Facies and Architecture of the Chimney Rock Member, Rock Springs Formation (Mesaverde Group), Southwest Wyoming

Adam R. VanHolland, Encana Oil & Gas (USA) Inc, Denver, CO 80209, phone: (303) 518-3630, [email protected] and Randi S. Martinsen, Dept of Geology and Geophysics, University of Wyoming, University of Wyoming, Laramie, WY 82071.

An outcrop study, a core well drilled through the outcrop, and well logs along the northern margin of the Rock Springs Uplift of southwestern Wyoming document the facies, architecture, and key stratigraphic surfaces within the Chimney Rock Member (basal clastic wedge) of the Rock Springs Formation. The Chimney Rock Member is comprised of three facies associations. The lowermost sections of the Chimney Rock Member are representative of deposition within a wave-dominated shoreface, with the overlying medial parts of the section consisting of incised-valley deposits (wave-dominated estuarine and tidal deposits). These two sections of the Chimney Rock Member are separated by a significant erosion surface, a sequence boundary that marks a relative fall in sea-level. The upper reaches of the Chimney Rock Member consist of a mixed strandplain and coastal plain succession. A throughgoing flooding surface and transgressive lag (likely TSE) separates the incised valley fill from the overlying mixed strandplain and coastal plain deposits.