Possible greenschist metamorphism at the base of a 22-km sedimentary section, Bay of Bengal

Reinterpretation of seismic refraction and reflection data in the Bay of Bengal suggests a maximum thickness of sedimentary deposits of more than 22 km beneath the Bangladesh continental shelf. Revised correlation of an early Eocene unconformity—which is interpreted as representing the time of the India-Asia collision—subdivides these deposits into (1) a Cretaceous and Paleocene continental-rise section up to 6 km thick off the Indian margin and (2) 16 km of overlying Bengal Fan sediments and sedimentary rocks derived mainly from erosion of the region uplifted following the collision. Pressure and temperature conditions within the deeply buried continental rise are in the field of greenschist facies metamorphism. The resulting metasedimentary rocks would have velocities and densities compatible with the refraction data and isostatic calculations.