Quaternary geology of the middle son valley, North Central India: Implications for prehistoric archaeology

Abstract

The late Quaternary alluvial history of the Son is very similar to that of the Nile, the Amazon and the Murray—Murrumbridgee. During the terminal Pleistocene cros-bedded sands were laid down as bedload by a highly seasonal, low-sinuosity stream. Early Holocene deposition of horizontally stratified silts and clays is the suspended load of regular overbank flooding by a less seasonal, more sinuous stream. The upward-fining sequence of the late Quaternary Son coincides with a global change in climate in the intertropical zone, from cold and dry in the terminal Pleistocene (⩽25,000 B.P.) to warm and wet in the Early Holocene. Two earlier alluvial formations are present in the middle Son valley. One, directly overlying eroded bedrock, comprises fanglomerates and clays of a mantled pediment sequence developed when river level was low and the climate dry. Lower Palaeolithic artifacts of upper Acheulian aspect are common near the fanglomerate—clay contact. The clay may be reworked aeolian dust. The other, younger formation is fluviatile. It represents an influx of allocthonous gravels under high flow regime during the Late Pleistocene (⩽75,000 B.P.). Middle Palaeolithic implements fashioned from the exotic gravels are found in situ in this formation produced by a return to wetter conditions. Earlier two-dimensional models which equate the north-central Indian Lower, Middle and Upper Palaeolithic, respectively with Gravels I, II and III of the Belan valley sequence now require amendment. The three-dimensional model proposed here to account for the Quaternary alluvial formations in the middle Son valley also has important implications for archaeological prospecting. Primary-context microlithic sites are generally confined to the outer margin of the early Holocene floodplain, along the piedmont zone of the Kaimur hills. Derived Middle Palaeolithic flakes and tools are scattered throughout the terminal Pleistocene cross-bedded sands of the Son; relatively undisturbed Middle Palaeolithic assemblages are stratified within the preceding alluvial formation.