| The Ganges-Brahmaputra river system and the Bengal Fan represent Earth’s largest source-to-
sink system. Previous research demonstrated an increase in sediment delivery from the
Brahmaputra drainage basin to the Bengal Fan at the Plio-Pleistocene transition (2.6 Ma) based
on detrital zircon (DZ) age distributions from samples collected by IODP Expedition 354.
However, a detailed record from modern upstream sediment sources is lacking. We collected
modern river sediments from the Ganges River in northern India and analyzed them using DZ U-
Pb geochronology. Results provide a first-order model of sediment routing for the region. On the
other hand, quantitative comparison of age distributions from the Bengal Fan reveals a change in
sedimentation evident in the DZ age modes marking the sedimentation shift before and after.
Mixture modeling shows that the Ganges-derived sediments were dominant contributors before
3.9 Ma, but after that, these sources decreased in response to an increase in Brahmaputra-derived
sediment. Mixture modeling shows that Western Himalayan sources were dominant contributors
to the downstream reaches of the Ganges River during the Miocene previous to the change in
sedimentation. Collectively, results support hypotheses that invoke changes in sediment
provenance due to the expansion of the Yarlung-Brahmaputra river system and a progressive
increase in sediment sourcing in northern Lhasa, in addition to the onset of northern hemisphere
glaciation, both of which worked to increase the supply of Jurassic to Eocene DZ sourced from
the high elevation Gangdese Mountains.
Keywords: Ganges River, Himalayan-Tibetan tectonostratigraphic domains, change, sediment
source., quantitative, S2S. |