HR: 17:30h
AN: S12E-06    [PDF]
TI: Quaternary Faults and Basin-fill Sediments of the Las Vegas Basin, Southern Nevada
AU: * Taylor, W J
EM: wjt@unlv.nevada.edu
AF: Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010 United States
AU: Fossett, E
EM: efossett@hotmail.com
AF: Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010 United States
AU: Luke, B
EM: bluke@egr.unlv.edu
AF: Civil & Environmental Engineering, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4015 United States
AU: Snelson, C
EM: csnelson@unlv.edu
AF: Geoscience, University of Nevada Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4010 United States
AU: Rasmussen, T
EM: tiana@seismo.unr.edu
AF: Seismological Laboratory, University of Nevada, 1664 N. Virginia Street, Reno, NV 89557-0141 United States
AU: McCallen, D
EM: mccallen2@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234 United States
AU: Rodgers, A
EM: rodgers7@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550-9234 United States
AU: Louie, J
EM: louie@seismo.unr.edu
AF: Seismological Laboratory, University of Nevada, 1664 N. Virginia Street, Reno, NV 89557-0141 United States
AB: The N-S elongated extensional Las Vegas basin, southern Nevada, contains 100's of meters of Cenozoic basin-fill sediments that are cut by several Quaternary (Q) faults. These faults define or influence the basin geometry. The basin is generally an asymmetrical half graben defined by the W-dipping, Q Frenchman Mountain fault (FMF) along its E side and a series of smaller offset E-dipping faults to the W. The N terminus of the basin is controlled by the Las Vegas Valley shear zone, along which the majority of the offset occurred prior to the Q. Here, we asses the influence of the Q faults on the distribution of the sedimentary units. Well, exposure, seismic reflection and seismic refraction data show that sedimentary units of different grain sizes or seismic velocity dominate different parts of the basin. Sections dominated by coarse clastic deposits occupy a narrow area along the E side of the basin. Coarse clastic sediments are mixed with finer grained sediments in a broader area along the W side of the basin. Based on provenance and alluvial fan distribution, the coarse deposits along the E side of the basin appear to be trapped in close proximity to the W-dipping FMF. The coarse-grained deposits along the opposite, W side of the basin, are sourced from the nearby Spring Mountains. Because of the structural asymmetry of the basin, these sediments traveled farther from their source area than those on the E side. Some of these E-dipping faults influence the depth to Paleozoic bedrock and some faults form small sub-basins filled with finer grained sediments. Along a WNW trend near the center of the basin and near the present-day Las Vegas Wash, a change in the grain size distribution occurs up stratgraphic section: continuous clay layers are less common and coarse-grained deposits are more common. This difference may reflect a change from internal drainage early in the basin history to external drainage through the Las Vegas Wash in the latter history of the basin-fill sedimentation. This interpretation implies that the FMF was breached by a wash connected to the Colorado River drainage system during basin development. The basin fill deposits suggest an early history of alluvial fan dominated deposits showing internal drainage. That depositional system was followed by E- and W-sloping alluvial fans cut by a NW-trending external drainage system that probably flowed to the Colorado River. The greatest structural influence on sediment distribution was from the Q FMF on the E side of the basin and the dominantly Miocene Las Vegas Valley shear zone on the north, but the structural influence is reduced as Colorado River system and base level imposes on the basin up section.
DE: 7230 Seismicity and seismotectonics
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
DE: 8107 Continental neotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting