This paper reports the structural and stratigraphic history of Buck Mountain, Nevada, and its regional significance in the development of southwestern Laurentia during the late Paleozoic. The two distinct generations of folding have similar style and/or timing to other fold sets in late Paleozoic strata of northern Nevada. Unconformities in the upper Paleozoic strata at Buck Mountain are consistent with unconformities documented in northern and east-central Nevada. Northwest-vergent folds (F 1 ) in the Morrowan–Atokan Ely Limestone are erosionally truncated and unconformably overlain by the middle Desmoinesian Hogan Formation and middle Wolfcampian (Sakmarian) Upper Strathearn Formation. This upper Paleozoic stratigraphic package was subsequently refolded by the Buck Mountain Syncline and associated mesoscale folds (F 2 ). F 2 folds lack tight age control but are interpreted to be associated with the Cretaceous central Nevada thrust belt. Critically, none of these structures are localized above or below low-angle faults. The unconformity between the Ely and Hogan formations is consistent with the C5 regional unconformity. Importantly, it constrains the age of northwest-vergent deformation on Buck Mountain. West-vergent folds and west-directed thrusts are documented at several locations in northern and east-central Nevada, but because of the dominance of the C6 unconformity and/or lack of robust age control, the age of these structures has not been tightly constrained. The evidence at Buck Mountain indicates that west-vergent structures predate the C5 unconformity. Buck Mountain is important because it: (1) precisely brackets the age of west-vergent deformation in Nevada to pre–mid-Desmoinesian (sub C5-unconformity) and (2) defines a southeastern edge to the late Paleozoic west-vergent deformation in northern and east-central Nevada.

Analysis and correlation of strata in ancient basins are commonly difficult due to a lack of high-resolution age control. This study tackled this problem for the latest Mississippian to middle Pennsylvanian Ely–Bird Spring basin. Here, 1095 new carbon isotope analyses combined with existing biostratigraphy at six sections throughout the basin constrain changes in relative sediment accumulation rates in time and space. The Ely–Bird Spring basin contains dominantly shallow-water carbonates exposed in eastern and southern Nevada, western Utah, and southeastern California. It formed as part of the complex late Paleozoic southwestern Laurentian plate margin. However, the detailed evolution of the basin, and hence the tectonic driver(s) of deformation, is poorly understood. The combined isotopic and biostratigraphic data were correlated using the Match-2.3 dynamic programming algorithm. The correlations show a complex picture of sediment accumulation throughout the life of the Ely–Bird Spring basin. Initially, the most rapid sediment accumulation was in the eastern part of the basin. Throughout Morrowan time, the most rapid sediment accumulation migrated to the northwestern part of the basin, culminating in a peak of sediment accumulation in Atokan time. This peak records tectonic loading at the north or northwest margin of the basin. Basin sedimentation was interrupted by early Desmoinesian time in the north by formation of northwest-directed thrust faults, folds, uplift, and an associated unconformity. Deposition continued in the south with a correlative conformity and increased clastic input. The combination of isotopic and biostratigraphic data for correlation is therefore a valuable tool for elucidating temporal basin evolution and can be readily applied to tectonically complex carbonate basins worldwide.

ABSTRACT Large-scale landslide deposits (covering >1 km 2 ) are prevalent throughout the Basin and Range province. However, their presence and importance in the evolution of the Basin and Range remain poorly recognized. On this field trip, we will visit four landslide deposits along the eastern flank of the Spring Mountains on the western margin of Las Vegas Valley. The first half of the day will be spent looking at vertical and lateral textures within the Blue Diamond landslide deposit, which mostly caps hills and ridges between the southern ends of the Wilson Cliffs and Blue Diamond Hill. We interpret this deposit as having a two-phase emplacement, with an initial rock avalanche emplacement onto Blue Diamond Hill, followed by failure as a rock compound landslide along weak gypsum layers in the Kaibab Formation. During the second half of the day, we will visit a smaller rock avalanche deposit (La Madre), a large rock compound slide that resulted from failure of the northern flank of Blue Diamond Hill (Red Rock Wash), and a large block of Paleozoic rock that likely was emplaced as either a rock compound slide or a rock planar slide (Lone Mountain).