Late Permian species diversity of the genus Glossopteris in and around Himgir, Ib River Basin, Odisha, India, with a clue on palaeoclimate and palaeoenvironment

The Ib River Basin, situated in the south-eastern part of the Mahanadi Master Basin, has always been in focus for its record of well-diversified Lower Gondwana plant mega fossils. A good number of plant mega fossils has been collected from a newly constructed road section near Himgir Village, Sundargarh District, Ib River Basin, Odisha, India (21°45′ 47″ N Latitude and 83° 42′ 28″ E Longitude). The collection of plant fossils from this locality represents the dominance of highly diversified Glossopteris genus (46 taxa) during the Late Permian time (Lopingian epoch). Altogether 46 species of genus Glossopteris were reported from two fossiliferous layers of the same ferruginous red shale bed. The majority of broad mesh form Glossopteris species along with few narrow and medium mesh forms, petiolate leaves and Glossopteris with thick midrib were reported from the upper floral zone, while the lower floral zone was dominated by narrow and medium mesh form species and leaves with thin midrib. A marked floral change has been noticed in these two fossiliferous horizons of this section, demonstrating the existence of two different floral zones in the rocks of Lower Kamthi Formation. The upper floral zone is assigned to the Changhsingian age, while the lower floral zone is of Wuchiapingian age. The existence of Late Permian floras, the absence of typical Triassic flora ( Dicroidium flora) in the present fossil assemblage and the lithology of the area (covered by fossiliferous ferruginous red shale, ferruginous red sandstone, yellowish shale and pebbly conglomerate) demonstrate that the exposure belongs to the Lower Kamthi Formation. The presence of well-diversified fossil assemblage represents a thick swampy dense and deciduous forest of Glossopteris . The different morphological characteristics of plant fossils depict a warm, humid and temperate climate with intermittent rainfall and adequate light intensity at the time of deposition.