Record of tide-wave influence on the coal-bearing Permian Barakar Formation,Raniganj Basin, India

摘要

The coal-bearing Barakar Formation (early Permian) of the Raniganj Gondwana basin was previously interpreted as continental fluvial sediments with little evidence for tide-wave influences. The present contribution details the sedimentary attributes of marginal marine tidal and wave activities preserved within an overall braided-meandering fluvial depositional setting from the Barakar Formation. Tide-dominated sedimentary features include (i) tidal-bundle sequences showing sandstone foresets with mud drapes, (ii) periodic variation in foreset thickness, (iii) lateral and vertical accretion of cross-strata bundles with a downcurrent change to sigmoidal cross-strata, (iv) mutually opposite cross-strata sets separated by sub-horizontal, plane laminated sandstone-mudstone, and (v) alternate sand- and mud-dominated rhythmites. Draping of the tidal stratifications by wavy laminated muddy-siltstone suggests immediate invasion by low energy, silt/mud depositing waves that helped preserve the tidal features during subsequent reworking. Open marine storm wave activities are evident from hummocky cross-stratification and various types of wave ripples, preserved separately within coarse- to fine-grained sandstone in the middle-upper part of the succession. Recognition of tide-storm influenced marine sedimentation significantly changes the existing paleogeo-graphic model to a fluvial-estuarine depositional environment.