PROVENACE OF DESMIONESIAN TO EARLY WOLFCAMPIAN STRATA IN THE ANCESTRAL ROCKY MOUNTIAN EAGLE AND PARADOX BASINS

The routing and provenance of clastic sediment in the Desmoinesian to early Wolfcampian Paradox and Eagle basins of the Ancestral Rocky Mountains (ARM) are enigmatic. Previous workers hypothesize that clastic sediments in the Eagle Basin of Colorado were derived from the Uncompahgre and Front Range uplifts; while others have used fault geometries to argue that the Uncompahgre uplift was not unroofed until mid-Permian time. Previous detrital zircon (DZ) investigations of the Eagle basin used probability peaks of <300 and 760-940 Ma in loessite and their absence in paleosols to suggest provenance shifts between glacial and interglacial periods. To test these ideas, we sampled marine mudstone (glacial) and fluvial and marine sandstone (interglacial) at multiple km-scale sections in Paradox and Eagle basins for DZ analysis. Paleocurrents from foresets adjacent to the Uncompahgre and Front Range uplifts show basinward paleo-flow directions in the both basins.

Paradox and Eagle basin DZ signatures suggests their sediment was sourced primarily from a mixture of Yavapai-Mazatzal (1.8-1.6 Ga) rocks in the Uncompahgre and Front Range uplift, and from the Grenville (1.0-1.3 Ga) and Taconic (400-450 Ma) orogenies. Within both basins, a distinctive suite of 1.3-1.5 Ga grains occur proximal to the Uncompahgre Uplift, which are absent in DZ spectra for samples adjacent to the Front Range uplift. The abundance of Grenville and Taconic aged grains appears to be highest during interglacial periods of high sea level, coincident with deposition of marine mudstone (Paradox) and shallow marine sandstone (Eagle). These grains are less abundant during glacial lowstands in eolian-fluvial (Paradox) and fluvial facies (Eagle). These new DZ data collectively suggest: (1) the Uncompahgre and Front Range uplifts were unroofed during the Desmoinesian, and actively shed arkosic sediments to adjacent basins; (2) Paradox and Eagle basins were independent depocenters from mid Desmoinesian to Wolfcampian; (3) locally-derived sediment mixed with long-traveled “Appalachian River” sediment; and (4) transport of Appalachian River sediment was favored during highstands due to sediment trapping by sea level rise, and/or increased eolian flux from the north.