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Durham University

Department of Geography

Staff Profile

Publication details for Professor Alexander Densmore

Dühnforth, M., Densmore, A.L., Ivy-Ochs, S., Allen, P.A. & Kubik, P.W. Timing and patterns of debris flow deposition on Shepherd and Symmes Creek fans, Owens Valley, California, deduced from cosmogenic 10Be. Journal of Geophysical Research: Earth Surface. 2007;112:F03S15.

Author(s) from Durham

Abstract

Debris-flow fans on the western side of Owens Valley, California, show differences in
their depths of fan head incision, and thus preserve significantly different surface
records of sedimentation over glacial-interglacial cycles. We mapped fan lobes on two
fans (Symmes and Shepherd Creek) based on the geometry of the deposits using field
observations and high-resolution Airborne Laser Swath Mapping (ALSM) data, and
established an absolute fan lobe chronology by using cosmogenic radionuclide
exposure dating of large debris-flow boulders. While both fans and their associated
catchments were subject to similar tectonic and base level conditions, the Shepherd
Creek catchment was significantly glaciated while that of Symmes Creek experienced
only minor glaciation. Differences in the depth of fan head incision have led to
cosmogenic surface age chronologies that differ in the length of the preserved depositional records. Symmes Creek fan preserves evidence of exclusively Holocene
deposition with cosmogenic 10Be ages ranging from 8 to 3 ka. In contrast, the
Shepherd Creek fan surface was formed by late Pleistocene and Holocene debris-flow
activity, with major deposition between 86-74, 33-15, and 11-3 ka. These age
constraints on the depositional timing in Owens Valley show that debris-flow
deposition in Owens Valley occurred during both glacial and interglacial periods, but
may have been enhanced during marine isotope stages 4 and 2. The striking
differences in the surface record of debris-flow deposition on adjacent fans have
implications for the use of fan surfaces as paleoenvironmental recorders, and for the
preservation of debris-flow deposits in the stratigraphic record.