Geological nature of the Pokaran Boulder Bed: Palaeoenvironmental, palaeoclimatic and stratigraphic implications

The Pokaran Boulder Bed forms the basal lithofacies of Neoproterozoic-Cambr ian Marwar Supergroup. The boulder bed denotes specific sedimentary milieus and palaeoclimatic settings during the terminal Proterozoic period and occ urs in three distinct forms, viz., massive conglomerate, boulder spread and stratified conglomerate. These three forms of the boulder bed independentl y rest over the basement of Malani rhyolite and/or granite (> 698 Ma) and m ark an erosional unconformity at the base of the Neoproterozoic Marwar Supe rgroup (1000-540 Ma). It is suggested that the massive conglomerate is a pr oduct of weathering and disintegration of the basement rocks operating unde r scmi-arid to and conditions. The boulder spread is envisaged to be glacio genic, whereas the stratified conglomerate is a product of glaciofluvial ac tion. The stratigraphy of Marwar Supergroup is believed to be linked to the global Neoproterozoic glaciation. The base of Marwar Supergroup is interpr eted to be late Neoproterozoic (< 610 Ma). The occurrence in the same basin of climatically incompatible glaciogenic Pokaran Boulder Bed and Hanseran Evaporite vis-a-vis diamictite-evaporite fill is visualized to be the effec t of ice rings orbiting the earth. This has implications for stratigraphic correlation of such unique sequences.