TIDAL SANDWAVES AND RELATED STORM DEPOSITS IN THE TRANSGRESSIVE PROTOPROTEROZOIC CHAIBASA FORMATION, INDIA

Despite deformation and metamorphism the 2.3 Ga fine-grained silicicla stic Chaibasa Formation of eastern India locally retains an excellent record of sandwave migration under the influence of tides and storms w ithin a precursor sandstone facies in a largely subtidal setting and p rovides a rare opportunity to detect tidal periodicities. In the finer facies locally preserved, minor features provide glimpses of the depo sitional mechanisms and settings. The silt-dominated precursor heterol ithic: (silt-mud) facies contain numerous slides and slumps and was fo rmed on a relatively steep slope between the fairweather and storm wav e bases. The shale facies formed in a deeper setting beneath the wave base. Earthquakes occasionally have interrupted normal sedimentation a nd massflow products are present in all the facies, but with increasin g frequency within the finer facies. The sandstone facies units, which were emplaced during repeated lowstands, were first subjected to prog radation and subsequently drowned, in an overall transgression trend. (C) 1997 Elsevier Science B.V.