Dhosa Oolite - A Transgressive Condensation Horizon of Oxfordian Age in Kachchh, Western India

Abstract

Dhosa Oolite, 1-3 m in thickness, makes a distinctive lithostratigraphic unit in the Kachchh Basin, exhibiting a characteristic lithology of fossil-rich oolitic limestone, often nodular in appearance. It is characterized by the abundance of fossils, sometimes encrusted, absence of wave- or current-formed structures, dense burrowing, often recognizable as Thalassinoides burrows. The ammonoids of the different zones of Oxfordian age are commonly present; but often mixed up. These features suggest that the Dhosa Oolite is a transgressive condensation horizon representing the Oxfordian time span, related to the worldwide sea-level rise. The mixing of the fauna of various ammonite zones is probably a result of the combination of processes of slow rate of sedimentation, burrowing activity of the organisms, and storm events causing sediment reworking.