Vertebrate fossils have been discovered at several locations in the Bighorn Basin (Wyoming). The Virginia Museum of Natural History's (VMNH) digsite is located in the eastern part of the Bighorn Basin, in the Coyote Basin. Many scientists have worked within these basins trying to describe the stratigraphy. One question specifically asked is where the boundary between the Morrison Fm. (Jurassic) and the Cloverly Fm. (Cretaceous) lies. This new study attempted to show if the current method (Kvale, 1986) of determining the boundary is appropriate. The stratigraphy of the area was examined using Kvale, 1986, Ostrom, 1970, and Moberly, 1960's work in order to see which model was more robust. The fossils in the VMNH digsite were used to supplement the stratigraphic data in determining the age of specific beds. All of Ostrom's units were identified throughout the study area. There is some doubt as to whether the units would be acceptable outside of the Coyote Basin because of laterally discontinuity. Nevertheless, his description of units is satisfactory for the study area, and is more appropriate than other methods. The geologic age of the dinosaurs uncovered in the VMNH quarry is in agreement with the age determined stratigraphically. The VMNH site is below Ostrom's Unit II, which would place it in the Late Jurassic. The determination of the Jurassic/Cretaceous stratigraphic boundary has not been resolved. However, since the Pryor Conglomerate member of the Cloverly Fm. can be identified throughout this area, it is proposed as the Morrison Fm./Cloverly Fm. boundary. / Master of Science

This study provides new insights on the mechanisms that controlled the development of solution-enhanced fractures and suprastratal deformation associated with the Mississippian Madison Sequence IV evaporite paleokarst complex. Based on detailed field mapping utilizing LiDAR, GPS, and field observations, we document a paleostructural high (oriented 145º) associated with the Ancestral Rockies uplift within the study area. One hundred twenty-one sediment-filled, solution-enhanced fractures within the Seq. IV cave roof were mapped and characterized by their dominant fill type (Amsden or Madison) and vertical extent. Spatial analysis reveals minimum spacing of these features occurs in areas uplifted during the Late Paleozoic suggesting a link between paleostructural position and solution feature spacing. Shape analysis of these solution features also supports structural position during the Late Paleozoic acted as a dominant control on fracture morphology: (1) downward tapering and fully penetrative features concentrate in areas that experienced uplift; (2) upward tapering concentrate in areas that were undeformed. Mapping of Seq. IV cave roof strata demonstrates vertical collapse variability exceeds 22 m and fault intensity increases in areas of increased collapse. These findings have significant implications for prediction and characterization of solution-enhanced fractures and suprastratal deformation within evaporite paleokarst systems. / text

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