Depositional Architecture of a Neoproterozoic Clastic Shelf: Clue from the Owk Shale Formation, Kurnool Group, India

Abstract

Abstract Process-based facies and facies association analysis from the Neoproterozoic Owk Shale Formation, Kurnool Group allowed identification of seven facies types, grouped under four facies associations viz. (i) Greenish grey shale without sand interbed, (ii) Grey shale with thin fine sandstone/siltstone interbeds (iii) Grey shale interbedded with HCS-bearing sheet sandstone (iv) Coarsegrained sandstone interbedded with reddish brown shale. A shallow-marine setting ranging from outer shoreface to distal shelf set-up is interpreted. From facies succession analysis, a steady progradation is documented in course of Owk shale depositional history whereby distal shelf shale is successively overlain by the mid, inner shelf shale and finally by outer shoreface succession. Stacked decimeter-thick progradational depositional cycles (demarcated by mid to inner shelf transitions) constitute the progradational depositional motif. The Owk shelf was storm influenced, though from restriction of storm features within the inner shelf deposit, it is argued that no large-scale coastal set-up occurred at the Owk coastline in course of storm events. Instead, a low to moderate offshore-ward pressure gradient is inferred with coriolis effect that possibly hindered active sediment transport in the distal part of the Owk shelf.