Scanning Electron Microscopy Study of the Quartz Overgrowths Within Neogene Sandstones of Bengal Basin, Bangladesh

Scanning electron microscopy study reveals successive stages of quartz overgrowth development during post depositional burial diagenesis in the Neogene sandstones of the Bengal Basin. The quartz overgrowths are most abundant and form major cement in Bhuban sandstones, are less common in Bokabil sandstones, While they are rare in Tipam sandstones. The growth of authigenic quartz proceeds from initial incipient and isolated quartz crystals to advance-terminated and euhedral quartz overgrowth completely engulfing the host detrital grain - the latter being formed by mergence of the incipient quartz units into a single unit. Mutual interlocking of adjacent quartz overgrowths of advance stage frequently produce sutured type contact that may be mistaken as pressure solution under optical petrographic studies. Development of quartz overgrowths is inhibited or retarded by the presence of thick authigenic chlorite rims around detrital grains. Two most important sources of quartz overgrowths are the pressure solution and the smectite to illite diagenesis in illite/smectite mixed layer clay mineral in the interbedded shales.