Redbeds in Wyoming: Reading Late Permian-Early Triassic Environments and Climates From the Red Peak and Crow Mountain Formations

Knapp, Jonathan; Benison, Kathleen C.; Andeskie, Anna Sofia

doi:10.1130/abs/2016am-285060

Cited by 2 publications

(3 citation statements)

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“…The textures of gypsum have been well-documented from modern environments, as well as Miocene deposits (Schreiber & Kinsman, 1975;Schreiber, 1987;Benison et al, 2007;Kiro et al, 2016;Knapp et al, 2016;Langford et al, 2016;Benison, 2019a). Modern examples include bottom-growth, cumulate, clastic and displacive gypsum from acid-saline lake systems in Western Australia, bottom-growth and clastic gypsum from acid-saline lake systems in northern Chile, and clastic gypsum from sandflats and dunes at White Sands National Monument in New Mexico, USA (McKee, 1966;Benison et al 2007;Langford et al, 2016;Benison, 2019a).…”

Section: Textures Of Gypsummentioning

confidence: 99%

“…The Red Peak Formation is the lowest formation of the Chugwater Group, considered to be approximately 170 m thick, and composed of red beds and bedded gypsum (Maughn, 1972; Figure 1). While the Chugwater Group and its distinctive bright-red colour are well-known to geologists familiar with Wyoming, the interpreted depositional environments remain contentious (Branson, 1915;Cavaroc & Flores, 1917;High & Picard, 1969;Picard, 1967;Irmen & Vondra, 2000;Lovelace & Lovelace, 2012;Knapp et al, 2015Knapp et al, , 2016Knapp, 2020). The bedded gypsum of the Chugwater Group has not yet been described in sedimentological detail; ancient bedded gypsum, in general, is understudied.…”

Section: Introductionmentioning

confidence: 99%

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Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

Bradford,

Benison

2024

The Depositional Record

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Bedded gypsum is relatively common in bedded evaporites associated with red bed siliciclastics of Permo‐Triassic Pangea. However, little attention has been paid to the textures of ancient gypsum, which can be used to refine interpretations of depositional environment and diagenetic history. This project describes the textures of bedded gypsum from an outcrop of the Triassic Red Peak Formation (Chugwater Group) near Greybull, Wyoming. Fieldwork, petrography and X‐ray diffraction reveal three distinct lithologies of bedded gypsum: bottom‐growth gypsum, laminated gypsum and clastic gypsum. Bottom‐growth gypsum precipitated at the bottom of shallow saline surface water bodies. Laminated gypsum probably formed in shallow saline lakes and mudflats. Clastic gypsum units are composed of aeolian‐reworked bottom‐growth gypsum crystals deposited in sandflats. Red siliciclastic mudstones are characterised by their massive nature and abundant blocky peds. Detailed study of this outcrop of the Red Peak Formation shows that it formed in shallow saline lakes and associated mudflats, sandflats and desert soils.

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Section: Textures Of Gypsummentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

Bradford,

Benison

2024

The Depositional Record

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“…Some of the bedded gypsum units may have been diagenetically replaced by calcite. In addition, we consider the stratigraphic context of the Minnekahta Limestone to help evaluate which depositional model is most compatible (Benison and Goldstein, 2000;Knapp et al, 2015Knapp et al, , 2016).…”

Section: Introductionmentioning

confidence: 99%

The Permian Minnekahta Limestone: a Saline Lake Gypsum Replaced by Calcite

Benison

Knapp²,

Difrisco³

et al. 2018

MT GEOL

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The late Permian Minnekahta Limestone of the Black Hills of South Dakota is not a typical limestone. Sandwiched stratigraphically between continental redbed siliciclastics, it is distinct in its gray-pink appearance and carbonate mineralogy and is considered a local and regional marker bed. Based on its calcite composition and stromatolites, it has previously been interpreted as a tidal flat deposit, leading to speculation of a regional late Permian marine transgression. Here, we show observations that question the original composition, reexamine and refine the sedimentary and stratigraphic characteristics, and suggest an alternate depositional environment. Petrography and x-ray diffraction indicate that the Minnekahta Limestone is dominated by an interlocking crystal mosaic of calcite and gypsum. We have documented pseudomorphs after bottom-growth gypsum crystals, alternating laminae of mm-scale bottom growth gypsum crystal shapes and mud drapes, as well as mudcracks, raindrop imprints, and stromatolites. No carbonate grains, fossils, or tidal rhythmites were noted. These observations suggest that the carbonate phase is a replacement of gypsum. In addition to the sedimentology and petrography, close stratigraphic association with overlying and underlying continental redbeds indicates that this was likely a shallow saline-lake deposit. Other Permo-Triassic carbonate strata in continental redbed sequences throughout the midcontinent of North America, such as those in the Goose Egg, Chugwater, Nippewalla, and Spearfish strata, may have similar continental origin. This study serves as a lesson that paired petrographic observations and mineral identifications are important data necessary for the best interpretation of depositional environments and diagenetic histories.

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Redbeds in Wyoming: Reading Late Permian-Early Triassic Environments and Climates From the Red Peak and Crow Mountain Formations

Cited by 2 publications

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Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

Gypsum lakes, sandflats and soils revealed from the Triassic Red Peak Formation of the Chugwater Group, north‐central Wyoming

The Permian Minnekahta Limestone: a Saline Lake Gypsum Replaced by Calcite

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