Petrography and geochemical characteristics of the sediments of the small River Hemavati, Southern India: Implications for provenance and weathering processes S. Sensarma a, ⁎ , V. Rajamani b , Jayant K. Tripathi b a Department of Geology, St. Anthony's College, Shillong, 793 001, India b National Facility for Geochemical Research, School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, 110 067, India Received 15 May 2007; received in revised form 14 January 2008; accepted 6 February 2008 Abstract Small rivers (≤ 100 km length) are likely to drain fewer rock types. Therefore, their solutes and sediments are good indicators of weathering environments typical of their basins and help constraining the nature of their source rocks. To understand this, the texture, mineralogy, major and trace element compositions of the sediments deposited by the River Hemavati, a northern upland tributary of the Cauvery River in southern India, are analyzed and discussed. The Hemavati sediments are overall of fine sand size (mean 2–3/), and have high concentrations of FeO (≤ 7 wt.%), TiO 2 (≤ 1.2 wt.%), Cr (≤ 350 ppm) and Ni (≤ 125 ppm). Major and trace element distribution call for a binary source for the sediments, and particularly point to contrasting climatic conditions of their provenances. The source areas in the upstream and downstream parts are exposed to sub-humid high relief and sub-arid low relief conditions, respectively, with distinct weathering characteristics. The CIA values (85–48) decrease from near the source to downstream, suggesting that the downstream rain-shadow part of the catchment suffered only minor chemical weathering. On the other hand, the REE distribution in the Hemavati sediments indicates contrasting lithologies in their provenance, and is not controlled by chemical weathering. On the basis of REE patterns, the sediments are divided into two compositional groups. The Type 1 sediments have a REE chemistry similar to the upper continental crust, and have been derived from the N 3.2 Ga composite peninsular gneisses occurring in the low- lying, semi-arid Mysore Plateau. The Type 2 sediments, however, have dominantly intermediate to mafic granulite contributions from the tectonically uplifted Western Ghats, weathered under sub-humid conditions. High concentrations of FeO, TiO 2 , Cr and Ni in the sediments suggest mafic-dominated source lithologies in the upper catchment, a feature also confirmed by field observations and petrographic study. © 2008 Elsevier B.V. All rights reserved. Keywords: Small rivers; Sediment; Geochemistry; Granulites; Gneisses; Southern India 1. Introduction The provenance of sediments includes all aspects of the drainage area, including source lithology, topographic relief, climate, transport energy, and hydrodynamics of the deposi- tional environment (e.g., Suttner, 1974; Basu, 1985; Johnsson, 1993), source lithology probably being the most important parameter (Oliva et al., 2003). Since the pioneering work of Garrels and Mackenzie (1971), the studies on source determina- tion and weathering processes of fluvial sediments based on geochemical methods include those of Borges and Huh (2007), Yang et al. (2002), Singh and Rajamani (2001), Gaillardet et al. (1999) and Cullers (1988). All the investigations are, however, focused on sediments of large rivers, mostly river bed and floodplain deposits. The study of large rivers drew more attention perhaps because (i) this provides better global information on sedimentary products and processes, integrating over large portions of the continental crust and varying climatic regions, and (ii) the fact that the 30 largest rivers of the world Available online at www.sciencedirect.com Sedimentary Geology 205 (2008) 111 – 125 www.elsevier.com/locate/sedgeo ⁎ Corresponding author. E-mail address: sensarma2002@yahoo.co.in (S. Sensarma). 0037-0738/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2008.02.001