Evidence of superimposition of storm waves on tidal currents in rocks from the Tithonian-Neocomian Umia Member, Kutch, India

Abstract

The general opinion is that hummocky cross-stratification is generated from superposition of storm waves on a unidirectional current. However, constraints on the type of the current field have not been clearly established. Sedimentary structures preserved in rocks of the Tithonian-Neocomian Umia Member, Kutch, India, indicate hummocky cross-stratification developed from storm wave interference with ebb-tide currents. Facies indicate repeated progradation of the shoreline and the increasingly important role of sand transport by currents in offshore direction. Stratigraphic analyses identify two major stages of shoreline progradation. Each is composed of distinctive shelf to shoreface transitions. In the tidally influenced shoreface parts of these transitions, the azimuths of units with nearly unidirectional hummocky cross-stratification are consistent with the direction of ebb-tidal cross-stratification, suggesting offshore sand transport by superposition of waves on an ebb-tidal current.