PROVENANCE OF THE PALEOGENE GOLER FORMATION, SOUTHERN CALIFORNIA, AND IMPLICATIONS FOR BASIN DEVELOPMENT IN THE SOUTHWESTERN US CORDILLERA

The Paleogene Goler Formation, located east of the southern Sierra Nevada and north of the Garlock Fault, is one of the only basins in the SW Cordillera that preserves early Cenozoic strata and uniquely records tectonic changes along the margin at that time. The Goler Fm. comprises about 3.5 km of mainly siltstones, sandstones, and conglomerates (described in a companion abstract by Trammell et al. (this meeting)). This study combines new and previously-published detrital zircon (DZ) U-Pb analyses to evaluate temporal changes in provenance of the Goler Formation. The lowest ~ 1000 m of Goler strata are dominated by Middle to Late Jurassic grains (90 – 95%) with a peak age of ca. 165 Ma. The remaining grains have Late Cretaceous ages (100 – 85 Ma). Plutons of Middle Jurassic age are somewhat uncommon; potential sources for the ca. 165 Ma grains include the Argus Range to the northeast, the southeastern Sierra Nevada to the west, and the Alvord Mountain and Iron Ridge regions of the Mojave to the south. The latter region also exposes Permian – Triassic intrusions, the ages which are notably absent in Goler DZ spectra. A source in the Argus Range is most consistent with west-directed paleocurrents in the lower Goler. Up section, the proportion of Late Cretaceous grains increases (up to 35%), and age spectra become more complex; Middle to Late Jurassic grains span a broader range of ages (175 – 145 Ma) and additional subordinate Late Triassic – Early Jurassic populations (peak ages of ca. 195 Ma) are observed. Late Cretaceous zircons, with peak ages between 97 – 90 Ma, are most likely sourced from the southern Sierra Nevada batholith, which bounds the Goler basin to the west and exposes voluminous granitoids of similar age. Igneous rocks of ca. 195 Ma age are rare in the SW Cordillera and zircon populations of that age may require input from a more distal source, possibly in the central Sierra Nevada batholith. Collectively, these DZ data suggest derivation of the lower Goler Formation from local sources to the east, transitioning through time to mixed souring from both eastern and western sources. These results align with a model of the Goler Basin forming in a Paleogene supra-detachment basin where provenance was limited to the hanging wall early in its history but switched to a mixed provenance as the footwall (Sierra Nevada) was exhumed.