Sub-Surface Geology and Evolution of the Barind Tract, Bangladesh

The Barind Tract is an elevated Pleistocene Terraces (about 11-48 m amsl) in northwestern Bangladesh. The geoscientists thought that the tract may have been evolved due to tectonic upliftment and /or exists as an erosional geomorphic feature but nobody agrees the same opinion. This problem represents different questions with variable dimension in the groundwater problem in the area. The present paper has tried to unveiling the evolution processes with the help of sub-surface geology and provides necessary information about sustainable development of the area. To unveil the processes, Plio-Pleistocene and Holocene lithostratigraphy has been constructed by analyzing the existing borehole data. Lithofacies and geometric analyses have been done to delineate of paleochannel and other fluvial sub-environments to identify sedimentological domains and paleoenvironments of deposition. The interpretation reveals that abrupt and remarkable variations in thicknesses of different lithologic units are clearly correlated with the presence of basement controlled faults as well as lineaments. Displacement of lithologic units, undulating nature, higher thickness of Pleistocene Clay at subsided area and presence of Barind clay below the Recent alluvium in the subsided areas etc. indicates the structural control in the origin of the elevated Barind Tract. In most of the stratigraphic cross-sections a remarkable change in depth and thickness of lithologic units along the boundaries of the Pleistocene Barind Tract and Recent alluvium, and coincidence of the basement controlled faults and lineaments with the areas are clearly identified. Basement surface of the northwestern part of Bangladesh is also criss-crossed by a series of faults of different magnitude and orientation. A large number of horsts and grabens like structures occur within the basement of the area. The Bogra Shelf and Platform area exhibit remarkable dissimilarities in the sedimentary succession and their thickness. Some sedimentary groups and formations present in the Bogra Shelf area completely missing in platform area. All these features and evidences strongly support the structural origin of the Barind Tract rather than only geomorphic origin, during Quaternary block adjustment of different parts of the Bengal Basin moved up and down in response to the compensating the N-S and E-W compressional stress developed due to the Himalayan upliftment.