Geologic Map of the Bayhorse Anticline, Custer County, Idaho: Windermere Supergroup West of the Lemhi Arch

Brennan, Daniel T.; Pearson, David; Link, Paul K.; Chamberlain, Kevin R.

doi:10.1130/abs/2019am-338148

Cited by 4 publications

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“…Our mapping documents (Figure 4; Brennan et al, 2020) that an approximately 250 m thick gradational stratigraphic contact, that consists of upward coarsening shale and siltstone to interlayered quartzite, shaly quartzite, and finally predominantly quartzite, marks the transition from the Ramshorn Slate to the overlying Clayton Mine Quartzite (Figure 5a). These field observations indicate that a relatively structurally intact stratigraphic section exists west from Daugherty Gulch (Figure 4).…”

Section: Resultsmentioning

confidence: 70%

“…These rocks were previously considered to be Ordovician in age (e.g., Hobbs et al, 1991). However, new geochronology, provenance analysis, and field‐based mapping (Figure 4; Brennan et al, 2020; Krohe et al, 2020) described here indicate an older, Neoproterozoic to Cambrian age. In addition to the new age designation, our work demonstrates a compelling correlation with better‐studied rift‐related and early passive margin strata exposed elsewhere along the western margin of Laurentia (e.g., Yonkee et al, 2014).…”

Section: Introductionmentioning

confidence: 54%

“…Note the locations of recently documented Neoproterozoic rocks west of the Lemhi arch at Edwardsburg (Lund et al, 2003), Stibnite (D. Stewart et al, 2016), and the Bayhorse region (this study; Brennan et al, 2020; Krohe et al, 2020). The 1:24,000 scale detailed geologic mapping of the Bayhorse region (Brennan et al, 2020) is denoted, of which a simplified map can be seen in Figure 4. Proposed Snake River transfer fault of Lund (2008) and the approximate extent of the Lemhi arch are shown.…”

Section: Introductionmentioning

confidence: 65%

“…This section consists of the 667 Ma tuff of Daugherty Gulch (Isakson, 2017; Lund et al, 2010), which is overlain by ~1.5 km of dolostone and argillite that coarsen upward into the ~1 km thick Clayton Mine Quartzite. Small (<100 m) gabbroic sill‐like bodies (hereby referred to as the Ramshorn gabbro; Brennan et al, 2020) intruded into the Ramshorn Slate within this gradational contact.…”

Section: Resultsmentioning

confidence: 99%

“…Simplified geologic map (adapted from 1:24,000 scale mapping of Brennan et al, 2020) of the northern portion of the Bayhorse anticline, central Idaho. The Daugherty Gulch borehole containing the Cryogenian 667.8 ± 0.22 Ma (Isakson, 2017) tuff in the northeastern corner of the field area, as well as detrital zircon sample locations, are denoted.…”

Section: Introductionmentioning

confidence: 99%

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Neoproterozoic Windermere Supergroup Near Bayhorse, Idaho: Late‐Stage Rodinian Rifting Was Deflected West Around the Belt Basin

et al. 2020

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Conflicting models of Rodinian rifting have been proposed to explain the recognized variation in the Neoproterozoic and early Cambrian tectonostratigraphic architecture of the western Laurentian margin. However, discrimination among rift models is hampered by limited exposure and metamorphism of the rocks. Southeastern Idaho preserves more than 6 km of Neoproterozoic and Cambrian strata. In contrast, along the inferred continuation of the margin in east central Idaho, correlative rocks are missing across the Lemhi arch. Our field mapping and U‐Pb dating studies, located approximately 50 km west of the Lemhi arch unconformity, focused on a succession of regionally extensive rocks that were previously assigned an Ordovician age. We show that ~1.5 km of strata here overlies a ~667 Ma reworked felsic tuff and was intruded by a 601 ± 27 Ma gabbro sill; we thus redesignate these rocks as Cryogenian and Ediacaran in age. These rocks are overlain by a ~1 km thick Ediacaran to middle Cambrian quartzite. Middle Ordovician quartzites overlie these middle Cambrian strata, indicating that though Neoproterozoic and lower Cambrian rocks are present west of the Lemhi arch, upper Cambrian and Lower Ordovician rocks are thin or absent. Comparison of this redesignated section to the closest correlative sections suggests an initial stage of symmetric rifting followed by later asymmetric rifting. We suggest that prerifting ~1,370 Ma magmatism within the Belt basin produced lithospheric rigidity that influenced the final stage of rifting and produced heterogeneity in the geometries of structural domains similar to those documented in other well‐defined, modern rift margins.

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Section: Resultsmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 65%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Neoproterozoic Windermere Supergroup Near Bayhorse, Idaho: Late‐Stage Rodinian Rifting Was Deflected West Around the Belt Basin

et al. 2020

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Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

Brennan

Pearson

Link

et al. 2023

Laurentia: Turning Points in the Evolution of a Continent

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The Windermere Supergroup in southern British Columbia and its correlatives (such as the Pocatello Formation and lower Brigham Group in southeastern Idaho) along the western North American Cordilleran margin are an archetype of Neoproterozoic to early Paleozoic tectonic, sedimentary, and climatic processes. The central Idaho portion of the margin remains relatively understudied when compared to regions to the south in southeastern Idaho or to the north in northeastern Washington. This is in part a legacy of early workers, who identified the absence of Neoproterozoic and Cambrian strata in east-central Idaho across the Lemhi arch. However, Neoproterozoic and Cambrian rocks are indeed present west of the Lemhi arch within the central Idaho section of the Cordillera. Here, we summarize recent advances in our understanding of these strata within central Idaho and correlate the Pocatello Formation and Brigham Group rocks from northern Utah/southeastern Idaho through central Idaho to northeastern Washington. We also provide new constraints that link Cambrian strata from central Idaho across the Lemhi arch to southwestern Montana. Collectively, this emerging tectono-stratigraphic framework suggests extensive, some likely diachronous, stratigraphic boundaries and magmatic events relating to (1) widespread rifting ca. 720–680 Ma; (2) early and late Cryogenian (Sturtian and Marinoan) glacial sedimentation; (3) base-level drawdown and formation of incised valleys, previously correlated to the Marinoan glacial interval, but which now appear to be younger (ca. 600 Ma) and perhaps related to tectonic activity; (4) onset of the Sauk I transgression 560–530(?) Ma; (5) the ca. 515 Ma Sauk II lowstand, perhaps related to final rifting in southern Laurentia; and (6) the Sauk III lowstand coeval with exhumation of 500–490 Ma Beaverhead plutons within the Lemhi arch. Magmatism occurred ca. 680 Ma, 660 Ma, 600 Ma, and 500 Ma, providing age ties. These observations suggest that Neoproterozoic and lower Paleozoic strata in the central Idaho sector of the North American Cordillera record similar processes and sedimentation as strata elsewhere along the margin.

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Supplemental Material: Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

Brennan¹,

al.²

2022

Preprint

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Geologic Map of the Bayhorse Anticline, Custer County, Idaho: Windermere Supergroup West of the Lemhi Arch

Cited by 4 publications

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Neoproterozoic Windermere Supergroup Near Bayhorse, Idaho: Late‐Stage Rodinian Rifting Was Deflected West Around the Belt Basin

Neoproterozoic Windermere Supergroup Near Bayhorse, Idaho: Late‐Stage Rodinian Rifting Was Deflected West Around the Belt Basin

Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

Supplemental Material: Neoproterozoic to early Paleozoic tectono-stratigraphic framework for central Idaho: Windermere Supergroup in the northern sector of the U.S. Cordillera

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