Quartz grain surface features and mineralogy of sediments in the Sundarbans Forest site, Bangladesh: Constraints on the depositional environment and provenance

An investigation on medium to coarse-grained quartz grains (QG) recovered from a ~ 100-m drilled core section of the Sundarbans Forest site in the southwestern Bangladesh was carried out to infer the source and depositional environment. Thirty-six microtextures were identified from 200 QG using a scanning electron microscopy (SEM). The QG surface features are categorized into mechanical (number of features n = 25), chemical (n = 5), and combined mechanical and chemical (n = 6), which provide invaluable insights on the transport mechanism, provenance, and depositional environment. Microtextures of mechanical origin include parallel striations, straight steps, crescentic percussion marks, conchoidal fractures, arcuate steps, fresh polished surfaces, V-shaped marks, broken edges, abrasion fatigue, and bulbous and meandering edges, which are more common in QG and ascribed to high-energy eolian and fluvial transports. The abundant chemical features such as crystalline overgrowth, silica globules, scaling, silica pellicle, and silica flower are omnipresent on QG surfaces, demonstrating a subaqueous diagenetic environment. Fracture plates/planes, high relief, elongated depressions, adhering particles, chatter marks, and oriented etch pits are common in the QG, suggesting a subaqueous nearshore marine environment. There is a high abundance of quartz (Si), feldspar (Na and K), titanite (Ti), and zircon (Zr) in the core sediments, indicating their derivation from felsic source rocks.