The Unconformity That Isn’t: A Sequence-Stratigraphic Reinterpretation of the J-5 Unconformity and the Redwater–Windy Hill–Morrison Transition in Wyoming, USA

Holland, Steven M.; Wright, Sarah N.

doi:10.1086/708433

“…As the Oxfordian regression of the Curtis Sea persisted and the climate became more humid (Demko et al ., 2004; Boucot et al ., 2013; Danise & Holland, 2017), the shoreline developed as a tide‐dominated deltaic system (Holland & Wright, 2020). These sandstone‐dominated strata, which belong to the Windy Hill Member of the Morrison Formation (Pipiringos, 1979), indicate that tidal currents lingered despite a shrinking sea (Uhlir et al ., 1988; Danise & Holland, 2018; Holland & Wright, 2020). As a result, fluvial processes might have impacted the coastal dynamics locally, but the lack of geological record prevents any interpretation of where and how strong these fluvial processes were.…”

Section: Geological Contextmentioning

confidence: 99%

“…North of the central Sundance Sea and up to the connection with the open ocean, the climate was more temperate than the arid climate prevailing around the Curtis Sea (Sellwood & Valdes, 2006; Uhl et al ., 2012). As the Oxfordian regression of the Curtis Sea persisted and the climate became more humid (Demko et al ., 2004; Boucot et al ., 2013; Danise & Holland, 2017), the shoreline developed as a tide‐dominated deltaic system (Holland & Wright, 2020). These sandstone‐dominated strata, which belong to the Windy Hill Member of the Morrison Formation (Pipiringos, 1979), indicate that tidal currents lingered despite a shrinking sea (Uhlir et al ., 1988; Danise & Holland, 2018; Holland & Wright, 2020).…”

Section: Geological Contextmentioning

confidence: 99%

“…). These sandstone-dominated strata, which belong to the Windy Hill Member of the Morrison Formation (Pipiringos, 1979), indicate that tidal currents lingered despite a shrinking sea (Uhlir et al, 1988;Danise & Holland, 2018;Holland & Wright, 2020). As a result, fluvial processes might have impacted the coastal dynamics locally, but the lack of geological record prevents any interpretation of where and how strong these fluvial processes were.…”

mentioning

confidence: 99%

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Tidal dynamics in palaeo‐seas in response to changes in physiography, tidal forcing and bed shear stress

Zuchuat

¹

,

Steel

²

,

Mulligan

³

et al. 2022

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Simulating hydrodynamic conditions in palaeo-ocean basins is needed to better understand the effects of tidal forcing on the sedimentary record. When combined with sedimentary analyses, hydrodynamic modelling can help inform complex temporal and spatial variability in the sediment distribution of tide-dominated palaeo-ocean basins. Herein, palaeotidal modelling of the epicontinental Upper Jurassic (160 Ma, lower Oxfordian) Sundance and Curtis seas of North America reveals possible regional-scale variations in tidal dynamics in response to changes in ocean tidal forcing, physiographic configuration and bottom drag coefficient. A numerical model forced with an M2 tidal constituent at the open boundary shows that the magnitude and location of tidal amplification, and the variability in current velocity and bed shear stress in the basin, were controlled by palaeophysiography. Numerical results obtained using a depth of 600 m at the ocean boundary of the system enable the prediction of major facies trends observed in the lower Curtis Formation. The simulation results also highlight that certain palaeophysiographic configurations can either permit or prevent tidal resonance, leading to an overall amplification or dampening of tides across the basin. Furthermore, some palaeophysiographic configurations generated additional tidal harmonics in specific parts of the basins. Consequently, similar sedimentary successions can emerge from a variety of relative sea-level scenarios, and a variety of sedimentary successions may be deposited in different parts of the basin in any given relative sea-level scenario. These results suggest that the interpretation of sedimentary successions deposited in strongly tide-influenced basins should consider changes in tidal dynamics in response to changing sea level and basin physiography.

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“…The lack of high-resolution biostratigraphy and absolute dating of Curtis-Summerville interval makes precise regional correlation between units in the Curtis Sea and Sundance Sea challenging. Nevertheless, as the Oxfordian regression of the Curtis Sea persisted and the climate became more humid (Demko et al, 2004;Boucot et al, 2013;Danise & Holland, 2017), the shoreline developed as a tide-dominated deltaic system (Holland & Wright, 2020). These sandstone-dominated strata, which belong to the Windy Hill Member of the Morrison Formation (Pipiringos, 1968), indicate that tidal currents lingered despite a shrinking sea (Uhlir et al, 1988;Danise & Holland, 2018;Holland & Wright, 2020).…”

Section: Geological Contextmentioning

confidence: 99%

Tidal dynamics in palaeo-seas in response to changes in bathymetry, tidal forcing, and bed shear stress

Zuchuat¹,

Steel²,

Mulligan³

et al. 2020

Preprint

1

0

View full text Add to dashboard Cite

Simulating hydrodynamic conditions in palaeo-ocean basins is needed to better understand the effects of tidal forcing on the sedimentary record. When combined with sedimentary analyses, hydrodynamic modelling can help inform complex temporal and spatial variability in the sediment distribution of tide-dominated palaeo-ocean basins. Herein, palaeotidal modelling of the epicontinental Upper Jurassic (160 Ma, lower Oxfordian) Sundance and Curtis seas of North America reveals possible regional-scale variations in tidal dynamics in response to changes in ocean tidal forcing, physiographic configuration and bottom drag coefficient. A numerical model forced with an M2 tidal constituent at the open boundary shows that the magnitude and location of tidal amplification, and the variability in current velocity and bed shear stress in the basin, were controlled by palaeophysiography. Numerical results obtained using a depth of 600 m at the ocean boundary of the system enable the prediction of major facies trends observed in the lower Curtis Formation. The simulation results also highlight that certain palaeophysiographic configurations can either permit or prevent tidal resonance, leading to an overall amplification or dampening of tides across the basin. Furthermore, some palaeophysiographic configurations generated additional tidal harmonics in specific parts of the basins. Consequently, similar sedimentary successions can emerge from a variety of relative sea-level scenarios, and a variety of sedimentary successions may be deposited in different parts of the basin in any given relative sea-level scenario. These results suggest that the interpretation of sedimentary successions deposited in strongly tide-influenced basins should consider changes in tidal dynamics in response to changing sea level and basin physiography.

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“…The J‐4 and J‐5 unconformities mark the boundaries between the lower and upper Sundance Formation, and the Sundance to Morrison Formation respectively in South Dakota, Wyoming, Utah and Colorado (Figure 2). The J‐5 unconformity is generally recognised as separating the Redwater Shale Member and older members of the Sundance Formation from the Windy Hill Sandstone of the Morrison Formation (Pipiringos, 1957; Pipiringos & O'Sullivan, 1978; McMullen et al, 2014; Meyers & Breithaupt, 2014; Uhlir et al, 1988), although its existence has recently been challenged (Danise & Holland, 2018; Holland & Wright, 2020; Kowallis et al, 1998).…”

Section: Introductionmentioning

confidence: 99%

Unconformity generation and the shift from storm‐dominated to tide‐dominated processes in a Jurassic retroarc foreland basin: Insights from ichnology

Wroblewski

¹

,

Morris

²

2023

The Depositional Record

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An enigmatic transition from the storm‐dominated, offshore to lower shoreface deposits of the Redwater Shale Member (Sundance Formation) to the overlying mixed tidal and aeolian Windy Hill Sandstone (Morrison Formation) in the Oxfordian of the North American Western Interior has long been a source of intrigue. Previously proposed drivers include the progradation of a large, tide‐dominated delta onto a storm‐dominated shelf, a complete reorganisation of the basin's hydrodynamics and climate, or the development of a regional unconformity (termed the J‐5). In south‐eastern Wyoming, the Redwater Shale is characterised as an offshore to distal shoreface deposit with glauconitic siltstones and sandstones punctuated by coquinoid and sandy tempestites and hosting a Cruziana Ichnofacies. The Windy Hill Sandstone, a time‐transgressive, sand‐rich, intertidal succession with classic Pteraichnus and stressed Skolithos Ichnofacies, sharply overlies the Redwater Shale and records an abrupt basinward shift in facies that accompanied at least tens of metres of sea‐level fall. New, detailed sedimentological, ichnological and architectural data collected across this transition in the study area provide fresh insights into the depositional history of these units and demonstrates the existence locally of a composite J‐5 unconformity. The unconformity developed as tectonically driven, prograding shoreline trajectories of the Redwater Shale gave way to degrading trajectories of the Windy Hill Sandstone, leading to a forced regression and formation of a regressive surface of marine erosion. The sharp juxtaposition of intertidal flat facies (Pteraichnus Ichnofacies) directly upon offshore to lower shoreface deposits (Cruziana Ichnofacies) is the key to recognising the unconformity and proves the value of the previously underutilised ichnological data.

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The Unconformity That Isn’t: A Sequence-Stratigraphic Reinterpretation of the J-5 Unconformity and the Redwater–Windy Hill–Morrison Transition in Wyoming, USA

Cited by 6 publications

References 60 publications

Tidal dynamics in palaeo‐seas in response to changes in physiography, tidal forcing and bed shear stress

Tidal dynamics in palaeo‐seas in response to changes in physiography, tidal forcing and bed shear stress

Tidal dynamics in palaeo-seas in response to changes in bathymetry, tidal forcing, and bed shear stress

Unconformity generation and the shift from storm‐dominated to tide‐dominated processes in a Jurassic retroarc foreland basin: Insights from ichnology

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