Some Critical Field Observations on the Genesis and Stratigraphical Status of Pokaran Boulder Bed, Western Rajasthan

Based on the present detailed field observations on the physiographic setting and the lithological nature of the Pokran Boulder Bed (PBB), the authors conclude that it is a consolidated sedimentary bed, apparently in the nature of a glacial drift and not a tillite (like Talchir Formation of Gondwana Supergroup). The denuded upper surface of bouldery hummocks of the PBB on the ground invariably shows presence of loose boulders. The consolidated horizons lie buried within the hummocks, wherever thicker horizons of PBB are still preserved. The weathered top of the PBB, forming rolling, hummocky topography is reminiscent of continental glaciated areas. It is likely that the PBB represents remnant of the Well-Known global Precambrian (Vendian) Ice Age. It rests directly over the rhyolitic (Malani Rhyolite) basement.

The field observations also lead to the conclusion that the thick succession of sandstones of the Jodhpur Group (sometimes referred as 'Jodhpur sandstone') of Marwar Supergroup (MSG) only occasionally overlie the PBB and always with a marked unconformity, such as at Gaphur Khan ki Dhani and elsewhere. Clearly the PBB does not form part of the stratigraphy of Marwar Supergroup.