Permian - Triassic boundary in the Peninsula

Abstract

The boundary between the Permian and Triassic systems is still a matter of controversy. The traditional view is that the base of the Otoceras beds marks the base of the Triassic and hence the top of the Permian. Though the basal Triassic is known, the topmost marine Permian is still to be recorded; this gap is not even represented by the non-marine sequence of rocks either in extra-peninsular India or in Salt Range, Pakistan.

In peninsular India, there is an undoubted non-marine (continuous) succession of Upper Permian and Lower Triassic age and no marine beds or intercalations are known. Similarly, from the extra-peninsular India, no terrestrial elements are known from the Upper Permian and Lower Triassic. Hence, the equivalence of the non-marine biozone to that of the marine is not known; only broad generalizations can be made.

The biota known from the non-marine Gondwana Sequence of Upper Permian and Lower Triassic are plants (mega as well microfloral elements), vertebrates and invertebrates are known from the Upper Permian but are so few in number, that these cannot be taken for discussion on Permian-Triassic boundary problems.

On reviewing the biota in the various peninsular basins, the Damodar Basin is considered significant for the problem of Permian and Triassic boundary. In the Raniganj Coalfield five sections, namely, Tatulakh, MAchkunda Jhor, Banspatelli, Nunia Nala and Nunia Khal have been studied extensively.

Summarizing, the following points are worth notice:

1. There was a peak development of the Glossopteris Flora in the upper part the Raniganj Formation. Normally, the peak development takes place just before the extinction. The complete extinction does not rule out the lingering of older forms.
2. The appearance of Lepidopteris and the small forms of Dicroidium is noted in the basal Panchet.
3. Glossopteris though became extinct at the lower altitudes has probably withdrawn to the higher altitudes, the climatic conditions of which were more akin the lower level. Dicroidium also was thriving simultaneously at higher altitudes at that time.
4. Higher up in the sequence but in the lower altitudes, Lystrosaurus and Estheriella
5. The miofloral zonations with respect to Raniganj and Panchet formations particularly with respect to Lystrosaurus zone, Estheriella Zone, Lepidopteris Zone are to be noted.

In the light of all the above considerations, the problem of the Permian and Triassic boundary is being reviewed.