Paleogeography |
The Sundance Seaway developed in the Middle-Late Jurassic (≈170-155 Ma) of the in US Western Interior. It formed in an elongated, retro-arc foreland basin connected to the Pacific Ocean, with the Cordilleran volcanic arc to the west and the North American craton to the east. The axis of the basin extended from southern Utah northward into northern British Columbia, a length of nearly 2000 km. The figure shows a palaeogeographical reconstruction of western North America in the Middle Jurassic (Bajocian Stage ~170 Ma). The map is based on maps produced by R. Blakey. |
Lithostratigraphy
The Gypsum Spring and Sundance formations are exposed in Wyoming along the flanks of Late Cretaceous to Cenozoic uplifts, including the Black Hills, Pryor Mountains, Bighorn Mountains, Wind River Mountains, Wyoming Range and Laramie Mountains.
The Gypsum Spring Formation, with a maximum thickness of about 80 m, was deposited on a mixed evaporate–carbonate–siliciclastic ramp, with depositional environments that include distal ooid shoals, open shallow subtidal, restricted shallow subtidal, peritidal, salinas and desert mud flat to sabkha (Clement & Holland 2016).
The Sundance Formation is approximately 100 m thick, records cyclical deposition on a mixed siliciclastic–carbonate system, and is divided into six members. The Canyon Springs and lower Hulett members are each dominated by carbonate rocks, deposited mainly in the shallow subtidal and on ooid shoals (McMullen et al. 2014). The Stockade Beaver Shale was deposited on a mixed carbonate–siliciclastic shelf, with offshore, carbonate mudstone facies to the west, and siliciclastic offshore and offshore transition facies to the east. The upper Hulett Member is a siliciclastic incised-valley fill capped by transgressive ooid shoal facies. The Redwater Shale Member was deposited on a wave-dominated siliciclastic shelf, and the Windy Hill Sandstone was deposited in a tidal estuary. The Windy Hill grades upward through progressive loss of tidal influence into overlying coastal plain deposits of the Upper Jurassic Morrison Formation (lower Oxfordian to lower Tithonian).
The Twin Creek Formation is exposed in the Wyoming Range of westernmost Wyoming and eastern Idaho, and comprises a thick sequence of marine carbonates and shales deposited on a mixed evaporate–carbonate ramp. The Twin Creek thickens to the west, where it reaches a maximum thickness of about 700 m in the Twin Creek Trough. It is subdivided into seven members that were deposited in spectrum of environments ranging from desert mudflat and sabkha to carbonate offshore ( Imlay 1967). The Twin Creek Formation is overlain by middle Callovian to Oxfordian Preuss and Stump formations, deposited in hypersaline intertidal mud flats (Kocurek & Dott 1983) and deltas (Patterson-Wittstrom 1980), and they are in turn unconformably overlain by the Cretaceous Gannett Group.
Text and figures modified after Danise and Holland 2017.
The Gypsum Spring Formation, with a maximum thickness of about 80 m, was deposited on a mixed evaporate–carbonate–siliciclastic ramp, with depositional environments that include distal ooid shoals, open shallow subtidal, restricted shallow subtidal, peritidal, salinas and desert mud flat to sabkha (Clement & Holland 2016).
The Sundance Formation is approximately 100 m thick, records cyclical deposition on a mixed siliciclastic–carbonate system, and is divided into six members. The Canyon Springs and lower Hulett members are each dominated by carbonate rocks, deposited mainly in the shallow subtidal and on ooid shoals (McMullen et al. 2014). The Stockade Beaver Shale was deposited on a mixed carbonate–siliciclastic shelf, with offshore, carbonate mudstone facies to the west, and siliciclastic offshore and offshore transition facies to the east. The upper Hulett Member is a siliciclastic incised-valley fill capped by transgressive ooid shoal facies. The Redwater Shale Member was deposited on a wave-dominated siliciclastic shelf, and the Windy Hill Sandstone was deposited in a tidal estuary. The Windy Hill grades upward through progressive loss of tidal influence into overlying coastal plain deposits of the Upper Jurassic Morrison Formation (lower Oxfordian to lower Tithonian).
The Twin Creek Formation is exposed in the Wyoming Range of westernmost Wyoming and eastern Idaho, and comprises a thick sequence of marine carbonates and shales deposited on a mixed evaporate–carbonate ramp. The Twin Creek thickens to the west, where it reaches a maximum thickness of about 700 m in the Twin Creek Trough. It is subdivided into seven members that were deposited in spectrum of environments ranging from desert mudflat and sabkha to carbonate offshore ( Imlay 1967). The Twin Creek Formation is overlain by middle Callovian to Oxfordian Preuss and Stump formations, deposited in hypersaline intertidal mud flats (Kocurek & Dott 1983) and deltas (Patterson-Wittstrom 1980), and they are in turn unconformably overlain by the Cretaceous Gannett Group.
Text and figures modified after Danise and Holland 2017.
Lithostratigraphic sections
Fossils
For Schools:
learning about the fossils of the Sundance Seaway
1_adaptation.pdf | |
File Size: | 95 kb |
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2_walk_like_a_dinosaur.pdf | |
File Size: | 875 kb |
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3_life_in_the_jurassic_sundance_seaway.pdf | |
File Size: | 197 kb |
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