GEOLOGY, June 2009 559 INTRODUCTION The Himalaya, a young orogenic belt, is undergoing widespread erosion resulting in the transfer of large amounts of particulate and dissolved materials to its foreland basin and to the Bay of Bengal (Galy and France-Lanord, 2001; Goodbred and Kuehl, 2000; Hay, 1998; Milliman and Syvitski, 1992; Sarin et al., 1989; Singh et al., 2005, 2008). The Ganga supplies ~500–1000 × 10 6 t of sediments annually to the Bay of Bengal (Galy and France-Lanord, 2001; Goodbred, 2003; Hay, 1998). These sediments are derived both from the Higher and Lesser Himalaya, the former dominating the contem- porary supply (Campbell et al., 2005; Foster and Carter, 2007; Singh et al., 2008). Most of these sediments are delivered during the south- west or summer monsoon (Goodbred, 2003), underscoring the significant role played by pre- cipitation and hence climate on sediment sup- ply. Therefore, spatial and temporal variations in the intensity of the monsoon and the extent of glacial cover over the Himalaya can affect the source of sediments to the Ganga and its deliv- ery (Goodbred, 2003). Studies of Bookhagen et al. (2005a), Clift et al. (2008), and Srivastava et al. (2008) demonstrated the influence of climate variations on provenance of sediments in the Himalaya. However, such studies on the Ganga Plain sediments are limited, though it is one of the largest continental sedimentary repositories that can serve as an excellent archive to inves- tigate the impact of climate (monsoon and/or glaciation) and/or tectonics on the erosion of the Himalaya over the time scales of 10 4 –10 5 a. The sediments of the Ganga Plain are more suited for studying variations in sediment provenance compared to sediments of the Bay of Bengal, as the latter is a more complex mixture of materi- als derived from multiple sources and different geological terrains (Ahmad et al., 2005; Colin et al., 1999; Liu et al., 2005). Such mixing of sediments can obscure provenance signatures. Furthermore, the sediments of the Ganga Plain are likely to provide better time resolution infor- mation, because they may respond faster to the cause of variations in sediment provenances (Goodbred, 2003). The Sr and Nd isotope com- positions of the Higher and Lesser Himalaya, the two major sources of sediments to the Ganga Plain, are quite distinct (Singh et al., 2008), and therefore can be used as tracers to track varia- tions in their relative proportion of sediments. The Sr and Nd isotope compositions of the silicate fraction of the sediments of the Bay of Bengal have been used to study variations in their provenance with time (Ahmad et al., 2005; Colin et al., 1999; France-Lanord et al., 1993; Liu et al., 2005). In this study, for the first time, Sr and Nd isotope compositions of the silicate fractions of sediments from a core in the Ganga Plain have been used to investigate temporal variations in the provenance of sediments and their causative factors. STUDY LOCATION AND SAMPLING This study was carried out on a 50-m-long core collected from the campus of the Indian Institute of Technology Kanpur (IITK) (Fig. 1). The core was subsampled along its entire length for chemical and isotope studies. The core site is in an interfluve setting located ~14 km south of the southern bank of the Ganga (Fig. 1). The only source of sediments to this site is the Himalaya, essentially brought by the Ganga River, which is formed by the confluence of two tributaries originating in the Higher Hima- laya, the Bhagirathi near Gangotri glacier and the Alaknanda in Mana Pass. They merge at Devprayag to form the Ganga, which debouches onto the plains at Haridwar (Fig. 1). The sedi- ments brought by the Ganga are therefore pri- marily sourced from the Higher and the Lesser Himalaya. The major lithologies in the Higher Himalaya are granite and gneiss, whereas the Lesser Himalaya consists of granite, gneiss, and sedimentary silicates and carbonates (Singh et al., 2008). The contemporary sediment budget of the Ganga in the plain is dominated by contri- butions from the Higher Himalaya (Campbell et al., 2005; Singh et al., 2008). The core analyzed in this study represents ~100 ka of floodplain deposition without any major break (Sinha et al., 2007). The chronol- ogy of this core is based on luminescence dating on etched K-feldspar (Sinha et al., 2007) and 14 C of carbonate nodules. The lithostraigraphy, facies, and chronology of the core are summa- rized in the GSA Data Repository. 1 RESULTS Nd and Sr isotope compositions of the IITK sediment samples are given in Table DR1 and Figure 2. Sr and Nd concentrations range from 49 to 225 and from 18 to 42 μg g –1 , respectively. Both Sr and Nd isotope compositions of the sedi- ments show significant variations with depth, but with opposite trends (Fig. 2); 87 Sr/ 86 Sr varies from 0.72701 to 0.76708, whereas the ε Nd (0) ranges from -14.4 to -16.6. The magnitude of these Geology, June 2009; v. 37; no. 6; p. 559–562; doi: 10.1130/G25425A.1; 3 figures; Data Repository item 2009129. © 2009 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or editing@geosociety.org. *E-mail: waliur@prl.res.in. Climate control on erosion distribution over the Himalaya during the past ~100 ka Waliur Rahaman 1* , Sunil K. Singh 1 , Rajiv Sinha 2 , and S.K. Tandon 3 1 Planetary and Geo-Sciences Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India 2 Engineering Geosciences Group, Indian Institute of Technology, Kanpur 208016, India 3 Department of Geology, University of Delhi, Delhi 110007, India ABSTRACT Sediment samples from a 50-m-long core representing ~100 ka of deposition, taken from the Ganga Plain on the campus of the Indian Institute of Technology, Kanpur, were analyzed for Sr and Nd isotope compositions. Both 87 Sr/ 86 Sr and ε Nd vary significantly with depth in the core, 0.72701–0.76708 and –14.4 to –16.6, respectively, within the range for silicate rocks of the Higher and the Lesser Himalaya. The variations in the isotope compositions reflect variations in the mixing proportion of sediments from the Higher and Lesser Himalaya, the two major sediment sources to the Ganga. The opposite trends in 87 Sr/ 86 Sr and ε Nd depth profiles further confirm this hypothesis. The isotope profiles exhibit two major excursions, ca. 20 ka and ca. 70 ka ago, coinciding with periods of precipitation minima and larger gla- cial cover. These excursions are the result of a decrease in the proportion of sediment from the Higher Himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation. This study highlights the significant influence of climate on erosion in the Himalaya. 1 GSA Data Repository item 2009129, description and chronology of the core; analytical methodology; data analyses; Sr, Nd concentrations and their iso- tope compositions of the sediments analyzed in this study; and 87 Sr/ 86 Sr and ε Nd end members of various litho-units contributing sediments to the Ganga sys- tem, is available online at www.geosociety.org/pubs/ ft2009.htm, or on request from editing@geosociety. org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.