Provenance of the Cenozoic Bengal Basin sediments: Insights from U–Pb ages and Hf isotopes of detrital zircons

Abstract

The Bengal Basin is located in the foreland of the eastern Himalaya and records late Palaeocene to Pleistocene sedimentation. This makes the Bengal Basin an ideal place to study the evolution of the eastern Himalaya by provenance researches. Even though there have been several studies about its provenance, a consensus has not been reached about when the Himalayan and Gangdese‐derived detritus started to deposit in the eastern Himalayan foreland. Here, we study the provenance of Eocene to Pleistocene sedimentary successions of the Bengal Basin by detrital zircon U–Pb geochronology and Hf isotope analyses. Detrital zircon U–Pb age spectra show a predominant peak of ~470–580 Ma in all the samples. A peak at this time is prominent in sediments of the Tethyan Himalaya and Lesser Himalaya, which means the detritus eroded from Himalaya may have been deposited in the Bengal Basin after the late Palaeocene‐early Eocene, synchronous with detritus derived from the western and central Himalaya. Gangdese‐derived zircons were firstly recorded in the late Eocene Kopili Formation, and they were sporadic from the late Eocene to middle Miocene, which was probably due to the long distance between the Bengal Basin and the Lhasa Block, to the forebulge in the Lesser Himalayan Sequence, or to a wide tectonic separation at that time. The first influx of abundant Gangdese‐derived zircons occurred in the lower part of the Boka Bil Formation in the late Miocene (~10 Ma), which was probably caused either by the Brahmaputra River capturing the Yarlung Tsangpo River or by a much later terminal collision between India and Eurasia, or both.

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

“…Previous provenance studies in the Bengal Basin have reported several sets of detrital zircon U-Pb ages (Bracciali et al, 2015;Najman et al, 2008;Vadlamani et al, 2015;Yang et al, 2019). These age spectra show similar plots, and they suggest that the Himalayan orogen was the dominant source for the Bengal Basin sediments, but nevertheless there are disputes over when the first influx of Himalayan detritus was deposited in the Bengal Basin and which lithotectonic unit of the Himalayan orogen this first influx of detritus came from.…”

“…The Himalayan orogen has been considered as the major provenance of the Bengal Basin sediments, and detritus from the Gangdese Arc, the Indian Craton, the Indo-Burma Ranges, and the Shillong Plateau have made a small contribution to the Bengal Basin (Allen et al, 2008;Bracciali et al, 2015;Najman et al, 2008;Rahman et al, 2017;Yang et al, 2019). The Gangdese Arc is generated by the northward subduction of the Neo-Tethyan oceanic crust beneath the Lhasa Block during Mesozoic-Cenozoic (Ji, Wu, Chung, Li, & Liu, 2009).…”

“…Kernel density plots were generated using DensityPlotter software (Vermeesch, 2012). Detrital zircon U-Pb age data of the Bengal Basin are from Bracciali et al (2015) and Yang et al (2019). Data of Nepal foreland basin are from Baral, Ding, and Chamlagain (2017) and DeCelles et al (2004).…”

“…The formation and tectonic evolution of the Bengal Basin are closely associated with the Indo-Asian collision and the consequent development of the Himalayan orogen to the north and the Indo-Burma Ranges to the east (Alam et al, 2003;Curray, 2014;Mitchell, 1993;Yang et al, 2020). Previous studies based on detrital zircon geochronology, isotopic and bulk-rock geochemistry and sandstone petrography have reached a consensus that sedimentary rocks of the Bengal Basin were mainly derived from the Himalayan orogen and the Gangdese Arc with a minor contribution from the Indian Craton and the Indo-Burma Ranges (Bracciali, Najman, Parrish, Akhter, & Millar, 2015;Hossain, Roser, & Kimura, 2010;Najman et al, 2008Najman et al, , 2012Rahman, Xiao, McCann, & Ao, 2017;Uddin & Lundberg, 1999Yang et al, 2019;Yang et al, 2020). However, dispute still exists about which lithotectonic unit the first influx of Himalayan detritus came from and when they were deposited in the Bengal Basin, which are important for learning about the exhumation and denudation of the Himalayan orogen.…”

“…with an age of 38 Ma. Vadlamani, Wu, and Ji (2015) suggested that detritus from the Tethyan Himalayan Sequences and the Gangdese (Yang et al, 2019). Geochemical composition of Eocene to Pliocene sedimentary strata of the Bengal Basin can be used to discriminate these different Himalayan lithotectonic sources due to their different lithologic composition.…”