HR: 10:50h
AN: T22C-03    [Abstracts]
TI: Possible Basin and Range Strain in the Great Plains
AU: * Maher, H D
EM: harmon_maher@mail.unomaha.edu
AF: University of Nebraska at Omaha, Department of Geography and Geology, Omaha, NE 68182-0199 United States
AB: Coherent stress fields related to plate boundary conditions persist well into continental interiors. Van der Pluijm and others (1997) document low-level compressive strain associated with the Sevier and Appalachian orogenies that penetrated for at least several hundred kilometers into the craton, and up to 2000 km from the plate margin. Such low level strain may be easily overlooked. In this context, small scale normal faulting at the following localities is noted: 1) Toadstool Geologic Park, NW Nebraska, 2) Big Badlands, South Dakota, 3) Slim Buttes, NW South Dakota, 4) Agate Fossil Beds, W-central Nebraska, 5) Harlan County Reservoir, S-central Nebraska, 6) Spencer Dam, NE Nebraska, 7) Tuttle Creek Reservoir Spillway, NE Kansas, and 8) drainage along the Missouri River drainage in S-central South Dakota. In the Toadstool area over 160 individual faults within a 10 square mile area have been mapped. Fault throws at the various sites are typically less than 100 m. For sites 1, 2 and 3 evidence exists that indicates faulting was during the Late Oligocene to Miocene. There is also a suggestion of a pre-Ogalalla Group age for site 5. The age of faulting is poorly constrained at the other localities, but permissive of a Miocene age. Multiple fault orientations exist at most sites, but some commonalities exist between sites. Sites 1, 5, 6, 7 and 8 have a set with strike azimuths of 320-0^circ, while sites 1, 2, 4, and 7 have a set with 60-100^circ strikes. The normal faults at these sites are typically attributed to independent local phenomena (e.g. basement reactivation). A more parsimonious explanation to explore may be that these faults are: a) an expression of Basin and Range strain sporadically distributed throughout the Great Plains region, and/or are, b) compaction related structures influenced by Tertiary sediment loading and a Basin and Range stress regime. Better timing constraints, identification of more sites, and a more careful documentation and comparison of site kinematics will help to evaluate this proposal.
DE: 8100 TECTONOPHYSICS
DE: 8109 Continental tectonics: extensional (0905)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: Fall Meeting 2005