Sedimentology, stratigraphy, and quantitative basin analysis of the middle Cretaceous (Cenomanian-Turonian) Greenhorn transgressive-regressive cycle in southwest Utah

Sedimentologic studies and quantitative basin analysis of the middle Cretaceous (Cenomanian-Turonian) Greenhorn transgressive-regressive marine cycle in southwestern Utah indicate that stratal patterns were influenced by the combined interactions of basin sea-level changes and variations in the rate of tectonic subsidence. High tectonic subsidence rates coupled with a rising basin sea level during the initial portion of the cycle (Late Cenomanian-Early Turonian, 94.9 Ma-92.8 Ma) produced an enhanced transgressive phase and trapped clastic sediment in the foredeep of the Sevier foreland basin. The regressive phase of the cycle (Middle Turonian-Early Coniacian, 92.8 Ma-88.6 Ma) took place during a period of reduced tectonic subsidence and a fall and subsequent rise of basin sea level. Tectonic subsidence rates were low enough during the regression to allow a 200 km-long basinward progradation of coarse fluvial sediment across the foredeep and delay the transgression of the next transgressive-regressive cycle (the Niobrara cycle). The fluvial progradation was conformable and deposition rates decreased during the later portions of the Greenhorn regressive cycle indicating that neither deep fluvial incision nor increased sedimentation rates were responsible for the extreme progradation of coarse clastic sediment.; Tectonic subsidence rates during the transgressive-regressive cycle were variable enough to substantially alter the timing and stratal patterns of the cycle from those predicted solely from eustatic sea-level changes. Middle Cretaceous stratal patterns, tectonic subsidence rates, and timing of transgressions and regressions in southwestern Utah are significantly different from those of central Utah. The findings suggest that tectonic subsidence rates can vary significantly over short time spans ({dollar}<{dollar}6 m.y.) and over short distances. Additionally, these temporal and spatial variations are great enough to control large-scale stratal patterns, progradation of sedimentary facies especially coarse-clastic sediment, and timing and extent of marine transgressions and regressions.