ABSTRACT: Late Cretaceous and Tertiary Paleogeographic Reconstructions--Uinta and Piceance Basins, Northeastern Utah and Northwestern Colorado
K. J. Franczyk, T. D. Fouch, R. C. Johnson, C. M. Molenaar
Paleographic reconstructions for Late Cretaceous through early Oligocene time in the Uinta and Piceance basins area illustrate several major geologic events: incursion of a Cretaceous sea, tectonism in the Sevier thrust belt, changes in eustacy, breakup of a Late Cretaceous foreland, formation of intermontane basins, and establishment and disappearance of large lacustrine complexes. Throughout most of the Late Cretaceous, the reconstruction area was part of a foreland in which depositional patterns were controlled both by tectonism in the Sevier thrust belt to the west and by eustatic changes. In late Campanian through early Maastrichtian time, the sea withdrew from much of this area, rates and centers of subsidence changed, and basement-involved uplifts became active. Sm ll intermontane basins began to form in the western part of this area at this time.
By late Maastrichtian time, the sea completely withdrew from this area, the basement-involved uplifts continued to form, and sediment accumulated only in these small, western intermontane basins. The more regionally extensive intermontane basins that characterized much of this area during the Paleogene formed by middle Paleocene time. Initially, deposition occurred primarily in alluvial fans and plains, wetlands, and shallow lakes. These lakes expanded until the early Eocene when they occupied large parts of both the Uinta and Piceance basins. The lakes expanded further, crossed the Douglas Creek arch, and joined to form a single major lake, Lake Uinta, in the middle Eocene. During the latter half of the middle Eocene, clastic sediments from the north began to fill the lake in the Pic ance basin. From then through the late Eocene, Lake Uinta retreated westward, and its remnant finally disappeared from the western end of the Uinta basin in latest Eocene or earliest Oligocene time.
AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990