Uttatur Group into the Terani For- carried out on samples collected from the outcrop area and mation, the Arogyapuram Formation and the Dalmiapuram mainly dealt with stratigraphic and depositional environment Formation. The Trichinopoly Group is divided into the lower problems. There are no detailed studies addressing the ver- Kulakkalnattam Formation and the upper Anaipadi Forma- tical isotopic variations and diagenetic signatures of carbon- tion (Fig. 2; Sundaram et al., 2001). Sundaram et al. (2001) ate rocks of Maastrichtian and Danian age. divided the Ariyalur Group into four distinct formations, i.e., The objectives of the present study are to understand the the Sillakkudi, Kallankurichchi, Kallamedu and Niniyur For- vertical isotopic (carbon and oxygen) variations in the carbonate mations. Sastry et al. (1972) gave separate group status to rocks of Lower Maastrichtian and Danian age, to identify Paleocene rocks of the Ariyalur area, and they placed these the degree of diagenetic alteration of carbon and oxygen iso- sedimentary sequences above the Ariyalur Group (Table 1). topic signals, to assess the strontium isotopic variations in the The Niniyur Formation has a conformable relationship with Kallankurichchi and Niniyur formations and to understand the Kallamedu Formation. This formation is mainly composed the probable reasons for the fluctuations in 87Sr/86Sr ratios in of , marl, calcareous sandstone, shale and silty shale. these carbonate rocks. Total thickness of the Niniyur Formation is about 100 m. The carbonate build-ups occur in four formations, i.e., the 2. GEOLOGY AND STRATIGRAPHY Dalmiapuram Formation (Uttattur Group; Aptian-Albian age), the Kulakkalnattam Formation (Trichinopoly Group; Santo- The Cauvery Basin formed as a result of fragmentation of nian age), the Kallankurichchi Formation (Ariyalur Group; Gondwanaland during early Cretaceous, and it continued Maastrichtian age) and the Niniyur Formation (Danian age). evolving until the end of the Tertiary through rift, pull-apart, These formations are rich in faunal assemblages and serve as shelf sag and tilt phases (Prabhakar and Zutshi, 1993). During an outcrop model for a transgressive and regressive carbon- that interval, many episodes of transgression, regression, ero- ate ramp bounded below and above by clastic sequences. sion and deposition occurred to fill the basin. The Cretaceous- The Niniyur Formation is the lowermost formation of Tertiary Tertiary succession of the Cauvery Basin is closely related to sedimentary rocks that is prominently figured in the study of the rifting and drifting phases of peninsular India. The base- the Cretaceous-Tertiary Boundary problem in the Cauvery Isotopic signatures in Maastrichtian-Danian limestones, South India 239

Fig. 1. Geological map of the Cauvery Basin (modified after Krishnan, 1982).

Basin. We have followed the lithostratigraphic classifications chi Formation and from the Periakurichchi quarry section of proposed by Sastry et al. (1972) and Sundaram et al. (2001). the Niniyur Formation (Figs. 2 and 3). The Vellipirangiyam Limestone samples were collected for the present study quarry section of the Kallankurichchi Formation shows five from the Vellipirangiyam quarry section of the Kallankurich- distinct units: lower oyster-Gryphaea limestone, Inoceramus 240 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran

Fig. 2. Location map of the Vellipirangiyam quarry section (modified after Sundaram et al., 2001). Isotopic signatures in Maastrichtian-Danian limestones, South India 241

Fig. 3. Location map of the Periakurichchi quarry section (after Madhavaraju and Lee, 2010). 242 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran

Fig. 4. Lithostratigraphic section of the Vellipirangiyam quarry sec- Fig. 5. (a) Inoceramus limestone exposed in the bottom part of the tion. Vellipirangiyam quarry section, (b) Field photograph exhibits the upper oyster-Gryphaea limestone and fossiliferous limestone in the limestone, upper oyster-Gryphaea limestone, fossiliferous Vellipirangiyam quarry section. limestone and marl (Fig. 4). The lower oyster-Gryphaea lime- stone unit is massive, hard and yellowish in color, with a total thickness of about 8 m. The succeeding bed is the Inoc- about 12.9 m (Fig. 7b). These beds are succeeded by sandstone eramus limestone, which is pale yellow in color and rich in beds of 2 m thick (Fig. 7c). The topmost unit of this section Inoceramus fauna (Fig. 5a). The total thickness of this unit is Marl (1 m thick). is 3 m. It is overlain by the upper oyster-Gryphaea limestone unit (Fig. 5b). It is hard and yellowish in color and contains 3. METHODOLOGY numerous oysters and Gryphea (5.2 m thick). It is succeeded by a thick, massive, hard and pale yellow fossiliferous lime- The cathodoluminescence study was done with a Relion stone unit (4 m thick). The topmost unit of this section is luminoscope at Instituto de Geología, Universidad Nacional marl (3 m thick). Autónoma de México (UNAM), México. Operating condi- The Periakurichchi quarry section of the Niniyur Forma- tions were as follows: accelerating potential 15 kV, 250 μA beam tion shows fossiliferous limestone, sandstone with boulders, current, and 0.01 torr for vacuum. Luminescence of replace- limestone interbedded with shale and sandstone, sandstone ment calcite and various calcite cements were recorded with and marl units (Fig. 6). Fossiliferous limestone (6 m thick) special attention focused on the presence or absence of lumi- is the bottom most unit of this section, which overlies the nescence zoning in the diagenetic mineral phases. sandstone of the Kallamedu Formation. The succeeding unit Mn concentration was measured with a Siemens SRS-3000 is sandstone that contains numerous boulders (7 m thick; Fig. X-ray fluorescence spectrometer with an Rh-anode X-ray 7a). It is overlain by thick bands of limestone interbedded tube as a radiation source. The Lachance and Traill (1966) with shale and sandstone beds. The thickness of this unit is method was used to correct the X-ray absorption/enhance- Isotopic signatures in Maastrichtian-Danian limestones, South India 243

Fig. 7. (a) Photograph shows the basal part of the limestone unit and sandstone boulders in the Periakurichchi quarry section, (b) Photograph exhibits limestone beds interbedded with shale and sandstone beds, (c) The upper part of the sandstone unit and marl unit are seen in the field photograph.

Pernambuco, Brazil. BSC (Borborema Skarn Calcite) refer- ence gas was used for the determination of carbon and oxygen isotopes, which calibrated against NBS-18, NBS-19, and 18 Fig. 6. Lithostratigraphic section of the Periakurichchi quarry sec- NBS-20 has a value of ‒11.28 ± 0.004‰ VPDB for δ O tion. and ‒8.58 ± 0.02‰ VPDB for δ13C (Sial et al., 2001). The results are reported in the notation δ‰ (per mil) in relation ment effects included in the SRS-3000 software. The geo- to international VPDB scale. chemical standard JGB1 (GSJ) was used to determine data Ten limestone samples were selected for Sr isotopic study. quality (Table 1). The analytical accuracy was better than 5% Care was taken to avoid input from silicate impurities while for Mn. Sr content was determined by an Agilent 7500 ce preparing powder samples (Bailey et al., 2000). Powder Inductively Coupled Plasma Mass Spectrometer (ICP-MS) samples of 10 mg were mixed with 84Sr and 87Rb spikes and according to standard analytical procedures suggested by Eggins then dissolved with a mixed acid (HF/HClO4 = 10:1) in Tef- et al. (1997). The geochemical standards IGLa-1 and SOD1 lon vessels. Rb and Sr fractions were separated by conventional were used to monitor the analytical reproducibility. The ana- cation column chemistry (Dowex AG50W-X8, H+ form) in lytical precision for Sr was better than 2%. HCl medium. The 87Sr/86Sr ratios were measured using a VG The limestone samples from the Kallankurichchi and Niniyur 54-30 thermal ionization mass spectrometer equipped with formations were treated with H3PO4 in vacuum at 25°C for nine Faraday cups at Korea Basic Science Institute. Instru- one day to determine the carbon and oxygen isotopes. The mental fractionation was normalized to 86Sr/88Sr = 0.1194, and resulting CO2 gas was analysed according to the method necessary corrections were made for the contributions of the proposed by Craig (1957). The gas was analyzed in a double added spikes in the measured 87Sr/86Sr ratio. Replicate analysis inlet, triple collector SIRA II mass spectrometer at the Stable of NBS 987 gave a mean 87Sr/86Sr ratio of 0.710245 ± 0.000003 Isotope Laboratory (LABISE) of the Federal University of (n = 30, 2se; two standard errors of the mean, as recom- 244 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran

Table 1. Lithostratigraphy of the Ariyalur Group, Cauvery Basin (modified after Sastry et al., 1972) Group Formation Lithology Thickness (m) Age Danian Niniyur Calcareous sandstone, fossiliferous limestone and claystone 50‒100 (65.5–61.1 Ma.) Unfossiliferous fine- to coarse-grained sandstone interbedded Kallamedu 60‒100 with siltstone, claystone, shale and marl Ottakkovil Fossiliferous calcareous sandstone interbedded with claystone 0‒60 Maastrichtian (70.6–65.5 Ma.) ARIYALUR Fossiliferous calcareous conglomeratic sandstone, fossiliferous Kallankurichchi calcareous sandstone interbedded with claystone, sandy fossilifer- 10‒40 ous limestone, fossiliferous limestone and marl Unfossiliferous to fossiliferous calcareous sandstone, interbedded Campanian Sillakkudi 300‒500 with claystone and thin band of sandy limestone (83.5–70.6 Ma.) Late Turonian to Santonian Trichinopoly (90.3–83.5 Ma.) mended by Verma, 2005). Total procedural blank levels were A few echinoid spines are also present. The internal parts of below 100 pg for Sr. The 87Sr/86Sr ratios presented in this the molluscan grains are partly filled with microsparite calcite study are adjusted to NBS 987 87Sr/86Sr ratio of 0.710230 cement. This petrographic type represents the middle part of (Verma, 1992; Verma and Hasenaka, 2004). We used the com- the Perriakurichchi quarry section (P12). The molluscan for- puter program OYNYL (Verma et al., 2006) for ordinary aminiferal wackestone is rich in organic constituents such as least-squares linear regression of our data. OYNYL has a foraminifera, molluscan fragments and few algal grains (Fig. 8c). built-in module for the detection of discordant outliers in The internal parts of the fossil grains are filled with sparry bivariate plots (Barnett and Lewis, 1994; Verma and Díaz- calcite cement. It represents the lower level of the Periakurichchi González, 2012). quarry section (P5).

4. RESULTS 4.1.2. Packstone The Sandy algal molluscan packstone contains corals, algae 4.1. Petrography and molluscan fragments (Fig. 8d). It also contains suban- gular quartz and feldspar grains within the matrix (>5%). The petrographic description of carbonate rocks was doc- Echinoid spines are present in minor amounts. Pore spaces umented using the carbonate classification of Dunham (1962) are filled with sparry calcite cement. The limestone includes and Embry and Klovan (1971). Twenty seven thin sections several species of Sporolithon and Lithothamnion. It is rep- were examined by both optical microscope and cathodolu- resented by the upper part of the Periakurichchi quarry section minescence. In carbonate rocks, four major petrographic types (P17). The Coral algal molluscan foraminiferal packstone were identified i.e., wackestone, packstone, grainstone and has algal, molluscan, coral and foraminiferal framework ele- boundstone. ments (Fig. 8e). Most of the framework grains are coated with micrite. Algal micritisation is also seen in the chambers 4.1.1. Wackestone of the foraminifera. It also contains numerous diagenetically Wackestone is a mud supported carbonate rocks which altered oyster and inoceramid fragments. The cement is largely enclosing more than 10% of skeletal grains. Three sub-types sparrite, however small patches of mud are also observed. of wackestone were identified. Iron oxide cement is also seen in places. Most of the pore The Sandy molluscan wackestone contains a small amount spaces are filled with poikilotopic cement. It represents the (around 2%) of quartz and feldspar grains and it represents lower and middle parts of the Vellipirangiyam quarry section the lower part of the Vellipirangiyam (VLP1 and VLP2) and (VLP5, VLP6, VLP8, VLP9 and VLP10). The Molluscan Periakurichchi quarry (P1) sections. Most of the quartz grains orbitoidal packstone, found in the top most part of the Vel- are monocrystalline, however few polycrystalline quartz grains lipirangiyam quarry section (VLP14 and VLP15), contains are also seen. The feldspars include orthoclase and plagioclase. molluscs, orbitoids and uniserial and biserial foraminiferal Quartz and feldspar grains are angular in shape. Algal and grains (Fig. 8f). Cement is sparry calcite. Some of the bioclasts molluscan grains are found in the micritic matrix (Fig. 8a). Also are dark red in color and coated with ferruginous cements. present are numerous oyster fragments that show different The limestone contains altered Inoceramus grains. types of growth patterns. The Silty molluscan algal wacke- stone contains silt sized quartz and feldspar grain (Fig. 8b). 4.1.3. Grainstone Algal and molluscan materials are found in the micritic matrix. Grainstones are grain supported carbonate rock, consisting Isotopic signatures in Maastrichtian-Danian limestones, South India 245

Fig. 8. (a) Sandy molluscan wackestone with algal, foraminifera and molluscan fragments; the pore spaces are partly filled with iron oxide cement (Scale bar = 0.5 mm), (b) Silty molluscan algal wackestone exhibits silt grade quartz and feldspar grains. It also encloses con- siderable amount of molluscan and algal fragments (Scale bar = 0.5 mm), (c) Photomicrograph shows fine grained clastic grains, mol- luscs and foraminifera. The pore spaces are filled with microsparrite and sparry calcite cement (Scale bar = 0.5 mm), (d) Sandy algal molluscan packstone contains corals, algal and molluscan fragments (Scale bar = 0.5 mm), (e) Photograph shows bryozoan, orbitoids and siderolites. The internal chamber of the fossils are partly or completely filled with iron oxide cement (Scale bar = 0.5 mm), (f) Pho- tomicrograph contains molluscs, orbitoids, uniserial and biserial foraminiera; altered inoceramus grain seen in the center of the photo- graph (Scale bar = 0.5 mm), (g) Molluscan algal grainstone includes algal and molluscan fragments. The limestone exhibits sparry calcite and blocky cement (Scale bar = 0.5 mm), (h) Algal boundstone contains few quartz grains and exhibit complete structure of algal growth (Scale bar = 0.5 mm). 246 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran of skeletal and non-skeletal grains. The Molluscan algal grain- erous limestone (VLP14‒VLP15), the oxygen isotope values stone has more than 10% of algal and molluscan fragments vary from ‒8.80 to ‒7.71‰ VPDB. in the sparry calcite cement (Fig. 8g). The limestone exhibits Three limestone samples from the Vellipirangiyam quarry numerous pore spaces that are filled with microsparite and section of the Kallankurichchi Formation were selected for sparry calcite cement. This petrographic type represents the the strontium isotope study. The studied samples show large upper part of the Periakurichchi quarry section (P18, P21, variations in 87Sr/86Sr values (0.709310 to 0.711962; Table 4). P22 and P23). The 87Sr/86Sr values of the Kallankurichchi Formation are much higher than the 87Sr/86Sr values of Maastrichian age and 4.1.4. Boundstone the average seawater values of 0.70916 (Davis et al., 2003). A lone petrographic type, Algal boundstone is recognized in the lower part of the Periakurichchi quarry section (P6). 4.2.2. Niniyur Formation The boundstone exhibits complete growth structure of algae The carbon and oxygen isotope variations of fourteen lime- (Fig. 8h). Algal micritisation is common. The common frame- stones samples of the Niniyur Formation are given in Figure 10. work constituents include foraminifera, and algal elements. The carbon isotope composition of fossiliferous limestone Sparry calcite cement is present in the pore spaces and vugs. (P1‒P8) ranges from ‒3.31 to ‒1.87‰ VPDB. Overall, the upper limestone unit shows large variations in carbon iso- 4.2. Isotopic Variations tope values (P12‒P23: ‒5.63 to ‒2.52‰ VPDB). The 18O values range from ‒6.86 to ‒5.77‰ VPDB for fossiliferous 4.2.1. Kallankurichchi Formation limestone (P1‒P8; Table 3). The upper limestone unit of The analyzed thirteen samples show large variations in Periyakurichchi quarry section shows significant variations carbon and oxygen isotope values (Table 2). The lower oys- in 18O values (P12‒P23: ‒8.56 to ‒5.57‰ VPDB). ter Gryphaea limestone shows negative to positive 13C values The 87Sr/86Sr values of seven limestone samples from Peri- (VLP1‒VLP6: ‒1.69 to +0.32‰ VPDB; Table 2). The Inoc- yakurichchi quarry sections of the Niniyur Formation vary eramid limestone exhibits negative carbon isotope values from 0.707828 to 0.708398 (Table 4). Most of the limestone (VLP8‒VLP9: ‒1.96 to ‒1.15‰ VPDB). Most of the limestones samples show higher 87Sr/86Sr values except for one sample that from upper oyster Gryphaea limestone show negative carbon shows a relatively pristine 87Sr/86Sr value (P13: 0.707828). isotope values (VLP10‒VLP13: ‒2.75 to ‒2.05‰ VPDB). Large carbon isotopic variations are observed in the fossiliferous 5. DISCUSSION limestone (VLP14‒VLP15: ‒4.73 to ‒3.81‰ VPDB). The lower oyster Gryphaea limestones show overall negative oxygen 5.1. Petrography isotope values (VLP1‒VLP6: ‒5.97 to ‒3.66‰ VPDB; Fig. 9). The Inoceramus limestone samples (VLP8‒VLP9) also show The limestones of Kallankurichchi and Niniyur formations negative values that vary between ‒7.68 and ‒5.52‰ VPDB. The are dominated by wackestone, packstone and grainstone upper oyster Gryphaea limestones also exhibit more negative lithofacies. The petrographic study indicates the presence of values (VLP10‒VLP13: ‒8.89 to ‒6.16‰ VPDB). In the fossilif- fibrous calcite, microsparite and isopachous blocky sparry

Table 2. Trace elements, carbon and oxygen isotopic values for whole rock limestone samples of Vellipirangiyam quarry section of the Kallankurichchi Formation Member/Sample No 13C (‰ VPDB) 18O (‰ VPDB) Mn (ppm) Sr (ppm) Mn/Sr Fossiliferous Limestone VLP15 ‒3.81 ‒8.80 2090 136 15.37 VLP14 ‒4.73 ‒7.71 1760 82 21.46 Upper Oyster Gryphaea Limestone VLP13 ‒2.75 ‒6.96 2350 149 15.77 VLP12 ‒2.05 ‒6.36 1940 116 16.72 VLP11 ‒2.41 ‒8.89 1880 150 12.53 VLP10 ‒2.05 ‒6.16 1320 169 7.81 Inocermus Limestone VLP9 ‒1.96 ‒7.68 1110 128 8.67 VLP8 ‒1.15 ‒5.52 1060 205 5.17 Lower Oyster Gryphaea Limestone VLP6 ‒1.69 ‒5.97 1060 133 7.97 VLP5 ‒1.45 ‒5.11 960 225 4.27 VLP4 ‒0.87 ‒5.43 1530 145 10.55 VLP2 ‒0.49 ‒4.74 1670 202 8.27 VLP1 0.32 ‒3.66 1790 232 7.72 Isotopic signatures in Maastrichtian-Danian limestones, South India 247

Fig. 9. Carbon and oxygen isotope variations in the limestones collected from the Vellipirangiyam quarry section of the Kallankurichchi Formation.

Table 3. Trace elements, carbon and oxygen isotopic values for whole rock limestone samples of Periyakurichchi quarry section of the Niniyur Formation Member/Sample No 13C (‰ VPDB) 18O (‰ VPDB) Mn (ppm) Sr (ppm) Mn/Sr Limestone interbedded with shale and sandstone P23 ‒5.63 ‒8.49 1760 130 13.59 P22 ‒5.46 ‒7.22 2070 156 13.26 P21 ‒3.96 ‒6.51 1590 275 5.78 P18 ‒3.71 ‒8.56 550 296 1.86 P17 ‒5.37 ‒5.57 2320 212 10.95 P15 ‒2.52 ‒8.28 2110 191 11.06 P13 ‒4.60 ‒6.34 280 185 1.51 P12 ‒5.03 ‒7.20 1900 133 14.32 Fossiliferous Limestone P8 ‒3.31 ‒6.86 1970 240 8.21 P7 ‒2.10 ‒5.41 1610 215 7.49 P6 ‒1.87 ‒6.83 2460 148 16.60 P5 ‒2.74 ‒6.68 560 176 3.18 P4 ‒2.73 ‒6.43 2200 180 12.25 P1 ‒3.30 ‒5.77 2430 231 10.51 248 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran

Table 4. Strontium isotope values for limestones of the Kallankurichchi and Niniyur formations. Numerical age derived after Howrath and McArthur (1997) and McArthur et al. (2001) (SIS Look-up Table Version 4: 08/04) Quarry Section/Sample No Formation Age 86Sr/87Sr 2se (10‒6)Agea Vellipirangiyam Quarry Section of Kallankurichchi Formation VLP14 Kallankurichchi Lower Maastrichtian 0.711962 5 VLP10 Kallankurichchi Lower Maastrichtian 0.709310 5 VLP4 Kallankurichchi Lower Maastrichtian 0.711697 5 Periakurichchi Quarry Section of Niniyur Formation P23 Niniyur Danian 0.708353 7 P21 Niniyur Danian 0.708398 5 P13 Niniyur Danian 0.707828 4 > 65.15 65.02 < 64.90 P12 Niniyur Danian 0.708395 5 P6 Niniyur Danian 0.708100 5 P5 Niniyur Danian 0.707954 12 P1 Niniyur Danian 0.708279 5

The analytical uncertainties mentioned for individual measurements are two times the standard error of the mean (2SE). Numerical agea reported in the table includes lower age limit (>), mean age and upper age limit (<) and the limiting age are presented at 95% confidence interval.

Fig. 10. Carbon and oxygen isotope values of the limestones collected from the Periakurichchi quarry section of the Niniyur Formation. Isotopic signatures in Maastrichtian-Danian limestones, South India 249

Fig. 11. (a) Photograph shows the growth pattern of blocky calcite cement (Scale bar = 0.5 mm), (b) Photomicrograph exhibits the growth pattern of isotpachous cement (Scale bar = 0.5 mm), (c) Inoceramus shell exhibits characteristic prismatic microstructure (Scale bar = 0.5 mm), (d) Photomicrograph exhibits the honeycomb pattern of inoceramus shell structure (Scale bar = 0.5 mm), (e) Oyster shell shows the alternating foliated and vesicular layers (Scale bar = 0.5 mm), (f) Cathodoluminescence photograph shows dull red and dull orange yellow color zonings (Scale bar = 0.5 mm), (g) Photograph shows alternating layer of dull red and dull organge yellow color layers (Scale bar = 0.5 mm), (h) Cathodoluminescence photomicrograph exhibits dull red and orange yellow zonings; this cement shows well developed zoning patterns (Scale bar = 0.5 mm). 250 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran calcite cement (Figs. 11a and b). Micritic cement is present by diagenesis. Furthermore, the data of the Kallankurichchi in considerable amount, suggesting early diagenesis on the Formation showed a statistically significant positive correla- sea floor. Most of the bioclasts show micritic envelope indi- tion at 99% confidence level between δ13C and δ18O values cating large scale micritisation. Many bioclast grains are (no. of bivariate data pairs n = 13, linear correlation coeffi- partly or fully replaced by calcite cement. The limestones of cient r = 0.83, probability of no-correlation Pc(r,n) = 0.0005; the Kallankurichchi Formation contain altered shells of oys- Fig. 12a), whereas the Niniyur Formation did not show a ters and inoceramids (Figs. 11c–e). The inoceramid fossils statistically significant correlation (n = 14, r = 0.19, Pc(r,n) = are important Cretaceous index fossils (McLeod and Ward, 0.5128; Fig. 12b). No outlying observations were detected 1990) and are used as diagenetic markers (Elzora and Garcia- by OYNYL as discordant in either of these two cases (see Garmilla, 1998). Both longitudinal and cross sections of inoc- Verma and Díaz-González, 2012 for discordancy tests). Cau- eramid shells exhibit significantly altered prismatic micro- tion is required in using concentration data directly (without structure (Figs. 11c and d), indicating that these limestones any transformation) in statistical analysis involving linear were altered significantly by meteoric diagenesis. In addition, correlations (e.g., Chayes, 1960; Aitchison, 1986; Verma, 2012). the cathodoluminescence study shows various growth stages Nevertheless, we evaluated linear correlations among the of diagenetic cements, viz. non-luminescence dull cement, isotopic data and Mn and Sr concentrations and Mn/Sr ratios mild-luminescence cement and bright orange yellow cements (Figs. 11f–h), suggesting that the limestones were affected by various types of fluids during the various stages of diagen- esis. The equant calcite cement, isopachous and blocky sparry calcite cement, altered oyster and inoceramid shells and cathodoluminescence results suggest that these limestones have undergone meteoric diagenesis.

5.2. Identification of Primary Carbon Isotope Values

Variations in trace element concentrations in carbonate rocks have been considered to be important indicators of dia- genetic alteration (e.g., Ditchfield et al., 1994; Jones et al., 1994a, b; Price and Sellwood, 1997; Podlaha et al., 1998; Hesselbo et al., 2000; Jenkyns et al., 2002; Grocke et al., 2003). These studies indicate that elevated concentrations of Fe and Mn are mainly linked with negative δ18O and δ13C values. In addition, variations in Mn and Sr contents in car- bonate rocks are useful in documenting diagenetic alteration. During diagenesis, Sr is easily leached from marine carbon- ate and Mn is readily incorporated (Brand and Veizer, 1980; Veizer, 1983; Veizer et al., 1992a, b). The limestones of the Kallankurichchi and Niniyur formations show large varia- tions in Mn (960 to 2350 ppm; 280 to 2460 ppm; respec- tively; Fig. 11) and Sr concentrations (82 to 232 ppm; 130 to 296 ppm; respectively). The marine limestones with Mn/ Sr ratios greater than 2 suggest that they were subjected to diagenetic alteration, whereas these ratios of less than 2 indicate the least altered or unaltered nature (Jacobsen and Kaufman, 1999; Sial et al., 2001; Marquillas et al., 2007; Nagarajan et al., 2008; Kakizaki and Kano, 2009; Madhavaraju et al., 2013a). The limestones of both the Kallankuchchi and Nini- yur formations show high Mn/Sr ratios (4.27 to 21.46; 3.18 to 16.60; respectively), but a few samples from the Niniyur Formation (P13 and P18) show low Mn/Sr ratios (1.51 to 1.86). The observed high Mn/Sr ratios (4.27−21.46) and low Sr concentrations (82 to 296 ppm) in limestones of the Fig. 12. (a) 13C-18O bivariate plot for the limestones of the Kallankurichchi and Niniyur Formations indicate that the Kallankurichchi Formation, (b) 13C-18O bivariate plot for the primary isotopic signatures have been altered significantly limestones of the Niniyur Formation. Isotopic signatures in Maastrichtian-Danian limestones, South India 251 from the Kallankurichchi and Niniyur formations. No sta- tope values (8.89 to 3.66‰ VPDB). The lower part of the tistically significant correlations between any one pair of vari- section shows little fluctuation in isotopic values whereas ables, except the one pointed out above (between δ13C and the middle and upper parts of the section exhibit more vari- δ18O), were observed, indicating that diagenesis probably ations in oxygen isotope values. The limestones collected changed the initial primary isotopic signatures of most of the from the Periyakurichchi quarry section of the Niniyur For- limestone samples. mation exhibit more negative oxygen isotope values ranging from ‒8.56 to ‒5.41‰ VPDB. The lower part of the section 5.3. Carbon Isotope Composition shows slight variations in oxygen isotope values whereas the upper part of the section shows more fluctuations in oxygen The carbonate sediments deposited under modern marine isotope values. settings have 13C values ranging from 0 to 4 (Hudson, The oxygen isotope values of limestones from the Kallankurich- 1977; Moore, 2001). Limestones deposited under pelagic chi and Niniyur formations certainly contain diagenetic sig- and hemipelagic settings show significant variations in car- natures. Marine limestones affected by diagenesis often show bon isotope values that have been documented from different more negative δ18O values (Land, 1970; Allan and Matthews, locations and time periods by various researchers (Weissert, 1989; 1977) as cementation and/or re-crystallization commonly Föllmi et al., 1994; Grötsch et al., 1998; Wendler et al., 2009). takes place in fluids (e.g., meteoric water) depleted in δ18O The carbon isotope curve shows two negative excursions with respect to sea water (Armstrong et al., 2009, 2011) or in the upper part of the Vellipirangiyam quarry section and at elevated temperatures (burial conditions). The primary three negative isotopic excursions in the upper part of the δ18O value of European chalks is about ‒2.90‰ (ranging between Periakurichchi quarry section. Most of the samples from the ‒2 and ‒4‰), whereas diagenetic alteration can lead to more upper parts of these sections show negative carbon isotope negative values, as low as ‒8‰ (Jorgensen, 1987). values. The negative values of 13C are mainly due to bio- The isotopic values of the Kallankurichchi and Niniyur genic production of CO2 in soil (Cerling and Hay, 1986) and formations suggest shallow marine conditions coincident with indicate subaerial exposure. Lighter carbon isotopes are incor- the Maastrichtian and Danian transgressions. The isotopic porated from soil-borne carbon dioxide and the decay of ter- shift observed in the limestones at the top of the Vellipirangi- restrial matter (Hudson, 1977). yam quarry section is probably related to a sudden change in An abrupt decrease in 13C is observed in the top most part of sedimentation conditions and to the effects of early meteoric the Vellipirangiyam quarry section (VLP14: 4.73‰ VPDB). diagenesis. The lowest δ18O value (‒8.89‰), occuring in the The limestone collected just below the subaerial exposure surface upper oyster Gryphaea limestone, may be due to progressive has more negative 13C values than the limestone deposited shallowing in the sedimentary basin that probably reached several meters below it (Allan and Matthews, 1982). In the sub aerial exposure, though no palaeosols have been observed. present study, one sample (VLP14) shows more negative value The presence of a non-isotopically homogeneous profile and than the limestones collected below this sample (Fig. 9), the absence of pedogenic evidence indicate a brief sub-aerial suggesting that this interval had close contact with subaerial exposure, as has been reported for both modern and ancient exposure and meteoric waters that subsequently altered the carbonates (Allan and Matthews, 1982) in which exposition original isotopic signature significantly in the limestone. levels show sudden changes in the carbon and oxygen isotopes The positive correlation between carbon and oxygen val- (Marquillas et al., 2007). Likewise, the top of the Periakurichchi ues indicates the infiltration of meteoric waters that contain- quarry section shows significant fluctuations in oxygen isotope ing isotopically light carbon and oxygen (Hudson, 1977; values, perhaps due to the efficient mixing of isotopically Allan and Matthews, 1982; Fisher et al., 2005). The signif- light freshwater (‒15 to ‒2‰, Dickson, 1992). Thus, the observed icant positive correlation between carbon and oxygen values lighter (negative) oxygen isotope values, and fluctuations in is clearly seen in the limestones of the Kallankurichchi For- the δ18O profile for the limestones of the Kallankurichchi and mation (Fig. 12a), suggesting that the carbon isotopic values Niniyur formations (8.89 to 3.66‰ VPDB; ‒8.56 to ‒5.41‰ changed significantly during early or burial diagenesis (e.g., VPDB; respectively) were the result of diagenesis of the Jenkyns, 1974; 1996; Jenkyns and Clayton, 1986). This cor- sediments. relation is not observed in the limestones of the Niniyur For- mation (Fig. 12a). In addition, the observed high Mn/Sr ratio 5.5. Strontium Isotopes in the Kallankurichchi and Niniyur formations indicate that these limestones were significantly affected during diagenesis. The strontium isotope compositions of seawater for sev- eral periods of the Phanerozoic have been well established 5.4. Oxygen Isotope Composition by many researchers (McArthur et al., 1994, 2000; Howarth and McArthur, 1997; Veizer et al., 1997, 1999). Therefore, The limestones from the Vellipirangiyam quarry section of strontium isotope stratigraphy plays a vital role in Phanero- the Kallankurichchi Formation show negative oxygen iso- zoic rocks where there is limited availability of biostrati- 252 Jayagopal Madhavaraju, Alcides N. Sial, Reghunathan Rakhinath, Sooriamuthu Ramasamy, Yong IL Lee, and Ariputhiran Ramachandran graphic and radiometric dating. It is essential to determine bioclasts and pore spaces. Thus, the observed higher 87Sr/ that the available 87Sr/86Sr ratios in the ancient limestones are 86Sr ratios in the Kallankurichchi limestones have resulted free from diagenetic effects. In addition, variations in trace from shallow burial diagenesis. elements in carbonate rocks have been considered to be reli- able technique to identify the diagenetic alteration (Brand 5.5.2. Strontium isotopes variations in Danian Limestone and Veizer, 1980; Ditchfield et al., 1994; Jones et al., 1994a, b; The limestones of the Niniyur Formation show significant Price and Sellwood, 1997; Podlaha et al., 1998; Hesselbo et fluctuation in 87Sr/86Sr ratios. We have observed two nega- al., 2000; Price et al., 2000; Jenkyns et al., 2002; Grocke et tive excursions in the Periyakurichchi quarry section (Sam- al., 2003). During diagenesis, Mn may be incorporated and ple Nos: P5, P13). The base of the section shows a higher Sr may be released from the carbonate system (Brand and 87Sr/86Sr ratio followed by a sudden decrease in the Sr iso- Veizer, 1980; Veizer, 1983). Thus, diagenetic modifications of tope value, then a gradual increase in 87Sr/86Sr ratio and a low-Mg calcite generally show low Sr content and high Mn sudden fall in the strontium isotope values, followed by an content (Veizer, 1983). abrupt increase in 87Sr/86Sr values and again a steady decrease in isotope values. This suggests that the fluctuations in 87Sr/ 5.5.1. Strontium isotopes variations in Lower Maastrich- 86Sr ratios are related to a decrease in riverine inputs. Such tian Limestone a short-term reduction could have been caused by climate- Because of the long residence time of strontium in the sea- induced reduction in weathering rates or by rising sea levels water the 87Sr/86Sr ratio is nearly stable throughout the oceans that reduced the area of continents exposed to weathering. for extended intervals of geological time (Burke et al., 1982; Probst et al. (2000) discussed the weathering process and Hodell et al., 1989). The 87Sr/86Sr ratio of seawater during variations in 87Sr/86Sr ratios and mentioned that there is an the Lower Maastrichtian is around 0.707760 (Howrath and initial spike of Sr composition ranging up to 0.742029. Source McArthur, 1997; McArthur et al., 2001). The strontium iso- areas rich in potash feldspar could also supply radiogenic topes are not fractionated during the precipitation of carbon- strontium to the sediments during weathering and soil for- ates from aqueous solution (Faure, 1986). Hence, the limestones mation (0.782738; Probst et al., 2000). The occurrences of of the Kallankurichchi Formation should record the stron- relatively higher 87Sr/86Sr ratios (0.707828 to 0.708398) in tium isotopic composition of Lower Maastrichtian seawater. the Periyakurichchi quarry section of the Niniyur Formation However, the limestones of the Kallankurichchi Formation of Danian age suggest significant weathering of granitic show higher 87Sr/86Sr ratios than the contemporary Lower gneiss and granitic provenance. The significant fluctuations Maastrichtian seawater, suggesting that these limestones in the 87Sr/86Sr values in the studied section may be related have been significantly modified by various geological factors. to variations in the episodic/periodic influx of siliciclastics Although, the seawater 87Sr/86Sr ratio is mainly controlled by from the provenance area. According to Bullen et al. (1997), numerous input sources and the isotopic composition of both significant quantities of radiogenic Sr may be leached from riverine and mid-ocean ridge hydrothermal Sr, variations in the K-feldspar during weathering of granitoid provenance. The Phanerozoic seawater Sr-isotope curve are mainly attributed source area of the Cauvery Basin is mainly composed of to riverine inputs (Millers et al., 1988; Hodell et al., 1989; Tardy charnockites and granitic gneisses that have released a sig- et al., 1989; Berner and Rye, 1992; Edmond, 1992). nificant amount of radiogenic Sr to these limestones through Diagenesis normally increases carbonate 87Sr/86Sr ratios in riverine Sr flux. The decrease in 87Sr/86Sr ratios at certain levels relation to unaltered carbonate rocks/sediments owing to the of the studied section indicates the influx of lesser amount of inclusion of radiogenic Sr from continental siliciclastics. Because radiogenic Sr to the Niniyur Formation. It also suggests the the limestones of the Kallankurichchi Formation have under- reduction of influence of chemical weathering. Alternatively, gone shallow burial diagenesis, radiogenic Sr might have been the decrease in Sr isotopic ratios at certain levels of the stud- supplied during diagenesis by meteoric waters draining an ied section could have been caused by an increase in more area consisting mainly of old crystalline rocks (Hodell et al., pristine carbonate. 1989) such as those present in the Cauvery Basin. Rocks that In the present study, we have observed two lower 87Sr/86Sr have been subjected to abundant riverine input have relatively ratios and considered them as minima. The 87Sr/86Sr ratios of higher 87Sr/86Sr ratios (0.7116) whereas hydrothermal sources seawater during the Danian vary between 0.707819 and 0.707833 would produce lower values (0.7037; Davis et al., 2003). (Howarth and McArthur, 1997; McArthur et al., 2001). Hence The limestones of the Kallankurichchi Formation show the limestones of the Niniyur Formation deposited during higher 87Sr/86Sr ratios (0.709310 to 0.711962) than Lower this interval should record the strontium isotope composition Maastrichtian seawater. In addition, the petrographic study of Danian seawater. The 87Sr/86Sr ratio of the limestones from of these limestones suggests the presence of sparry calcite the present study shows two lower 87Sr/86Sr values i.e., and blocky cement that strongly support the meteoric diagenesis. 0.707828 and 0.707954, but, the 87Sr/86Sr value of 0.707954 Also, the cathodoluminescence study indicates the presence is still higher than the Danian seawater and another sample of various growth stages of cements deposited between the exhibits a 87Sr/86Sr ratio similar to the isotope ratio of con- Isotopic signatures in Maastrichtian-Danian limestones, South India 253 temporary seawater (0.707828). Autónoma de México for powdering of limestone samples for isotope On the basis of the 87Sr/86Sr values, numerical ages were analyses. We also thank Ms. Adriana Aime Orci Romero for preparing derived by means of a “look-up table (Version 4:08/04) pro- thin section for petrographic study. We thank M.C. Macías-Romo, Instituto de Geología, Universidad Nacional Autónoma de México for vided by Howarth and McArthur (1997) and McArthur et al. her help in the cathodoluminescence study. This study was also supported (2001). The unaltered Sr isotope values of the Niniyur For- by the Korea Research Foundation (grant 2010-0009765 to YIL). mation show a 87Sr/86Sr value of 0.707828 and are interpreted to indicate 65.02 Ma (Table 4). The numerical age derived REFERENCES from the strontium isotope composition on the whole rock sample (P13) is consistent with the previously published Aitchison, J., 1986, The statistical analysis of compositional data. palaeontological ages. 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