J. Earth Syst. Sci. (2017) 126: 27 c Indian Academy of Sciences DOI 10.1007/s12040-017-0803-5 Provenance, tectonic setting and source-area weathering of the lower Cambrian sediments of the Parahio valley in the Spiti basin, India Shivani Pandey∗ and Suraj K Parcha Wadia Institute of Himalayan Geology, G.M.S Road, Dehra Dun 248 001, India. ∗Corresponding author. e-mail: [email protected] The geochemical study of siliciclastic rocks from the Lower Cambrian of Parahio Valley has been studied to describe the provenance, chemical weathering and tectonic setting. The K2O/Al2O3 ratio and positive correlation of Co (r =0.85), Ni (r =0.86),Zn(r =0.82),Rb(r =0.98) with K2O reflects that the presence of clay minerals control the abundances of these elements and suggests a warm and humid climate for this region. The chondrite normalized REE pattern of the samples is equivalent to upper continental crust, which reflects enriched LREE and flat HREE with negative Eu anomaly. The tectonic setting discriminant diagram log[K2O/Na2O] vs. SiO2;[SiO2/Al2O3] vs. log[K2O/Na2O]; [SiO2/20] – [K2O+Na2O] – [TiO2+Fe2O3+MgO] indicates transitional tectonic setting from an active continental margin to a passive margin. The discriminant function plot indicates quartzose sedimentary provenance, and to some extent, the felsic igneous provenance, derived from weathered granite, gneissic terrain and/or from pre-existing sedimentary terrain. The CIA value indicates low to moderate degree of chemical weathering and the average ICV values suggests immature sediments deposited in tectonically active settings. The A–CN–K diagram indicates that these sediments were generated from source rocks of the upper continental crust. 1. Introduction Pandey and Parcha 2013). Myrow et al. (2010) carried out detrital zircon studies in order to correlate The Spiti basin represents an extensive trace of the Tethyan sediments with those of the Lesser sediments which exposes a continuous fossiliferous Himalayan succession. Paleozoic succession. In Spiti basin, Haimanta The geochemical analysis of sedimentary rocks Group represents the basal part of the Tethys are used to define the provenancial characteristics, sedimentary rock and reflects an age range from composition of source rock and tectonic setting Neoproterozoic to Cambrian. The present study is (Dickinson and Suczek 1979; Bhatia 1983; Bhatia focused in the Lower Cambrian succession of Spiti and Cook 1986; Roser and Korsch 1986; McLen- basin, exposed in the Parahio valley. Earlier many nan and Taylor 1991; Nagarajan et al. 2007a, b; workers broadly studied and defined the stratigra- Madhavaraju and Lee 2010; Madhavaraju and phy and faunal data of Cambrian succession (Reed Gonzalez-Leon 2012; Armstrong-Altrin et al. 2013, 1910; Bhargava et al. 1982; Bhargava and Srikantia 2015; Madhavaraju 2015, Madhavaraju et al. 2016). 1985; Bhargava and Bassi 1986, 1988; Parcha 1996, The average composition of upper continental 1998, 1999; Peng et al. 2009; Parcha and Pandey 2011; crust is represented by geochemical analysis of Keywords. Lower Cambrian; provenance; tectonic setting; chemical weathering. 1 27 Page 2 of 16 J. Earth Syst. Sci. (2017) 126: 27 fine-grained sediments more than any other (ITSZ) and in the south by Central Crystalline sedimentary rocks (DaPeng et al. 2012). Certain zone. This Neoproterozoic to Cretaceous sedimentary REE ratios and other elemental ratios are used to succession rests over the Crystallines of Vaikrita find the source rock composition, because these ele- Group, referred as the Peri–Gondwana Tethyan ments are not redistributed in the sedimentation succession (Matsuda 1985). Various workers define process, lithogenesis and in metamorphism (Fu et al. the contact as tectonic (Thakur 1992), conformable 2010; Etemad-Saeed et al. 2011; Zaid 2012). The and gradational (Gansser 1964; Fuchs 1981; Srikantia present work is the first attempt to understand 1981; Ranga Rao et al. 1982, Parcha 1996, 1998, the geochemical signatures (paleoweathering and 1999; Myrow et al. 2006) and unconformable provenance signatures using major, trace, and rare (Srikantia and Bhargava 1998) between Tethyan earth element geochemistry) of silicicalstic rocks of sedimentary succession and the crystalline rocks. the Lower Cambrian in Parahio valley. The Spiti basin, of which the present area forms a part, has developed within the Haimanta Group. 2. Geological setting The Haimanta Group of rocks are the lower- most sedimentary succession of this basin. The The Tethyan sedimentary succession is deposited Haimanta Group ranges from Neoproterozoic to beside the northern margin of the Indian continen- Cambrian in age and is divided into Batal and tal shelf in Proterozoic to Early Eocene Period Kunzum La formations (Kumar et al. 1984; (Griesbach 1891; Hayden 1904; Heim and Gansser Srikantia and Bhargava 1998). The Batal Formation 1939; Srikantia 1981; Fuchs 1982; Bhargava et al. is Neoproterozoic in age and devoid of any signifi- 1991; Srikantia and Bhargava 1998; Bhargava cant fossils except for Cryptarch, by Kumar et al. 2008a, b). The sequence overlies the crystalline (1984). On the contrary, the Kunzum La Forma- rocks of the Higher Himalayan Zone and is fully tion has rich assemblage of trace fossil and arthro- developed in Kashmir, Zanskar and Spiti basins, pods of Cambrian age. The present study lies in the in its western part. The Spiti basin is bounded Khemangar–Debsakhad section of Parahio valley, in the north by the Indus–Tsangpo Suture Zone which is Lower Cambrian in age (figure 1). Figure 1. Geological map of the Parahio valley of the Spiti basin. J. Earth Syst. Sci. (2017) 126: 27 Page 3 of 16 27 Figure 2. (a–d) Photomicrographs of sandstone, presence of feldspar, quartz and lithic fragments. (e–f) Siltstone with quartz, feldspar and mica. Mica grains show alignment in one direction. (g–h) Photomicrographs showing shale with quartz and lithic fragments. Qz: quartz; M: mica; F: feldspar; Lt: lithic. 27 Page 4 of 16 Table 1. Major oxide concentration data of the Lower Cambrian sedimentary rocks of Kunzum La Formation, Spiti basin. Sample no. Lithology Na2O% MgO% Al2O3%SiO2%P2O5%K2O% CaO% TiO2%MnO%Fe2O3%SiO2/Al2O3 K2O/Na2OK2O/Al2O3 CIA ICV PD1 Shale 1.2 2.76 18.88 57.99 0.098 4.83 0.21 0.97 0.066 6.92 3.07 4.03 0.26 75.16 10.40 PD2 Sandstone 2.51 2.49 13.88 65.9 0.122 3.28 0.59 0.62 0.066 5.62 4.75 1.31 0.24 68.51 9.96 PD3 Sandstone 2.35 2.53 15.61 62.56 0.142 3.68 0.89 0.94 0.073 5.79 4.01 1.57 0.24 69.29 10.83 PD4 Sandstone 3.67 1.75 8.61 76.92 0.1 1.67 1.13 0.36 0.107 3.29 8.93 0.46 0.19 57.1 9.07 PD5 Siltstone 2.08 2.74 13.98 65.91 0.147 3.43 0.46 0.62 0.064 5.57 4.71 1.65 0.25 70.08 9.79 PD6 Sandstone 4.29 1.56 9.21 78.1 0.093 1.96 0.52 0.34 0.108 3.37 8.48 0.46 0.21 57.63 9.14 PD7 Sandstone 3.51 1.31 10.33 81.86 0.087 2.97 0.23 0.31 0.044 2.5 7.92 0.85 0.29 60.62 8.62 PD8 Sandstone 3.75 0.98 8.27 69.57 0.073 2.35 0.21 0.18 0.053 2.09 8.41 0.63 0.28 56.72 7.78 PD9 Sandstone 2.74 2.06 13.03 80.89 0.145 3.43 0.26 0.68 0.043 3.9 6.21 1.25 0.26 66.96 9.51 PD10 Sandstone 2.94 1.44 8.23 57.74 0.148 2.13 0.36 0.37 0.063 2.85 7.02 0.72 0.26 60.25 7.65 PD11 Shale 1.43 3.2 17.36 78.48 0.119 4.26 0.2 0.92 0.065 7.64 4.52 2.98 0.25 74.67 10.52 PD12 Sandstone 3.68 1.41 8.45 62.98 0.081 2.21 0.41 0.27 0.07 2.73 7.45 0.60 0.26 57.29 8.37 PD13 Siltstone 2.26 3.2 15.89 64.81 0.168 3.49 0.28 0.91 0.055 5.75 4.08 1.54 0.22 72.49 10.56 PD14 Siltstone 1.31 2.59 15.34 60.94 0.101 4.58 0.16 0.78 0.048 5.37 3.97 3.50 0.30 71.72 9.82 PD15 Siltstone 1.44 3.19 16.18 74.01 0.122 4.13 0.19 0.91 0.064 6.92 4.57 2.87 0.26 73.75 10.35 PD16 Sandstone 3.13 2.05 10.79 69.62 0.131 2.96 0.24 0.67 0.063 3.99 6.45 0.95 0.27 63.03 9.48 PD17 Sandstone 3.02 2.23 11.47 72.48 0.139 3.13 0.72 0.83 0.069 4.63 6.32 1.04 0.27 62.54 10.40 PD18 Shale 2.9 2.14 10.39 66.09 0.165 2.99 0.6 1.08 0.074 4.51 6.36 1.03 0.29 61.55 10.22 PD19 Siltstone 2.72 2.5 13.75 78.24 0.116 3.89 0.24 0.67 0.045 5.24 5.69 1.43 0.28 66.75 10.45 PD20 Siltstone 4.88 1.04 9.71 76.6 0.103 2.23 0.21 0.38 0.066 2.85 7.89 0.46 0.23 57.02 9.10 PD21 Siltstone 5.13 0.95 10.31 62.99 0.062 2.42 0.1 0.22 0.022 2.84 6.11 0.47 0.23 57.41 9.12 PD22 Siltstone 2.1 2.99 15.25 72.04 0.102 4.01 0.19 0.68 0.056 6.5 4.72 1.91 0.26 70.77 10.45 J.