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Tectono-Sedimentary Evolution of the Western Margin of the Colorado Plateau During the Latest Cenomanian and Early Turonian
The sedimentary record of latest Cenomanian to Early Turonian strata in the western, marginal part of the Western Interior basin has been linked in prior studies to coeval deposits in the basin center. The aim of this research is to develop a more detailed depositional history for the marginal marine part of the transect in order to further evaluate allocyclic vs. autocyclic controls on sedimentation, and to provide new data on tectonic history of the Sevier foredeep.
Three major depositional sequences are recognized in the Late Cenomanian record based on sedimentologic and stratigraphic evidence. These sequences represent relative sea level (RSL) fluctuations superimposed on long-term RSL rise that reached a maximum during Early Turonian time. Correlation of the section to well-dated hemipelagic facies in the basin center allows the duration of these relative sea level changes to be estimated. The RSL cycles appear to have been at least quasiperiodic, with durations between 80 and 100ka. Collectively, our preliminary data suggest that eustatic rather than tectonic control was the triggering mechanism of the RSL changes.
Sequence stratigraphic/chronostratigraphic subdivision of the study interval allows detailed spatial and temporal assessment of subsidence changes to be made. As a result, two major phases of development of the proximal foreland are distinguished. Observed northeasterly migration of the major subsidence axis may have been caused by basinward approach of the thrust front in an in-sequence mode (emplacement of a blind thrust beneath the western part of the area of study), and possible strike-slip reactivation of NE-trending structures. Late Cenomanian tectonic history did not include any significant vertical movements along present-day Sevier and Paunsaugunt faults. These faults might have become activated latter, during Early Turonian.
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