Permian–Triassic palynofloral transition in Sohagpur Coalfield, South Rewa Gondwana Basin, Madhya Pradesh, India

Abstract

A 1300 m thick sedimentary sequence in borehole SNB–1 around Jaisinghnagar area in the western part of the South Rewa Basin has been lithologically designated as the Pali Formation. However, palynological investigation reveals presence of three distinct palynoassemblage zones belonging to late Permian, early and late Triassic ages in ascending order. Palynoassemblage I (Striatopodocarpites magnificus–Crescentipollenites fuscus) recorded between a depth of 1213.40–1164.10 m showing dominance of striate bisaccate pollen taxa chiefly―Striatopodocarpites ovatus, Faunipollenites varius and Crescentipollenites fuscus in association with Alisporites ovalis, Lunatisporites pellucidus, Densipollenites indicus and Lahirites rarus is late Permian (Raniganj) in age. Palynoassemblage II (Lundbladispora densispinosa–Densoisporites playfordii) recorded between a depth of 1054.30–956.00 m and showing dominance of cavate/cingulate spores, like Lundbladispora microconata, Densoisporites complicatus along with Kraeuselisporites rallus, Lapposisporites lapposus, Playfordiaspora crenulata, Goubinispora indica, Klausipollenites schaubergeri, Limatulasporites fossulatus and Reduviasporonites chalastus indicates an early Triassic age. Palynoassemblage III (Aulisporites astigmosus–Falcisporites nuthallensis) recorded between a depth of 404.40–53.60 m and characterized by the dominance of Aulisporites astigmosus along with Falcisporites nuthallensis, Tikisporites balmei, Dubrajisporites unicus, Enzonalasporites densus, Leschikisporites aduncus, Lunatisporites rhaeticus, Lueckisporites virkkiae, Playfordiaspora vellata, Polycingulatisporites crenulatus, Cingulizonates indicus, Neoraistrickia taylori and Aratrisporites fischeri is equated with late Triassic (Supra–Panchet) age. The Permian–Triassic boundary is delineated at the contact of coal/shale bearing upper part of the Middle Member and lower part of the Upper Member of the Pali Formation (between 1164.10–1075.15 m depth). At the P/T boundary, the abrupt change of the palynoflora is marked by the disappearance of the striate bisaccate pollen grains and appearance of non–striate bisaccate grains in association with cingulate–cavate/zonate trilete spores. The Permian/Triassic palynofloras recorded in South Rewa Basin show close similarities with those of the uppermost Bainmedart Coal Measures (McKinnon Member) and Flagstone Bench Formation of east Antarctica.