Lower Gondwana marine incursions: periods and pathways
Keywords:Lower Gondwana, Marine incursions, Acritarchs, Leiosphaerids, Continental facies (India)
Marine nature of sediments in the Talchir Formation and its equivalent horizons is well established by the occurrence of invertebrate faunas in Umaria, Manendragrah, Daltonganj, Rajhara, Ranjit Pebble Slate, Subansiri and Bap Boulder Bed. Most of these sediments also contain acritarchs, leiosphaerids and other palynofossils of marine origin in association with spores and pollen. The terrestrial palynofossil assemblage attributes an Early Permian age to these sequences, Leiosphaerids in the Karharbari and Barakar formations are, so far, known only in the Son Graben, indicating continuation of marginal marine environments. The discovery of phosphorite in the Barren Measures of Kelo River, Son Graben and palynofossils in these sediments confirm marine influence also in the Late Permian. Thus, the so far accepted model of predominantly continental facies for the Lower Gondwana stands challenged. It appears that during the Early Permian, almost all the low-lying embryonic basinal depressions experienced marine transgression from an eastern bay. To the west and northwest the network of marine pathways was connected with Arabian Sea and the Salt Range Sea. The evidences for continuation of marine transgression in the Middle and Late Permian of central India further demand a search for such signatures which could establish the remnant pathways to the heart of the peninsula. The marine leiosphaerid group of palynofossils can be purposefully utilized for Palaeoenvironmental reconstructions.