Waxing and waning of continental ice sheets on Gondwana during the late Paleozoic ice age induced high-magnitude eustatic sea-level fluctuations that have long been attributed to orbitally driven insolation variation and are recorded in mid-Mississippian through Early Permian cyclic marine strata worldwide. These strata are particularly prominent in western North America, where a series of basins contain thick 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 stratigraphic sections of conodont-bearing upper Pennsylvanian through lower Permian strata along the western Laurentian margin, sampled carbonate for stable isotope analysis, and collected handheld gamma ray logs of the Keeler Canyon Formation at Ubehebe Mine and Cerro Gordo, California, and the coeval Bird Spring Formation at Arrow Canyon, Nevada, USA. The Keeler Canyon Formation is a 1-km-thick succession of intercalated gravity flow deposits, turbidites, and marlstones and was deposited coeval with the Bird Spring Formation, which consists predominantly of shallow-marine carbonates. Cyclicity at Ubehebe Mine and Cerro Gordo is a prominent facies alternation between intervals of debrites and turbidites with high carbonate δ13C values (−4.12‰ to 2.80‰; 0.92‰ average, from the Cerro Gordo section) and intervals of organic-rich silty marlstones with low δ13C values (−5.68‰ to 3.73‰; 0.05‰ average, from the Cerro Gordo section). Coeval strata at Arrow Canyon consist of shallower marine carbonate lithofacies with less prominent variation in lithofacies and generally high (−1.10‰ to 5.02‰; 3.42‰ average) carbonate δ13C values. During the Pleistocene icehouse, low- and high-δ13C marine carbonates accumulated during interglacial highstands and glacial lowstands, respectively, with 13C enrichment attributed to glacially enhanced thermohaline circulation and resultant productivity and accumulation of 12C as organic matter in marine sediments. Using the Pleistocene icehouse as analog, coarse-grained turbidite and debrite intervals of the Keeler Canyon Formation represent increased shelf instability and gravity-flow transport to the deep sea due to lowered sea level during glaciations, and intervening organic-rich marlstone intervals represent interglacial periods when the shelf was inundated and deposition was focused up-dip. Asselian Stage strata yield the highest δ13C values in the Keeler−Bird Spring record, consistent with the global Asselian record of significant glaciation and associated low sea level. To better understand the dynamics of lithofacies cyclicity and their relationship with orbital forcing, we constructed a high-resolution time scale and analyzed gamma ray−measured elemental K, U, and Th concentrations and δ13C time-series constrained by U-Pb-dated conodont zones using the “Astrochron” R package. Evolutive harmonic analysis reveals prominent bundled periodicities that closely match predicted late Paleozoic orbital cycles and the existing record of late Paleozoic orbital cycles. The 405 k.y., 123 k.y., and 95 k.y. eccentricity cycles were identified at all locations, and obliquity and precession are apparent in densely sampled portions of the Keeler Canyon Formation. The results indicate that long- and short-eccentricity cycles are discernable across both shelf and deep sea deposits of equivalent age, and likely controlled the timing of sea-level fluctuations and deposition of debrites and coarse-grained turbidites in the Keeler Canyon Formation, which have average recurrence intervals of 404 k.y. and 102 k.y., respectively, suggesting that deposition of these lithofacies was paced by the long- and short-eccentricity cycles. Enhanced deposition of these lithofacies during sea-level lowstand was likely paced by minima in the eccentricity cycles, which are thought to reduce seasonal contrast and summer ice melting, leading to greater ice sheet accumulation and glacioeustatic sea-level lowering.
Stauffer et al. (Wed,) studied this question.