The Cretaceous Almond Formation, located in the Greater Green River Basin, records deposition of coastal plain fluvial sandstones and shallow marginal-marine sandstones in a net-transgressive sequence along the western margin of the Cretaceous Interior Seaway (CIS) from the late Campanian to early Maastrichtian. The Almond Formation is an important hydrocarbon reservoir, with development mainly along the Wamsutter Arch and the northeast margins of the Washakie Basin. Previous studies have primarily focused on outcrops along the eastern flank of the Rock Springs Uplift and subsurface data targeting the Wamsutter Arch. Further development of the Almond petroleum system requires extending our understanding of lateral facies changes and sequence stratigraphic architecture away from areas that have been previously studied. The aim of this research is to build a predictive model of lateral and temporal facies transitions and associated reservoir character along the Cherokee Arch in southern Wyoming. This structural feature marks the southern margin of the Washakie Basin and is roughly perpendicular to the shoreline of the CIS. Outcrop examination at either end of the arch shows that lower Almond strata along the western margin of the Washakie Basin transition from coastal plain facies associations to time-equivalent shallow-marine strata to the east, while the upper Almond strata transition from shallow-marine sands to offshore and prodeltaic muds across the ~125 km separating the two outcrop localities. This reveals clear facies associations shifts at the basin scale, which are difficult to interpret using only well data. The preservation of shoreface strata and related near-shore, fluvio-deltaics across large distances in the dip direction shows the large magnitude of shoreline migration. This also suggests that the system gradient was likely very gentle, leading to wide facies belts, and that reservoir continuity could be complex over significant distances. Stacking patterns observed in outcrop, core, and log curves demonstrate an early progradational sequence across the basin from the west to east. This time equivalent strata suggests sediment supply outpaced accommodation during deposition of the lower Almond and equivalent basinward strata, leading to progradation and eventually to some aggradation before relative sea-level rose. This is significant as the Almond is thought primarily as an overall retrogradational system. Within the upper Almond and basinward equivalent strata, stacking patterns reveal a well preserved retrogradational sequence as accommodation outpaced sediment supply during the final transgression of the Mesaverde Group. Core and outcrop analysis to the east at this time show facies associations that potentially represent an inundated, estuarine deltaic environment of deposition transitioning to deltaic depofacies to the west. Clinoformal geometry and an additional sand found in the subsurface of a cluster of only southern wells corroborate a deltaic interpretation. This sand is interpreted as a lobate deposit flanked by shale to the north. Shorelines span a short distance in the east and a much broader distance to the west with a clear facies shift in between allowing for marine shale to directly overlay coastal plain facies. Outcrop, core, and subsurface datasets have led to a better understanding of sediment partitioning and preservation during this transgressive phase of the CIS in the western United States. A better understanding of these spatial and temporal patterns will help to remove risk associated with exploration along this trend, as well as serve as an analogue for other transgressive deposits. Additional data would increase knowledge of this system and lead to solidification of new ideas presented for the Almond Formation along the Cherokee Arch.
| Identifer | oai:union.ndltd.org:BGMYU2/oai:scholarsarchive.byu.edu:etd-9731 |
| Date | 07 December 2020 |
| Creators | Phillips, Joseph E. |
| Publisher | BYU ScholarsArchive |
| Source Sets | Brigham Young University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | https://lib.byu.edu/about/copyright/ |
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