Permian palynofossils from the eastern Himalaya and their genetic relationship

Abstract

Palynofossils from the Permian sediments of the eastern Himalaya have been critically revised with reference to the marine invertebrate fossils contained at various levels. The Pebble Slate Member of the Rangit Formation having sporadic presence of Eurydesma (Biozone 1) has not yielded palynofossils but the younger Rilu Member has yielded a radial monosaccate rich assemblage (Biozone 2). The association of Leiosphaeridia in this assemblage in Barpathar area characteristically indicates marine influence. Biozone 3 characterised by Callumispora + Parasaccites association is present in marine Garu Formation in Siang and Subansiri, non-marine Bhareli Formation in Kameng and Lower Coal Measures in Darjeeling District. Scheuringipollenites rich Biozone 4 is characteristically associated with the marine invertebrates in Siang District (Garu Formation) only; elsewhere it occurs independently. Biozones 5 and 6 are characterized by the abundance of striate-disaccate pollen grains, the latter having Indospora, Thymospora and Crescentipollenites and represent Upper Barakar and Raniganj palynofloras, respectively.

                 The Permian sediments in eastern Himalaya are in lithological contrast with the intracratonic continental sediments of the Peninsula but their floristic resemblances are close. Biozones 1 and 2 are comparable to Talchir palynoflora which is related to glacio-marine model of sedimentation. During the deposition of sediments containing Biozone 3, comparable to Karharbari palynoflora, the marine environment seems to have existed continuously from Siang to eastern Kameng but westwards certain areas were under fresh water environment. Similarly, Biozone 4 is associated with marine fossils in Siang only but elsewhere it is typically associated with fluvial sediments. Thus an eastward regression of the sea is plausible during Karharbari and Lower Barakar times. During the younger palynofloras having Upper Barakar (Biozone 5) and Raniganj (Biozone 6) affinities the conditions of deposition appear to be exclusively fluvial in nature. It is clearly indicated that a larger segment of sedimentation in these marginal basins of eastern Himalayas has continued under marine environment while in peninsular India the intracratonic depositional basins were under fluvial environment during the same time span.