New observations on Rajahmundry Traps of the Krishna-Godavari Basin

The Rajahmundry Traps of the Krishna Godavari Basin (K-G Basin) consist of three distinct basalt flows interbedded with two intertrappean sedimentary horizons, which in turn are underlain by the late Cretaceous fossiliferous limestone bed (infratrappean) and overlain by the Cenozoic Rajahmundry Formation (conglomerate/sandstone). Among the three, the lower flow is characterized by the presence of the physical volcanological features such as rootless cones, tumuli and dyke like forms along with single to multitier columnar and radial jointing. The middle and upper flows are simple, massive and vesicular and exhibit spheroidal weathering. Physical volcanological features and lithological attributes indicate that the lower flow was formed by an explosive volcanic activity in hydrous environment, followed by sub aerial eruption to form the middle and upper flows. The fossiliferous limestone bed is a representative horizon for the K-T boundary mass extinction caused due to intense volcanism. Intertrappean sediments exhibit weathered soil profiles (palaeosols) with limestone beds denoting a distinct time gap during various phases of lava eruption. Evaluation of the palaeogeographic scenario of the Krishna and Godavari Rivers does not provide any evidence for the existence of Cretaceous palaeovalley which would have provided pathway for lava transportation from the Deccan volcanic province of western India to the K-G Basin situated along the east coast. The present study opens up an alternative approach to explain the origin of basalt flows at Rajahmundry. In all probability the lavas could be intrabasinal. NW-SE and NESW faults or their intersection zones are probable pathways for lava eruption in the K-G Basin.