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New sedimentological and stratigraphical data on the Permian and Triassic in northeastern Utah, USA

Abstract : We present the Permian to Triassic sedimentological evolution in the Vernal area, northeastern Utah, to determine: (1) the magnitude of the Permian-Triassic (P-T) unconformity, (2) the depositional environments above the unconformity, as well as (3) their evolution in space and time. Within this area, Permian deposits consists of the Weber Sandstone, which represents aeolian deposits, overlain by the Park City Formation, composed of silty and sandy marine limestones, dolomites and phosphatic shales. In some places, an unconformity is observed at the top of the Weber Sandstone, which is directly overlain by the Moenkopi Group. This formation is mostly composed of siltstone, with gypsiferous levels and ripple marks, deposited in nearshore continental to marine environments. Within the studied area, this formation is assumed to be Early Triassic. A second unconformity at the base of the Chinle Group truncates the Moenkopi Group. The base of the Chinle Group is characterized by the Gartra Formation composed of coarse-grained and conglomeratic sandstones that are stream and river deposits overlain by red beds that are stream (primarily floodplain) and lake deposits. The P-T succession in northeastern Utah encompasses a profound unconformity and is not a complete succession that could be used to analyze P-T boundary extinctions. Detailed sedimentological analyses allow the characterization of the depositional environments across the P-T unconformity. The upper Permian deposits preserved below the unconformity show erosion or non-deposition in the Vernal area. Above the unconformity, sandstone facies including coiled and uncoiled nautiloids, as well as stromatolite mounds, which suggest an open marine environment and attributed to the Permian based on its faunal content. These marine deposits are abruptly overlain, above a breccia surface, by more classical Moenkopi facies attributed here to delta and turbidite facies overlain by sabkha deposits with gypsum and microbialites. The unconformity above the Moenkopi Group is overlain by either fluvial deposits of the Gartra Formation or red bed facies of the Chinle Group. This study also helps to define the relationships between the Gartra Formation, the red beds and the paleosols within the Petrified Forest Formation of the Chinle Group.
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Submitted on : Monday, October 11, 2021 - 2:56:08 PM
Last modification on : Tuesday, October 19, 2021 - 10:53:11 PM

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  • HAL Id : insu-03373443, version 1

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Sylvie Bourquin, Romain Rubi, Guy Desaubliaux, Emmanuelle Vennin, Arnaud Brayard, et al.. New sedimentological and stratigraphical data on the Permian and Triassic in northeastern Utah, USA. 35th IAS Meeting of Sedimentology, Jun 2021, Virtual, Czech Republic. pp.73. ⟨insu-03373443⟩

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