HIGH RESOLUTION LATE PALEOZOIC CYCLOSTRATIGRAPHY OF THE KEELER BASIN, INYO MOUNTAINS, CALIFORNIA, SOUTHWEST LAURENTIA

Strata deposited during the Late Paleozoic encapsulate an important transition in Earth’s history where peak icehouse climate conditions transitioned to greenhouse conditions. Strata in the Inyo Mountains of eastern California contain a uniquely-continuous 6 Myr deep marine record of Virgilian through Asseliean stages that spans the Pennsylvanian–Permian boundary. To better understand the evolution of southwest Laurentia and its interaction with glacially-driven eustacy, we measured two >500 m composite stratigraphic sections of the Keeler Canyon Formation at the decimeter scale, and collected a handheld gamma ray log. These strata alternate at the five to twenty meter scale, between intervals of carbonate turbidites and debrites and pink siliciclastic mudstone containing tan siliciclastic turbidites. Deformation during several tectonic events complicates field relationships, but detailed (1:5,000) mapping of faults and folds permits reassembly of two continuous sections. Based on facies characteristics and a prominent marker horizon, we propose subdividing the Keeler Canyon Fm. into four new members, from oldest to youngest: the Pennsylvanian Cerro Gordo and Salt Tram Members; the Pennsylvanian-Permian Cable Member; and the Permian Estelle Member. With published conodont biostratigraphy and correlative U-Pb geochronology from eastern Europe we estimate sediment accumulation rates within the Keeler Canyon Formation. Then we use spectral analysis using R package “astrochron” to examine the periodicity in facies repetitions and develop an astrochronologic model for sediment accumulation rate across the study interval. This analysis reveals prominent eccentricity forcing at both sections. Sediment accumulation rates calculated using the average spectral misfit method decrease during the upper Pennsylvanian, reach a minimum near the Pennsylvanian–Permian boundary, then accelerate sharply into the Asselian. This increase could reflect eustatic enhancement of carbonate productivity or sediment routing during the Asselian icehouse, or alternatively, could reflect the approach of the enigmatic Last Chance thrust and a transition to a wedge-top setting during the Permian.