Tectonic, eustatic, and process controls on the stratigraphic development and paleogeographic evolution of the Mesaverde Group, Wyoming, Utah, and Colorado
Creators: name: Minor, Keith Patrick
name: 0000-0002-0814-8400
Publisher: name: The University of Texas at Austin
Year: 2022
Subjects: Tectonics
Eustatic
Paleogeography
Wave-dominant
Seaway current-dominant
Tide-influenced
Shoreface
Marine shelf
Campanian
Western Interior Seaway

description: A combination of measured sections, well-log correlations, lithofacies, ichnofacies, sedimentary structures, and grain-size and paleocurrent measurements were used to better understand the interplay among tectonic, eustatic, and process controls on deposition during the Campanian and Maastrichtian of the Wyoming-Colorado-Utah region. Two new stratigraphic correlation diagrams, thirty-five new paleogeographic reconstructions, six new tectonic diagrams, one 2-D well-log line, and one isopach map were created to analyze the drivers of deposition in the region. Two time-scales of organization were identified, including 100-300 k.y.-scale, eustatically-driven packages that stack in groups of ten to fifteen offset, regressive-transgressive cycles to form 3.0-4.0 m.y.-scale, tectonically-driven packages herein defined as clastic wedges. Dynamic subsidence may have also played a role in the depositional patterns in the region. Four clastic wedges were identified from the latest Santonian/earliest Campanian to the Early Maastrichtian, including the Adaville, Rock Springs, Iles, and Williams Fork clastic wedges. The onset of deposition of the Mesaverde Group in the region is characterized by large-scale coastal plain construction that advanced the shoreline several hundreds of kilometers from the Middle Cretaceous general shoreline position. This dramatic shoreline advance marked the change from the dominance of flexure-driven tectonics to “thick-skinned” Laramide-driven tectonics, which began to partition the region into sub-basins bounded by surrounding uplifts that defined drainage patterns and transgressive shoreline configurations for millions of years. The southern Wyoming region is a classic example of such a Laramide sub-basin. Beginning in the Early to Middle Campanian, it alternated between a coastal plain, during emergent times, and marine embayment during marine transgressions, controlled by deep thrusting of Laramide blocks. Southern Wyoming was a major west-to-east fluvial drainage, as recorded by the thick fluvial sandstones of the Ericson Formation (Trail and Canyon Creek members). Transgressions into the region occurred in stages. The first marine incursion, which occurred during the late Middle Campanian to early Late Campanian, produced a shallow embayment that reached the Rock Springs uplift in southwestern Wyoming. The second transgression was much larger, and is characterized by accelerated subsidence during the later, in-filling stages of the embayment, which produced deepwater conditions. Supply was high during this time, due in large part to the exhumation of Upper Cretaceous sediments deposited during previous regressive-transgressive cycles on the crests of Laramide blocks, such as the Moxa Arch. Progradation and uplift caused the retreat of the Western Interior Seaway, as recorded by the strong shoreline trajectories in the region. However, marine transgressions are recorded in southeastern Wyoming during the Latest Cretaceous into the Paleogene, indicating that an epeiric sea persisted in the U.S. Western Interior into the Tertiary. Laramide tectonics created a shallow-shelf setting which promoted large shoreline oscillations and widespread deposition of sand on the marine shelf during eustatic sea-level cycles. These sands were modified by seaway and tidal currents. The marine shorefaces are characterized by intensely burrowed, hummocky cross-stratified sandstones associated with strong wave action. Based on paleocurrent directions, the offshore sands tend to be reworked by the prevailing north-to-south seaway currents. There is also evidence of tidal (and in some cases strong tidal) reworking of the offshore sands. The paleogeographic associations of the dominant processes are likely related to water depth, and thus to relative storm-wave energy in the reworking of the seaway current and tidally generated bedforms.