JOURNAL OF QUATERNARY SCIENCE (1997) 12 (5) 391–403 CCC 0267-8179/97/050391–13$17.50  1997 by John Wiley & Sons, Ltd. Colluvial deposits in northwest Deccan, India: their significance in the interpretation of Late Quaternary history VEEN A U . JO SH I 1,* and VISHWAS S. KALE 2 1 Department of Geography, S.P. College, Pune 411 030, India 2 Department of Geography, University of Pune, Pune 411 007, India Joshi, V. U. and Kale, V. S. 1997. Colluvial deposits in northwest Deccan, India: their significance in the interpretation of Late Quaternary history. J. Quaternary Sci., Vol. 12, 391–403, ISSN 0267-8179 (No. of Figures: 12 No. of Tables: 4 No. of References: 12) Received 13 December 1995 Revised 1 March 1997 Accepted 1 March 1997 ABSTRACT: The Deccan Trap region exhibits an erosional landscape over a relatively ancient and stable Deccan shield. The Quaternary history of the area has been reconstructed on the basis of evidence from alluvial deposits occurring along the major rivers. However, recent investigations have revealed that evidence for geo-environmental change during the Quaternary Period is also contained in the colluvial deposits that occur in the foothill zones. The colluvial deposits, ranging in thickness from 1 to 10 m, invariably occupy gently inclined pediment slopes. The sediments are presently deeply dissected by gullies, and the process of colluviation has almost ceased. These deposits are best preserved in the semi-arid parts of the region. Detailed textural, geochemical and stratigraphical studies at four different sites reveal similar input processes, the slight variations being attributed to local environmental factors. Scanning electron microscopy studies of some grains indicate marginal contribution of aeolian processes at the time of deposition. Mesolithic artefacts and a few U/Th dates indicate that the colluviation took place during the Late Quaternary. The properties of the deposits suggest relatively high energy conditions as well as a remarkable variability in the intensity of hillslope processes. These properties are indicative of semi-arid conditions during which the regolith was stripped from devegetated hillslopes and was deposited on the pediments. A variety of evidence indicates that the period of colluviation coincided with arid conditions during the Last Glacial Maximum. The geomorphological and archaeological evidence also indicates that incision by gully systems was initiated during the early Holocene humid phase. The environmental conditions deduced for the study area are similar to those reported for other partsof the intertropical zone.  1997 by John Wiley & Sons, Ltd. KEYW ORDS: colluvial deposits; northwest Deccan, India; Late Quaternary; mesolithic Introduction The Deccan Trap region is a major physiographic feature of the Indian Deccan Peninsula. Despite its strong geological, geomorphological, climatic and biogeographical identity, it has not interested Quaternary geologists as much as the Himalayas and the Indo-Ganges plains. Unlike the extrapen- insular region, the Deccan Trap essentially exhibits an ero- sional landscape, over a relatively ancient block (Kale and Rajaguru, 1988). In contrast to the relatively detailed alluvial chronologies now available for the Upland Deccan rivers, colluvial deposits in the foothills of the western Upland Deccan Trap region are poorly understood. * Correspondence to: V. U. Joshi, Department of Geography, S.P. College, Pune 411 030, India. The main purpose of this paper is to present geomorphol- ogical, sedimentological and stratigraphical data and to reconstruct the nature of the processes operating on hillslopes during the Late Quaternary Period. The study area: an introduction The western Deccan Upland region is dominated by the fluvial dynamics of allochthonous rivers flowing from the humid Western Ghats to the drier east. The landscape is characterised by high-level erosional surfaces on the water- sheds, sometimes occupied by early Tertiary laterites. Resting on the pediments and valley floors are colluvial deposits, interfingered with black soil, and alluvial deposits (Kale and