AbstractsEarth & Environmental Science

Sedimentary basins throughout the Western Interior of North America preserve a record of Late Cretaceous through latest Eocene sedimentation derived from flanking Laramide uplifts. In northern and western basins, the strata contain a well-documented proxy history of Laramide-style exhumation and climatic conditions within the region. However, the tectonic and climatic histories of more southerly basins, such as the Huerfano Basin studied herein, are comparatively underdeveloped despite being key in understanding the spatiotemporal evolution of Laramide tectonism and regional climatic gradients. This study addresses this issue and presents the first detailed lithofacies analysis and provenance analysis of the Poison Canyon, Cuchara, and Huerfano formations in the Huerfano Basin (south-central, Colorado, U.S.A.). We interpret a suite of alluvial sub-environments within these formations whose upsection variability and broad depositional patterns are similar to those observed in other early Paleogene successions in Laramide basins. Specifically, these features include deposition of organic-rich strata during the Paleocene; Eocene strata dominated by red-bed formation; and an anomalously coarse-grained intervening fluvial unit. The major difference in the Huerfano Basin compared to other Laramide basins is the exceptionally coarse-grained nature of all the units, which is likely related to its proximal position to Laramide ranges. Overall, the patterns are consistent with the widespread climatic shift between the wet, cooler Paleocene, and the drier, warmer, potentially more seasonal Eocene climate. As part of our provenance analysis, we characterized petrographic compositions of sand-bodies (N = 31 thin sections) and U–Pb detrital zircon age spectra (N = 848 age determinations) from fluvial sandstones within each of the three formations. The results indicate a new unroofing and source history for the sediment within the basin that contradicts previous hypotheses. Diagnostic zircon peaks at 516-517 Ma, 1423-1430 Ma, and 1678-1687 Ma show that sediment delivered to the Huerfano Basin did not originate in the San Luis Highlands or incipient Sangre de Cristo Mountains, but that the Precambrian crystalline core and associated Cambrian plutons of the Wet Mountains were exposed by the time Laramide deposition initiated in the basin. There are no provenance shifts upsection, indicating a largely stable or lithologically uniform sediment source from the Paleocene through at least ~51 Ma. This suggests the major changes in deposition are more likely related to tectonic and climatic conditions rather than lithologic controls on stratigraphic patterns. Advisors/Committee Members: Foreman, Brady, Housen, Bernard Arthur, Snell, Katie.