Geomorphology, Structural Model and Active Tectonics of the Rashidpur Structure, Bengal Basin, Bangladesh

Abstract

 The Rashidpur Structure is a NS trending, moderate in amplitude and asymmetric anticline situated at the north western end of the Chittagong-Tripura Fold Belt (CTFB) and the southern edge of the Sylhet Trough. This structure and related fold belt of the Bengal Basin developed as a consequence of the oblique collision between Indian and Burmese Plates. The neotectonic activity is still continuing and shaping the geomorphology of this area. This study is conducted based on the geomorphological observation of the topo maps and satellite images, analysis of the seismic sections, and surface geology. Three geomorphic indices: Standard Sinuosity Index (SSI), Mountain Front Sinuosity (Smf), and Valley Floor Width-to-Height Ratio (Vf) have been analyzed to understand geomorphic implications and active tectonics of the Rashidpur Structure and its adjoining area. The SSI values for the two channels, one in east and another in west side of the structure, are close to 1, indicating sinuosity controlled by topographic factors in turn active tectonics. The Smf also indicates that the area is tectonically active. However, the high Vf value might be related to soft sediments exposed in the area and the signatures of the tectonic activities are eroded by the weathering processes, which implies that Vf values from soft sedimentary terrain may not be suitable for interpreting active tectonics if the area is subjected to intense weathering. A 3D schematic structural model, based mainly on the seismic sections and geomorphic observations, reveals thrusts controlled wedge-shape upliftment of the central part as a pop-up anticlinal structure. Finally, the findings not only heighten the understanding of geomorphic evolution and active tectonics of the Rashidpur Structure but also provide the overall tectonic and geomorphic evolution of the north-westernmost folded part of the CTFB.