Early Permian (Asselian) flora from the Talchir Formation, Son Basin, India: Biostratigraphical and palaeoenvironmental implications

Abstract

The Talchir Formation (Asselian–Sakmarian), the lowermost non-coaliferous sedimentary sequence of the Lower Gondwana Group is of utmost significance to understand evolution and proliferation of the Glossopteris Flora in the Gondwanan continents. After the Carboniferous deglaciation, a distinct new flora, i.e., the Glossopteris Flora appeared in the southern high palaeolatitudes during the onset of the Permian. This flora is widely distributed in the Permian successions of Peninsular India and sporadically distributed in extra Peninsular, i.e., Himalayan regions of India. Therefore, floral records obtained from the Talchir Formation are pertinent to understanding the evolution and radiation of the Glossopteris Flora. The present study assesses the early Permian floral diversity, palaeoenvironment, and palaeoclimate inferred from Talchir deposits of Chirmiri area, Son Basin, Chhattisgarh, India. This study considerably adds to our current understanding of the radiation of the early Glossopteris Flora in India immediately after the Permian–Carboniferous deglaciation. A rich macroflora has been recovered from reddish siltstone and grey shale units of two sections of the Talchir Formation and is the largest floral composite recovered so far, from this formation. The floral assemblage reveals dominance of Cordaitales (Noeggerathiopsis and Euryphyllum), Equisetales (Paracalamites) followed by Glossopteridales (Gangamopteris, Glossopteris, scale leaf and seed). The prolific occurrence of Cordaitales implies that this plant group was also flourishing on the raised grounds along with glossopterids during the early Permian. Typical Euryphyllum-Noeggerathiopsis-Gangamopteris assemblage suggests that studied strata is of ‘Upper Floristic zone’ of the Talchir equivalent to ‘Rikba beds’ and is Asselian in age. Furthermore, the occurrence of thick reddish colour siltstone units indicates localized ‘Red beds’ and shift in climate from cool humid to arid. The floral composite is corroborated with coeval flora of India and other Gondwana continents to understand palaeogeographical distribution of these plant groups. The floral composition suggests the existence of terrestrial marshy ecosystem with cooler climatic conditions.