J. Earth Syst. Sci. (2021) 130:60 Ó Indian Academy of Sciences

https://doi.org/10.1007/s12040-020-01551-5 (0123456789().,-volV)(0123456789().,-volV)

Mineralogy and geochemistry of the sediments in rivers along the east coast of : Inferences on weathering and provenance

1 1, 1 SHAIK SAI BABU ,VENIGALLA PURNACHANDRA RAO *, NANNAPANENI SATYASREE , 1 2 2 RAVIPATI VENKATA RAMANA ,MEKALA RAM MOHAN and SARIPOOT SAWANT 1Vignan’s Foundation for Science, Technology and Research (VFSTR), Deemed to be Vignan’s University, Vadlamudi, Guntur 522 213, India. 2CSIR-National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, India. *Corresponding author. e-mail: [email protected]

MS received 25 July 2020; revised 19 November 2020; accepted 25 November 2020

The clay fraction of sediments in the lower reaches of 15 rivers along the east coast of India showed high kaolinite followed by illite and smectite for the rivers dominantly draining the Archaean–Precambrian Terrain (APT), high smectite followed by illite and kaolinite for those draining the Deccan Trap Volcanic Terrain (DVT) and, high illite followed by kaolinite, smectite or chlorite for those draining through Mixed-Lithology Terrain (MLT). The CIA (Chemical Index of Alteration) and PIA (Plagioclase Index of Alteration) values, depletion of Ca, K, Na and Sr and enrichment of Al, Fe and Ti, high Rb/Sr and Th/U ratios of sediments relative to the Upper Continental Crust indicate moderate to intense chemical weathering on source rocks. The average composition of clays exhibits slight enrichment of Fe, Mg, Sc, V, Co, Cr and Ni and depletion of Nb, Zr, Hf, Y and Ta relative to the Post-Archaean average Australian Shale. The Cu, Zn and Pb contents were in the range ‘significantly polluted to moderately polluted’ in APT- and DVT-sediments. The plots of TiO2 vs. Fe2O3+MgO, Th/Sc vs. Sc and La–Th–Sc showed sediment composition intermediate between granite and basalt, while the plots of TiO2 vs. Zr, Th vs. Sc and V–Ni–Th indicate intermediate provenance between maBc and felsic sources. The mineralogy of the sediments indicates mixed sources, but their chemical composition is aAected by weathering and the provenance is intermediate between maBc and felsic sources. Keywords. Clay minerals; trace metals; river sediments; provenance; chemical weathering; maBc/felsic sources.

1. Introduction Therefore, the composition of river sediments depends on several factors such as the lithology, Rivers are the primary agents to transport the relief, climate, weathering type, transportation, eroded materials from continents to oceans. The and diagenesis (Pettijohn et al. 1972; McLennan sediments transported and deposited by the rivers et al. 1993; Cox et al. 1995). By investigating the are from diverse sources, which comprise of differ- sediment geochemistry, one can gain knowledge ent geological formations that weather under dif- about the net inCuence of provenance, weathering, ferent physiographic settings and climatic regimes. tectonic and Cuvial processes involved in making 60 Page 2 of 24 J. Earth Syst. Sci. (2021) 130:60 up the composition of the sediments (Nesbitt and predominant on source rocks of the Himalayan Young 1982; Taylor and McLennan 1985; Cullers rivers. Contrastingly, the peninsular rivers of India 1988; Tripathi and Rajamani 1999; Singh and weather source rocks under humid, tropical con- France-Lanord 2002; Borges et al. 2008; Rahaman ditions, wherein chemical weathering is predomi- et al. 2009; Garzanti et al. 2010, 2011; Lupker et al. nant (Nesbitt and Young 1989). The sediments 2012; Armstrong-Altrin et al. 2013; Sharma et al. from a few peninsular rivers of India have been 2013; Hossain et al. 2017; Madhavaraju et al. investigated for their geochemistry (Singh and 2017, 2019, 2020; Nagarajan et al. 2017; Maharana Rajamani 2001; Madhavaraju et al. 2002, 2015; et al. 2018; Chaudhuri et al. 2020). In addition, Sensarma et al. 2008; Rajamani et al. 2009; Sharma human activity can sometimes strongly inCuence et al. 2013), and sediments from more rivers have the trace element chemistry of the Cuvial to be investigated to better understand the controls sediments. on provenance, weathering and other sedimentary The chemical/physical weathering acting on processes. Moreover, it has been established that source rocks inCuences the texture, mineralogy and the Bne-grained fraction of sediment is a better geochemistry of the sediments transported by the representative to provide clues regarding prove- rivers (Chamley 1989). For example, chemical nance and composition of the upper crust (Cullers weathering produces abundant Bne-grained sedi- et al. 1979; McLennan et al. 1993; McLennan 2001; ments, while physical weathering produces more Fralick and Kronberg 1997; Weltje and Eynatten silts and sands. Variable degree of chemical 2004; Condie 2005; Chakrabarti et al. 2007). Sai- weathering produces clay minerals such as smectite babu et al. (2020, 2021) reported the composition and kaolinite, while intense chemical weathering of the peninsular India rivers average clay produces kaolinite and gibbsite-dominated sedi- (PIRAC) and REE, but these papers do not discuss ments. Physical weathering produces illite and weathering and provenance of the sediments. In chlorite-dominated sediments. Intense chemical this study, the clay fraction of sediments in the weathering selectively leaches cations such as Ca, lower reaches of 15 rivers and a freshwater lake Na and Sr from the weathering proBle, and Bxes () along the east coast of India were cations such as Cs, Ba and Rb to the weathering investigated for their mineralogy and major and proBle and by adsorbing onto clays (Nesbitt and trace element geochemistry with an aim to deter- Young 1989; Roddaz et al. 2006). Trace elements mine the inCuence of weathering and their are enriched in heavy minerals and clays, compared provenance. to silts and sands (He et al. 2015). Trace elements are also aAected by precipitation and co-precipi- tation as well as adsorption on Fe, Mn oxides and 2. Geology of the drainage basins Al-hydroxides (gibbsite), kaolinite and organic of the rivers matter surfaces and anthropogenic processes (Ma- harana et al. 2018). The sediments from diverse The rivers of the east coast of India (Bgure 1) drain source areas are admixed during transportation through three dominant geological formations: and sedimentation. The textural and mineralogical (a) the Archaean–Precambrian Terrain (APT) modiBcations associated with weathering, frac- drained by the Cauvery, Ponnaiyar, Palar, Pennar, tionation and other sedimentary processes result in Nagavali and Vamsadhara rivers. The Cauvery geochemical heterogeneity of Cuvial sediments and river comprises of the Dharwar system, peninsular as a consequence their original signature is largely granite gneiss, charnockite and closepet granite obscured. It thus becomes a challenge in utilizing (Krishnan 1982) with Cretaceous sedimentary sediment chemistry for the provenance, weathering formations (phosphatic limestones, sandstones, and crustal evolution. clays) in the coastal tract. The Studies on the sediments of large rivers origi- comprises of Archaean rocks with Cretaceous for- nated from the Himalayan mountain ranges have mations (calcareous sandstones, claystones, Cud- highlighted the role of tectonics, lithology, weath- dalore sandstone and recent alluvium) in the ering and Cuvial processes on clastic sediment coastal region (Krishnan 1982). The Pennar river composition (Yang et al. 2004; Roddaz et al. 2006; comprises of granitoid gneisses (hornblende-biotite Liu et al. 2007, 2011; Borges et al. 2008; Garzanti gneiss, migmatitic gneiss and intrusive granites) et al. 2011; Singh 2010; Shao et al. 2012; Chetelat and supracrustal rocks of tholeiitic and komatiitic et al. 2013;Heet al. 2015). Physical weathering is aDnity in the upper reaches (Balakrishnan and J. Earth Syst. Sci. (2021) 130:60 Page 3 of 24 60

Figure 1. Sample locations in the river sediments along the east coast of India. Geology of the area is also shown.

Rajamani 1987) and charnockites in the middle the lower reaches. Ore deposits such as iron, reaches followed by Gondwana deposits, granulites copper, coal, bauxite, chromite and mica are found and recent coastal alluvium. The pre-Cambrian in its basin (Giri et al. 2013). Similarly, the Hoogly Khondalites in the are the primary and Haldia rivers are tributaries of the source rocks for the Nagavali and Vamsadhara River, which drains and weather pre-Cambrian rivers. They consist of sillimanite, garnet-rich formations under glacial conditions in the Hima- schists and gneisses with quartz, K-feldspars and layas and deltaic sediments in the lower reaches plagioclases as major constituents (Das et al. 2005). (Biswas 1985). Ferro-manganese deposits are also reported in the Eastern Ghats. (b) The Deccan Trap Volcanic Terrain (DVT) is drained by the Krishna and 3. Materials and methods Godavari rivers. They also drain pre-Cambrian rocks and deltaic sediments in the lower reaches Sediment samples were collected in the lower (Jha et al. 2009). (c) The mixed-lithology terrain reaches of 15 major and medium rivers and a (MLT) is drained by the , Brahmani, freshwater lake (Kolleru) along the east coast of Baitarani and Subarnarekha rivers. The Mahanadi India (Bgure 1), using Peterson Grab and mecha- and Brahmani rivers drain through igneous rocks nised boat. The top portion of the sediments was and Late Archaean, the ore deposits of oxides and preserved in polythene bags and numbered and sulphides in the upper reaches (Singhbhum for- brought to the laboratory. Part of the sample was mations), lateritic, yellow and red soils and deltaic taken in a 500-ml glass beaker and allowed to dry soils in the lower reaches (Ray et al. 1984). The in an oven at 60°C. The sand, silt and clay contents drains through high ilmenite, of the sediments were determined, following Folk rutile, zirconium and rare earth minerals in its (1968). The \ 62 lm fraction of the sediment was drainage basin (Bhattacharya et al. 2012). The separated from the total sediment by wet sieving, comprises of Archaean rocks using 230 (ASTM) mesh sieve. This fraction was (granite gneiss) in the upper reaches and Pleis- collected in a measuring glass cylinder, made the tocene and recent alluvium and marine deposits in volume 1000 ml with distilled water and stirred 60 Page 4 of 24 J. Earth Syst. Sci. (2021) 130:60 vigorously for homogeneity. The\2 lm fraction of 4. Results the sediment solution of *250 ml was separated into a 500-ml beaker, based on the Stoke’s settling 4.1 Mineralogy velocity (Folk 1968). In order to remove calcium carbonate and organic matter, 10 ml acetic acid The major clay mineral groups present in the river sediments were kaolinite, smectite, illite and chlo- and 20 ml H2O2, respectively, were added to the clay solution and allowed to react overnight. rite. The proportions of clay minerals in the sedi- Excess acid was removed from the beaker by ments, however, varied from one river to another. repeated washing. One ml of concentrated clay Chlorite was present in trace amounts (\5%) in solution was pipetted on a glass slide and allowed APT- and DVT-sediments, but it reaches up to to dry in air. Two slides were prepared for each 15% in the MLT-sediments. Kaolinite (43%) fol- sample. A bowl containing 150 ml of ethylene lowed by illite (30%) and smectite (22%) were glycol was taken in a desiccator and covered the present in the Archaean–Precambrian Terrain bowl with a holed ceramic tile. One clay slide from (APT)-dominated river sediments, while the DVT- each sample was placed on the ceramic tile and dominated river sediments showed high smectite closed the desiccator with its lid. Then the desic- (40%), followed by illite (30%) and kaolinite (25%). cator was placed in an oven and heated at 150°C Highest kaolinite (av. 46%) was present in the for 1 hr. In this process, the clay on the slides was Nagavali and Vamsadhara river sediments. Illite exposed to ethylene glycol vapors. After 1 hr, the (45%) was the predominant mineral in all MLT desiccator was brought to room temperature. The sediments. Apart from high illite, the Mahanadi, unglycolated and glycolated sample slides were Brahmani and Baitarini sediments showed kaolin- scanned from 3° to 28° 2h at 1° 2h/min, on a ite (35%) and smectite (10%) and chlorite (10%), Rigaku X-ray diAractometer, using nickel-Bltered while the sediments of the Subarnarekha, Haldia Cu-Ka radiation. Clay minerals were identiBed and semi-quantitatively measured their concentrations, Table 1. Comparative data of certiBed reference materials following Biscaye (1965). The complete procedure (MAG-1) in lg/g against the obtained by HR-ICP-MS in the for quantiBcation of clay minerals was given in Rao present study. et al. (1988). MAG-1 (calibrating standard) The clay fraction (\4 lm) of sediments was used for the geochemical study. This fraction was sepa- Mass RSD Analyte no. ABSD(%) rated from clay solution, dried in an oven at 60°C and then powdered. For major elements, about 1–2 Sc 45 17.943 17.200 0.222 1.24 grams of Bne powder was spread over collapsible V 51 145.193 140.000 2.726 1.88 aluminum cups Blled with boric acid and pressed at Cr 53 101.023 97.000 2.116 2.09 25 tons for 30 sec in a hydraulic pellet pressing Co 59 21.110 20.400 0.400 1.90 Ni 60 56.730 53.000 4.323 7.62 machine. Major elements were determined with Cu 63 30.923 30.000 0.811 2.62 X-ray Cuorescence spectrometer, ‘WD-XRF’ Zn 66 131.408 130.000 4.893 3.72 Model Axios mAX, PAN-analytical, using JSd-1 as Ga 71 20.892 20.400 0.696 3.33 the standard, at the CSIR-National Geophysical Rb 85 152.421 149.000 3.435 2.25 Research Institute (CSIR-NGRI), Hyderabad. For Sr 88 151.644 150.000 1.201 0.79 trace elements, closed acid digestion, using Y 89 28.743 28.000 0.811 2.82 HF:HNO3 is adopted. Detailed procedure for the Zr 90 129.655 126.000 3.331 2.57 preparation of sample solutions for trace elements Nb 93 12.201 12.000 0.217 1.78 was given in Saibabu et al. (2020). Trace elements Cs 133 9.084 8.600 0.248 2.72 were analyzed by High-Resolution Inductively Ba 137 503.058 479.000 13.871 2.76 Coupled Plasma Mass Spectrometer (HR-ICP- Hf 178 3.695 3.700 0.062 1.68 MS), Nu Instruments, UK at CSIR-NGRI. Nine- Ta 181 1.123 1.100 0.016 1.41 Pb 208 25.358 24.000 1.013 3.99 teen trace elements (Sc, V, Cr, Co, Ni, Cu, Zn, Pb, Th 232 12.467 11.900 0.379 3.04 Ga, Rb, Sr, Nb, Cs, Ba, Zr, Hf, Th, U, and Ta) U 238 2.840 2.700 0.102 3.59 were analyzed in this study. Table 1 shows relative standard deviation (RSD) for MAG-1 standard. A: CertiBed values of MAG-1. B: Results obtained from HR-ICP-MS analysis for MAG-1 (average of 4 analysis). Tables 2 and 3 show analytical data on major Reported values are from Govindaraju (1994) and GEOREM elements and trace elements, respectively. (georem.mpch-mainz.gwdg.de). .ErhSs.Sci. Syst. Earth J.

Table 2. Major element chemistry (%) of the clay fraction (\4 lm) of sediments in the rivers of the east coast of India.

Name of the SiO2/ Al2O3/ K2O/ (2021) 130:60 River SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2OK2O TiO2 P2O5 CIA PIA Al2O3 TiO2 Al2O3 Archean-Precambrian Cauvery** 52.35 18.62 13.07 0.16 2.77 1.83 0.64 1.72 1.72 0.55 81.63 87.27 2.81 10.82 0.09 Terrain (APT)- Ponnaiyar* 52.49 19.71 11.75 0.11 4.39 1.91 1.80 1.59 0.78 0.18 78.80 83.02 2.66 25.30 0.08 dominated sediments Palar* 52.91 17.92 12.73 0.58 3.99 0.93 1.52 1.65 0.76 0.25 81.38 86.90 2.95 23.45 0.09 Pennar** 55.96 17.68 12.27 0.30 4.24 1.55 1.27 2.43 0.89 0.22 77.10 84.40 3.16 19.93 0.14 Nagavali* 53.46 22.03 11.46 0.22 2.33 0.39 0.82 2.16 0.85 0.20 86.73 94.26 2.42 25.88 0.10 Vamsadhara* 53.35 22.95 12.15 0.12 2.29 0.36 1.53 2.51 0.72 0.21 83.91 91.53 2.32 31.74 0.11 Avg. 53.42 19.81 12.23 0.24 3.33 1.16 1.26 2.01 0.95 0.26 81.59 91.53 2.69 20.45 0.10 Deccan trap Volcanic Krishna** 51.86 15.83 14.55 0.19 5.27 1.46 3.55 1.91 1.28 0.12 69.58 73.52 3.27 12.36 0.12 Terrain (DVT)- Kolleru Lake 54.56 15.81 12.21 0.13 3.25 0.98 0.51 2.10 1.13 0.23 81.49 90.23 3.45 14.03 0.13 dominated sediments Vasista Godavari** 54.46 17.18 14.50 0.14 4.39 1.01 3.05 2.24 1.58 0.13 73.16 78.65 3.17 10.89 0.13 Gautami Godavari** 51.70 22.16 14.12 0.15 2.69 1.08 3.25 1.94 1.12 0.21 77.94 82.36 2.33 19.76 0.09 Avg. 53.15 17.74 13.84 0.15 3.90 1.13 2.59 2.05 1.28 0.17 75.54 81.19 2.99 13.90 0.12 Multi Lithology Mahanadi** 58.21 20.10 10.68 0.07 2.32 0.36 0.61 2.70 1.09 0.17 84.56 94.73 2.89 18.36 0.13 Terrain (MLT)- Brahmani** 53.19 22.18 12.24 0.17 2.59 0.40 1.55 2.47 1.07 0.17 83.38 91.01 2.39 20.76 0.11 dominated sediments Baitarani* 56.93 20.60 11.70 0.16 3.00 0.62 2.10 2.74 0.96 0.16 79.04 86.78 2.76 21.52 0.13 Subharnarekha* 56.31 20.84 11.24 0.18 3.37 0.49 1.56 3.24 0.93 0.17 79.25 89.54 2.70 22.45 0.16 Haldia* 57.02 19.43 10.26 0.15 3.41 1.21 1.08 3.37 0.95 0.16 77.44 87.54 2.93 20.53 0.17 Hoogly* 57.35 19.81 10.03 0.14 3.46 1.53 1.51 3.46 0.94 0.17 75.29 84.35 2.89 21.09 0.17 Avg. 56.50 20.49 11.02 0.14 3.02 0.77 1.40 3.00 0.99 0.17 79.41 88.99 2.75 20.72 0.15 Avg. of all sediments 54.51 19.55 12.18 0.19 3.36 1.01 1.65 2.39 1.05 0.21 78.91 86.63 2.78 18.61 0.12 Reference sediments UCC 66.20 15.30 5.57 0.09 2.47 3.57 3.25 2.78 0.63 0.15 61.44 64.73 4.32 24.28 0.18 PAAS 62.80 18.90 7.22 0.11 2.20 1.30 1.20 3.70 1.00 0.16 75.29 85.87 3.32 18.90 0.20 WRAC 52.09 21.84 9.80 0.05 2.59 0.53 0.65 2.91 0.87 0.34 84.22 94.13 2.38 25.10 0.13

Values of Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) are also given. 24 of 5 Page CIA: Chemical Index of Alteration (Nesbitt and Young 1982); PIA: Plagioclase Index of Alteration (Fedo et al. 1995); PAAS: Post-Archean average Australian Shale (Pourmand et al. 2012); UCC: Upper Continental Crust (Rudnick and Gao 2003); WRAC: World Rivers Average Clay (Bayon et al. 2015). * Medium rivers and ** Major rivers (after Rao 1979). 60 60 Table 3. Trace element chemistry (lg/g) of the clay fraction (\4 lm) of sediments in the rivers of the east coast of India.

Name of the River Sc V Cr Co Ni Cu Zn Ga Rb Sr Nb

Archean-Precambrian Terrain (APT)- Cauvery 13.32 92.53 168.92 25.28 84.93 214.92 1103.14 11.87 47.69 116.90 5.68 24 of 6 Page dominated sediments Ponnaiyar 13.12 71.72 119.18 19.28 66.84 1068.14 1519.56 12.87 52.44 172.29 4.89 Palar 12.85 89.36 110.40 25.29 61.87 543.39 751.85 12.76 56.47 96.73 4.76 Pennar 17.64 100.06 113.04 24.80 75.34 151.89 386.43 17.56 112.75 121.99 9.02 Nagavali 23.79 119.76 105.39 38.89 66.17 137.37 274.03 17.97 77.66 75.08 6.49 Vamsadhara 21.04 104.80 100.03 22.35 62.92 458.66 624.68 18.30 124.64 68.41 6.66 Avg. 16.96 96.37 119.49 25.98 69.67 429.06 776.61 15.22 78.61 108.56 6.25 Deccan trap Volcanic Terrain (DVT)- Krishna 23.89 186.74 117.10 31.04 75.38 151.29 467.08 16.52 68.56 98.94 7.20 dominated sediments Kolleru Lake 26.25 183.17 137.42 26.27 76.43 71.48 324.38 20.58 106.35 115.4 9.18 Vasista Godavari 25.92 201.09 126.27 31.14 72.84 206.77 366.50 19.24 98.48 75.41 9.69 Gautami Godavari 24.28 156.52 142.33 33.86 77.17 228.60 391.23 20.69 94.06 124.79 11.24 Avg. 25.08 181.88 130.78 30.57 75.45 164.53 387.29 19.25 91.86 103.63 9.32 Multi Lithology Terrain (MLT)- Mahanadi 20.99 133.51 117.76 20.37 58.43 73.18 137.38 21.40 139.21 68.62 12.54 dominated sediments Brahmani 19.17 141.72 142.52 40.87 70.21 70.28 113.83 21.89 99.79 47.38 12.00 Baitarani 20.46 122.33 137.49 22.79 65.43 57.27 199.89 20.68 135.6 78.51 10.93 Subharnarekha 14.89 94.87 101.38 19.58 58.12 104.42 186.01 15.79 112.49 62.62 7.96 Haldia 15.72 91.96 88.55 15.21 54.64 59.46 132.35 16.39 126.92 93.07 9.02 Hooghly 15.24 97.89 91.43 15.73 47.52 56.51 205.65 14.08 126.93 100.77 9.02 Avg. 17.74 113.71 113.18 22.42 59.06 70.18 162.52 18.37 123.49 75.16 10.24 Avg. of all sediments 19.28 124.25 119.95 25.79 67.14 228.35 448.99 17.41 98.75 94.81 8.51 Reference sediments UCC 14.00 97.00 92.30 17.30 47.30 27.70 67.00 17.50 82.00 320.00 11.80 Sci. Syst. Earth J. PAAS 15.89 150.00 110.00 23.00 55.00 50.00 85.00 20.00 160.00 200.00 19.00

Cs Ba Hf Th U Zr Ta Pb Y La Ce Yb Archean-Precambrian Terrain (APT)- 1.51 358.57 1.58 6.25 1.34 47.72 0.52 163.19 27.45 34.76 75.56 2.41 dominated sediments 1.62 235.45 1.59 7.03 1.41 49.01 0.46 126.08 19.53 35.09 73.61 1.66 1.86 189.59 1.37 7.07 1.73 45.16 0.45 69.98 18.48 29.71 65.09 1.56 6.41 277.55 2.97 16.04 2.75 102.34 0.94 39.95 26.52 41.15 94.84 2.40 (2021) 130:60 3.43 439.51 1.64 10.16 1.44 56.35 0.63 38.34 60.49 45.41 105.38 5.42 4.84 319.13 1.81 9.61 1.74 63.01 0.63 41.82 50.09 34.12 73.38 4.41 3.27 303.3 1.82 9.36 1.73 60.60 0.60 78.89 33.76 36.70 81.31 2.97 J. Earth Syst. Sci. (2021) 130:60 Page 7 of 24 60

and Hoogly rivers showed smectite (25%), chlorite (15%) and kaolinite (15%).

4.2 Geochemistry

4.2.1 Major elements

The SiO2 and Al2O3 contents are controlled by quartz and aluminous clay contents of the sedi- ments. The average SiO2 content of the river clays (54.5%; range: 51.7–58.2%; table 2) was much lower than in the Upper Continental Crust (UCC:

). 66.2%) and Post-Archaean average Australian Shale (PAAS: 62.8%), but slightly higher than in 2003 World River Average Clay (WRAC: 52.1%; Bayon et al. 2015). The average Al2O3 content (19.6%) was higher than in UCC (15.3%) and PAAS (18.9%), but lower than in WRAC (21.8%). The Fe2O3 content ranged from 10% to 14.6% with an average value of 12.2%. Abundances of TiO2 varied from 0.7% to 1.7% with an average value of 1.0%, similar to that of PAAS (1.0%), but higher than in UCC (0.6%). The average MgO (3.4%) and Na2O (1.7%) contents of river sediments were higher than in PAAS (2.2% and 1.2%, respectively). The variations in MgO, Na2O and TiO2 were similar in river sediments, with high values corresponding to DVT-, followed by APT- and MLT-sediments. The average CaO content (1.0%) was much lower than in UCC (3.6%) and PAAS (1.3%), while the aver- age K2O content (2.4%) was lower than in both

) and UCC: Upper Continental Crust (Rudnick and Gao UCC (2.8%) and PAAS (3.7%). The average P2O5 and MnO contents of river sediments were higher 2012 than in UCC and PAAS (table 2). The average

et al. composition of river sediments showed lower CaO, Na2O and K2O and higher Al2O3,Fe2O3, MgO and TiO2 than in UCC (table 2). The PAAS-normal- ized multi-major element diagram (Bgure 2A) showed distinct enrichment of Fe2O3, MgO, MnO Cs Ba Hf Th U Zr Ta Pb Y La Ce Yb 3.725.444.90 130.674.76 284.40 3.31 200.558.68 3.11 325.648.9 3.66 7.709.58 3.13 332.97 12.498.10 12.51 1.74 549.529.69 2.83 2.17 272.67 18.348.86 1.85 257.20 2.61 119.03 2.59 2.90 279.64 19.76 118.03 1.79 263.27 129.76 12.77 0.74 2.04 3.56 18.38 0.78 110.91 2.52 13.62 0.9 2.96 17.38 2.56 16.37 1.09 103.96 24.48 1.97 14.76 23.54 27.39 94.37 2.33 1.14 47.34 29.26 95.82 2.12 65.94 35.72 23.34 1.14 34.27 44.29 33.15 1.07 75.66 0.75 77.88 38.18 54.83 32.91 42.96 63.18 0.92 70.62 36.72 1.09 40.76 2.38 81.14 27.54 126.78 57.54 2.72 33.73 35.13 27.08 26.74 3.10 37.22 3.58 118.24 31.12 48.71 29.47 34.96 160.24 3.70 100.87 36.31 34.17 2.85 73.69 3.11 75.45 2.28 70.91 2.72 2.73 4.70 235.31 3.30 12.768.97 2.165.77 325.87 119.43 294.77 2.39 0.87 2.41 15.94 28.18 12.67 2.58 34.16 2.16 39.46 85.60 84.68 83.34 1.02 0.83 2.94 34.24 49.85 32.16 33.26 41.48 39.18 99.90 88.78 2.89 2.94 15.00 650.00and 5.00 P 14.602O5 and 3.10 depletion 210.00 1.50 of 20.00 CaO 27.31 and 44.56 K2O. 88.25 Na 3.012 2O values were higher in DVT sediments, but lower or similar to that of PAAS in APT- and MLT-sedi- ments. Similarly, TiO2 was enriched in DVT and MLT, but depleted in APT sediments. The Al2O3 content of sediments showed moder- ate correlation with SiO2,Fe2O3, TiO2 and K2O and strong correlation with P2O5 (Bgure 3). It showed negative correlation with MgO, CaO and MnO. The Al2O3/TiO2 ratio varied widely from 10.8 to 31.7 with an average value of 18.6 (table 2). (Continued.) Hossain et al. (2017) suggested that the Al2O3/ TiO2 ratio is lowest (3–8) with low SiO2 values dominated sediments dominated sediments Table 3. Deccan trap Volcanic Terrain (DVT)- Multi Lithology Terrain (MLT)- Reference sedimentsPAAS: Post Archean average Australian Shale (Pourmand (45–52%) 4.10 in 624.00 maBc 5.26 igneous 10.10 2.63 rocks, 193.00 intermediate 0.88 17.00 21.00 31.40 63.40 2.04 60 Page 8 of 24 J. Earth Syst. Sci. (2021) 130:60

Figure 2. Post-Archaean average Australian Shale (PAAS) – normalized multi-elements distribution in different rivers. (A) Major elements and (B) trace elements.

(8–21) with SiO2 values of 53–66% and highest 1123.67–1484.84 lg/g, much lower than in UCC (21–70) with SiO2 values of 66–76% in felsic (1633.5P lg/g). The total rare earth element content igneous rocks. The K2O/Na2O ratio ranged from ( REE) of theP river clays (Bgure 4A) showed both 0.60 to 4.4, with an average ratio of 1.5, much high and low REE compared to the PAAS and lower than in PAAS (3.08), but higher than in was not dependent on the size of the river.P Inter- UCC (0.86). estingly, several river clays with high TE con- Ptent (Cauvery, Ponnaiyar and Palar)P showed low 4.2.2 Trace elements REE and, river clays with low TE content P (Nagavali, Mahanadi,P Brahmani and Baitarani) The total trace element content ( TE) of the showed high REE (Bgure 4A). sediments (Bgure 4A) varied widely from 1123.67 The average concentrations of trace elements in to 3542 lg/g with an average value of 1716.98 lg/ river clays showed that the Cu, Zn and Pb were g, lower than in PAAS (1807.2 lg/g; Pourmand much higher than in UCC and PAAS (table 3). et al. 2012), but higher than in UCC (1633.5 Plg/g; These metals showed much larger variations in Rudnick and Gao 2003). The high and low TE APT- than in DVT- and MLT-dominated sedi- values were distributed bothP in major and medium ments. A few transition elements (Sc, V, Cr, Co rivers. For example, the TE of two major rivers and Ni) showed slightly higher concentrations than (Cauvery and Gauthami Godavari) and three in UCC and PAAS (table 3). They were much medium rivers (Ponnaiyar, Palar and Vamsad- higher in DVT- than in APT- and MLT-dominated hara) were in the range 1818.88–3542.98 lg/g, river clays. The concentrations of alkaline earth Pmuch higher than in PAAS (1807.2 lg/g). The elements (Ba, Rb, Th, K, Ca and Sr) varied widely TE of four major rivers (Pennar, Krishna, with respect to UCC and PAAS. The average Sr Mahanadi and Brahmani) and six medium rivers content was at least 2–3 times lower than in UCC (Vasishta Godavari, Nagavali, Baitarani, Sub- and PAAS (table 3). The high-Beld strength ele- arnarekha, Haldia and Hooghly) were in the range ments (HFSEs–Nb, Zr, Hf, Y and Ta) showed J. Earth Syst. Sci. (2021) 130:60 Page 9 of 24 60

Figure 3. Scatter plots of major elements vs. Al2O3.

lower values than in PAAS. The HFSEs, Cs and U Zr) were correlated with TiO2. Sr was negatively contents were relatively high in MLT-dominated correlated with Al2O3 and K2O but, positively river clays, followed by DVT- and APT-dominated correlated with CaO (table 4). Among the trace clays. The PAAS-normalized multi-trace element metals, Sc was positively correlated with V, Ga, Hf diagram (Bgure 2B) showed anomalously high and Zr. Cr was correlated with Ni and Co. The Nb, enrichment of Cu, Zn and Pb and similar or Cs, Th, U, Hf, Zr and Ta were interrelated and slightly enriched values of transition metals (Sc, V, moderately correlated among them. Cr, Ni and Co). Sr was strongly depleted. Metals such as Ga, Th and U were slightly enriched or 5. Discussion similar values as that of PAAS. Scatter plots (Bgure 5) and correlation matrix 5.1 InCuence of weathering on mineralogy (table 4) indicate that the Al2O3 showed strong of the sediments correlation with Sc, V, Pb, Ga, Rb, Ba, Th, Zr and Ce, moderate correlation with Cr, Ni, Y, Nb and The river basins of peninsular India experience Th and no correlation with Cu, Zn, Cs, U and Hf. humid, tropical climate, wherein chemical weath- The Rb, Cs and, to some extent, Th were corre- ering is predominant. Under such conditions, lated with SiO2 and K2O (table 4). A few trace rainfall and temperature play major roles on the metals (V, Cr, Ni, Cu, Zn and Pb) showed positive composition of parent rocks in the river basins, by correlation with Fe2O3 and others (Sc, V, Hf and hydrolysing the minerals and favouring weathering 60 Page 10 of 24 J. Earth Syst. Sci. (2021) 130:60

P P Figure 4. Distribution of (A) TE and REE in the river sediments. (B) The mean enrichment factor (mEF) of trace elements in river sediments with reference to PAAS. products, smectite and kaolinite. With increasing rocks indicate chlorite is probably lost to the hydrolysis, some cations are lost to the solution solution during chemical weathering. Illite followed and weathering products are more towards by kaolinite, smectite and chlorite in the Maha- kaolinite and gibbsite (Chamley 1989). nadi, Brahmani and clays suggest The clay minerals reported here represent mixed source rock signatures and chemical weathering. mineral assemblages controlled by both source rock Illite, smectite, chlorite and kaolinite in the Sub- composition and chemical weathering. Kaolinite arnarekha, Haldia and Hoogly river sediments followed by illite and smectite in APT-dominated indicate the dominance of source rock signatures river clays indicate signatures of chemical weath- and physical weathering. The Hoogly and Haldia ering on parent rocks (granitic and gneissic rocks). rivers are the tributaries of the Ganges river, which Kaolinite is a major mineral in granites and gran- drains the Himalayas under glacial or physical odiorites. Highest kaolinite in the Nagavali and weathering conditions. Several workers reported Vamsadhara river sediments indicates intense illite and chlorite as dominant clay minerals in the chemical weathering in the Eastern Ghats. Rao Ganges– sediments (Rao et al. (1991) reported kaolinite and illite-dominated 1988; Rao 1991). Relatively low CIA values and, sediments, as the weathering products of Eastern illite–chlorite dominated sediments also support Ghats gneissic province. Similarly, dominant the dominance of physical weathering products in smectite followed by illite and kaolinite in DVT- the Hoogly and Haldia rivers. dominated rivers probably represents mixture of sediments dominantly from Deccan Trap volcanic rocks in the upper reaches and gneissic rocks in the 5.2 InCuence of weathering on geochemistry lower reaches. Smectite is the dominant clay min- of the sediments eral in Deccan Trap volcanic terrain (Rao and Rao 1995), which weather more easily than gran- Chemical weathering inCuences the alkali and ites and gneisses. Traces of chlorite in APT- and alkaline earth element concentrations of the sedi- DVT-sediments despite the presence of gneissic ments (Nesbitt et al. 1980; Nesbitt and Young 1989). J. Earth Syst. Sci. (2021) 130:60 Page 11 of 24 60

Figure 5. Correlation of trace elements with Al2O3 in the river sediments.

Average sediment composition exhibiting strong source rock signatures. The strong depletion of Ca depletion of Ca, Na and K and enhancement of Al and Sr in the PAAS-normalized multi-element dia- and Fe relative to UCC (Bgure 2; table 2) indicates gram (Bgure 2) and, strong correlation of CaO with loss of mobile elements into solution and enrichment Sr (table 4) indicate that the Sr and Ca probably of immobile elements in residual sediments, sup- resided in plagioclase and therefore strongly deple- porting the impact of chemical weathering (e.g., ted due to high degree of chemical weathering Nesbitt and Young 1982; Wronkiewicz and Condie (Nesbitt et al. 1997; Rahman and Suzuki 2007). 1987). Relatively high Na in DVT- and high K in High Th/U ratio of river clays (av. 6.0; table 5) MLT-sediments (table 2) are in conformity with the compared to UCC (3.8) indicates significant oxida- smectite and illite-dominated clay mineral assem- tive weathering and loss of hexavalent U from the blages, respectively. This supports the dominance of sediments, resulting in elevated Th/U ratios 60 Table 4. Correlation matrix.

SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2OK2O TiO2 P2O5 Sc V Cr Co Ni Cu Zn Pb Ga

SiO2 1 24 of 12 Page Al2O3 0.63 1 Fe2O3 À0.78 0.73 1 MnO À0.23 À0.48 0.23 1 MgO À0.16 À0.98 0.41 0.31 1 CaO À0.24 À0.74 0.21 0.21 0.61 1 Na2O À0.41 0.52 0.69 0.16 0.52 0.15 1 K2O 0.82 0.55 À0.72 À0.32 À0.23 À0.3 À0.21 1 TiO2 À0.01 0.72 0.55 À0.31 0.31 0.01 0.53 À0.1 1 P2O5 À0.31 0.9 0.14 0.11 À0.27 0.35 À0.44 À0.41 À0.29 1 Sc 0.12 À0.12 0.44 À0.33 À0.12 À0.38 0.34 À0.13 0.65 À0.13 1 V À0.18 0.83 0.62 À0.23 0.16 À0.19 0.48 À0.19 0.88 À0.32 0.88 1 Cr À0.43 0.57 0.53 À0.13 À0.16 0.15 0.06 À0.56 0.29 0.57 0.17 0.32 1 Co À0.59 0.13 0.58 0.13 À0.13 À0.3 0.28 À0.48 0.35 À0.01 0.55 0.54 0.45 1 Ni À0.65 0.62 0.77 0.01 0.13 0.29 0.21 À0.73 0.33 0.49 0.35 0.43 0.81 0.57 1 Cu À0.48 À0.12 0.78 0.18 0.28 0.35 0.11 À0.56 À0.4 0.02 À0.38 À0.41 0.04 À0.16 0.04 1 Zn À0.58 À0.14 0.79 0.12 0.28 0.6 0.01 À0.69 À0.34 0.49 À0.43 À0.37 0.27 À0.14 0.35 0.86 1 Pb À0.4 0.88 0.62 0.06 À0.03 0.53 À0.25 À0.51 À0.41 0.79 À0.61 À0.53 0.46 À0.15 0.34 0.56 0.85 1 Ga 0.2 0.86 0.08 À0.37 À0.4 À0.64 0.12 0.18 0.44 À0.45 0.76 0.62 0.18 0.43 0.11 À0.49 À0.66 À0.65 1 Rb 0.81 0.69 À0.51 À0.4 À0.36 À0.48 À0.14 0.82 0.08 À0.47 0.24 0.1 À0.37 À0.35 À0.52 À0.56 À0.74 À0.66 0.59

Sr À0.32 À0.83 0.14 0.02 0.43 0.83 0.07 À0.48 À0.18 0.27 À0.25 À0.22 0.17 À0.25 0.32 0.59 0.71 0.54 À0.47 Sci. Syst. Earth J. Nb 0.43 0.7 À0.1 À0.42 À0.33 À0.41 0.1 0.45 0.49 À0.38 0.45 0.45 0.17 0.16 À0.07 À0.63 À0.73 À0.56 0.83 Cs 0.8 0.25 À0.56 À0.35 À0.27 À0.41 À0.12 0.88 0.12 À0.48 0.06 0.03 À0.28 À0.26 À0.54 À0.65 À0.8 À0.61 0.52 Ba À0.01 0.83 À0.25 À0.23 À0.77 À0.44 À0.44 0.08 À0.19 0.22 0.06 À0.1 0.29 0.48 0.1 À0.26 À0.24 0.06 0.4 Hf À0.12 0.39 0.43 À0.31 0.27 0.01 0.49 0.06 0.84 À0.42 0.71 0.83 0.21 0.26 0.29 À0.46 À0.46 À0.59 0.63 Th 0.69 0.7 À0.34 À0.32 À0.33 À0.33 À0.12 0.61 0.21 À0.39 0.26 0.14 À0.11 À0.16 À0.3 À0.56 À0.71 À0.53 0.65 U 0.49 0.19 À0.2 À0.19 À0.31 À0.36 À0.03 0.37 0.22 À0.32 0.23 0.21 0.18 0.02 À0.13 À0.47 À0.61 À0.46 0.71 Zr 0.15 0.77 0.41 À0.31 0.22 À0.09 0.46 0.08 0.83 À0.45 0.76 0.86 0.2 0.27 0.29 À0.5 À0.52 À0.64 0.71 (2021) 130:60 Ta 0.54 0.21 À0.18 À0.38 À0.25 À0.28 0.15 0.57 0.42 À0.43 0.34 0.35 0.01 0.06 À0.21 À0.65 À0.75 À0.6 0.7 Y 0.02 0.55 À0.05 À0.33 À0.63 À0.57 À0.05 0.11 À0.08 À0.11 0.58 0.21 À0.01 0.33 À0.04 À0.27 0.35 À0.31 0.49 La 0.22 0.49 À0.08 À0.28 À0.55 À0.32 0.11 0.07 À0.01 À0.06 0.3 0.08 0.22 0.15 0.02 À0.2 À0.29 À0.1 0.56 Ce 0.02 0.57 À0.03 À0.18 À0.56 À0.46 À0.03 0.05 À0.01 À0.1 0.23 0.14 0.35 0.56 0.11 À0.28 À0.38 À0.16 0.67 PYb 0.04 0.55 À0.09 À0.34 À0.66 À0.61 À0.11 0.14 À0.09 À0.12 0.59 0.22 À0.11 0.38 À0.05 À0.32 À0.39 0.34 0.52 PLREE 0.12 0.57 À0.05 À0.25 À0.61 À0.45 À0.01 0.07 À0.01 À0.1 0.31 0.15 0.32 0.43 0.09 À0.28 À0.39 À0.16 0.69 PHREE 0.05 0.55 À0.08 À0.35 À0.65 À0.6 À0.09 0.14 0.08 À0.12 0.6 0.22 À0.11 0.36 À0.05 À0.31 À0.39 0.41 0.52 PMREE 0.12 0.44 À0.01 À0.36 À0.57 À0.5 0.02 0.1 0.01 À0.13 0.63 0.29 À0.01 0.27 0.01 À0.32 À0.39 À0.32 0.56 REE 0.13 0.6 À0.05 À0.28 À0.65 À0.49 À0.01 0.08 À0.01 À0.11 0.38 0.18 0.28 0.44 0.08 À0.31 À0.41 À0.2 0.71 .ErhSs.Sci. Syst. Earth J. Table 4. (Continued.) P P P P Rb Sr Nb Cs Ba Hf Th U Zr Ta Y La Ce Yb LREE HREE MREE REE

SiO2 Al2O3 Fe2O3 MnO

MgO (2021) 130:60 CaO Na2O K2O TiO2 P2O5 Sc V Cr Co Ni Cu Zn Pb Ga Rb 1 Sr À0.48 1 Nb 0.71 À0.41 1 Cs 0.88 À0.53 0.76 1 Ba 0.11 À0.37 0.34 0.23 1 Hf 0.35 À0.07 0.67 0.31 À0.17 1 Th 0.82 À0.25 0.86 0.8 0.15 0.48 1 U 0.65 À0.28 0.89 0.69 0.3 0.51 0.85 1 Zr 0.39 À0.14 0.71 0.35 À0.15 0.98 0.51 0.54 1 Ta 0.74 À0.37 0.95 0.82 0.28 0.65 0.87 0.85 0.65 1

Y À0.31 0.39 0.23 0.07 0.41 0.05 0.27 1.01 0.08 0.18 1 24 of 13 Page La 37 À0.05 0.62 0.27 0.36 0.23 0.72 0.64 0.25 0.55 0.54 1 Ce 0.24 À0.34 0.69 0.37 0.79 0.21 0.49 0.68 0.23 0.61 0.33 0.67 1 PYb 0.34 À0.44 0.25 0.12 0.5 0.06 0.25 0.11 0.09 0.22 0.98 0.49 0.38 1 PLREE 0.32 À0.25 0.72 0.36 0.66 0.25 0.65 0.72 0.27 0.64 0.48 0.89 0.93 0.49 1 PHREE 0.34 À0.43 0.25 0.12 0.47 0.06 0.27 0.12 0.1 0.21 0.99 0.51 0.36 0.99 0.49 1 MREE 0.37 0.27 0.38 0.13 0.29 0.22 0.47 0.26 0.25 0.32 0.94 0.74 0.37 0.9 0.59 0.92 1 P À 60 REE 0.35 À0.28 0.7 0.34 0.65 0.25 0.65 0.68 0.28 0.62 0.91 0.91 0.89 0.59 0.99 0.6 0.7 1 60 ae1 f24 of 14 Page

Table 5. Trace element ratios for the river sediments investigated in this study.

Name of the Th/ Zr/ Cr/ Y/ Co/ La/ Th/ Zr/ La/ Th/ Th/ Rb/ Cr/ Cr/ Sc/ river Sc Sc V Ni Th Sc Co Co Th Yb U Sr Th Ni Th V/Th Archean-Precambrian Terrain (APT)- Cauvery 0.47 3.58 1.83 0.32 4.04 2.61 0.25 1.89 5.56 2.59 4.66 0.41 27.00 1.99 2.13 14.80 dominated sediments Ponnaiyar 0.54 3.74 1.66 0.29 2.74 2.67 0.36 2.54 4.99 4.23 4.99 0.30 17.00 1.78 1.87 10.20 Palar 0.55 3.51 1.24 0.30 3.58 2.31 0.28 1.79 4.20 4.53 4.09 0.58 15.60 1.78 1.82 12.60 Pennar 0.91 5.80 1.13 0.35 1.55 2.33 0.65 4.13 2.57 6.68 5.83 0.92 7.05 1.50 1.10 6.24 Nagavali 0.43 2.37 0.88 0.91 3.83 1.91 0.26 1.45 4.47 1.87 7.06 1.03 10.40 1.59 2.34 11.80 Vamsadhara 0.46 2.99 0.95 0.80 2.33 1.62 0.43 2.82 3.55 2.18 5.52 1.82 10.40 1.59 2.19 10.90 Avg. 0.55 3.57 1.24 0.48 2.78 2.78 0.36 2.33 3.92 3.15 5.41 0.72 12.80 1.72 1.81 10.30 Deccan trap Volcanic Terrain (DVT)- Krishna 0.32 4.98 0.63 0.36 4.03 0.98 0.25 3.83 3.03 3.24 4.43 0.69 15.20 1.55 3.10 24.30 dominated sediments Kolleru Lake 0.48 4.50 0.75 0.38 2.10 1.26 0.48 4.49 2.65 4.59 5.76 0.92 11.00 1.80 2.10 14.70 Vasista 0.48 5.01 0.63 0.49 2.49 1.47 0.40 4.17 3.05 4.04 6.76 1.31 10.10 1.73 2.07 16.10 Godavari Gautami 0.76 4.57 0.91 0.57 1.85 2.60 0.54 3.28 3.44 5.12 6.32 0.75 7.76 1.84 1.32 8.53 Godavari Avg. 0.51 4.76 0.72 0.45 2.40 1.57 0.42 3.91 3.09 4.34 5.91 0.89 10.20 1.73 1.97 14.30 Sci. Syst. Earth J. Multi Lithology Terrain (MLT)- Mahanadi 0.94 4.95 0.88 0.74 1.03 2.74 0.97 5.10 2.91 5.34 5.55 2.03 5.96 2.02 1.06 6.76 dominated sediments Brahmani 0.67 4.92 1.01 0.39 3.20 1.94 0.31 2.31 2.91 4.48 4.31 2.11 11.20 2.03 1.50 11.10 Baitarani 0.90 4.68 1.12 0.54 1.24 2.38 0.81 4.20 2.65 5.91 7.18 1.73 7.48 2.10 1.11 6.66 Subharnarekha 0.91 4.43 1.07 0.46 1.44 2.35 0.70 3.37 2.57 5.97 6.91 1.80 7.44 1.74 1.09 6.97 Haldia 1.04 4.81 0.96 0.57 0.93 2.31 1.08 4.97 2.22 6.02 7.03 1.36 5.41 1.62 0.96 5.62 Hooghly 0.97 5.11 0.93 0.62 1.07 2.24 0.94 4.95 2.32 5.41 6.96 1.26 6.19 1.92 1.03 6.63

Avg. 0.90 4.83 1.00 0.54 1.41 2.34 0.71 3.82 2.60 5.52 6.18 1.64 7.10 1.92 1.11 7.13 (2021) 130:60 Reference sediments UCC 0.72 13.80 0.95 0.44 1.71 2.24 0.58 11.20 3.11 4.95 3.84 0.26 9.14 1.95 1.52 9.81 PAAS 0.92 13.20 0.73 0.50 1.58 2.80 0.63 9.13 3.05 4.85 4.71 0.80 7.53 2.00 1.39 9.60 PAAS: Post Archean average Australian Shale (Pourmand et al. 2012) and UCC: Upper Continental Crust (Rudnick and Gao 2003). J. Earth Syst. Sci. (2021) 130:60 Page 15 of 24 60

(McLennan and Taylor 1980; McLennan et al. 1993). CIA values are expected for their weathered products Similarly, much higher Rb/Sr ratio of river clays in tropical settings. The relatively low CIA values in (av. 1.15; table 5) than in UCC (0.26; Rudnick and DVT-sediments may be because the source rocks are Gao 2003) indicates strong depletion of Sr (McLen- younger in age and therefore weathered less time nan et al. 1993). Therefore, high Th/U and Rb/Sr than the older, pre-Cambrian rocks, which weath- ratios imply strong inCuence of chemical weathering ered longer. It is also possible that quick removal of on source rocks. weathered material from the weathering zones dur- ing the seasonal, heavy SW monsoon rains resulted in Chemical Index of Alteration (CIA): The CIA low CIA values and high smectite in DVT sediments. has been used to quantify weathering intensity due Positive correlation between Al O and TiO also to progressive alteration of plagioclase and potas- 2 3 2 supports strong chemical weathering of source rocks sium feldspars to aluminous weathering products (Young and Nesbitt 1998). Relatively low CIA values (clay minerals). The major oxides of Al, Ca, Na and in the Subarnarekha, Haldia and Hoogly sediments K are used to compute CIA. The CIA is deBned by (table 2) may be due to strong physical weathering. the equation of Nesbitt and Young (1984) The low CIA values for the clays in the Brahmaputra and Jamuna rivers (51–63; average: 53; Bhuiyan CIA ¼ ½ŠAl2O3=ðÞAl2O3 þ CaO* þ Na2O þ K2O et al. 2011), the Ganges River (48–55; Singh 2010)  100; and Yamuna River system (*51 to 69; average *60; Dalai et al. 2002) indicate dominance of physical where all elements are in molecular proportions. weathering products. Hossain et al. (2017)suggested CaO* represents the amount of CaO in silicate that the CIA values range from 70 to 75 for shales and fractions. We do not have CO2 data for our anal- close to 100 for residual clays. yses and thus unable to correct Ca in carbonates to Plagioclase Index of Alteration (PIA): PIA is obtain CaO. The average CaO value in river sedi- a better index than CIA and widely used to ments (1.0%) was lower than in Na O (1.7%; 2 quantify the degree of weathering of plagioclase table 2). Bock et al. (1998) recommended to accept feldspar (Nesbitt and Young 1982; Fedo et al. the value of CaO, if CaO \ Na O. 2 1995, 1996; Hassan et al. 1999; Hofmann et al. Using the above equation, the CIA values of river 2003). The PIA is deBned by the equation: clays were in the range 69.6 to 86.7 (table 2). Several investigators reported high CIA values ([80) for PIA ¼ ½ŠðÞAl2O3ÀK2O =ðÞAl2O3 þ CaO* þ Na2OÀK2O intense chemical weathering, intermediate values  100; (80–60) for moderate weathering, low values (60–50) for low weathering and\50 for absence of weathering where all elements are in molecular proportions. on source rocks (Nesbitt and Young 1982; Hassan The PIA values of river clays (table 2) ranged from et al. 1999;Hofmannet al. 2003;Liuet al. 2011; 73 to 94 (av. 87). Following Fedo et al. (1995, 1996), Armstrong-Altrin et al. 2013; Madhavaraju 2015; the PIA value of 100 implies strong chemical weath- Madhavaraju et al. 2016, 2017, 2019, 2020). The plot ering related to the production of kaolinite and of major elements in the ternary diagram (A–CN–K gibbsite, while the value 50 implies unweathered (Al2O3–(CaO+Na2O)–K2O; Bgure 6A) indicate that plagioclase The plot of major elements in the ternary the samples plot parallel to the A–CN axis, with diagram (CaO–Na2O–(Al2O3–K2O); Bgure 6B) APT-sediments plot more towards A (Al2O3) apex indicate high degree of plagioclase weathering for and DVT-sediments slightly away from A apex and APT- and MLT-sediments and, low to moderate MLT-sediments plot between APT- and DVT-sedi- degree of plagioclase weathering for DVT-sediments. ments and close to PAAS. The average CIA value The PIA values of PAAS and WRAC also showed (79) and plot of CIA values in A–CN–K diagram high degree of plagioclase weathering. (Bgure 6A) indicate intermediate or moderate weathering, while high CIA values of APT sediments indicate an advanced stage of chemical weathering, 5.3 Trace element concentrations i.e., the extent of conversion of feldspar into clays. and associations High CIA values are in agreement with dominant P kaolinite in APT-sediments, supporting intense The high TE values in APT- and DVT-sedi- chemical weathering (Bgure 6A). Since volcanic ments (Bgure 4A) are due to very high concentra- rocks weather more easily than intrusive rocks, high tions of Cu, Zn and Pb, suggesting anthropogenic 60 Page 16 of 24 J. Earth Syst. Sci. (2021) 130:60

Figure 6. Ternary diagrams of (A) Chemical Index Alteration (CIA) (after Nesbitt and Young 1982), (B) Plagioclase Index of Alteration (after Fedo et al. 1995) and (C) maBc diagram of A–CNK–FM (Al2O3–(Cao+Na2O+K2O)–(Fe2O3+MgO)) (after Nesbitt and Young 1989, 1996). pollution of these metals. The mean enrichment range ‘significant pollution’ and Pb in ‘moderate factor (mEF) of trace elements with reference to pollution’ in APT-sediments and, Cu and Zn are in PAAS (Bgure 4B) shows that Cu and Zn are in the the range ‘moderate pollution’ in DVT-sediments J. Earth Syst. Sci. (2021) 130:60 Page 17 of 24 60

(Bgure 4B). The mEF of all other trace metals are (table 4) suggest significant contribution from in the rangeP ‘no or minimum pollution’. The very Deccan basalts. high TE corresponds to medium rivers Strong correlation of Ba with Al2O3 (r = 0.83) (Bgure 4A) implying that the sediments from and lack of correlation between Ba and K2O(r = medium rivers are polluted, maybe because the 0.08) suggest that Ba is associated with clays sediments are less dispersed. The Cu, Zn and Pb (Taylor 1965). Similarly, the correlation of Ga with are moderately correlated with each other (r = 0.56 Al2O3 (Bgure 5), Sc and V (table 4) suggest that to 0.85; table 4). Moreover, the linear correlations Ga is associated with clays (Roser et al. 2000) and of Cu and Zn with Fe2O3 and, Zn and Pb with transition metals. The large-ion lithophile elements P2O5 and, Pb with both Al2O3 (Bgure 5) and Fe2O3 (LILEs) such as Rb and Cs are linearly correlated (table 4) suggest that these metals are associated with SiO2 (r = [0.80) preserving their original with phosphate minerals and also as adsorbed magmatic signature. Th is associated with clays components on Al- and Fe-oxyhydroxides with and heavy minerals (Condie 2005). The average Th some contribution from parent rocks. A geochem- content (12.67 lm/g) is intermediate between ical study, using sequential extraction method, on UCC (10.1 lm/g) and PAAS (14.6 lm/g) values. heavy metals in the river sediments of Moreover, Th is well correlated with Al, Ga, Rb, (Hejabi and Basavarajappa 2013) indicated that Nb, Cs and SiO2 (table 4). These suggest that the Cu, Zn and Pb were to some extent derived alumino-silicate is the major carrier phase for Th, from multisource anthropogenic inputs besides compared to heavy minerals. geochemical background contributions. Silva et al. High-Beld strength elements (HFSEs: Zr, Nb, Hf, (2014) reported enrichment of Cu, Cr and Zn and Y, Ta), in general are immobile and reCect the positive correlation of Cu and Zn with CaCO3 in provenance composition. Heavy minerals such as the oAshore sediments of the Cauvery delta and zircon, rutile and tourmaline usually contain high suggested the role of carbonatesP in precipitating Zr, Th and Nb. The average Zr, Hf and Nb con- these metals. Very low TE in several river sedi- tents of river sediments are much lower than in ments (Bgure 4A) indicates most of the TE are lost UCC and PAAS (table 3). The Zr and Hf are cor- during chemical weathering. The Mahanadi, relatedP with each other and also with Al, Ti, Sc, V, Brahmani, Baitarani and Nagavali drain through Ga, HREE and other HFSEs (table 4). These mineral deposits of oxides andP sulBdes, andP their suggest that Zr is more associated with clays sediments exhibit very low TE but high REE derived from maBc rocks and Ti-minerals like rutile (Bgure 4A). This implies that the trace elements and ilmenite, rather than with mineral zircon. are stripped away from mineral depositsP and lost Other HFSEs, such as Nb and Y are also correlated during chemical weathering but REE corre- with Al2O3 (Bgure 5) and, Ta is moderately cor- sponds to the mineralP content of the sediments.P related with SiO2 (table 4). Since HFSEs in sedi- Similarly, high TE associated with low REE ments are lower than in UCC and PAAS (Bgure 2; in the Cauvery, Ponnaiyar and Palar rivers table 3) and derive mainly from felsic sources (Bgure 4A) is due to the enrichment of TE by the (Rahman and Suzuki 2007), we suggest that the human-induced activity and anthropogenic input. sediment contribution is more from maBc sources Higher concentrations of Fe, Mg, Sc, V, Co, Cr than from felsic sources. and Ni than in UCC and PAAS (Bgure 2; tables 2–3), strong correlations among Sc, V and Ti, positive correlation of Cr, Co and Ni with 5.4 Dominance of maBc vs. felsic source Fe2O3 (r = 0.6 to 0.8; table 4), strong to moderate components in river sediments correlation of V, Cr and Ni with Al2O3 (table 4) suggest that the transition elements are hosted in The maBc diagram of A–CNK–FM (Al2O3–(CaO+ Fe and Ti oxides and/or clays transported from Na2O+K2O)–(Fe2O3+MgO)) has been used to maBc rocks. The Sc, Co and Cr preferentially understand the eAect of maBc component on sedi- concentrate in the maBc rocks. Cr and Ni behave ment chemistry (Nesbitt and Young 1989). In this similarly in river sediments and present as Cr, Ni- diagram almost all samples from APT- and MLT- bearing detrital phases and/or adsorbed compo- dominated river clays fall in the range between nents on clay minerals (Badawy et al. 2019). High feldspar and smectite composition, while DVT Cr and Ni contents in DVT-sediments (table 3) samples oriented towards FM apex (Bgure 6C). and their fair correlations with TiO2 and Fe2O3 This implies that the DVT sediments contain 60 Page 18 of 24 J. Earth Syst. Sci. (2021) 130:60 considerable proportion of maBc components (Fe and Mg oxides), likely from basaltic source rocks, abundant in the upper reaches of the Krishna and Godavari rivers. The Al, Fe, Ti and Zr remain immobile in sedi- mentary processes and their ratios can be used to infer source rock composition (Hayashi et al. 1997). The Al2O3 vs. TiO2 plot suggests felsic provenance for APT- and MLT-sediments, while DVT-sedi- ments fall in the intermediate zone between felsic and maBc provenances (Bgure 7A). Relatively higher Fe, Mg and Ti than in UCC and PAAS (table 2), and samples spread more towards high Fe2O3+MgO in the TiO2 vs. Fe2O3+MgO plot (Bgure 7B) indicate higher contribution of maBc component to the sediments. Higher TiO2 and Fe2O3 in DVT-sediments (table 2) than in APT- and MLT-sediments suggests that they are weathered largely from basalts, which contain abundant Ti (ilmenite, rutile) and Fe (magnetite) minerals. The plot of TiO2 vs. Zr indicates the samples fall in the intermediate zone between felsic and maBc provenances (Bgure 7C). More samples falling in the felsic provenance in the Al2O3–TiO2 diagram (Bgure 7A) and intermediate provenance in the TiO2–Zr diagram (Bgure 7C) seem contra- dictory. Al resides mostly in feldspars and Ti in maBc and heavy minerals. It is likely that immobile elements like Al and Fe are more enriched in the sediments during chemical weathering and there- fore samples plot more towards high Al in the Al2O3 vs. TiO2 diagram. Moreover, the clay frac- tion was investigated in this study and this fraction usually contains low heavy mineral content. The Sc, Co and Cr are compatible and prefer- entially concentrated in maBc rocks, whereas Th and La, being incompatible are enriched in felsic rocks. Relative contributions from felsic vs. maBc sources can be deduced from their concentrations and/or ratios, such as Cr/Th, Co/Th, La/Sc, Th/ Sc, Zr/Sc, La/Th (e.g., Taylor and McLennan 1985; Tran et al. 2003; Raza et al. 2010; Fatima and Khan 2012; Wang et al. 2012; Madhavaraju et al. 2016, 2017; Hossain et al. 2017). The low Th/Sc ratios (av. 0.67; range: 0.32–1.04) compared to UCC (0.78) and PAAS (0.91) probably reCect more contribution from maBc component. Taylor and McLennan (1985) suggested that the Th/Sc ratio is Figure 7. Element-based provenance discrimination diagrams

\1 for Archaean and maBc rocks, *1 for Post- of river clays. (A) Al2O3 vs. TiO2; (B) Fe2O3+MgO vs. TiO2

Archaean UCC and higher for granitic rocks. Cul- (after Bhatia 1983); (C) Zr vs. TiO2. Discrimination lines for lers (2000) suggested that the Th/Sc ratio is in the the felsic, intermediate and maBc provenances in (A) and range from 0.05 to 0.4 for Bne-grained sediments (C) are adopted from Bhatia (1983) and Absar and Sreenivas derived from basic sources and, 0.64–18.1 from (2015). J. Earth Syst. Sci. (2021) 130:60 Page 19 of 24 60

Figure 8. Source rock discrimination based on scatter plots and ternary diagrams of trace metals: Scatter plots of (A) Th vs. Sc (adopted from Cullers 2002), (B) Sc vs. Th/Sc (adopted from Nagarajan et al. 2017); (C) ratio–ratio plots of Th/Yb vs. La/Th, (D) Cr/V vs. Y/Ni (adopted from Mclennan et al. 1993 and Mongelli et al. 2006). (E–F) Ternary diagrams for La–Sc–Th and V–Ni–Th910 (adopted from Bracciali et al. 2007). silicic sources. The plot of Th vs. Sc (Bgure 8A) values (table 3) and much lower Zr/Sc ratios (av. indicates that the samples fall in the intermediate 4.3; range: 2.36–5.11; table 5) than in UCC (13.97) zone between felsic and maBc provenance, while and PAAS (13.1) may suggest more of maBc source the plot of Sc vs. Th/Sc (Bgure 8B) shows the component (Bhattacharya et al. 2012). Strong sediment composition between granite and basalts. correlation of La and Sc (r = 0.77; p \0.001) and Higher ratios of Cr/Th (11), Co/Th (av. 2.16), Sc/ La/Sc ratio (av. 2.04) of river clays close to UCC Th (1.64) and lower La/Sc (2.0) compared to that (2.2) and PAAS (2.38) indicate more contribution in UCC and PAAS (table 5) indicate substantial from maBc component. McLennan et al. (1993) contribution from maBc rocks. It has been sug- suggested high La/Sc ratio ([8.0) for felsic com- gested that the maBc rocks will have high ratios of ponent, and low La/Sc ratio (1–2) for maBc com- Cr/Th, Co/Th, Sc/Th and Sc/La and for felsic ponent. Cullers (2000) suggested low La/Sc ratio rocks, they are low. The near uniform and low Zr (0.4–1.1) for the Bne sediments from basic sources 60 Page 20 of 24 J. Earth Syst. Sci. (2021) 130:60 and high La/SC ratio (0.7–27.7) for sediments from ternary diagram (Bgure 8F) shows that the sam- silicic sources. Maharana et al. (2018) reported low ples fall between maBc and felsic sources, with La/Sc (1.4–2.1) and Th/Sc (0.5–0.7) ratios for MLT sediments more towards felsic source. As one suspended sediments from peninsular rivers and can see from Bgures 7 and 8, the trace element attributed their source to less evolved maBc source. composition showed relatively wide variations in High Th/Yb ratios and high La/Th ratios indicate APT- and DVT-sediments than in MLT sediments, more felsic character (McLennan et al. 1980). The which fall close to one another. Though the river La/Th ratio in river clays ranges from 5.56 to 2.2, clays, in general, exhibit intermediate provenance with an average ratio of 3.28 (table 5). Taylor and between felsic and maBc sources, the APT- and McLennan (1985) suggested low La/Th ratio DVT-clays are probably dominated by maBc ([4.0) for maBc source rocks. The ratio–ratio plot components and MLT-clays are dominated by of Th/Yb vs. La/Th (Bgure 8C) shows low Th/Yb felsic component. values with an average value (4.48) close to gran- odiorite. The sediments are probably mixed type 6. Conclusions with distinct maBc signature in APT-sediment (av. La/Th = 4.22; Table 5). Borges et al. (2008) The mineralogy and, major and trace element reported La/Th, Th/Yb, Th/Co and Zr/Co ratios geochemistry of the clay fraction of the sediments for the sediments of the rivers draining the eastern in 15 rivers and a freshwater lake indicate the Tibetan Plateau and Russia far east and reported following: low La/Th (av. 2.2) and high Th/Yb (av. 8.0), Th/ Co (av. 5.0) and Zr/Co (av. 29.0) ratios, indicating • The order of abundance of clay minerals in the felsic character for those in Salween river sedi- APT-, DVT and MLT-dominated sediments ments and, high La/Th (4.7) and low Th/Yb (3.5) reCects the inCuence of source rock geology and and Th/Co (av. 0.5) and Zr/Co (av. 12.0) ratios chemical weathering. indicating maBc character for those in Lena River. • Marked depletion of Ca, Na, K and Sr and The Cr/Ni ratio of river sediments ranges from enrichment of Al, Fe and Ti indicate the 1.71 to 1.92 with an average value of 1.79 (table 5). inCuence of chemical weathering on sediments. Garver et al. (1996) suggested that the low Cr/Ni • The CIA and PIA values high Rb/Sr and U/Th ratios (1.3–1.5) are characteristic of ultrabasic ratios indicate moderate to intense chemical rocks and high ratios (2–7) imply sources other weathering on source rocks. than basic/ultramaBc rocks and probably con- • Very high Cu, Zn and Pb contents in APT- and trolled by heavy minerals and Cr-minerals. The DVT indicate anthropogenic pollution in the average Cr/V and Y/Ni ratios of the river sedi- sediments of a few rivers. ments are 0.99 and 0.49, respectively. McLennan • Relatively high concentrations of transition et al. (1993) suggested high Cr/V ([8) and low metals and lower concentrations of high-Beld Y/Ni (\0.5) ratios for maBc/ultramaBc rock sour- strength elements indicate more contribution ces and, Cr/V ratio \1 and variable Y/Ni ratios, from maBc component. deBning a by Cat trend towards higher Y/Ni ([0.5) • The ratio–ratio plots and ternary diagrams for for UCC and calc-alkaline volcanic rocks. Bhat- several trace metals, in general, suggest sedi- tacharya et al. (2012) reported Cr/V value 1.28 for ment provenance between maBc and felsic granitic rocks, 7.8 for maBc rocks and significantly sources. high Cr/V and Y/Ni values ([4.5) for ultramaBc rocks. In the plot Cr/V vs. Y/Ni (Bgure 8D), the low Y/Ni and Cr/V ratios indicate the mixture of Acknowledgements granitic and volcanic rocks and sediment composition close to basalts. Authors sincerely thank the Vice Chancellor, The plot of La–Th–Sc values in the ternary Vignan University for encouragement and Direc- diagram (Bgure 8E) shows that the samples fall tor, CSIR-NGRI for extending analytical facilities. between granite and basalt and in the La–Sc line, Shaik Saibabu thanks the University for research with APT-sediments close to granodiorite, DVT fellowship. This work is carried out under the sediments more towards Sc and, MLT-sediments Emeritus Scientist Project of V P Rao. We thank falling between APT- and DVT-sediments. Simi- Dr Pratima Kessarkar for helping us with clay larly, the plot of V, Ni and Th910 values in the mineralogy, using X-ray diAractometer. J. Earth Syst. Sci. (2021) 130:60 Page 21 of 24 60

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