Unroofing history of the eastern Himalaya and the Indo-Burman ranges; heavy-mineral study of Cenozoic sediments from the Bengal Basin, Bangladesh

Abstract Upper Eocene to Neogene fill of the Bengal basin provides an earlier unroofing history of the eastern Himalaya and Indo-Burman ranges than that provided by drilling of the Bengal fan, and analysis of heavy minerals in these sequences provides useful provenance constraints. Quartzose sandstones of the Eocene Kopili and Oligocene Barail Formations contain only 0.2% heavy minerals, comprising abundant opaque minerals and stable minerals such as tourmaline, garnet, rutile, and zircon. This assemblage suggests sediment sources dominated by low- to intermediate-grade metamorphic, silicic igneous, and metasedimentary rocks; the low heavy-mineral content and abundance of stable minerals suggest intense chemical weathering. These sediments may have been derived in part from incipient uplifts of the proto-Himalaya and/or the Indo-Burman ranges, but…