Coarse aeolianites: sand sheets and zibar–interzibar facies from the Mesoproterozoic Cuddapah Basin, India

Abstract

The Mesoproterozoic arenaceous successions of the Egalapenta Member, Cuddapah Basin, India are regionally developed and cover hundreds of square kilometers in and around the Krishna Gorge near the northern limit of the basin. They are dominated by aeolian sand sheets. Major facies attributes of the aeolian sandsheets are coarse-grained, low-relief bedforms with packages of wind-ripple laminae that constitute the zibar facies and medium- to coarse-grained sandstones with bundles of wind-ripple laminae that represent the interzibar deposits. Depending on the angle of climb and migration, the zibars and interzibars produced two depositional successions which include an amalgamated interzibar facies devoid of zibars and an interbedded zibar–interzibar facies. In addition, other attributes include low-angle cross-stratification, coarse-grained high-index ripple lamination, gently dipping irregular erosional surfaces and normal to inversely graded horizontal lamination. Fine- to medium-grained sandstones with high-angle cross-stratification represent the dune facies which are interstratified with the sandsheets. These are associated with calcareous mudstone–sandstones forming the sabkha facies and the laminated-, tabular cross-stratified, channelised fine- to coarse-grained sandstones representing the ephemeral fluvial deposits. Extensive outcrops of the Egalapenta Member bear strong signatures of aeolian dune–interdune facies. Sand sheets with zibar and interzibar deposits have been considered as marginal erg facies.