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

Abstract

Research Article| August 08, 2018 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; J.L. Pickering † 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA †Present address: Shell International Exploration and Production, Inc., Houston, Texas 77082, USA; jennifer.pickering@shell.com. Search for other works by this author on: GSW Google Scholar M.S. Diamond; M.S. Diamond 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar S.L. Goodbred; S.L. Goodbred 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar C. Grall; C. Grall 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar J.M. Martin; J.M. Martin 3Shell International Exploration and Production, Inc., Houston, Texas 77082, USA Search for other works by this author on: GSW Google Scholar L. Palamenghi; L. Palamenghi 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar C. Paola; C. Paola 5Department of Earth Sciences and St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar T. Schwenk; T. Schwenk 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar R.S. Sincavage; R.S. Sincavage 1Department of Earth and Environmental Science, Vanderbilt University, Nashville, Tennessee 37235, USA Search for other works by this author on: GSW Google Scholar V. Spieß V. Spieß 4Faculty of Geosciences, University of Bremen, Bremen 28359, Germany Search for other works by this author on: GSW Google Scholar GSA Bulletin (2019) 131 (1-2): 58–70. https://doi.org/10.1130/B31941.1 Article history received: 08 Oct 2017 rev-recd: 02 Mar 2018 accepted: 15 Jun 2018 first online: 08 Aug 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation 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; 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. GSA Bulletin 2018;; 131 (1-2): 58–70. doi: https://doi.org/10.1130/B31941.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search 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 boulder-sized 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 sea-level 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. You do not currently have access to this article.