Palynostratigraphy and palaeoenvironment of the Permian sediments in Mand Coalfield, Mahanadi Basin, Chhattisgarh, India

Abstract

Palynological investigation of 483.00 m deep subsurface Permian sediments of borehole MSK–1, in Sithra–Kurekela Block of Mand Coalfield, revealed four distinct palynoassemblage zones. These palynoassemblages belong to Lower and Upper Barakar (Early Permian), Barren Measures and Raniganj (Late Permian) palynofloras of Indian Gondwana. The oldest Palynoassemblage–I, (Scheuringipollenites barakarensis) recorded between 483.60–309.00 m depths, shows dominance of non–striate bisaccate pollen grains chiefly ― Scheuringipollenites followed by Faunipollenites in association with Indotriradites, Dentatispora, Verrucosispora and Microbaculispora related to Lower Barakar palynoflora. Palynoassemblage–II, (Faunipollenites varius) recorded between 303.40–139.40 m depths, showing the dominance of Faunipollenitesin association with Scheuringipollenites, Striatopodocarpites, Brevitriletes, Horriditriletes and Striamonosaccites, indicates Upper Barakar palynoflora. Palynoassemblage–III, (Densipollenites indicus) recorded between 135.55 to 92.50 m depths, showing the prominence of enveloping monosaccate pollen (Densipollenites) in association with Faunipollenites, Microfoveolatispora, Striatopodocarpites and Verticipollenites, indicates Barren Measures palynoflora. Palynoassemblage–IV, (Densipollenites magnicorpus) recorded between 90.90–27.00 m depths, is characterized by the dominance of striate bisaccate pollen taxa chiefly Striatopodocarpites and Faunipollenites along with Densipollenites, Navalesporites, Distriatites, Hamiapollenites, Crescentipollenites and Guttulapollenites indicating late Permian (Raniganj) age. Raniganj palynoflora has been demarcated in lithologically designated Barren Measures Formation. This is the first report of Late Permian (Raniganj) palynoflora from Sithra–Kurekela area of this coalfield. The age correlation also gets support from comparative studies with similar palynoassemblages known from Indian Gondwana. Palynofloral evidences indicate the prevalence of warm and humid conditions. Dominance of gymnosperms represented by glossopterids, conifers and cordaites along with low percentage of trilete spores (filicopsids and sphenopsids) suggests that the sediments were deposited under fresh to brackish water environment.