Pressing flowers between pages…
Isopach mapping and stratigraphic studies in the Douglas Creek arch area, a north-south-trending structure that separates the Uinta basin of Utah from the Piceance Creek basin of Colorado, indicate that the arch was formed largely during the Laramide orogeny (Late Cretaceous, late Campanian through Eocene). Formation was contemporaneous with the formation of the Uinta and Piceance Creek basins, but may have been present as a very broad, low-amplitude structure earlier during the Sevier orogeny. Recent paleogeographic reconstructions by other workers, however, suggest that the Douglas Creek arch was largely pre-Laramide. The Dakota to Castlegate Sandstone interval, which predates the Laramide orogeny, thickness toward the northwest on the west flank of the arch and toward the northeast on the east flank. This thickenings roughly outlines the arch, but is much broader, and more closely parallels the Uncompahgre uplift south of the arch. The thickness of the Castlegate to Cretaceous-Tertiary unconformity interval, which brackets the early stages of the Laramide orogeny, is nearly uniform west of the arch, but thickens abruptly east of the crest of the arch. This interval has been modified by an unknown amount of erosion during the following hiatus. Upper Paleocene rocks above the unconformity lap out towardmore » the arch from both directions, indicating that the arch was rising during the hiatus. The intervals from the Cretaceous-Tertiary unconformity to the lower Eocene Long Point bed and from the Long Point bed to the middle Eocene Mahogany bed thicken away from the arch, indicating that the arch was active during early to middle Eocene. A structure contour map of the top of the Mahogany bed indicates considerable post-Mahogany movement as well. The arch was therefore largely if not totally a Laramide structure.« less
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