Purana Sedimentation in Parts of the Godavari Valley

Study of the type area (Warangal District) of the Purana Super-Group in the Godavari Valley has led to the following picture of the Purana sedimentation.

Archaean crystallines dominated by granite acted as the provenance which was situated on the western side of the basin of sedimentation. Rock fragments having identical petrographic characters as those of some of the neighbouring Archaean crystallines were met with in the basal conglomerates and arkoses.

The derivation of the material was chiefly by mechanical disintegration, as indicated by dominance of fresh feldspars almost throughout the whole succession.

The transportational phase appears to be of moderate duration as suggested by the size and shape characteristics of the arenites and rudites.

The deposition took place in a marine epineritic environment. Evidences suggestive of such an environment include (a) presence of glauconite, (b) presence of bedded chert, (c) high magnesia content of the carbonates, (d) moderate to well sorted nature of the arenites and (e) secondary overgrowth of potash feldspar.

The lithologic association is characterised by arkose, carbonate and silty shale with subordinate orthoquartzite, a high value of total thickness, somewhat cyclic repetition of beds, moderate to good size-sorting and rounding, presence of considerable amount of red beds and by absence of distinct nonmarine beds of evaporites. These characteristics have been interpreted in terms of an unstable shelf association.