Geological Society of America

23 Megafloods, Paleohydrology, and Fluvial Processes on Earth and Beyond: In Recognition of the Scientific Contributions of Victor R. Baker (Posters)

Thursday, 19 May 2016
8:00 AM - 5:00 PM
Clearwater Room

ISOTOPE GEOCHEMISTRY OF SCABLAND FLOOD DEPOSITS

Paper number: 23-2
Program: Theme Sessions
Time: 8:00 AM – 5:00 PM

Authors

Joel Gombiner Presenting Author
Seattle, WA
Sidney Hemming
Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY
Ingrid Hendy
University of Michigan, Ann Arbor, MI
Julia G. Bryce
Dept. of Earth Sciences, Durham, NH
Janne Blichert-Toft
Ecole Normale Supérieure de Lyon, Lyon

Abstract

Argon and neodymium isotope geochemistry provide a means of tracking Scabland Flood sediment from source to sink. Analysis of sediment from locations along the flood path and from two marine sediment accumulation sites elucidate patterns of sediment mixing on land, subsequent unmixing at sea, and marine sediment transport pathways. Slackwater deposits in the Tucannon and Willamette valleys are characterized by old K/Ar ages of fine-grained sediment (240 to 360 Ma), younger ⁴⁰Ar/³⁹Ar ages of individual micas (mean ages from 70 to 150 Ma), and moderately negative ε_Ndvalues (-8.5 to -10.5). Similarly old K/Ar ages (210 to 390 Ma) and negative ε_Ndvalues (-8.5) link glacial outburst flood layers from sediment core MD02-2496 offshore Vancouver Island to the Scabland Floods. This isotopic link shows that Scabland Floods sent plumes of fine-grained sediment >400 km to the north in the Pacific Ocean. A high-resolution geochemical record from MD02-2496 identifies 44 Scabland Flood layers in the core. Sixteen radiocarbon dates spanning the glacial flood interval provide an absolute chronology, showing cyclical deposition with ~50- to 80-year periodicity between ~19.3 and ~14.9 ka. Additionally, ⁴⁰Ar/³⁹Ar age spectra of individual mica grains from a late Pleistocene Astoria Fan turbidite bed are similar to age spectra from Scabland Flood slackwater deposits, reinforcing the connection between this turbidite sequence and glacial outburst floods.

Geological Society of America Abstracts with Programs. Vol. 48, No. 6

doi: 10.1130/abs/2016RM-276243

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