Abstract

Sedimentary basins throughout the western interior of North America preserve a record of Late Cretaceous through latest Eocene sedimentation derived from flanking Laramide uplifts and Sevier hinterland. In northern and western basins, the strata contain a well-documented record of Laramide-style exhumation. However, the tectonic histories of more southerly basins, such as the Huerfano Basin studied herein, are comparatively poorly known despite being key for understanding the spatiotemporal evolution of Laramide tectonism. In this study we address this issue with a comprehensive analysis of provenance for the Poison Canyon, Cuchara, and Huerfano formations in the Huerfano Basin (south-central, Colorado, U.S.A.). As part of our provenance analysis, we characterized gravel clast composition, petrographic compositions of sandstone bodies (N = 31 thin sections), and U–Pb detrital-zircon age spectra (n = 848 age determinations) from fluvial sandstone units in each of the three formations. The results are used to construct a new unroofing and source history for the sediments in 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 the incipient Sangre de Cristo Mountains, but from the Precambrian crystalline core and associated Cambrian plutons of the Wet Mountains, which were exposed by the time Laramide deposition began in the basin. There are no detected provenance shifts upsection, indicating a largely stable or lithologically uniform sediment source from the Paleocene through at least ∼ 51 Ma. This suggests that the major changes recorded in the rock record were more likely related to variations in tectonic and climatic conditions rather than changes in lithology of the rocks being eroded.

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