Provenance, Tectonic Setting and Source-Area Weathering of the Lower Cambrian Sediments of the Parahio Valley in the Spiti Basin, India

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.

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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 J. Earth Syst. Sci. (2017) 126: 27 CIA ICV 3 O 2 O/Al 2 OK 2 O/Na 2 K 3 O 2 /Al 2 %SiO 3 O 2 %MnO%Fe 2 O% CaO% TiO 2 %K 5 O 2 %P 2 %SiO 3 O 2 O% MgO% Al 2 Major oxide concentration data of the Lower Cambrian sedimentary rocks of Kunzum La Formation, Spiti basin. Table 1. Sample no. LithologyPD1 Na PD2PD3 ShalePD4 SandstonePD5 SandstonePD6 2.51 1.2 SandstonePD7 2.35 2.49 SiltstonePD8 3.67 2.53 Sandstone 2.76PD9 13.88 2.08 1.75 SandstonePD10 4.29 15.61 18.88 Sandstone 65.9PD11 3.51 2.74 1.56 Sandstone 8.61 62.56 57.99PD12 3.75 Sandstone 0.122 1.31PD13 13.98 2.74 0.142 0.098 76.92 Shale 2.94 0.98 9.21PD14 3.28 65.91 Sandstone 10.33 0.1 3.68 4.83 2.06PD15 78.1 1.44 Siltstone 0.59 0.147 3.68 8.27 81.86PD16 0.89 0.21 1.43 Siltstone 13.03 1.67PD17 0.093 0.62 3.43 0.087 2.26 69.57 1.41 Siltstone 8.23 0.94 0.97 80.89PD18 3.2 1.31 1.13 1.96 Sandstone 0.066 0.073 0.46 2.97 57.74PD19 3.2 0.073 0.066 0.145 1.44 Sandstone 8.45 3.13 0.36 0.52PD20 2.59 2.35 17.36 0.23 0.148 0.62 5.62 Shale 3.43 3.02 5.79 6.92 62.98PD21 3.19 15.89 0.107 2.05 Siltstone 0.34 0.21 78.48 15.34 2.13 0.064 0.31PD22 0.26 0.081 64.81 2.23 Siltstone 16.18 0.119 0.108PD23 4.75 3.29 60.94 0.18 10.79 0.36 0.044 2.72 5.57 Siltstone 2.9 4.01 3.07 2.21 0.68 0.168PD24 74.01 11.47 4.88 4.26 0.101 Siltstone 69.62 0.053 3.37 0.37 2.5PD25 2.5 0.41 3.49 0.043 5.13 0.122 Sandstone 2.14 72.48 8.93 0.2 4.58 0.131PD26 1.04 4.71 0.063 2.09 2.1 1.31 Siltstone 0.28 0.27 3.27 4.13 0.139 3.9 1.57 4.03PD27 0.95 13.75 10.39 0.16 2.96 8.48 Siltstone 0.92 2.85PD28 7.92 9.71 0.07 0.91 1.44 0.19 3.13 2.99 78.24 1.91 Siltstone 66.09 10.31 0.24 0.78PD29 8.41 0.46 0.065 2.3 1.65 76.6 Shale 0.24 0.055 0.116 0.72 0.165 0.91PD30 6.21 3.1 15.25 62.99 11.12 0.24 0.26 2.73 2.07 0.048 0.67 Siltstone 7.02 0.46 7.64PD31 0.103 3.89 0.85 2.99 0.064 0.83 0.062 5.75 2.71 72.04 Sandstone 72.04 68.51 0.063 5.37 2.98 18.73 69.29 75.16 2.02 0.63 0.19 1.68 Siltstone 2.23 9.96 0.24 0.25 0.102 2.84 2.42 0.069 0.132 10.83 10.40 0.6 7.45 6.92 14.43 1.25 56.98 3.99 Siltstone 4.52 15.93 0.72 0.21 2.93 0.21 3.21 4.08 4.01 0.67 1.74 0.1 2.75 57.1 63.74 4.63 2.24 0.29 70.08 0.118 3.97 1.08 61.81 1.52 0.28 0.38 13.28 0.19 0.045 0.12 4.57 9.79 15.06 0.49 9.07 57.63 2.97 11.96 4.88 0.074 6.45 0.22 0.60 0.118 0.26 60.62 2.98 2.97 9.14 67.18 0.066 59.93 0.26 6.32 0.68 0.52 5.24 1.54 73.17 3.59 56.72 8.62 14.78 0.19 0.022 4.05 4.51 3.50 0.105 0.152 66.96 7.78 16.85 0.056 2.85 0.076 0.096 2.87 0.71 64.32 60.25 0.99 0.35 2.84 0.95 0.26 9.51 3.44 3.7 60.44 5.69 0.25 7.65 3.01 0.108 6.5 4.35 1.04 6.36 0.68 0.22 0.061 0.84 0.23 0.30 0118 7.89 57.29 0.19 0.68 3.91 0.09 6.11 74.67 0.26 0.076 6.97 8.37 72.49 0.27 0.69 10.52 4.56 6.48 0.23 71.72 0.45 0.85 10.56 1.43 4.72 0.27 1.03 6.54 6.02 0.067 73.75 9.82 0.31 0.46 0.062 63.03 0.097 0.82 10.35 3.04 0.47 62.54 9.48 6.01 0.92 0.065 10.40 4.93 7.19 0.84 0.28 3.88 1.91 4.42 0.29 0.076 6.1 0.23 3.39 0.23 66.75 5.06 6.69 6.12 61.55 3.98 10.45 0.25 10.22 1.96 0.26 57.02 1.56 57.41 4.35 9.10 0.26 9.12 63.07 3.59 1.70 70.77 1.06 2.20 10.45 9.41 0.25 0.25 74.21 11.03 2.25 3.00 0.26 71.12 68.62 0.25 0.25 10.78 10.50 70.01 0.26 66.44 71.31 9.83 10.69 0.27 9.20 71.54 10.15 72.5 10.75 J. Earth Syst. Sci. (2017) 126: 27 Page 5 of 16 27

3. Materials and method values were compared with the GSR-1 values by Govindaraju (1994). Analytical accuracy was A total of 31 samples were analysed for petrological better than ±0.5% for SiO2 and Al2O3, better and geochemical analysis from the Lower Cam- than ±0.17% for Fe2O3 and Na2O, whereas accu- brian sedimentary succession of the Parahio valley. racy was better than ±0.8% for MgO, K2O, MnO, The samples were analysed for major, trace and TiO2 and P2O5. The precision of trace elements rare earth element (REE) at Wadia Institute of was better than ±0.71% for Sc, Zn, Ga, Th and Himalayan Geology, Dehradun. Major oxide and Zr, and was better than ±2% for Rb and Sr. The trace elements data were analysed using the Wave major and trace element data were recalculated to Length Dispersive XRF system (Siemens SRS 100% after deduction of loss of ignition. To cal- 3000). Ten grams of each sample were powdered in an culate the loss of ignition (LOI), 1 g dried rock agate mortar. Major and trace elements were anal- powder is ignited in alumina crucible at 950◦C ysed by using pressed powder pellet mode of sam- for about 1 hr. Inductively Coupled Plasma Mass ple preparation. For the better accuracy, analytical Spectrometry (ICP–MS; Perkin Elmer) was used

Figure 3. Major elements vs. Al2O3 graph showing the distribution of samples from the Lower Cambrian succession of Kunzum La Formation in the Parahio Valley. +: sandstone; ◦: siltstone; :shale. 27 Page 6 of 16 J. Earth Syst. Sci. (2017) 126: 27 to analyse rare earth elements (REE) data. REE of fine-grained sandstone. Sandstone mainly comprise data were normalised to chondrite values of Taylor of quartz (about 85%) associated with feldspar and McLennan (1985). The analysis done by acid and lithic fragments (figure 2a–d). Feldspar is gen- digestion that involves frequent treatment with erally less abundant than quartz, and is ∼5–10% HF–HClO4 in 1:2 for 24 hrs in open system. The of sandstone composition. The matrix is between samples were dissolved in the acid mixture for 2–3 10 and 15%, and contains clay minerals and lithic treatments until a clear solution was obtained. The fragments. Quartz grains are poorly–moderately residue was dissolved in 1N HNO3 and 100 ml of sorted and shows straight to concavo–convex con- solution was then ready for analysis. The Ce/Ce* tacts (figure 2a–d). The siltstone clearly shows and Eu/Eu* ratios were calculated based on for- fine-grained matrix with few coarse mafic minerals mula given by Bauand Dulski (1996). The ana- and feldspar mainly plagioclase (figure 2e–f). In lytical accuracy for all the REE was better than siltstone, quartz is the most abundant mineral ±10%. (∼50–60%), and the other minerals, like feldspar, mica and lithic fragments, occur in less abun- dance. The siltstone consists ∼20–30% of matrix, 4. Results comprising of clay minerals, lithic and feldspathic fragments, fine-grained quartz and mica. The mica Thirty one representative samples from flakes show alignment in one direction and at few Khemangar–Debsakhad were selected for petrogra- places, quartz grains are wrapped by the mica phy and geochemical analysis. Thirteen samples grains (figure 2e–f). Quartz grains show angular, of sandstone, 14 of siltstone and four of shale rounded to sub-rounded and irregular shapes. were studied. The basal part of the Khemangar– Dark, blackish-reddish-brown shale is composed Debsakhad (Lower Cambrian) section is composed mainly of clay and silt size quartz and mica flakes

Table 2. Trace element concentration data of the Lower Cambrian sedimentary rocks of Kunzum La Formation, Spiti basin. Sample no. Lithology Co Ni Cu Zn Ga Pb Th Rb U Sr Y Zr Nb PD1 Shale 19 44 47 77 24 16 23 225 4.46 37 29 153 19 PD2 Sandstone 17 39 26 64 16 12 18 138 3.59 69 34 215 13 PD3 Sandstone 17 37 15 65 21 14 23 159 1.58 91 29 293 19 PD4 Sandstone 8 15 12 24 9 32 20 53 2.23 97 23 233 7 PD5 Siltstone 15 38 37 56 16 15 23 142 6.67 70 39 269 12 PD6 Sandstone 9 17 9 30 10 14 18 66 0.64 101 18 192 9 PD7 Sandstone 7 17 12 18 12 14 15 95 0.9 91 21 138 7 PD8 Sandstone 8 13 12 15 10 11 6 72 0.68 97 18 80 3 PD9 Sandstone 11 23 11 32 16 17 33 117 1.14 90 28 388 14 PD10 Sandstone 7 15 9 18 9 11 19 66 0.64 73 25 226 8 PD11 Shale 20 51 45 79 21 14 20 197 7.75 44 33 212 17 PD12 Sandstone 8 14 9 22 10 12 12 64 0.62 62 15 148 4 PD13 Siltstone 15 36 29 61 20 22 35 145 6.17 56 35 473 19 PD14 Siltstone 22 36 126 46 20 91 26 195 1.93 37 26 183 16 PD15 Siltstone 17 45 39 77 21 14 20 191 1.92 37 32 216 19 PD16 Sandstone 11 23 9 40 14 16 30 105 3.95 54 32 407 14 PD17 Sandstone 16 27 10 46 15 22 39 117 1.16 103 32 632 21 PD18 Shale 15 21 12 45 13 33 53 106 4.67 98 42 797 24 PD19 Siltstone 18 42 12 57 19 15 12 172 8.48 78 23 174 16 PD20 Siltstone 9 20 11 23 10 14 19 79 0.75 119 21 161 9 PD21 Siltstone 8 18 13 19 10 11 6 83 0.79 134 13 59 5 PD22 Siltstone 22 54 15 84 23 9 4 180 5.21 82 23 82 16 PD23 Sandstone 13 30 20 41 13 16 15 97 3.26 112 28 277 11 PD24 Siltstone 19 49 29 75 24 15 23 222 2.23 46 29 203 18 PD25 Siltstone 18 45 23 65 18 13 15 160 1.58 74 28 171 12 PD26 Siltstone 20 51 19 81 21 8 12 181 5.15 61 27 145 17 PD27 Shale 22 48 32 81 19 10 15 164 1.65 57 32 204 17 PD28 Siltstone 16 39 41 70 18 26 25 145 4.43 50 31 276 15 PD29 Sandstone 16 32 33 53 14 25 15 117 3.02 70 26 163 11 PD30 Siltstone 18 42 44 72 19 21 22 168 1.68 46 29 261 16 PD31 Siltstone 19 44 28 78 20 23 19 204 8.05 45 27 192 17 J. Earth Syst. Sci. (2017) 126: 27 Page 7 of 16 27

(figure 2g–h). It shows discontinuous, wavy and a similarity with the upper continental crust. The straight parallel laminae. Besides this, some angular significant negative Eu and light Ce anomalies silt particles composed of quartz are also observed. indicate a marine depositional environment of the The concentrations of major oxides (wt%) are sediments. The Ce/Ce* and Eu/Eu* ratios are cal- given in table 1. The sandstone contains moderate– culated based on the formula given by Bau and high concentrations of SiO2 (57.74–81.86; average Dulski (1996). The Eu/Eu* anomaly ranges from 71%), whereas siltstone and shale contains low (0.41–0.91) (average 0.62; n = 31) and Ce/Ce* SiO2 (56.9–78.2; average 66%). The binary rela- anomaly ranges from 0.95 to 1.04 (average 1.01; tionship of major oxides vs. Al2O3 reflects the n = 31). A good correlation between Ce/Ce* and abundance of the different major element oxide Eu/Eu* (r =0.81) was observed, which suggested (figure 3). Oxides such as TiO2 (r =0.87), Fe2O3 that the effect of diagenetic process on the REE (r =0.92), MgO (r =0.87) and K2O(r =0.94) concentrations is high (Liu et al. 2006). A posi- exhibit positive correlation with Al2O3 (r = tive correlation is observed between La and Al2O3 coefficient correlation) (figure 3). A marked (r =0.52) suggesting that, in the study area, the increase in the abundance of these elements indi- REE fractionation in the sediment is low and are cates enrichment of clay minerals (Nagarajan et al. derived mainly from the source/detrital compo- 2007a, b). The TiO2 concentration is more in silt- nents (Nath et al. 2000). stone (average ∼0.72) as compared to sandstone (average ∼0.50), which suggests a low amount of phyllosilicate among them (Dabard 1990; Condie 5. Discussion et al. 1992; Nagarajan et al. 2007a). The K2O/ Al2O3 ratios can be used to define the original Bhatia (1983) and McLennan et al. (1993) considered composition of ancient sediments (Ramachandran that the geochemical composition of sedimentary et al. 2016). According to Cox and Lowe (1995) rock helps to establish the provenance, weath- the K2O/Al2O3 ratio for clay minerals ranges from ering and depositional condition. The chemi- 0.1 to 0.3, and from 0.3 to 0.9 for feldspars. In the cal compositions of siliciclastic rocks are mainly present study, the K2O/Al2O3 ratio ranges between controlled by the plate tectonic settings of their 0.19 and 0.30, which denotes that the rocks contain provenances, as a result, siliclastic rocks from diffe- considerable amounts of clay minerals. Sandstone rent tectonic settings have specific geochemical samples reflect the highest SiO2 and a lower Al2O3 signatures (Bhatia 1983; Bhatia and Cook 1986; than siltstone, which further suggest the pres- Roser and Korsch 1986). The major element anal- ence of quartz and absence of Al-bearing mineral ysis was used to discriminate the tectonic set- (Nagarajan et al. 2007b). ting and provenance (Bhatia 1983; Roser and The concentrations of trace elements data is Korsch 1986). The tectonic setting discriminant given in table 2. In sandstone, the concentration of diagrams can provide reliable results for siliciclas- Th, Zr, Co and Ni are comparatively lower than tic rocks because they are not affected too much in siltstone (table 2), which reflects a higher clay by post-depositional weathering/metasomatism/ mineral content in siltstone (Nagarajan et al. metamorphism (McLennan et al. 1993). Bhatia 2007b). A well-defined positive correlation is shown (1983), Bhatia and Cook (1986), Roser and Korsch by the trace elements Co (r = 0.80), Rb (r =0.96), (1986), Peterson (2009) and Sari and Koca (2012) Ni (r =0.90), Nb (r =0.81), Zn (r =0.78) and used major element chemistry to define the tectonic Ga (r =0.96), when plotted against Al2O3 (figure 4). settings. The discriminant diagrams by Bhatia Co (r =0.85), Ni (r =0.86), Zn (r =0.82), Rb and Cook (1986) classify provenances into four (r =0.98) also exhibit positive correlations with categories: PM – Passive margin; ACM – Active K2O (figure 5), which again suggests that these continental margin; ARC – Island Arc (oceanic/ elements are primarily controlled by clay mineral continental). Chemical analyses data of the present and concentrated during weathering (Nagarajan siliciclastic rocks have been plotted on three tec- et al. 2007a, b; Ramachandran et al. 2016). Ni tonic setting discriminant diagrams ([K2O/Na2O] (r =0.91) and Zn (r =0.93) exhibit a positive vs. SiO2;[SiO2/Al2O3] vs. log[K2O/Na2O]; [SiO2/ correlation with MgO (figure 5), which indicates 20]–[K2O+Na2O] – [TiO2+Fe2O3+MgO]), follow- that Ni and Zn are the constituent components ing the study by Bhatia (1983), Roser and Korsch of clay minerals along with other detrital material (1986) and Kroonenberg (1994). The discriminant (McCann 1991). diagram indicates that majority of samples plot The concentration of rare earth elements is within the active continental margin, while few plot shown in table 3. Chondrite-normalised REE plot within the passive marginal setting (figures 7–9). of siliciclastic rocks reflect an enriched LREE (La, The samples falling in the ACM reveal that the Ce, Nd and Sm) and depleted HREE (Tb, Dy, sediments are delivered from mixed sources and Yb and Lu) pattern (figure 6a–c), which shows stored on or adjacent to active plate margins and 27 Page 8 of 16 J. Earth Syst. Sci. (2017) 126: 27

Figure 4. Trace elements vs.Al2O3 graph showing the distribution of samples from the Lower Cambrian succession of Kunzum La Formation in Parahio valley. Symbols are as in figure 3. J. Earth Syst. Sci. (2017) 126: 27 Page 9 of 16 27

Figure 5. Trace elements vs.K2O and MgO graph showing the distribution of samples from the Lower Cambrian succession of Kunzum La Formation in Parahio valley. Symbols are as in figure 3. 27 Page 10 of 16 J. Earth Syst. Sci. (2017) 126: 27

Table 3. Rare earth element concentration data of the Lower Cambrian sedimentary rocks of Kunzum La Formation, Spiti basin. LREE/ Sample no. Lithology La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Eu* Ce* HREE PD1 Shale 169.6 124.8 91.1 70.3 42.0 18.9 24.9 21.1 17.4 15.5 15.9 16.0 13.5 13.2 0.57 0.96 3.2 PD2 Sandstone 130.7 100.1 69.6 54.2 32.0 15.3 18.3 14.4 10.6 8.9 8.7 8.1 7.1 7.1 0.61 1.00 3.9 PD3 Sandstone 226.2 182.9 124.1 98.5 48.2 19.6 27.4 19.5 13.7 11.3 11.4 10.9 9.7 9.8 0.52 1.04 5.1 PD4 Sandstone 119.1 91.8 63.2 49.1 28.1 12.3 15.7 11.1 7.6 6.3 6.3 5.8 5.7 5.3 0.56 1.01 4.6 PD5 Siltstone 226.2 169.3 115.9 88.6 49.6 22.0 27.4 20.7 15.0 11.9 11.8 10.7 8.9 8.6 0.57 0.99 4.7 PD6 Sandstone 86.7 66.3 45.4 33.7 19.3 10.7 11.0 8.4 6.0 5.1 5.1 5.1 4.8 4.7 0.71 1.00 4.1 PD7 Sandstone 80.8 62.3 42.6 32.9 20.8 10.9 12.8 11.1 9.5 8.7 8.9 9.1 7.7 7.3 0.65 1.01 2.8 PD8 Sandstone 52.8 40.7 27.7 21.7 14.3 8.8 9.2 8.5 7.6 6.9 6.9 6.9 5.9 5.6 0.75 1.01 2.4 PD9 Sandstone 169.4 130.5 91.3 68.4 40.5 16.6 23.0 17.7 13.9 11.9 12.3 12.0 10.3 9.9 0.52 1.00 3.9 PD10 Sandstone 131.8 101.1 70.5 54.6 32.8 15.4 19.8 16.4 13.1 11.5 11.4 10.7 9.1 8.7 0.59 1.00 3.4 PD11 Shale 160.5 120.2 86.6 65.7 39.6 17.4 23.1 19.4 15.4 13.4 13.4 13.5 11.2 11.0 0.55 0.97 3.4 PD12 Sandstone 72.9 55.7 37.4 27.7 16.6 12.0 9.6 7.5 5.7 4.6 4.6 4.4 3.9 3.9 0.91 1.01 3.7 PD13 Siltstone 256.1 196.4 134.3 101.3 60.3 20.1 31.1 25.1 19.6 16.7 17.0 16.4 13.9 13.8 0.44 1.01 4.3 PD14 Siltstone 152.6 116.0 82.0 63.3 37.8 17.3 23.1 19.7 16.3 14.4 15.0 14.9 12.6 12.5 0.57 0.99 3.1 PD15 Siltstone 158.0 119.3 85.7 67.9 41.0 18.6 25.2 22.4 19.1 17.4 17.2 17.6 14.3 13.8 0.56 0.98 2.9 PD16 Sandstone 234.3 177.6 119.0 88.6 52.8 17.4 25.8 19.2 13.8 11.6 11.7 11.6 10.0 9.6 0.44 1.01 5.1 PD17 Sandstone 246.2 192.3 127.7 95.0 53.9 21.6 27.7 21.9 16.7 14.6 15.1 14.7 12.6 12.3 0.53 1.03 4.5 PD18 Shale 411.4 310.3 204.4 154.7 86.0 27.7 48.7 32.4 24.2 20.6 21.0 19.6 16.5 15.9 0.41 1.01 5.1 PD19 Siltstone 91.5 72.2 49.4 38.8 23.2 13.3 13.6 10.8 8.5 7.3 7.1 7.1 5.7 5.6 0.73 1.02 3.5 PD20 Siltstone 91.9 71.4 48.1 37.9 22.4 13.3 13.6 11.6 9.7 8.9 8.9 9.0 7.5 7.3 0.74 1.02 3.0 PD21 Siltstone 39.9 30.6 20.0 15.4 9.5 8.9 5.5 4.4 3.6 3.3 3.3 3.5 2.9 3.0 1.19 1.02 3.0 PD22 Siltstone 66.6 52.9 36.0 29.3 19.1 13.3 12.0 11.1 9.7 9.0 8.8 9.0 7.4 7.3 0.86 1.03 2.3 PD23 Sandstone 140.3 104.9 75.0 59.7 34.0 16.2 20.6 17.8 14.9 13.7 13.6 13.8 11.4 11.1 0.59 0.97 3.1 PD24 Siltstone 160.5 122.3 88.0 67.8 40.0 17.6 23.3 20.4 16.8 15.1 15.2 15.3 13.1 13.0 0.56 0.98 3.2 PD25 Siltstone 99.7 77.0 53.8 43.1 26.7 14.4 16.7 15.6 14.1 13.1 13.1 13.1 11.0 10.4 0.66 1.00 2.5 PD26 Siltstone 107.1 84.0 57.8 45.8 28.5 15.5 17.4 15.1 12.4 10.9 10.9 10.8 8.9 8.9 0.68 1.02 2.9 PD27 Shale 142.0 109.0 78.5 61.1 37.6 17.1 22.7 20.6 17.3 15.8 15.7 15.4 12.7 12.3 0.57 0.99 2.9 PD28 Siltstone 120.6 92.2 64.7 51.1 30.8 15.2 19.6 17.9 15.5 14.2 14.2 14.2 11.7 11.1 0.60 1.00 2.7 PD29 Sandstone 102.9 79.2 54.3 41.4 25.3 13.4 15.7 13.6 11.4 10.2 10.5 10.3 9.0 8.5 0.65 1.01 3.0 PD30 Siltstone 143.7 111.3 78.3 58.6 35.2 17.0 21.0 18.0 14.7 12.9 13.2 13.3 11.4 11.4 0.60 1.00 3.2 PD31 Siltstone 175.3 133.9 95.6 72.0 41.7 18.1 24.0 18.9 14.4 12.6 12.9 12.8 11.5 11.5 0.55 0.99 3.8

in strike-slip settings, whereas PM indicates that and Korsch’s (1988) study, discriminant diagram the rocks are derived from stable continental blocks boundaries of the P4 field (quartzose sedimentary and deposited in several types of basins including provenance) were drawn based on the chemi- rift basins (Roser and Korsch 1986). cal compositional rock data of the Ordovician To discriminate the provenance, Roser and Greenland Group in New Zealand. This terrain is Korsch (1986) define four major group of rocks: composed of sandstones and argillites of Ordovician. mafic igneous, intermediate, felsic and quart- These sedimentary rocks were derived either from zose sedimentary provenances. The major element a weathered granitic–gneissic terrain (Laird 1972) discriminant function diagram reflects that the or from a pre-existing sedimentary terrain (Nathan samples mostly lie in the quartzose sedimentary 1976). In the present study, the plot shows a quart- provenance, with few in felsic igneous provenance zose sedimentary provenance and to some extent (figure 10). The quartzose sedimentary source of the felsic igneous provenance, derived from weath- siliciclastic sediments may be composed of var- ered granite, gneiss terrain and/or from a pre- ied sedimentary lithounits and the detrital com- existing sedimentary terrain (Roser and Korsch ponents involved in their formation seems to be 1988; Rahman and Sujuki 2007). derived from different crystalline rocks and/or The REE patterns and Eu anamoly in the from pre-existing sedimentary rocks. In Roser sedimentary rocks help reveal the source rock J. Earth Syst. Sci. (2017) 126: 27 Page 11 of 16 27

(PIA) (Fedo et al. 1996), the chemical index of weathering (CIW) (Harnois 1988) are used. In a weathering profile, larger cations, e.g., Al2O3 and Rb, remain fixed, in comparison to lower cations, e.g., Ca, Na, Sr. The transformation of these chemical signature to sedimentary record is use- ful to define the source area weathering condition (Nesbitt and Young 1982, 1984; McLennan et al. 1993; Fedo et al. 1995). To quantify weathering effects, few indices of weathering have been pro- posed based on molecular composition (Na2O, CaO, K2OandAl2O3). To determine the degree of source-area weathering CIA (Nesbitt and Young 1982) and to determine the compositional matu- rity, ICV (Cox and Lowe 1995) is used in the present study. The data analysed based on these two indices for the Lower Cambrian are given in table 1. The equations of the above indices are: ∗ CIA={Al2O3/(Al2O3 +CaO

+Na2O+K2O)}×100,

ICA={Fe 2O3 +K2O+Na2O + CaO

+MgO+MnO+TiO2}/Al2O3 CaO∗(CaO in silicate fraction). The higher CIA values, ranging between 76 and 100, indicate the intensive chemical weather- ing in the source areas (Nesbitt and Young 1982; Fedo et al. 1995), whereas values <50 indicates near absence of chemical alteration and reflect cool and/or arid conditions or unweathered source Figure 6. Chondrites-normalized REE distribution spectra areas (Fedo et al. 1995). In the present study, the of Lower Cambrian succession of Kunzum La Formation in analysed CIA values range between 56 and 76, with Parahio valley. an average of ∼64 (table 1). The CIA values of Lower Cambrian samples indicate moderate chem- ical weathering. The molar proportion of Al2O3, signatures (Taylor and McLennan 1985; Fu et al. 2010; Na2O and CaO* (CaO in silicate fraction) are plot- Madhavaraju and Lee 2010; Armstrong-Altrin ted in A–CN–K ternary diagram to evaluate the et al. 2013; Madhavaraju et al. 2010). According mobility of elements during the progress of chem- to Nyakairu and Koeerl (2001), relative depletion ical weathering. The CIA values were plotted in in HREEs in comparison to LREEs was due to an A–CN–K ternary diagram (figure 11). In the ∗ the lower concentration of heavy minerals. The A–CN–K diagram (A=Al2O3; CN=CaO +Na2O; silicic rocks usually contain higher LREE/HREE K=K2O) all the rocks fall above the plagioclase– ratios and negative Eu anomaly, whereas the basic feldspar join line. All the samples (sandstone, rocks contain low LREE/HREE ratios and no Eu siltstone and shale) exhibit a definite trend. The anomaly (Cullers and Graf 1983). The pattern of A–CN–K plot depicts the clustering of points near chondrite-normalised REE (including a negative the A–K edge, towards the illite composition, Eu anomaly), in the present high LREE/HREE which suggests moderate weathering (figure 11). ratio (2.32–5.14), suggests that the granites are The advantage of the A–CN–K ternary plot is that the likely source rocks. the source rock composition can be determined by To interpret the degree of chemical weathering backward projection and parallel to the A–CN line and compositional maturity, the Chemical Index of of the weathered samples to a point on the feldspar Alteration (CIA) proposed by Nesbitt and Young join (Fedo et al. 1997; Tang et al. 2012). The silici- (1982), index of compositional variability (ICV) by clastic rocks of the present study lie along a trend Cox and Lowe (1995), plagioclase index of alteration line parallel to A–CN axis emerging from granite as 27 Page 12 of 16 J. Earth Syst. Sci. (2017) 126: 27

Figure 7. Plots of log K2O/Na2O vs.SiO2 relations for samples of the Lower Cambrian succession of Kunzum La Formation in Parahio Valley, on the tectonic setting discrimination diagrams. Fields are after Roser and Korsch (1986). PM: Passive margin; ACM: Active continental margin; ARC: Oceanic Island Arc. Symbols are as in figure 3.

Figure 8. Plot of SiO2/Al2O3 ratios vs.K2O/Na2O ratios, fields after Roser and Korsch (1986). Symbols are as in figure 3. a potential ultimate source reaching up to the illite of the upper continental crust affected by moderate stability zone. The A–CN–K diagram indicates intensity of chemical weathering Madhavaraju that the samples were generated from source rocks et al. (Madhavaraju et al. 2016). J. Earth Syst. Sci. (2017) 126: 27 Page 13 of 16 27

Similarly, sedimentary rocks which show higher active settings, whereas, those with ICV <1are ICV (>1) are compositionally immature with the compositionally mature and are deposited in a first cycle of sediments deposited in tectonically tectonically quiescent or cratonic environment, where the recycling of sediment is active (van de Kamp and Leake 1985; Cox and Lowe 1995; Perri et al. 2012). As weathering progresses, ICV values decrease due to conversion of feldspar to Al-bearing clay. Thus, variability in ICV values is mainly due to variation in source rock composition and difference in weathering (Cox and Lowe 1995; Potter et al. 2005). In the present study, the ICV values for the Lower Cambrian siliciclastic rocks vary from 7.61 to 11.03 (mean=9.2). On the basis of average ICV values, it can be interpreted that Lower Cambrian sediments are compositionally immature and deposited in tectonically active settings. There- fore, CIA and average ICV values of siliciclastic rocks indicate low–moderate degree weathering conditions during the Lower Cambrian in the study area. The Al2O3 vs. Na2O plot provides the character- istic fields, which further indicate the intensity of weathering of the source rocks (Madhavaraju Figure 9. Plot of the major element composition on the and Ramasamy 2002). In the present study, it tectonic setting discrimination diagram by Kroonenberg (1994). A: oceanic island arc, B: continental island arc, C: was found that the Lower Cambrian rocks fall in active continental margin, D: passive margin. Symbols are thefieldoflow-gradeArcheanshale,suggesting as in figure 3. thereby low–moderate chemical weathering.

Figure 10. Discriminant function 1 against discriminant function 2 variation diagram. Fields after Roser and Korsch (1988), wherein F1 = −1.733TiO2 +0.607Al2O3 +0.76Fe2O3 − 1.5MgO + 0.616CaO + 0.509Na2O − 1.224K2O − 9.09, and F2 = 0.445TiO2 +0.07Al2O3 −0.25Fe2O3 −1.142MgO+0.438CaO+1.475Na2O+1.426K2O−6.86. Provenance fields: (P1) mafic igneous provenance, (P2) intermediate igneous provenance, (P3) felsic igneous provenance, and (P4) quartzose sedimentary provenance. Symbols are as in figure 3. 27 Page 14 of 16 J. Earth Syst. Sci. (2017) 126: 27

Figure 11. A–CN–K diagram showing the weathering trend of the siliciclastic rocks (after Nesbitt and Young 1982). A: ∗ Al2O3;CN:CaO +Na2O; K: K2O (molecular composition).

6. Conclusion providing facilities and giving permission to publish this work. They are thankful to the anonymous The geochemical analysis of Lower Cambrian reviewers for their insightful reviews. The authors siliciclastic rocks of Parahio valley is employed to also thank Dr Hakim Rai and Dr D R Rao for giv- reveal weathering, provenance and tectonic setting ing critical comments and corrections to shape the of inferred source areas. The major elemental ratio manuscript in the present form. and correlation with trace elements suggest the presence of clay minerals denoting a warm and humid climatic conditions for Lower Cambrian suc- References cession. The REE profile shows enrichment in the LREE and flat HREE with negative Eu anomaly Armstrong-Altrin J S, Nagarajan R, Madhavaraju J, are equivalent to the profile of upper continen- Rosalez-Hoz L, Lee Y I, Balaram V, Cruz-Mart´ınez A tal crust as a whole. The elemental ratios, such and Avila-Ram´ırez G 2013 Geochemistry of the Jurassic and Upper Cretaceous shales from the Molango Region, as CIA and ICV indices provide useful informa- Hidalgo, eastern Mexico: Implications for source-area tion of weathering and the maturity of the rocks. weathering, provenance, and tectonic setting; Comptes CIA values reflect a low to moderate degree of Rendus Geosci. 345 185–202. chemical weathering and the average ICV values Armstrong-Altrin J S, Machain-Castillo M L, Rosales-Hoz suggest immature sediments, first-cycle deposits L, Carranza-Edwards A, Sanchez-Cabeza J A and Ru´ız- Fern´andez A C 2015 Geochemistry of deep sea sediments to tectonically active settings. The A–CN–K plot from the south-western Gulf of Mexico, Mexico: Implication and the provenance discriminant diagrams sug- for depositional environment; Cont. Shelf Res. 95 15–26. gests an upper continental crust provenance dom- Bau M and Dulski P 1996 Distribution of yttrium and inated by quartzose sedimentary to felsic rocks of rare-earth elements in the Penge and Kuruman iron- average granite composition basically derived from formations, Transvaal Supergroup, South Africa; Precamb. Res. 79 37–55. granite or pre-existing sedimentary rocks. Based Bhargava O N 2008a Paleozoic successions of Indian Plate; on all discriminant diagrams(log [K2O/Na2O] vs. Geol. Soc. India Memoir 74 209–244. SiO2;[SiO2/Al2O3] vs. log [K2O/Na2O]; [SiO2/20] Bhargava O N 2008b An update of introduction to the Spiti geology; J. Palaeontol. Soc. India 53(2) 113–128. –[K2O+Na2O]–[TiO2+Fe2O3+MgO], we conclude that Lower Cambrian sediments were deposited Bhargava O N and Srikantia S V 1985 Trilobite and other trace fossils from the Kunzum La Formation, Eastern in a transitional tectonic setting from an active Lahaul Valley, Himachal Himalaya; J. Geol. Soc. India continental margin to a passive margin. 26 880–886. Bhargava O N and Bassi U K 1986 Silurian reefal buildups, Acknowledgements Spiti–Kinnaur, Himachal Himalaya, India; Facies 15 35–52. Bhargava O N and Bassi U K 1988 Trace fossils from the Paleozoic–Mesozoic sequence of Spiti–Kinnaur (Himachal The authors are thankful to the Director, Wadia Himalaya) with comments on palaeoenvironmental control Institute of Himalayan Geology, Dehradun, for on their frequency; J. Geol. Soc. India 32 227–238. J. Earth Syst. Sci. (2017) 126: 27 Page 15 of 16 27

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MS received 28 April 2016; revised 9 October 2016; accepted 16 October 2016

Corresponding editor: N V Chalapathi Rao