GENERATION AND DISTRIBUTION OF OVERPRESSURE IN MIOCENE STRATA IN THE EASTERN BENGAL BASIN
The average geothermal gradient in the eastern
The Bhuban sediments exhibit loss/gradual decrease of the illite/smectite mixed layer clay with increasing burial depth. Compaction–induced hydrofracturing and clay injection have been identified in several wells below the overpressure zone. Secondary porosity development is also a common occurrence in the Bengal basin as evidenced from feldspar dissolution.
40Ar/39Ar analysis of Miocene detrital muscovite grains provides cooling ages between ca 15 Ma and 554 Ma. The average cooling age and depth of the samples reveal that the estimated rate of deposition for the Miocene sequence was high.
Incomplete dewatering of fine–grained sediments, smectite dehydration, increase in pressure gradients toward the east, secondary porosity development, and high rates of sedimentation contributed toward the generation of overpressure in the eastern Bengal basin.