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Carbon, Oxygen and Strontium Isotopic Signatures in Maastrichtian-Danian Limestones of the Cauvery Basin, South India

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Carbon, Oxygen and Strontium Isotopic Signatures in Maastrichtian-Danian Limestones of the Cauvery Basin, South India 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 Maastrichtian-Danian limestones 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 Cretaceous 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
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