PALEO-BIO-CLIMATOLOGICAL EVOLUTION AND BIOMARKER EVIDENCE FOR EARLY PERMIAN COAL DEPOSITS FROM BARAPUKURIA BASIN, NORTH-WESTERN BANGLADESH

Coal is indeed a rare commodity in Bangladesh and occurs only in sub-surface deposits in the northern part of the country at Barapukuria Basin, Dinajpur District. They located seven seams occurring between the depths of 130 m to 509 m below the surface. The average composite thickness of the seams is 51 m and seam VI is the thickest with a maximum thickness of 42 m (Bakr et al. 1996). The coal belongs to the Gondwana Supergroup and was deposited in an asymmetrical, faulted, half graben type of intracratonic basin. The sediments of the Gondwana Supergroup are sandwiched unconformably between the Precambrian basement complex and the Pliocene Dupitila Formation (Bakr et al. 1996, Khan 1991, Rahman 1993). Palynological investigation of bore-hole GDH-42, drilled at Barapukuria Basin, Dinajpur District, Bangladesh has for the first time indicated that the coal belongs to Barakar Formation of Early Permian age. The palynological assemblage comprises 27 genera belonging to trilete (4), monolete (1), monosaccate (6), striate bisaccate (8), non-striate bisaccate (4), polysaccate (2), monocolpate (1) and polyplicate (1) types. In the sample at 213.30m depth scheuringipollenites (27%) is most abundant, closely followed by Striatopodocarpites (25%) and Faunipollenites (20%). Other commonly occurring genera are Rhizomaspora (5%), Verticipollenites (4%), Corisaccites (3%) and Cuneatisporites (3%). Six monosaccate genera viz. Virkkipollenites, Parasaccites, Crucisaccites, Striomonosaccites, Barakarites and Divarisaccus are present and of them Parsaccites (2%), Divarisaccus (2%), Virkkipollenites (1%) and Barakarites (1%) are occasionally found in the count. The presence of good number of monosaccate genera at this level also strengthens its placement in the basal part of Barakar Formation. Palynological investigation of bore-hole GDH-42, drilled at Barapukuria Basin, Dinajpur District, Bangladesh, has for the first time indicated that the coal belongs to Barakar Formation of Early Permian age. Earlier known occurrences of coal from the same basin had placed the deposits in the Raniganj Formation.Facies modelling using maceral composition and palynological investigation suggest that an environment of forest swamps with alternating oxic–anoxic depositional conditions and under fluvio-lacustrine control, accompanied by the development of upper to lower deltaic plain conditions were prevailed during the Permian period. A terrestrial origin