Permian-Triassic boundary in the Southwestern United States: Hiatus or continuity?

Álvarez, Walter; O'Connor, Diane

doi:10.1130/0-8137-2356-6.385

Cited by 9 publications

(6 citation statements)

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“…In North America, the Permian-Triassic record has traditionally been regarded as unconformable (e.g., Collinson et al, 1976), and the apparent lack of data from the western Pangean margin has in part hindered understanding of the mass extinction. However, the discovery of complete Permian-Triassic sections in the Canadian Rockies (Henderson, 1997), in sections previously believed unconformable, lends credence to the possibility of complete sections in the American portion of the Cordillera (Alvarez and O'Connor, 2002). This paper presents evidence from the Quinn River Formation, exposed in the Bilk Creek Mountains of northwestern Nevada, suggesting that it contains one of the fi rst documented Permian-Triassic boundary sections in the western United States.…”

Section: Introductionmentioning

confidence: 82%

A Permian-Triassic boundary section at Quinn River Crossing, northwestern Nevada, and implications for the cause of the Early Triassic chert gap on the western Pangean margin

Sperling

Ingle

2006

Geological Society of America Bulletin

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The Upper Permian-Lower Triassic Quinn River Formation in northwestern Nevada was previously thought to represent an incomplete Permian-Triassic boundary sequence, owing to an inferred disconformable relationship between Permian radiolarian-and spicule-rich chert and overlying Triassic siltstone. Petrographic and geochemical studies demonstrate that the "siltstone" is in fact a radiolarian-bearing early authigenic dolomicrite, with both the chert and dolomicrite deposited conformably in deep water. Chert production declined or ceased in the Late Permian and reappeared in the Spathian, forming a widespread "chert gap" in Permian-Triassic sequences. Given the conformable lithofacies relationships, deepwater depositional setting, new radiolarian data extending ranges of key taxa, and the presence of the global chert gap, sedimentation in the Quinn River Formation was apparently continuous across the Permian-Triassic boundary. This represents the fi rst Permian-Triassic boundary section in the United States portion of the North American Cordillera, and one of the few deep-water sections worldwide. Organic carbon isotope stratigraphy of the Quinn River Formation displays multiple excursions through sediments of Wuchiapingian-Anisian age, with a negative excursion 1.54 m above the chertshale transition likely representing the Permian-Triassic boundary.The multiple excursions in the organic carbon record verify studies of the carbonate carbon record in China that suggest insta-bility in the isotopic record throughout the Early Triassic, and demonstrate that the Permian-Triassic boundary isotope excursion was not an isolated event. Stratigraphic variation in redox-sensitive trace metals indicates that seawater became less oxic slightly before the chert-shale transition, in turn impacting siliceous sponge communities and creating the widespread chert gap. The distinctive dolomicrites in the Quinn River Formation represent a widespread lithofacies deposited in many localities during the Late Permian-Early Triassic and express early authigenic formation of dolomite via microbial sulfate reduction in organic-rich, low-oxygen environments.

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Section: Introductionmentioning

confidence: 82%

A Permian-Triassic boundary section at Quinn River Crossing, northwestern Nevada, and implications for the cause of the Early Triassic chert gap on the western Pangean margin

Sperling

Ingle

2006

Geological Society of America Bulletin

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“…400) for a compendium. Microbialites have also been reported in Nevada and Utah, in low latitude western Pangaea (Pruss et al, 2006); however those microbialites are late Early Triassic, and it is notable that identification of the PTB in western Pangaea is an unresolved issue (Alvarez and O'Connor, 2002). Consequently, current evidence does not include earliest Triassic microbialites in western Pangaea, and remains a gap in the dataset.…”

Section: C Carbon Isotopes Microbialites and Tethys Oceanmentioning

confidence: 88%

High-resolution carbon isotope changes in the Permian–Triassic boundary interval, Chongqing, South China; implications for control and growth of earliest Triassic microbialites

Kershaw

et al. 2009

Journal of Asian Earth Sciences

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High-resolution δ 13 C CARB analysis of the Permian-Triassic boundary (PTB) interval at the Laolongdong section, Beibei, near the city of Chongqing, south China, encompasses the latest Permian and earliest Triassic major facies changes in the South China Block (SCB). Microbialites form a distinctive unit in the lowermost 190 cm above the top of the Changhsing Formation (latest Permian) at Laolongdong, comparable to a range of earliest Triassic sites in low latitudes in the Tethyan area. The data show that declining values of δ 13 C CARB , well-known globally, began at the base of the microbialite. High positive values (+3-4 ppt) of δ 13 C CARB in the Late Permian are interpreted to indicate storage of 12 C in the deep waters of a stratified ocean, that was released during ocean overturn in the earliest Triassic, contributing to the distinctive fall in isotope values; this interpretation has been stated by other authors and is followed here. The δ 13 C CARB curve shows fluctuations within the microbialite unit, which are not reflected in the microbialite structure. Comparisons between microbialite branches and adjacent micritic sediment show little difference in δ 13 C CARB , demonstrating that the microbialite grew in equilibrium with surrounding seawater. The Early Triassic microbialites are interpreted to be a response to upwelling of bicarbonate-rich poorly-oxygenated water in low latitudes of Tethys ocean, consistent with current ocean models for the PTB interval. However, the decline of δ 13 C CARB may be due to a combination of processes, including productivity collapse resulting from mass extinction, return of deep water to ocean surface,

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“…2005a). Sedimentation was, however, discontinuous across western North America during the Permo‐Triassic, with only a few boundary sections known (Alvarez & O’Connor 2002; Sperling & Ingle 2006). By the later Early Triassic, the Moenkopi Formation was deposited on a broad shallow epicontinental shelf that extended from southern Idaho to southern Arizona (Marzolf 1993).…”

Section: Geological Settingmentioning

confidence: 99%

An Early Triassic small shelly fossil-style assemblage from the Virgin Limestone Member, Moenkopi Formation, western United States

Maxwell

Thuy

Pruss

2021

LET

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Small shelly fossils (SSFs) are minute fossils moulded or replaced by apatite, and less commonly, other minerals like glauconite and iron oxides. This taphonomic mode is best known from Cambrian deposits, though some occurrences occur across geological time. Instances of small shelly‐style preservation were found in insoluble residues from the Lower Triassic Virgin Limestone Member exposed in southern Nevada, the western United States, a second such occurrence known from this unit. Fossil steinkerns of tiny brachiopods, echinoid spines and ophiuroids are fluorapatite, with scarce phosphatic internal moulds of bivalves and two replaced ostracods. In contrast, the crinoid ossicles, almost all of which are >1000 µm, are preserved as stereomic moulds of silica or dolomite. Though the style of preservation is similar to another Virgin Limestone small shelly fossils‐style assemblage, this assemblage preserves greater diversity, likely reflecting the variation in palaeocommunities across the shelf. The size selectivity of phosphatization is clear, as the majority of the fossils <1000 µm are phosphatized. Importantly, the original skeletal material does not exert the strongest control on style of preservation: crinoid ossicles are replaced or moulded by silica whilst ophiuroid and echinoid fragments are phosphatized. It is likely that the underlying phosphatization mechanisms are related to the small particle size of the skeletons or skeletal elements coupled with the local pore water environment. Early Triassic equatorial seas characterized by warm temperatures and lower oxygen levels likely fostered small shelly fossil‐style preservation across the shelf during this time.

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Permian-Triassic boundary in the Southwestern United States: Hiatus or continuity?

Cited by 9 publications

References 0 publications

A Permian-Triassic boundary section at Quinn River Crossing, northwestern Nevada, and implications for the cause of the Early Triassic chert gap on the western Pangean margin

A Permian-Triassic boundary section at Quinn River Crossing, northwestern Nevada, and implications for the cause of the Early Triassic chert gap on the western Pangean margin

High-resolution carbon isotope changes in the Permian–Triassic boundary interval, Chongqing, South China; implications for control and growth of earliest Triassic microbialites

An Early Triassic small shelly fossil-style assemblage from the Virgin Limestone Member, Moenkopi Formation, western United States

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