Kansas Geological Survey, Subsurface Geology 12, p. 17-18
J. A. Thorne1 and D. J. P. Swift2
1ARCO Oil and Gas Company
2Old Dominion University
A two-dimensional numerical model of basin formation and sedimentation is developed to simulate the characteristic sequence geometry of sediment fill in a foreland-basin setting. We describe a simple model for sediment dispersion on a wave-dominated shelf. In this approximation, waves and bottom currents are treated as random variables, producing dominantly longshore transport and a net offshore diffusive transport dependent on water depth and grain size.
The model is used to investigate the controlling factors on sequence geometry of the U.S. Western Interior Cretaceous basin. Initial results show that the sedimentation history of the Cretaceous basin has developed in response to 1) major thrusting events at 110, 100, and 90 Ma and 2) basement movements relating to the start of Laramide tectonics at 80 Ma. Each thrust-related sequence can be described by two stages of sedimentation. In the first, alluvial-fan conglomerates and sandstones grade rapidly seaward into dominantly shaly, relatively deep-water, strike-fed deposits. In the second stage, progradation of a low-relief shelf edge forms a thickening sandy clastic wedge. In contrast, the response of sedimentation to vertical tectonics is illustrated by a sequence of prograding clinoforms developed during the Campanian. As simulated by the model (fig. 1), changes in progradational style develop in response to relative changes in sea level associated with the regional rate of subsidence/ uplift in the Wyoming area.
Figure 1--The predicted pattern of progradation in response to Late Cretaceous vertical tectonics in the Powder River basin matches the observed E-log cross section from Asquith (1970); A) Powder River well-log section and B) simulated model.
Asquith, D. O., 1970, Depositional topographies and major marine environments, Late Cretaceous, Wyoming: American Association of Petroleum Geologists, Bulletin, v. 57, p. 1, 184-1,224
Kansas Geological Survey
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Web version May 7, 2010. Original publication date 1989.