Geochemistry of Eocene to Pliocene strata of the Bengal Basin: Implications for provenance and erosion of the Himalaya

Abstract

The earliest record of Himalayan detritus in the Himalayan foreland and the erosion sequence of different lithotectonic units of the Himalaya are critical for reconstructing collision and crustal deformation of the orogenic belt. In this study, bulk-rock major, trace and rare earth elements of 19 fine-grained clastic sedimentary rock samples from Eocene to Pliocene strata of the Bengal Basin were examined to study their provenance and erosion of the Himalaya. Combining with previous detrital zircon age data from the Bengal Basin, Nepal foreland basin, and South Tibet, we suggest that detritus from the uplifted Tethyan Himalayan Sequences and the Gangdese Arc had not been carried into the Himalayan foreland at least before Late Miocene, and that the Bengal Basin was in a passive continental margin setting from Eocene to Early Miocene, receiving detritus from a felsic sedimentary rock source.The earliest Himalayan detritus recorded in the Eocene strata of Bengal Basin were probably derived from the antecedent sedimentary cover of the Greater Himalayan crystalline rocks. We assume that the lack of Cretaceous Gangdese detritus in the Himalayan foreland from Eocene to Middle Miocene is due to a geomorphic barrier between the Tethyan Himalaya and the Himalayan foreland. Detritus from the Greater Himalayan crystalline rocks were first recorded in the Middle-Late Miocene Boka Bil Formation of the Bengal Basin, which is consistent with the uplift and exhumation time of the Greater Himalayan Sequences.