Advent and decline of the genus Glossopteris Brongniart in the Talcher Coalfield, Mahanadi Basin, Odisha, India

Abstract

The paper deals with the distribution of the genus Glossopteris and its fructifications in different Lower Gondwana formations of Talcher Coalfield of Odisha State. We demonstrate how this taxon appeared in this basin in the earliest Permian Talchir Formation and evolved and diversified through the Karharbari, Barakar, Barren Measures and lower part of Kamthi formations and ultimately vanished in the early Triassic in the upper part of Kamthi Formation. Amongst fifty one species of the genus Glossopteris recorded in all, one species each has been found in the Talchir and upper part of Kamthi formations and two, sixteen and forty seven species respectively are represented in Karharbari, Barakar and the lower part of Kamthi formations. Barren Measures Formation is devoid of any megaplant fossil. Similarly, out of twenty seven taxa of fertile organs belonging to the Glossopteris, two each are found in the Talchir and Barakar formations respectively, whereas twenty four are recorded from the lower part of Kamthi Formation. It is observed that Glossopteris is less diversified in Early Permian Karharbari Formation. However, it diversified and proliferated during Barakar and Late Permian lower part of Kamthi formations. Further, it shows declination in the Early Triassic upper part of Kamthi Formation. The study shows that the lower part of Kamthi Formation of Talcher Coalfield has the maximum diversity of Glossopteris (forty seven species) among all the known localities of this formation exposed in Indian Gondwana. The existence of meagre Glossopteris species against many Gangamopteris species in the needle shale confirms its association with the lower floral zone of Talchir Formation instead of the upper floral zone established by previous workers in this basin. Very low diversity of Glossopteris in the upper part of Kamthi Formation of Talcher Basin demonstrates that this palaeogeographic area would have experienced more arid conditions in early–middle Triassic period as compared to the mellowing climatic conditions prevailing during the same time period in the Panchet Formation (=Upper Kamthi Formation) of other areas of Son–Mahanadi Basin and the Damodar Basin.