UPPER CAMBRIAN CYCLICITY AND STABLE-ISOTOPE RECORD OF A DROWNING UNCONFORMITY IN THE CATLIN MEMBER OF THE WINDFALL FORMATION, EASTERN GREAT BASIN, USA

Cambrian strata across western Utah and eastern Nevada were deposited on a carbonate ramp during late Elvinia chron. The top of Elvinia zone is marked by a crisis interval recognized as Irvingella major zone, a faunal extinction that caps the Pterocephallid biomere. In Utah, the biomere boundary is found in the middle part of the Sneakover Limestone Member of the Orr Formation. The Sneakover consists of meter-scale cyclic carbonates that continue upward through much of the Hellnmaria Member of the Notch Peak Formation. In Nevada, the crisis interval is found at the top of the Barton Canyon Limestone Member of the Windfall Formation. It too is cyclic and composed of meter-scale carbonate beds, but in contrast with Utah sections, overlying strata of the Catlin Member of the Windfall Formation are composed of turbidites. Upward, these are overlain by wavy-bedded carbonate strata and ultimately, the more massive Bullwhacker Limestone Member. Previous investigators have noted the correlation of turbidites with the thick succession of meter-scale cycles in Utah and interpreted the top of the Barton Canyon Limestone as a drowning unconformity.

Various investigations have posited that meter-scale cyclicity of the Sneakover Limestone largely was related to precessional cycles. The aims of this study are two-fold: 1, evaluate and potentially correlate cyclicity within the Sneakover Limestone and Barton Canyon members, and, 2, examine the stable isotopic record of δ¹³C of the drowning unconformity in the lower Catlin Member. Seven stratigraphic sections were measured, described, and logged for gamma-ray profiles at 30-cm-scale for correlation. Gamma-ray cross sections are be hung from the Pterocephaliid-Ptycaspid biomere boundary for the correlation of cycles across the carbonate ramp. Coupling synchronous correlations of cyclicity with stratigraphic thicknesses allows for high-resolution estimation of accommodation rates. Combining this with δ¹³C data from overlying deep-water turbidities can help to understand the regional patterns of sedimentation associated with rapid subsidence combined with sea-level rise on the western margin of Laurentia.