High-resolution late Paleozoic cyclostratigraphy and tectonic evolution of the Keeler Basin, California, southwest Laurentia

Cyclic strata exposed in the Inyo Moun-tains of eastern California contain a continu-ous 6 m.y. record of deep marine deposition that spans the Pennsylvanian-Permian boundary. To better understand the geo-logic evolution of southwest Laurentia and the role of glacially driven eustasy in upper Paleozoic stratigraphy, we measured two detailed similar to 600 m composite stratigraphic sections of the Keeler Canyon Formation and collected a handheld spectral gamma ray log. Post-depositional deformation com-plicates field relationships, but 1:5000 scale mapping of faults and folds permits assem-bly of two continuous sections. Measured strata alternate at the 5-20 m scale between intervals of fine-grained laminated marl-stone and intervals of mixed carbonate and siliciclastic turbidites and debrites. Based on facies characteristics and a prominent marker horizon, we reassign the Pennsyl-vanian-Permian age upper Salt Tram unit of the upper Keeler Canyon Formation to a new Estelle Member. We estimate sedi-ment accumulation rates within the Keeler Canyon Formation using published con-odont biostratigraphy and correlative U-Pb geochronology from Eastern Europe com-bined with spectral analysis and timescale optimization using the Astrochron R pack-age. Evolutive harmonic analysis of gamma ray-derived element concentrations reveals prominent bundled periodicities that are consistent with both long and short eccen-tricity cycles. Average sediment accumula-tion rates calculated using the time scale optimization function of Astrochron suggest a gradual increase from 40-60 m/m.y. to similar to 120 m/m.y. during the late Pennsylvanian and then a minima of similar to 50 m/m.y. near the Pennsylvanian-Permian boundary, which is followed by an increase to similar to 175 m/m.y. into the Early Permian. This trend in sediment accumulation rates and subsequent Perm-ian contractile deformation are compatible with flexural subsidence in a SW-migrating foreland basin related to the southern part of the late Antler orogenic system.

Automated summary

This study examines the deep marine deposition during the late Pennsylvanian-Early Permian period in eastern California and reveals the variations in sediment accumulation rates. It also proposes a new division of the Estelle Member and suggests a link between sediment accumulation rates and flexural subsidence.