APTIAN-ALBIAN DEPOSITION WITHIN AN AXIALLY-DRAINED SYNTECTONIC BASIN IN THE SEVIER HINTERLAND IN NORTH-CENTRAL NEVADA: INSIGHTS FROM MAPPING AND U-PB GEOCHRONOLOGY FROM THE NEWARK CANYON FORMATION IN THE CORTEZ MOUNTAINS

Syntectonic sedimentary basins provide details on the style, timing, and magnitude of deformation within fold-thrust belts, which are essential for understanding orogen dynamics. Within the hinterland of the Sevier thrust belt in Nevada, the timing and magnitude of contractional deformation are poorly constrained. In central Nevada, exposures of the Newark Canyon Formation (NCF), a Cretaceous unit interpreted to be related to regional contractional deformation, offer the opportunity to interpret basin evolution and bracket deformation timing. Here, we present new mapping, facies analysis, and U-Pb geochronology from an exposure of the NCF in the Cortez Mountains, in north-central Nevada.

We divided the NCF into five members. The base of the section consists of unconsolidated mudstone with channelized sandstone and conglomerate which grades upward into a coarse-clastic meandering system, and capped by a fine-grain system with carbonate-paleosol beds. Map pattern exhibit an overall fining-to-south pattern. U-Pb zircon ages from tuffaceous intervals near the base and the top of the section yielded deposition ages of 119.8 ± 3.4 Ma and 109.1 ± 3.8 Ma, respectively (1σ).

The entire exposure dips ~30° eastward and is disconformably overlain by Paleogene volcanic rocks. Therefore, all eastward tilting can be attributed to post-Paleogene extension. Outcrop-scale, NE-striking thrust-sense wedge faults form at acute angles to bedding throughout the section, and are the only contractional structures observed.

Based on exposure-wide distribution of conglomerates with identical clast composition, characteristic fluvial-depositional facies, and an overall southward fining, we interpret that the NCF was deposited in a S-draining alluvial plain system. Development of topography during growth of the SE-vergent Garamundi anticline and Adobe syncline, which are exposed in the Abode Range to the northeast, may have generated accommodation for the basin. The wedge faults that deform the NCF strike subparallel to the trend of these folds, and may indicate minor, post-depositional shortening related to fold growth. The axis of the Adobe syncline projects SW to the NCF exposure, and therefore the NCF basin may have accommodated axial drainage along a topographic low generated along the Adobe syncline axis.