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Early to Late Pleistocene history of debris-flow fan evolution in western Death Valley (California) using cosmogenic 10Be and 26Al

Dühnforth, Miriam; Densmore, Alexander L.; Ivy-Ochs, Susan; Allen, Philip; Kubik, Peter W.

Early to Late Pleistocene history of debris-flow fan evolution in western Death Valley (California) using cosmogenic 10Be and 26Al Thumbnail


Authors

Miriam Dühnforth

Susan Ivy-Ochs

Philip Allen

Peter W. Kubik



Abstract

Debris-flow fans with depositional records over several 105 years may be useful archives for the understanding of fan construction by debris flows and post-depositional surface modification over long timescales. Reading these archives, however, requires that we establish the temporal and spatial pattern of debris-flow activity over time. We used a combination of geomorphic mapping of fan surface characteristics, digital topographic analysis, and cosmogenic radionuclide dating using 10Be and 26Al to study the evolution of the Warm Springs fan on the west side of southern Death Valley, California. The 10Be concentrations yield dates that vary from 989 ± 43 to 595 ± 17 ka on the proximal fan and between 369 ± 13 and 125 ± 5 ka on distal fan surfaces. The interpretation of these results as true depositional ages though is complicated by high inheritance with a minimum of 65 ka measured at the catchment outlet and of at least 125 ka at the distal fan. Results from the 26Al measurements suggest that most sample locations on the fan surfaces underwent simple exposure and were not affected by complex histories of burial and re-exposure. This implies that Warm Springs fan is a relatively stable landform that underwent several 105 years of fan aggradation before fan head incision caused abandonment of the proximal and central fan surfaces and deposition continued on a younger unit at the distal fan. We show that the primary depositional debris-flow morphology is eliminated over a time scale of less than 105 years, which prevents the delineation of individual debris flows as well as the precise reconstruction of lateral shifts in deposition as we find it on younger debris-flow fans. Secondary post-depositional processes control subsequent evolution of surface morphology with the dissection of planar surfaces while smoothing of convex-up interfluves between incised channels continues through time.

Citation

Dühnforth, M., Densmore, A. L., Ivy-Ochs, S., Allen, P., & Kubik, P. W. (2017). Early to Late Pleistocene history of debris-flow fan evolution in western Death Valley (California) using cosmogenic 10Be and 26Al. Geomorphology, 281, 53-65. https://doi.org/10.1016/j.geomorph.2016.12.020

Journal Article Type Article
Acceptance Date Dec 22, 2016
Online Publication Date Dec 24, 2016
Publication Date Mar 15, 2017
Deposit Date Apr 28, 2017
Publicly Available Date Mar 29, 2024
Journal Geomorphology
Print ISSN 0169-555X
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 281
Pages 53-65
DOI https://doi.org/10.1016/j.geomorph.2016.12.020

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