News & Events

Noon seminar - Bengal Fan sediment archive: A record of tectonic, climatic and/or autogenic signals?

Monday, September 16, 2019, 12:15PM - 1:15PM

Speaker

Yani Najman

INSTAAR/CIRES

Location:

SEEC room S228 (Sievers Room)

Sediment records can preserve an archive of climatic changes, tectonics of their upland source region, and autogenic influences. Marine records have an advantage over continental records in that the depositional age dating is usually more precise, and the records more complete. However, their distal nature can result in less well-constrained interpretations, compared to histories obtained from continental sediment records located more proximal to their source.

IODP Expedition 354 drilled a 350 km east-west transect across the Neogene-Late Paleogene Bengal Fan in 2015. The Bengal Fan is fed predominantly by the Himalayan-draining Ganges and Brahmaputra Rivers and the main drivers affecting the sediment record on millennial timescales are Eastern Himalayan tectonics, the Asian monsoons and the onset of Northern Hemisphere Glaciation. Combined detrital geochronological (zircon U-Pb; Blum et al., Nature SR 2018) and thermochronological data (rutile U-Pb, white mica Ar-Ar, zircon fission track; Najman et al., GSAB 2019) from the Bengal Fan show that a period of rapid exhumation commenced some time between 3.5 and 5.5 Ma, broadly coincident with a significant increase in Transhimalayan material sourced from the India-Asia suture zone. The increase in Trans-Himalayan suture zone material may reflect the onset of Northern Hemisphere Glaciation, with preferential glacial erosion of the highland suture zone region. The proportion of suture zone material decreases again in the modern Brahmaputra sample; this decrease may reflect the change from glacial to interglacial conditions, at which time glacial erosion of the suture zone high ground played a less dominant role in sediment generation again. Alternatively, the increase in Trans-Himalayan suture zone material may reflect onset of rapid exhumation of the eastern Himalayan syntaxis from beneath its Trans-Himalayan carapace, consistent with some bedrock geological data (see various papers of Burg et al, although note that numerous papers of Zeitler et al suggest rapid exhumation of the syntaxis began closer to 10 Ma). Also needing to be taken into account is that: (1) preliminary 10Be dating from the Bengal Fan core (Lenard et al. 2018) indicates that erosion rates have remained steady over the Plio-Pleistocene period and (2) the western Bengal Fan was not cored and thus the potential effects of channel lobe switching cannot be well assessed.

Audience

Free and open to the public.