Evolution of the Pennsylvanian Ely–Bird Spring Basin: Insights from Carbon Isotope Stratigraphy

Abstract

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.