Petrography and detrital zircon U-Ph dating of the Neogene sandstones in the Sylhet Trough, Bengal Basin (Bangladesh): Implications for Provenance

The Sylhet Trough is located in the northeastern part of the Indian plate, was developed as a part of a foreland basin (i.e., the Bengal Basin) in response to the uplift of the mountain belts of Himalaya and Indo-Burman Ranges and accommodated one of the thickest sedimentary piles. The present study aims to understand the possible provenance of the Neogene sediments in the trough based on results from detrital zircon U-Pb dating and detrital mode of sandstone petrography. Provenance analysis based on the modal composition of these Neogene sediments indicates a 'recycled orogen', suggesting significant reworking and recycling of the detrital sediments during the mountain building process. The detrital zircon age spectra of the Miocene Surma Group and Plio-Pleistone Dupitila sediments from the Sylhet Trough suggest that the sediments were mostly derived from three Himalayan litho-tectonic units; the Tethyan Himalaya, the Higher Himalaya and the Lesser Himalaya. However, younger detrital zircons (<200 Ma) from the Sylhet Trough are aged similar to 143-32 Ma, are identical to similar to 85-50 Ma Gangdese batholith, located north of the Himalayan belt. Such observation suggests that the sediments of the Sylhet Trough are sourced from the Late Cretaceous-Eocene Gangdese Trans Himalayan Batholith that includes the Bomi-Chayu, the Dianxi-Burma and the Northern Magmatic Belt (i.e., the Northern Lhasa block).