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ABSTRACT: Latest Cretaceous-Paleogene Basin Development and Resultant Sedimentation Patterns in the Thrust Belt and Broken Foreland of Central Utah

T. F. Lawton, K. J. Franczyk, J. K. Pitman

Latest Cretaceous tectonism in central and east-central Utah formed several intermontane basins both atop thrust sheets and between the thrust front and basement-involved uplifts in the former foreland basin. The upper Campanian Castlegate Sandstone and its inferred western equivalents were the last strata deposited prior to segmentation of the foreland basin. Thereafter, eastward transport of the thrust allochthon uplifted the most proximal part of the Castlegate depositional wedge. West of the thrust front, small intermontane basins formed on the allochthon. Sediment was transported into these basins from both eastern and western sources. In each basin, facies grade from basin-margin conglomeratic alluvial fan deposits to basin-interior flood-plain and lacustrine deposi s within a few kilometers. These intermontane basins existed from latest Campanian through the late Paleocene, and may have been transported a short distance eastward as they formed.

East of the thrust front in the latest Campanian and contemporaneous with basin formation on the allochthon, a northward-northeastward-flowing big river system transported sediment into the foreland basin from feldspar-rich source areas southwest of the study area. Subsequently, major movement of the San Rafael uplift in the very late Campanian or early Maastrichtian gave rise to an intermontane basin between the thrust front and the San Rafael uplift. Northwestward-flowing, pebble-bearing braided rivers deposited the oldest sediments in this basin prior to an influx from the south and southwest of sediment that formed a thick Maastrichtian clastic sequence. In contrast to deposition in basins on the allochthon, deposition east of the thrust front in the Paleocene was intermittent and restricted to rapidly shifting centers of basin subsidence. By the early Eocene, all the isolated basins both east and west of the thrust front had filled, and the depositional systems of the region were integrated into a single, large, lacustrine-dominated complex.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990