Impact of glacial-lake paleofloods on valley development since glacial termination II: A conundrum of hydrology and scale for the lowstand Brahmaputra-Jamuna paleovalley system

J. L. Pickering, M. S. Diamond, S. L. Goodbred, C. Grall, J. M. Martin, L. Palamenghi, C. Paola, T. Schwenk, R. S. Sincavage, V. Spieß

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

To better define the base of the Brahmaputra River paleovalley, we analyzed an extensive borehole data set from the subaerial Bengal delta and a 255-km-long multichannel seismic survey along the modern river. The data reveal that the paleovalley floor is defined by a gravel unit containing bouldersized clasts up to 30 cm in diameter, deposited after ca. 30 ka but before ca. 9 ka. Paleohydrology during that time and the previous glacial maximum was characterized by a weak monsoon and reduced river discharge, both of which are inconsistent with large valley formation. However, our work indicates that glacial-lake outburst floods sourced from the Tibetan reaches of the Brahmaputra were routed through the lowstand valley, producing megaflood-scale discharge capable of transporting gravel and cannibalizing the valley margins. The timing of these glacial-lake outburst flood-driven discharge events was coincident with valley development and explains the anomalously large width of the valley and basal gravel surface. Despite the underfit scale of Brahmaputra discharge following the last glacial period, a strengthening monsoon and high sediment discharge in the early Holocene subsequently contributed to the efficient infilling of the massive paleovalley by the mid-Holocene. In a sequence stratigraphic context, this work provides an example of a major unconformity that developed late in the eustatic cycle (i.e., during early transgression rather than an earlier, protracted response to sealevel lowering) and in response to a perturbation originating in the catchment instead of changing accommodation in the basin. As such, it represents a geologically instantaneous time surface that can be used as a marker for stratigraphic correlation but one that is not in phase with eustatic sea-level fall.

Original languageEnglish (US)
Pages (from-to)58-70
Number of pages13
JournalBulletin of the Geological Society of America
Volume131
Issue number1-2
DOIs
StatePublished - Jan 1 2019

Bibliographical note

Funding Information:
This research was conducted through the BanglaPIRE project (banglapire.org) funded by a National Science Foundation (NSF) Partnerships for International Research and Education (PIRE) grant (NSF 0968354). Acquisition of seismic data was supported by BanglaPIRE and the German Research Foundation (DFG grant SCHW1551/3-1). We thank M. da Silva, N. Fekete, C. Ramos, B. Ngwana, S. Wenau, J. Haberkern, and H. Keil at Bremen Universität for their insights during processing and interpretation of the seismic reflection survey. Thanks go to S.H. Akhter and the many Dhaka University students and contractors who assisted with borehole drilling over the course of the PIRE project, to J.P. Mauldin for reference retrieval in Tokyo, and to J. Oster, the editors, S. Lahiri, and an anonymous reviewer for comments that improved the focus of this manuscript.

Funding Information:
This research was conducted through the BanglaPIRE project (banglapire.org) funded by a National Science Foundation (NSF) Partnerships for International Research and Education (PIRE) grant (NSF 0968354). Acquisition of seismic data was supported by BanglaPIRE and the German Research Foundation (DFG grant SCHW1551/3-1). We thank M. da Silva, N. Fekete, C. Ramos, B. Ngwana, S. Wenau, J. Haberkern, and H. Keil at Bremen Uni-versität for their insights during processing and interpretation of the seismic reflection survey. Thanks go to S.H. Akhter and the many Dhaka University students and contractors who assisted with borehole drilling over the course of the PIRE project, to J.P. Mauldin for reference retrieval in Tokyo, and to J. Oster, the editors, S. Lahiri, and an anonymous reviewer for comments that improved the focus of this manuscript.

Fingerprint

Dive into the research topics of 'Impact of glacial-lake paleofloods on valley development since glacial termination II: A conundrum of hydrology and scale for the lowstand Brahmaputra-Jamuna paleovalley system'. Together they form a unique fingerprint.

Cite this