Gondwana Sequence of the northern Pranhita-Godavari Valley: its stratigraphy and vertebrate faunas

Abstract

The Gondwana Sequence in the northern part of the Pranhita-Godavari Valley consists of four formations of the Lower Gondwana and seven formations of the Upper Gondwana. The gross lithological characters and mappability are considered as the major criteria for delineating the formations. The name Kamthi Formation which has been used by different authors in different senses, is here used in the sense of Sengupta (1970). The rocks between the Barakar and this Kamthi are divided into four lithozones for limitations of mappability. Although some of these lithozones have earlier been designated as formations, at present not sufficient information is available to justify this. Only two breaks, both within the Upper Gondwana, are found to be present: there is no recognisable break between the Lower and the Upper Gondwana. A summary of this succession is presented in tabular form taking into account the words of earlier authors. The alternative views that are radically different from the one presented here are also discussed briefly. The usefulness of plant megafossils and fossil vertebrates in understanding the stratigraphy is discussed briefly and their role in determining the possible geological ages of some of the formations is mentioned.

The vertebrate fauna from a number of formations is listed. At least seven formations are fossiliferous as far as vertebrates are concerned. Of these, two belonging to the Triassic and one belonging to the Jurassic are quite well-documented. The other four are less well known, but serve as very useful time markers. All these vertebrate-bearing formations can be correlated with co-eval rocks elsewhere in the world. The difficulty of correlating continental deposits is realized and keeping this in view a tentative correlation is presented.