Petrographic Analysis of the Early Tertiary Subathu Formation rocks from the Kalakot Area, western Himalayan Foreland Basin, India

The megascopic and microscopic investigations of the Early Tertiary sediments of the Subathu Formation identified nine facies exhibiting cyclic arrangements in the Subathu Formation in Jammu area, with top of the formation showing tidal cyclicity in the form of alternating thick marl and thin limestone laminae. The abundance of pyrite framboids indicate strongly reducing conditions and their early diagenetic origin in the presence of adequate amounts of iron and sulphur. Small phosphate nodules probably formed just beneath the sediment-water interface. The high ash contents of carbonaceous shales and coals and euxinic conditions probably causing high sulphur content was due to the intermittent sedimentation. The benthic foraminiferal assemblage present in the lime-mudstone indicates a sub tidal bathymetry falling. The lime-mudstone was deposited in low-energy conditions in a turbid lagoon. The presence of mud cracks reveals shallowing of the basin and exposure of the sediments. The coarse-grained limestone with full of oyster shells indicates high-energy conditions. Mixed fresh and brackish water fauna indicate an estuary or outer tidal-flat, suggesting infrequent flooding during high wind-tides under prolonged exposure originated purple shale in supratidal zone.