T207 Rocky Mountains III: Post-Laramide Uplift and Erosion of the Rocky Mountains and Colorado Plateau (Posters)
CENOZOIC TECTONICS OF THE BLACK HILLS, SOUTH DAKOTA: DEFORMATION OF A UNIQUE WHITE RIVER GROUP (ORELLAN) LAKE DEPOSIT AND OTHER REGIONAL EVIDENCE
Paper number: T207-15
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM
Authors
Abstract
Other indications of post-Oligocene uplift of the Black Hills region include normal faulting in the Badlands area to the southeast, and in the Short Pine Hills and Slim Buttes of northwestern SD. Offsets in these regions are generally less than a few hundred feet within the White River and Arikaree Groups. Documented timing constraints based on offsets in Tertiary strata indicate episodes of deformation during late Oligocene (31ma-25ma) and early Miocene (20ma) in Nebraska. Changes in base level are represented in the mid-Tertiary sedimentary record in areas surrounding the Black Hills. The Eocene Chadron Formation (White River Group) and the Oligocene Gering Formation and Miocene Upper Harrison Beds (Arikaree Group) contain coarse clastics, providing evidence of erosion of westward upland source areas. Uplift and erosion on a regional scale is likely related to a continuum of Laramide deformation of this northern Rocky Mountain region, creating an overall flexure with broad-beam style upwarping of the crust.