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ABSTRACT Current investigations into the Albian–Cenomanian sedimentary record within the Western Interior have identified multiple complex tectono‐sedimentary process–response systems during the ongoing evolution of North America. One key sedimentary succession, the upper Cedar Mountain Formation (Short Canyon Member and Mussentuchit Member), has historically been linked to various regionally and continentally significant tectonic events, including Sevier fold‐and‐thrust deformation. However, the linkage between the Short Canyon Member and active Sevier tectonism has been unclear due to a lack of high‐precision age constraints. To establish temporal context, this study compares maximum depositional ages from detrital zircons recovered from the Short Canyon Member with that of a modified Bayesian age stratigraphic model (top‐down) to infer that the Short Canyon Member was deposited atca100 Ma, penecontemporaneous with rejuvenated thrusting across Utah [Pavant (Pahvant), Iron Springs and Nebo thrusts]. These also indicate a short depositional hiatus with the lowermost portion of the overlying Mussentuchit Member. The Short Canyon Member and Mussentuchit Member preserve markedly different sedimentary successions, with the Short Canyon Member interpreted to be composed of para‐autochthonous orogen–transverse (across the Sevier highlands) clastics deposited within a series of stacked distributive fluvial fans. Meanwhile, the muddy paralic Mussentuchit Member was a mix of orogen–transverse (Sevier highlands and Cordilleran Arc) and orogen–parallel basinal sediments and suspension settling fines within the developing collisional foredeep. However, the informally named last chance sandstone (middle sandstone of the Mussentuchit Member) is identified as an orogen–transverse sandy debris flow originating from the Sevier highlands, similar to the underlying Short Canyon Member. During this phase of landscape evolution, the Short Canyon Member – Mussentuchit Member depocentre was a sedimentary conduit system that would fertilize the Western Interior Seaway with ash‐rich sediments. These volcaniclastic contributions, along with penecontemporaneous deposits across the western coastal margin of the Western Interior Seaway, eventually would have lowered oxygen content and resulted in a contributing antecedent trigger for the Cenomanian–Turonian transition Oceanic Anoxic Event 2.
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A 40 Ar/ 39 Ar and U–Pb timescale for the Cretaceous Western Interior Basin, North America
Abstract Improvements in analytical procedures in parallel with intercalibration of40Ar/39Ar and U–Pb methods and laboratories, spurred since 2003 by the EarthTime geochronology community initiative, have led to ±2σuncertainties of the order of 50–100 ka, or better, for Cretaceous ash beds. Assembled here are 5740Ar/39Ar ages and 17238U–206Pb ages of volcanic ash beds in strata of the Western Interior Basin of North America determined during the last 15 years since these improvements have been made. These age determinations span from 108 Ma in the middle Albian to 66 Ma in the latest Maastrichtian. Five of the40Ar/39Ar ages from Campanian and Maastrichtian strata are newly reported here, whereas the remainder are from the literature. Building on the pioneering work of John Obradovich and Bill Cobban, where possible these age determinations are tied to ammonite and inoceramid biostratigraphy. For most ash beds, the temporal uncertainties, unlike earlier timescales for the Western Interior Basin, are much shorter than the duration of fossil biozones. Proposed ages for stage boundaries based on this review of the radioisotopic ages include: Maastrichtian–Danian, 66.02 ± 0.08 Ma; Campanian–Maastrichtian, 72.20 ± 0.20 Ma; Santonian–Campanian, 84.19 ± 0.38 Ma; Coniacian–Santonian, 86.49 ± 0.44 Ma; Turonian–Coniacian, 89.75 ± 0.38 Ma; Cenomanian–Turonian, 93.95 ± 0.05 Ma; Albian–Cenomanian, 100.00 ± 0.40 Ma. Six bentonites that occur within theVascoceras diartianum, Neocardiocerus juddi, Prionocylus macombi, Scaphites preventricosus, Scaphites depressusandDesmoscaphites bassleriammonite zones, dated using both40Ar/39Ar and U–Pb methods, yield ages in agreement to within 150 ka and form the backbone of the Western Interior Basin timescale. In parallel, improvements in the taxonomy of ammonites, inoceramids and foraminifera, and recent field work, are better establishing the biostratigraphic framework for these age determinations. Each of these efforts contributes to the progressive refinement of the chronostratigraphic framework of the Western Interior Basin, and enhances its utility for global correlation.
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- Award ID(s):
- 1951812
- PAR ID:
- 10649942
- Editor(s):
- Hart, MB
- Publisher / Repository:
- Geological Society London
- Date Published:
- Journal Name:
- Geological Society, London, Special Publications
- Volume:
- 544
- Issue:
- 1
- ISSN:
- 0305-8719
- Page Range / eLocation ID:
- 367 to 391
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1144/SP544-2023-76
