Palaeobiodiversity of the Lower Gondwana rocks in the Korba Coalfield, Chhattisgarh, India and observations on the genus Gangamopteris McCoy

Abstract

The Korba Coalfield occupies the south-central part of Son-Mahanadi Master basin and is situated in the Korba and Bilaspur districts of Chhattisgarh State. With five open cast mines (Gevra, Dipika, Manikpur, Kusmunda and Laxman) spreading over 530 sq. kms, this coalfield is the biggest coal producing unit in India, however it was never explored for megafloral studies. Extensive investigations were recently conducted in this coalfield to discover the fossiliferous beds in the Lower Gondwana deposits and as a result a large number of plant fossils were recovered from these collieries and their extension sites belonging to the Barakar Formation. The complete flora includes 38 taxa, representing 13 genera of the orders Equisetales, Cordaitales and Glossopteridales. The order Glossopteridales is highly diversified with 34 taxa and the genus Glossopteris with 22 species dominates the flora followed by the genera Vertebraria, Sakoarota (equisetalean stems), Cordaites, Dictyopteridium, scale leaves of fertile organs, Gangamopteris, Noeggerathiopsis, Euryphyllum and Rubidgea. This is the first ever collection and record of any mega plant fossil from this coalfield. The groups Lycopodiales, Sphenophyllales, Filicales, Ginkgoales, Cycadales and Coniferales are completely absent in this area which shows that the area might not be adequately cool and humid to facilitate the growth of these shade loving under-story plants. The genus Cordaites, which is a northern hemisphere taxon has been reported along with Glossopteris floral elements. An equisetalean genus Sakoarota, described from Madagascar has been reported for the first time from the Indian Gondwana. The genus Gangamopteris comprising six species, viz. G. cyclopteroides, G. cyclopteroides var. subauriculata, G. angustifolia, G. rajaensis, G. clarkeana and Gangamopteris sp. has been systematically described and discussed in this paper. The occurrence of Rubidgea, Euryphyllum, Noeggerathiopsis, Cordaites and Gangamopteris along with Glossopteris is indicative of the presence of Karharbari sediments (Early Permian=Lower Artinskian) in the lower part of the Barakar Formation exposed in the Gevra and Dipika collieries. The recovered plant assemblage indicates an Early Permian age, Lower Artinskian (Early Barakar) in the case of the Gevra and Dipika collieries and Upper Artinskian (Late Barakar) for the Manikpur, Kusmunda and Laxman collieries.