Shelf storm flow dynamics: insight from the Mesoproterozoic Rampur Shale, central India

Abstract

The intracratonic rift-related Mesoproterozoic Rampur Shale in Kudri, India formed in the marine mid- and outer shelf domain. It bears a dominant imprint of shore-parallel, storm-driven flow, as predicted by oceanographers for modem shelves, and thus differs from other ancient storm deposits in the geological record. In the Rampur Shale, gutters are shore-parallel, while tool marks of various kinds are both shore-parallel and shore-normal, and show bipolarity in both directions. Hydrodynamic analysis and inter-relationships between the flow features suggest that the storm-driven flow was shore-parallel, dominantly unidirectional and steady initially, and that it became increasingly unsteady thereafter, while also becoming dominantly shore-normal during peak oscillation. As storm conditions waned, the gutters were filled by sediments under dominant wave influence. These Rampur data are consistent with observations made in modem seas and suggest that storm-driven flows, in general, have evolved in the same way over time, although their geological records may vary in details because of local constraints. (C) 2002 .