Sedimentary facies of the Mesoproterozoic Srisailam Formation, Cuddapah basin, India: Implications for depositional environment and basin evolution

Sedimentary facies of the Mesoproterozoic (similar to 1400-1327 Ma) Srisailam Formation, exposed in the Srisailam sub-basin in the northern part of the Cuddapah basin, India, were analyzed. It helped in identifying eighteen different facies that can be grouped into six facies associations (FA-I to VI) - alluvial fan/fan-delta, delta top, delta front, lacustrine, fluvial, and aeolian. Hinterland geology, integrated palaeomagnetic, geochemical and sedimentological observations, and inferred palaeohydrological condition and palaeoclimate indicate more control of tectonic regime on the evolution of the facies architecture. Analysis of vertico-lateral disposition of the identified facies suggests that the deposition of the Srisailam sediments was initiated in a number of fault-controlled isolated depocenters (riftogenic lakes). However, those isolated lakes were deep enough to allow the evolution of lacustrine and deltaic depositional regimes. Basin-wide lacustrine environment was established during subsequent rifting and regional peak subsidence (rift-climax) of the basin floor. Cessation of further basin subsidence facilitated progradation of fluvial sediments. During low-stage fluvial sediments were reworked locally by aeolian processes, and during protracted dry periods, aeolian regimes were established over considerable stretches of the Srisailam sub-basin. It is likely that the Srisailam half-graben, adjacent to the Nallamalai Fold Belt, was developed due to lithospheric doming and limited crustal stretching during a mantle upwelling event responsible for lamproite (alkaline) magmatism in the northern part of the Cuddapah basin. The evolution of the Srisailam rift-basin may be compared with the Cenozoic rift system of Europe, where rift development took place simultaneously with the orogenic activity in the Alps and Pyrenees. The style of sedimentation in the Srisailam sub-basin may be considered as a variant of the Newark-type lacustrine facies complex, and the tripartite basin filling model of half-graben lacustrine complexes may possibly be extended to the Mesoproterozoic era.