4 - Permo-Triassic boundary on the Indian peninsula

Summary

Introduction

The Gondwana sequence of peninsular India is mainly terrestrial in nature and exhibits different patterns of sedimentation in each basin. This situation arose because deposition took place in linear, fault-bounded belts in which recurrent uplift or subsidence at varying rates created different tectonic regimes (Fig. 4.1). Consequently there are problems in interbasinal correlation. As a working system for correlation, however, various stratigraphic packages in a sequence are identified on the basis of lithic characters observed in discrete regions. These are then arrayed in a framework of greater spatial extent and this arrangement may be correlated precisely if biozones are available to use. However, biozones may or may not correspond with lithic units.

In recent years, a few widely spaced datum planes have been identified, along which biostratigraphic control matches well-delineated lithostratigraphic suites. The Permo-Triassic boundary has been one of the focal points for such an evaluation.

The conventional correlation of Gondwana formations is given in Fig. 4.2 (Datta & Mitra, 1982) and the Upper Permian–Lower Triassic interval is shown in greater detail in Fig. 4.3, which also includes information on general lithic characters. Some alterations based on recent data have been added.

The Upper Permian is characterized by diversification of the Glossopteris flora, which includes Glossopteris, Vertebraria, Raniganjia, Schizoneura, Tryzygia, Asansolia, and Damudopteris. The Lower Triassic flora records the advent of Dicroidium along with Lepidopteris, Podozamites, Macrotaenopteris, Pseudoctensis, and Pterophyllum. Palynologically, the Upper Permian assemblage is dominated by striate disaccate pollen (Striatopodocarpites, Faunipollenites, Crescentipollenites, Striatites, etc.) and qualifying taxa (Densipollenites, Gondisporites, Thymospora, Guttulapollenites, Indospora, etc.). On the other hand, the Lower Triassic assemblage is composed mainly of Klausipollenites, Lunatisporites, Lundbladispora, Densoisporites, Callumispora, Verrucosisporites, Playfordiaspora, Alisporites, and Satsangisaccites.