Microtextures on quartz grain surfaces in the Bay of Bengal shoreline sediments, Bangladesh: Implications for sediment transport process and depositional environment

SEM and SEM-EDS studies of quartz grains in the shoreline sediments of the Bay of Bengal, Bangladesh were carried out to evaluate the mode of origin, paleoclimate, and depositional environment. A total of 38 microtexture types were identified, which were grouped into mechanical (23 features), mechanical/chemical (6 features), and chemical (9 features) origins. The morphology of quartz grains in the shorelines was dominantly subangular to sub-rounded in shape, which represents robust energy conditions, short residence time, low weathering, and nearby sediment provenance. The microtextures of mechanical origin such as straight and curved scratches, pits, broken edges, and crescent-shaped features were relatively abundant in the eastern site samples (Section-I) indicating high-energy, fluvial, and beach environments. The abundance of V-shaped marks and smooth surfaces of quartz grains indicate high-velocity storm conditions and/or high-energy impact events. The well-rounded outline, low relief with dish-shaped depressions, mechanically upturned plates, and arcuate steps were also observed on quartz grain surfaces. These features suggest that they were developed during an aeolian process in the beach berm environment. Etching, solution/irregular pits, and differential relief on quartz grains were somewhat elevated in the western site samples (Section-III), reflecting that these microtextures were associated with a subaqueous collision and humid climates in the fluvial and nearshore environments. Quartz grains in all sections represented microtextures of high energetic subaqueous environment as well as wind events. However, the absence of corrosion channels and high density of voids in the quartz grains revealed low degree of weathering.