Palynostratigraphy of subsurface Upper Permian and Mesozoic Succession, Rakshitpur area, Raniganj Coalfield, West Bengal

In borehole RRK-1, Rakshitpur, Raniganj Coalfield in Damodar Basin, the lithounits identified in the interval of 115.00–610.00 m are in unconformable contact with each other. Tertiary sediments (115.00–179.70 m) that contain Callialasporites, Araucariacites, and Podocarpidites show continuity with the underlying supra-trappean strata (179.70–185.70 m). The two palynozones identified within the Rajmahal Formation (Foraminisporis asymmetricus 179.70–185.70 m and Foraminisporis wonthaggiensis 198.92–216.63 m) suggest Valanginian to Barremian age. The chocolate facies of the Panchet Formation (253.70–471.70 m) is devoid of palyniferous matter except at 260.55 m depth where the Foraminisporis wonthaggiensis assemblage of the younger horizon (inter-trappean) continues to occur. Downwards, at 261.20–262.40 m depth, Permian taxa Striatopodocarpites, Faunipollenites, and Densipollenites are abundant, but Arcuatipollenites pellucidus, Playfordiaspora cancellosa, and Goubinispora indica are rare. Besides, Callialasporites turbatus/C. microvelatus, first occurred at 262.40 m depth, are still present in the Panchet Formation. This kind of mixed population of palynomorphs is suggestive of disturbed zone in the deposite, and had happened at the on-set of volcanic activity in the study area, and re-defines the status of this part (253.70–262.40 m) to be infra-trappean. Occurrence of pebble bed at 262.40–262.80 m further supplements this hiatus. In the coal horizon (471.70–610.00 m), two identified palynoassemblages, Densipollenites magnicorpus and Gondisporites raniganjensis, indicate Late Permian age for this part of the Raniganj Formation. Abundant wood shreads, plant tissues in the chocolate facies of the Panchet Formation and at intervals in the Coal horizon suggest high-energy flow during sedimentation in the study area.