TOLLESTRUP, A. KURT, CHARLES L. ANGEVINE, and JAMES R. STEIDMANN, University of Wyoming, Department of Geology and Geophysics, Laramie, WY

ABSTRACT: A Geometric and Subsidence Analysis of the Uinta Basin Using Combined Flexural Modeling Techniques and Regional Paleocurrent Analyses

The Uinta basin in Utah is a significant oil-bearing, foreland basin that developed during the Laramide orogeny (late Cretaceous to the early Tertiary). We use flexural modeling techniques to predict the accumulation of basin sediments through time as a function of uplift of the Uinta Mountains and changes in regional base level. Four time intervals represented by the thicknesses between the tops of the Mancos shale, Mesaverde Formation, Wasatch Formation, Green River Formation and the Uinta Formation were studied. The crustal configuration that best describes the Uinta basin's sediment geometry is a 415 to 460 km long elastic plate with a flexural rigidity ofbetween 1 x 10{24} and 3 x 10{24} Newton meters whose northern end is loaded by a mountain block 32 to 56 km wide.

Observed and predicted sediment accumulation in the intervals between 80 to 43 m.y. (Mancos shale to Green River Formation) agree well if the rate of mountain building was between 0.2 to 0.5 km/m.y. and base levels rose 0 to 30 meters/m.y. However for agreement between the observed and theoretical accumulations during the youngest time interval (Green River Formation to the Uinta Formation) the predicted uplift rates had to be dramatically increased to between 0.4 and 1.1 km/m.y. while base levels fell.

Regional paleocurrent measurement show that base level changes were controlled by extra-basinal Laramide uplifts. We have shown that by using combined theoretical and field techniques it is possible to differentiate between intra and extra-basinal controls on subsidence.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.