Integrated Seismic and Sequence Stratigraphic Analysis of the Northwestern Bengal Basin: Implications for Cretaceous to Late Miocene Depositional Evolution, Shelf‐Margin Dynamics and Hydrocarbon Prospectivity

ABSTRACT

An integrated seismic and sequence‐stratigraphic analysis of the northwestern Bengal Basin elucidates the tectono‐sedimentary evolution, shelf‐margin dynamics and hydrocarbon prospectivity along the hinge zone. Interpretation of ~2000 line‐km of 2D seismic profiles calibrated to the Singra‐1 and Mobarakpur‐1 wells identifies eight depositional sequences from the Pre‐Cretaceous to Late Miocene, recording a transition from syn‐rift continental to post‐rift deltaic systems. Quantitative shelf‐edge trajectory analysis reveals distinct phases of margin evolution: retrogradational stacking during the Eocene, strongly progradational growth in the Oligocene‐Miocene ( P _se / A _se > 10), and late aggradation in the Pliocene. The Oligocene forced‐regressive phase (SS‐5) represents maximum basinward progradation (~12 km) and the formation of the Mobarakpur Canyon System (MCS), a 16 km wide and 2.2 km deep erosional–depositional feature developed under moderate sea‐level fall and increased Himalayan sediment flux. Three higher‐order canyon‐fill sequences (MCS‐1 to MCS‐3) record successive incision, bypass and infill stages. Integration of seismic facies with lithostratigraphy indicates a shift from early clastic progradation, through transgressive carbonate deposition (Sylhet Limestone), to renewed clastic progradation dominated by the Barail and Surma groups. The canyon‐fill, slope‐fan and deltaic sandstones within these units represent potential reservoir targets, with candidate source rocks (Kopili and Sylhet Limestone) and seals (intraformational and regional marine shales) inferred by analogy with the adjacent Surma Basin. The recognized canyon‐wall pinch‐outs, slope‐fan onlaps and basin‐floor fans suggest new stratigraphic trap configurations that may refine the depositional and petroleum‐system framework of the Bengal Basin and inform future hydrocarbon exploration.