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Pre-Laramide salt tectonism in the western Eagle basin of central Colorado
Thorson, Haley Renee
Thorson, Haley Renee
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2022
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Abstract
Located west of the Front Range and situated between the Sawatch Range to the southeast and the Piceance Basin to the west, the Eagle Basin of central Colorado is a flexural foreland basin originally formed in the footwalls of the converging Uncompahgre and Front Range Ancestral Rocky Mountains Uplifts. Previous studies of this area highlight Laramide orogenic events as the main phase of tectonic deformation in this region. However, a closer evaluation of the complex array of structures in the Eagle Basin, along with the Pennsylvanian Eagle Evaporite Formation and adjacent and overlying Late Pennsylvanian to Jurassic strata provide evidence for a period of salt tectonics in the region pre-dating the Laramide Orogeny. Building on recent work completed by two Colorado School of Mines graduate students, this research seeks to provide further evidence of pre-Laramide salt tectonics and associated halokinetic deformation in the western part of the Eagle Basin. Field work completed in the western portion of the Eagle Basin demonstrates that sedimentary layers of varying thickness and the presence of folding, faulting, and overturned beds point to the growth of a series of Late Pennsylvanian to Early Permian salt walls and associated minibasins that may have been overlooked in the past. The western Eagle Basin contains diapiric salt walls, tongues, and canopies that were welded between minibasins during more recent, Laramide-aged shortening events. Salt diapirism explains the dramatic formation thickness variations and local overturning seen in the Late Pennsylvanian Eagle Valley and Permian Maroon Formations. A modern examination of the Eagle Basin provides insight into current salt tectonics theories and serves as a field analog of salt structures and minibasins in other comparable salt basins.
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