Eolian-aqueous interactions in the development of a proterozoic sand sheet: Shikaoda Formation, Hosangabad, India

A 40-m-thick eolian sand sheet deposit characterizes the upper part of the Proterozoic Shikaoda Formation near Hosangabad. It sharply overlies shorefa ce deposits and comprises wind-ripple strata (similar to 50%), adhesion str ata (similar to 17%) and subaqueous strata (similar to 33%), Each stratific ation type defines stratal packages tens of centimeters thick and few meter s wide that are superposed upon one another in a nearly random fashion, The eolian facies is inferred to have been deposited in a low-gradient, sandy supratidal setting, The subaqueous deposits of the sand sheet also reflect a tide-affected, westward-opening coastal setting with an approximately nor th-south shoreline, Abundance of aqueous and adhesion strata coupled with t he absence of granule-rich coarse-grained layers, corrugated erosion surfac es and evaporites are the typical features of the Shikaoda eolian sand shee t. These features indicate that in spite of abundant sand supply from the c oastal sources and a net aggradational setting, repeated flooding and high surface moisture were the principal factors that inhibited dune-building pr ocesses and favored the growth of a flat-bedded eolian sand sheet in the Sh ikaoda Sandstone. Numerous subhorizontal, nearly flat bounding surfaces split the sand sheet succession into tabular sediment bodies 50-100 cm thick. Each of the boundi ng surfaces can be traced for a few tens of meters and can be correlated to an event of aqueous flooding. Vertical stacking of tabular sandstone bodie s implies that long-term sediment aggradation rate in the low-lying suprati dal region kept pace with that of basin subsidence. The sedimentological features of the Shikaoda sand sheet facies when compar ed with known modern and ancient sand-sheet deposits suggest that the Shika oda sand sheet developed independent of an erg in a comparatively wet clima tic setting. The sub-humid coastal eolian sedimentary system of Padre Islan d, Texas is probably the closest modern analogue of the Shikaoda sand-sheet facies.