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Hiller, K., Head of Oil and Natural Gas Section Federal Institute for Geosciences and Natural Resources (BGR), Hannover, Federal Republic of Germany 1981–83, Head of German Geological Advisory Group with Petrobangla Dhaka, Bangladesh
Abstract The Surma Basin in the Northeast of Bangladesh is a proven Miocene Gasprovince and was structurally stamped by the contemporaneous interference of two major tectonic movements, ie. the emerging Shillong Massif in the North and the West-prograding mobile Indo-Burman Fold Belt. Basin relief, structural elements, growth and style as well as geochemical data with respect to hydrocarbons, source rocks and maturity are discussed. Related to the clear cut pre- and post-early Pliocene situation, change of migration pattern and coincidence between hydrocarbon generation, migration, accumulation and trap growth are analysed. Finally, the further prospectivity of the Surma Basin is commented upon. prospectivity of the Surma Basin is commented upon.
GEOLOGICAL SETTING The Surma Basin (Figure 1) is situated in the Northeastern-most part of Bangladesh and forms a portion of the late to post-geosynclinal Bengal Basin, subsiding from Oligocene or earlier times onwards (HOLTROP and KEIZER) with its peek of subsidence since Pliocene. The Surma Basin covers an area of roughly 2.5 million acres and is framed by the pre-Cambrian basement (PASCOE, WADIA) of the Shillong Massif and its skirting Barail Ranges in the North, by the Barail-Imphal Ridge in the East towards Assam, and in the South by the Tripura High. In the West, the Surma Basin ascends gradually towards the Eocene Hinge Zone, while passing into the Bengal Foredeep over a ridge at about 24 N latitude towards the Southwest (see Figure B-13, 2 at HOLTROP and KEIZER).
Based on seismic control, the Surma Basin cumulatively comprises about 57000 ft from post-Eocene Sylhet Limestone to recent clastic sediments (Figure 2, 7), this thickness being in fairly good concurrence with the maximum 55500 ft post-Eocene thick sediments as compared to the adjacent Assam area (DAS GUPTA); Sylhet Limestone and older (Poleocene, ?Cretaceous) sediments may account for another few thousand feet of sedimentary fill.