J. Earth Syst. Sci. (2017) 126: 45 c Indian Academy of Sciences DOI 10.1007/s12040-017-0821-3 Geochemical characteristics of sandstones from Cretaceous Garudamangalam area of Ariyalur, Tamilnadu, India: Implications of provenance and tectonic setting Babu K Department of Civil Engineering, Bannari Amman Institute of Technology, Sathyamangalam, Erode 638 401, India. e-mail: [email protected] The Trichinopoly Group (later redesignated as Garudamangalam) has unconformable relationship with underlying Uttatur Group and is divided into lower Kulakanattam Formation and upper Anaipadi For- mation. These calcareous sandstones are analysed major, trace and rare earth elements (REEs) to find out CIA, CIW, provenance and tectonic setting. The silica content of fossiliferous calcareous sandstone show wide variation ranging from 12.93 to 42.56%. Alumina content ranged from 3.49 to 8.47%. Higher values of Fe2O3 (2.29–22.02%) and low MgO content (0.75–2.44%) are observed in the Garudamangalam Formation. CaO (23.53–45.90) is high in these sandstones due to the presence of calcite as cement- ing material. Major element geochemistry of clastic rocks (Al2O3 vs. Na2O) plot and trace elemental ratio (Th/U) reveal the moderate to intense weathering of the source rocks. The Cr/Zr ratio of clas- tic rocks reveal with an average of 1.74 suggesting of felsic provenance. In clastic rocks, high ratios of LREE/ HREE, La/Sc, Th/Sc, Th/Co, La/Co and low ratios of Cr/Zr, and positive Eu anomaly ranges from (Eu/Eu* = 1.87–5.30) reveal felsic nature of the source rocks. 1. Introduction (1996) and many others. The geochemistry of clastic sediments has been effectively used for the eval- The Cretaceous period was one of the most eventful uation of tectonic setting and provenance deter- time spans in the Indian geological history. The mination (Bhatia 1983; McLennan et al. 1983; study area occupies one of the important palaeo- Taylor and McLennan 1985; Roser and Korsch geographical locations in Indo-Pacific region during 1986, 1988; Condie et al. 1992; Condie 1993). the Cretaceous period. The Cretaceous successions Though, the chemical record of clastic sedimentary of Tiruchirapalli district, Tamilnadu, are the best rocks is affected by many other factors, such as developed and Blanford (1862)wasthefirstto chemical weathering, transport distance, sorting work out the stratigraphy and he named three processes during transport, sedimentation and groups: the Uttatur, the Trichinopoly and the post-depositional diagentic reactions (McLennan Ariyalur (figure 1). The geology and stratigraphy 1989; Nesbitt and Young 1996;Nesbittet al. of this area are accounted by Ramarao (1956); 1996), still if the influence of these processes is Ramanathan (1968); Banerji (1972); Sastry et al. minor (e.g., the first cycle sandstones), the com- (1972); ONGC (1977); Sundaram and Rao (1979, position of siliclastic rocks predominantly reflect 1986); Ramasamy and Banerji (1991); Banerji et al. the nature and proportion of their detrital Keywords. Sandstone; geochemistry; provenance; Garudamangalam Formation; Ariyalur; India. 1 45 Page 2 of 13 J. Earth Syst. Sci. (2017) 126: 45 Figure 1. Location map of the study area. components and hence their provenance (Bhatia in palaeontological and lithostratigraphic aspects and Crook 1986; Roser and Korsch 1986). only. No existing data for this formation is found in Bhatia (1983) classified the tectonic settings of sed- geochemical study. This paper reveals Garudaman- imentary basins, containing significant wackes, into galam Formation in geochemical characterization four main types: Oceanic Island Arc (OIA), Conti- of sandstones. nental Island Arc (mainly sourced from felsic vol- canic rocks), Active Continental margin (ACM) and Passive margin (PM) on the basis of relative 2. Geological setting enrichment and depletion of the mobile and immo- bile elements. Other authors (Bhatia and Crook The Trichinopoly Group (later redesignated as 1986; Roser and Korsch, op.cit.) have also pre- Garudamangalam) has unconformable relationship sented different discrimination diagrams by which with underlying Uttatur Group and it is sep- one can infer the provenance and tectonic set- arated into lower Kulakanattam Formation and tings of sandstone. The classification proposed upper Anaipadi Formation (Sundaram and Rao by Sundaram et al. (2001) has been followed in 1986). The Kulakanattam Formation comprises of this study. Many have worked in this formation conglomerate bands, hard calcareous sandstone, J. Earth Syst. Sci. (2017) 126: 45 Page 3 of 13 45 fossilliferous limestone, pebbly and cobbly sandstone, 4. Sirukalpur–Alundalaipur–MelArasur, soft sandstone, clays, shales and silt. The lower 5. Peruvalapur–Varakuppai–Kallakudi, portion is mainly composed of hard calcareous 6. Siruvayalur–Tappy–Kallakudi, sandstone bands which are conglomeratic in 7. Nattakadu–Sattanur–Pilimisai, nature. The middle portion is predominantly clays, 8. Kottarai–Adanur, while the upper one is made up of sequences of 9. Odiyam–Moongilpadi–Periyammapalayam, and shell limestone, soft sandstone, calcareous shales 10. Kunnam (figure 2). and clays. The maximum width of 5.5 km is noticed in the southern portion of the basin, which grad- Samples were analysed for major oxides using ually narrows down towards the north-east (50– XRF by R&D Centre, India Cements Ltd, Dalavoi. 100 m). A conglomerate band with 700 m width Rare earth element (REE) was determined for is noticed near Kottarai, which is formed due to representative samples using ICP-MS at Shiva intense drag folding (Sundaram et al. 2001). Analyticals Pvt Ltd, Bangalore. The ICP-Mass Anaipadi Formation is further divided into two Spectrometer used for this work is the Plasma members, the lower member comprises of shale, Quad PQl (Fisons Instruments, UK) controlled by silt, sandy clays, limestone bands and calcareous an IBM PC-XT micro computer and necessary sandstone. It is well developed near Anaipadi vil- software. lage and the total thickness is about 164 m. The upper member is mainly composed of yellowish or 4. Results reddish sands/sandstone with minor bands of fos- siliferous grit. The total thickness is around 75 m 4.1 Major elements and these two members merge towards the north- ern end. As a result, yellowish sandy clay and Ten samples of fossiliferous calcareous gritty sand- lenses of highly fossiliferous calcareous sandstone stones were analyzed and the results are given in occur alternatively. These two members merge table 1. Five samples were analyzed trace and REE into a sequence of alternating shale, clay and soft concentrations are listed in tables 2 and 3.The argillaceous sandstone beds towards its southern elemental variations of major and trace elements extremity. shown in tables 4 and 5. The silica content of fos- siliferous calcareous sandstone show wide variation ranging from 12.93 to 42.56%. Alumina content 3. Methodology ranging from 3.49 to 8.47%. Higher values of Fe2O3 (2.29–22.02%) and low MgO content (0.75–2.44%) Field/outcrops features, such as bed geometry, are observed in the Garudamangalam Formation. texture, sedimentary structure, erosional surfaces, CaO (23.53–45.90) is high in these sandstones due etc., serve as evidence for depositional environ- to the presence of calcite as cementing material. ments. Such features are carefully observed in the K2O content is ranging from 0.44 to 1.62%. Na2O field. Field techniques also included documentation (0.25–2.01%) is depleted. TiO2 (0.20–0.60%) due of the geometry of features (description, photos, to their high quartz contents and lesser mafic and measurements). Field descriptions were aided components (Shilin Liu et al. 2007)andMnO with the use of a 10× hand lens, dilute HCl (to (0.05– 0.40%) are consistently low. test for carbonate cement) and grain size chart Chemical classification of samples from the (to standardize grain size descriptions). Samples Garudamangalam Formation sandstones based were collected for geochemical analysis from beds on well-classified scattergrams log(SiO2/Al2O3) of representative and variable lithologies. Extensive vs. log(Na2O/K2O) and log(SiO2/Al2O3) vs. field work was carried out by using 1:50000 scale log(Fe2O3/K2O) (figure 3). The log(SiO2/Al2O3) maps for the period of 6 months in the Perambalur vs. log(Na2O/K2O) scattergram shows that sand- and Ariyalur area. The traverse-wise collection of stones of the studied samples predominantly fall in these samples in general dip direction has helped the litharenite. The log(SiO2/Al2O3) vs. log(Fe2O3/ to study their variation in stratigraphic order. In K2O) scattergram shows that the same sand- addition, samples were also collected from isolated stone samples dominantly fall in the Fe-sand field patches, stream sections, well cuttings, quarry sec- (figure 4), through a few samples mark an Fe- tions and shallow boreholes. Totally 200 samples shale field, and a couple of samples of the Garu- were collected from 10 traverses. The following are damangalam Formation shift to the shale field of 10 traverses selected for the present study: the diagram. The shift of sandstone to various fields is due to a wide range in the variation of 1. Kulakanattam–Gudalur, relative proportion of matrix, feldspar and lithic 2. Anaipadi–Kulattur, components (Lindsey et al. 2003). Variation in 3. Nallur–Garudamangalam–Saradamangalam, Na2O/K2O on log(SiO2/Al2O3) scattergrams may 45 Page 4 of 13 J. Earth Syst. Sci. (2017) 126: 45 Figure 2. Map showing sample locations and traverses of Garudamangalam Formation. Table 1. Major element