Interplay of Paleostructure, Sedimentation and Preservation of Middle Jurassic Rocks, Bighorn Basin, Wyoming

'The Middle Jurassic rocks of the Bighorn Basin are an ideal sequence in which to stucly the interaction of uplift and erosion, and their influences on marine deposition and preservation. 'The basin contains thousands of well penetrations and excellent outcrops. An unclerstancling of the interaction of paleOSCI-UC~U~~, secllmentation, and preservation, provicles might to the complex geologic history of this reglon. Rock units of interest to this stucly are the Gypsum Spring, Piper and lower Sundance formations. 'Shree significant uplift episodes are also evident in this sequence, representecl by the J,, J2 and J4 unconformities. The position and timing of these tectonic events resultecl in changes in the preservation potential of the underlying sedimentary package 'The J, unconformity represents uplift and erosion prior to Gypsum Spring deposition. The J2 unconformity reflects uplift and erosion of the Gypsum Spring Formation, which set up a comples bathymetly for the aclvancing Sundance Sea. A large north to northwesterly oriented paleohigh (Black Mount:~in High), cleveloped in the southeastern portion of the Bighorn Basin, influencing seclinienc~tion clurmg lower Sundance deposition. The final uplift and erosion event is expressecl by the J4 unconformity. This unconformity caps the Miclclle Jurassic sequence. Data suggest that the SI~ericlan Arch was uplifted during this time, not post Gypsum Spring time as previously suggested.