Pennsylvanian-permian lithostratigraphy, chemostratigaphy, and astrochronology of the Western Laurentian margin, California and Nevada, U.S.A.

Stauffer, Eric Alexander (2022) Pennsylvanian-permian lithostratigraphy, chemostratigaphy, and astrochronology of the Western Laurentian margin, California and Nevada, U.S.A. Masters thesis, Northern Arizona University.

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Abstract

Waxing and waning of continental ice sheets on Gondwana during the Late Paleozoic Ice Age induced high-magnitude eustatic sea-level fluctuations from the mid Mississippian to early Permian that have been long-attributed to orbitally-driven insolation variation. These changes are recorded in cyclic marine strata worldwide, and are particularly prominent in North America, where a series of basins contains the deposits of paleoequatorial seas. To better understand orbital forcing, glacial-interglacial cycles, and the expression of shelf and slope lithofacies across a deep- to shallow-marine stratigraphic transect, we measured several thick sections of conodont-bearing upper Pennsylvanian through lower Permian strata along the western Laurentian margin. Decimeter-scale stratigraphy and a gamma ray log of the Keeler Canyon Formation were measured at Ubehebe Mine, CA, adding to an existing record at Cerro Gordo, CA. These strata are a thick succession of intercalated gravity flow deposits, turbidites, and marlstones. We also documented the coeval shallow marine Bird Spring Formation at Arrow Canyon, NV, and collected 150 carbonate samples at 0.5-meter intervals across the Pennsylvanian-Permian boundary. Cyclicity at Ubehebe Mine is expressed by prominent oscillations between intervals of debrites and turbidites and thinner intervals of silty marlstones, whereas at Arrow Canyon, shallow water carbonate facies predominate, and compositional cyclicity is less prominent. δ13C values vary between 1‰ and 4‰ across the section at the 5 to 40 meter scale and likely correspond to oscillations in global marine waters between interglacial sea-level highstands and glacial sea-level lowstands. During the Pleistocene icehouse, higher δ13C values in marine carbonates have been widely interpreted to correspond to enhanced oceanic productivity during the onset of glaciation, whereas lower δ13C values are typically interpreted to represent decreased oceanic productivity from less vigorous thermohaline circulation during interglacial periods. The highest δ13C values and shallowest lithofacies from the Arrow Canyon section occur in early Asselian strata, consistent with a glacial period and sea-level lowstand, and global Pennsylvanian-Permian δ13C records. Coarse-grained turbidites and debrites from the Keeler Canyon Formation often record higher δ13C values, which are consistent with an increase in shelf instability and gravity-flow processes during sea-level lowstand. Marlstone intervals typically have lower δ13C values, and record intervals during which the shelf was inundated and deposition was focused up-dip. Silt in these intervals may record enhanced aeolian transport. Correlations between the Cerro Gordo and Ubehebe Mine sections suggest that both the outer and mid apron sections record depositional cyclicity, consistent with allocyclic forcing due to glacioeustatic sea-level fluctuations. Systematic changes in sediment accumulation rate can be correlated across the Keeler Canyon Formation from sections ~40 km apart, including lulls at the Kasimovian-Gzhelian and Pennsylvanian-Permian boundaries. The lull across the Pennsylvanian -Permian boundary could record the transition from a shelf-proximal setting to a sediment-starved foredeep basin, and also coincides with contractile deformation in northern Nevada. Spectral analysis of gamma ray and δ13C time series reveal prominent bundled periodicities that closely match predicted Late Paleozoic orbital cycles and the existing record of Late Paleozoic orbital cycles. The 405, 123, and 95 Ky eccentricity cycles were identified at all locations, and obliquity and precession are apparent in several densely-sampled portions of the Keeler Canyon Formation. Additionally, the average durations between intervals of the debrite and coarse-grained turbidite lithofacies are consistent with the periods of long-and short-eccentricity, respectively. This suggests that orbital forcing, and particularly eccentricity cycles, modulated the Late Paleozoic glacial-interglacial oscillations, glacioeustatic sea-level fluctuations, and cyclostratigraphic marine deposition. Biostratigraphic age-control, apparently continuous and relatively high sediment accumulation rates, and a detailed lithostatigraphic and astrochronologic record, make the Keeler Canyon Formation at Ubehebe Mine a potential candidate to be the Global Boundary Stratotype Section and Point (GSSP) to define the base of the Gzhelian Stage in the global chronostratigraphic scale.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Astrogeology; Carbonates; Planetary geology; Sedimentology; Stratigraphy; Tectonics; Western Laurentian margin; California; Nevada
Subjects:	Q Science > QE Geology
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of the Environment, Forestry, and Natural Sciences > School of Earth Sciences and Environmental Sustainability
Date Deposited:	14 Jun 2023 16:45
Last Modified:	14 Jun 2023 16:45
URI:	https://openknowledge.nau.edu/id/eprint/6021

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