Recumbent flame structures in the Lower Gondwana rocks of the Jharia Basin, India — a plausible origin

Abstract

A set of recumbent flame structures was found within a stacked channel complex belonging to the Raniganj Formation (Upper Permian) of the Lower Gondwana sediments of the Jharia Basin, India. The characteristics, particularly the relation with the erosional base of the overlying channel, the nature of the host layer and the geometry of the flame structures suggest that the horizontal gradient in pore fluid pressure, developed within the concealed layer, in response to the differential loading due to partial removal of the overburden during erosional incision, was responsible for triggering the static liquefaction of the sediments and the density-driven deformation of the sand–mud interface took place. Rounded excrescence of sand bulged downward into the underlying mud, which in turn was projected upward in the form of sharp flames following the trajectory of the pore fluid. Gradual bending of the flow trajectory towards the horizontal direction due to the presence of the overlying impermeable mud layer led to the development of the recumbent geometry of the flame structures.