HR: 1340h
AN: OS33A-1000    [Abstracts]
TI: Clastic Sedimentation in Lake Tahoe as a Record of Submarine Landsliding and Seismic Shaking
AU: * Smith, S B
EM: sbsmith@unr.nevada.edu
AF: University of Nevada, Reno, Department of Geological Sciences/172, Reno, NV 89557- 0138, United States
AU: Karlin, R
EM: karlin@mines.unr.edu
AF: University of Nevada, Reno, Department of Geological Sciences/172, Reno, NV 89557- 0138, United States
AU: Seitz, G
EM: seitz3@mail.earthlink.net
AF: San Diego State University, Department of Geological Sciences/1020, San Diego, CA 92182, United States
AU: Kent, G
EM: gkent@ucsd.edu
AF: Scripps Institute of Oceanography, University of California, San Diego, 9500 Gilman, La Jolla, CA 92093, United States
AB: Episodic turbidites, densites, and underwater debrites found in Lake Tahoe gravity and piston cores comprise more than 50% of the Holocene sediment signal in the lake. These deposits can be correlated throughout the lake basin using AMS ¹⁴C dating, visual descriptions, stratigraphy, and other sediment analyses. For a given event, depositional pattern show a continuum of processes varying areally from debris flows to intermediate density flows to turbidity currents. Anomalous lithologies can be quantified by variations in anisotropy of magnetic susceptibility and grainsize measurements. Debrites occur in close proximity to source areas, densites are found in intermediate zones, and turbidites occur distal to the source areas. Turbidites may be further sub-classified into proximal and distal on the basis of whole core magnetic susceptibility values and grain-size within the turbidite base. Whole-core magnetic susceptibility, anisotropy of magnetic susceptibility, %opal (diatoms), and grain size measurements demonstrate that material within these episodic deposits consists of remobilized lacustrine sediment. Multiple source areas for an individual event are associated with basin margins and known areas of underwater landslides. The remobilization of lacustrine sediments, in conjunction with the locations of source areas and the presence of multiple source areas for individual events, eliminates stream input, delta collapse, and large flood events as potential causes of these episodic deposits. Submarine landslides were initiated at different elevations around the lake, suggesting that lake level change is not a causative factor. Traditional paleoseismic trenching and dating have not been done on the major faults within the basin, with the exception of the relatively minor Incline Village fault. Other fault systems outside the basin, such as the Mt. Rose and Genoa fault systems to the east, can also lead to strong shaking and potential landslides in the Tahoe basin. The timing of episodic deposits in Lake Tahoe is consistent with late Holocene records from the faults that have been trenched, which indicates that a seismic source is the driver for these types of deposits. The lacustrine sediment stratigraphy provides a complete Holocene strong shaking record for the region and extends the paleoseismic record far beyond that of traditional onshore methods.
DE: 7221 Paleoseismology (8036)
DE: 9345 Large bodies of water (e.g., lakes and inland seas) (0746)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting