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 This field guide synthesizes more than a half century of research by many geologists and paleontologists on Frenchman Mountain and Rainbow Gardens, southern Nevada, USA. The field-trip consists of seven stops to be visited in one day. The guide was written not only for field-trip participants on the occasion of the 2022 ­Cordilleran/Rocky Mountain Geological Society of America Joint Section Meeting in Las Vegas, but also with future users in mind. The Frenchman Mountain/Rainbow Gardens block of crust exposes an extraordinary sample of Earth history. The geologic features include (1) Proterozoic crystalline rocks, (2) the Great Unconformity, (2) a Paleozoic interval that is essentially a ­tilted section of the western Grand Canyon, (3) a Mesozoic interval that preserves strata that were eroded off the southern Colorado Plateau during the Miocene “Great Denudation” episode, and (4) a Cenozoic section that records a wealth of paleo­climatic, paleontological, and tectonic data. Among the many stories that are recorded in the rocks of the Frenchman Mountain/Rainbow Gardens block, I have chosen three to emphasize in this field guide: (1) the history recorded in the Proterozoic Vishnu Basement Complex and the Great Unconformity; (2) the stratigraphy, sedimentology, paleontology, and geochronology of the Cambrian Tonto Group [with a focus on (a) trilobite biostratigraphy in the Bright Angel Formation, (b) the significance of the abundance of glauconite in the Tonto Group, and (c) the Frenchman Mountain Dolostone]; and (3) the tectonic story recorded in the Thumb Member of the Horse Spring Formation. The basement rocks record events and processes associated with the assembly of supercontinents Nuna and Rodinia. The Great Unconformity records the breakup of Rodinia and the associated denudation interval that played a role in triggering the Cambrian explosion. The Tonto Group, which was recently expanded to include the Frenchman Mountain Dolostone, records the Sauk Transgression. And the Thumb Member of the Horse Spring Formation contains rock avalanche deposits that have played a key role in sorting out the tectonic history of the southern Nevada region and the translational history of the Frenchman Mountain/Rainbow Gardens block.

ABSTRACT This field trip will visit the southern Black Mountains volcanic center (SBMVC) and its associated products in northwestern Arizona. Post-volcanic extension and erosion of this semi-arid area afford the opportunity to examine a Miocene-aged (ca. 19–17 Ma) volcanic terrain in detail, using an approach that integrates fieldwork, petrography and geochemistry, and remotely sensed data. This approach was recently used in a three-year National Science Foundation Research Experience for Undergraduate (NSF REU) program, from which some results will be highlighted. This integrated approach can provide insight into the amounts and types of information that can be gleaned from various types of remotely sensed data of a volcanic terrain. Over three days, we will work our way through the volcanic section associated with the SBMVC as exposed near Oatman and Kingman, Arizona, to observe: (1) felsic to mafic shallow intrusions; (2) deposits from felsic to intermediate explosive and effusive eruptions; (3) deposits from sedimentary processes; and (4) the results of subsequent extensional faulting. The petrologic, physical volcanic, and morphologic characteristics of observed outcrops will be discussed at each field stop, and will be used as points of discussion while in the field, for observations of presumably volcanic terrains on other planetary bodies. An appended road log serves as a geologic guide to this volcanic center and associated rocks.