HR: 1340h
AN: T33C-1393    [Abstracts]
TI: Neogene Tectonics in the Saratoga Valley, Wyoming: Preliminary Results From a Study Combining ASTER, Landsat, and Aerial Imagery With Field Work and GIS
AU: * Smith, A M
EM: amsmith@uwyo.edu
AF: University of Wyoming, 1000 University Avenue Dept 3006, Laramie, WY 82071
AB: The Laramide orogeny created many compressional structures and basement-cored uplifts in Wyoming and Colorado, including the Medicine Bow Mountains and the Sierra Madre/ Park Range. Within the uplifted core, the Rio Grande Rift along the Front Range in Colorado has given rise to several extensional basins. The Saratoga Valley lies on the border between Wyoming and Colorado, in line with the Rio Grand Rift, and its structural origin as a Laramide compressional basin is generally assumed. However, extensional features have been reported, leaving the tectonic history of the Saratoga valley subject to question. This study aims to identify the timing, dip, and offset of normal faults and erosional surfaces to constrain the tectonic history of the Saratoga Valley. To determine whether the northwest trending valley is primarily a Laramide syncline or is, instead, a Neogene half-graben, linear features such as faults, ridges, and rivers were mapped from ASTER, Landsat, and aerial imagery and confirmed in the field. Two sets of linear features trend N30W and roughly N20E. Visible offset of linear features indicates right-lateral movement along a northwest trending fault located south of Encampment. Faulting of unknown offset is also present along the southeast front of the Sierra Madre Mountains. Location of sedimentary units in the field has constrained a pre-Miocene paleosol in the eastern valley and post-Miocene normal faulting within the Saratoga Valley. Combining these results with multiple data-types in a GIS format allows display of both detailed surface topography and subsurface geology. The imagery and fieldwork lead to the conclusion that a composite of several tectonic episodes have created northeast and northwest trending, cross-cutting faults, some of which are extensional. Nevertheless, to confidently describe the Saratoga Valley as a Neogene half-graben thousands of feet of offset along a normal fault or series of faults would be required. This amount of normal fault motion is not yet verified.
DE: 9604 Cenozoic
DE: 8010 Fractures and faults
DE: 8040 Remote sensing
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting