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Abstract Middle to Upper Jurassic strata in the Paradox Basin and Central Colorado trough (CCT; southwestern United States) record a pronounced change in sediment dispersal from dominantly aeolian deposition with an Appalachian source (Entrada Sandstone) to dominantly fluvial deposition with a source in the Mogollon and/or Sevier orogenic highlands (Salt Wash Member of the Morrison Formation). An enigmatic abundance of Cambrian (ca. 527–519 Ma) grains at this provenance transition in the CCT at Escalante Canyon, Colorado, was recently suggested to reflect a local sediment source from the Ancestral Front Range, despite previous interpretations that local basement uplifts were largely buried by Middle to Late Jurassic time. This study aims to delineate spatial and temporal patterns in provenance of these Jurassic sandstones containing Cambrian grains within the Paradox Basin and CCT using sandstone petrography, detrital zircon U-Pb geochronology, and detrital zircon trace elemental and rare-earth elemental (REE) geochemistry. We report 7887 new U-Pb detrital zircon analyses from 31 sandstone samples collected within seven transects in western Colorado and eastern Utah. Three clusters of zircon ages are consistently present (1.53–1.3 Ga, 1.3–0.9 Ga, and 500–300 Ma) that are interpreted to reflect sources associated with the Appalachian orogen in southeastern Laurentia (mid-continent, Grenville, Appalachian, and peri-Gondwanan terranes). Ca. 540–500 Ma zircon grains are anomalously abundant locally in the uppermost Entrada Sandstone and Wanakah Formation but are either lacking or present in small fractions in the overlying Salt Wash and Tidwell Members of the Morrison Formation. A comparison of zircon REE geochemistry between Cambrian detrital zircon and igneous zircon from potential sources shows that these 540–500 Ma detrital zircon are primarily magmatic. Although variability in both detrital and igneous REE concentrations precludes definitive identification of provenance, several considerations suggest that distal sources from the Cambrian granitic and rhyolitic provinces of the Southern Oklahoma aulacogen is also likely, in addition to a proximal source identified in the McClure Mountain syenite of the Wet Mountains, Colorado. The abundance of Cambrian grains in samples from the central CCT, particularly in the Entrada Sandstone and Wanakah Formation, suggests northwesterly sediment transport within the CCT, with sediment sourced from Ancestral Rocky Mountains uplifts of the southern Wet Mountains and/or Amarillo-Wichita Mountains in southwestern Oklahoma. The lack of Cambrian grains within the Paradox Basin suggests that the Uncompahgre uplift (southwestern Colorado) acted as a barrier to sediment transport from the CCT.
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Cambrian trilobites and associated fossils from the Uinta Mountains of Utah (USA)
Abstract Fossils are rare in Cambrian strata of the Uinta Mountains of northeastern Utah, and are important because they can help integrate our understanding of laterally adjacent but discontiguous rock units, e. g., the Tintic Quartzite of Utah and the Lodore Formation of Utah-Colorado. New body fossils from strata previously mapped as Tintic or Cambrian Undifferentiated, but here interpreted as the Ophir Formation, include indeterminate hyoliths and hyolithids, brachiopods including a linguloid, and the trilobitesTrachycheilusResser, 1945 andElrathiellaPoulsen, 1927. The last two assign these strata to theEhmaniellaBiozone (uppermost Wuliuan Stage; Miaolingian Series) or traditional Laurentian middle Cambrian. These data, together with fossil occurrences elsewhere in Utah, require that the Tintic Quartzite was deposited prior to and/or during the early Wuliuan, and suggest that the unit could be correlative to much of the Lodore Formation of Utah and Colorado.
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- Award ID(s):
- 1954634
- PAR ID:
- 10528046
- Publisher / Repository:
- Journal of Paleontology; Published by Cambridge University Press on behalf of The Paleontological Society
- Date Published:
- Journal Name:
- Journal of Paleontology
- ISSN:
- 0022-3360
- Page Range / eLocation ID:
- 1 to 8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1017/jpa.2023.82
