A super-thick (~22 km) sedimentary basin under the northern Bay of Bengal is proposed. The hypothesis is based on data from surface wave dispersion, seismic refraction, Sn attenuation, and geology. We present new high frequency Sn data which indicate a cold upper mantle beneath the Bay of Bengal. We propose that the oceanic crust in this region is in fact nearly normal, and that the sedimentary section is at least 6 km thicker than previously thought, with velocities at the base of the sediments having been increased to near 6.5 km/sec by high pressure metamorphism. Reinterpretation of the refraction data indicate a post India-Asia collision thickness of over 16 km. ¿ American Geophysical Union 1992