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

Upper Cambrian strata were deposited on a rapidly subsiding carbonate ramp that, in western Utah and eastern Nevada, developed into a carbonate shelf with major eustatic rise during late Elvinia chron into Irvingella major and Taenicephalus chrons. Irvingella major caps the Steptoean stage and Pterocephallid biomere, and Taenicephalus chron marks the base of the Sunwaptan stage. The Sneakover Limestone of the Orr Formation spans the Steptoean-Sunwaptan boundary and is characterized by meter-scale cycles across the eastern Great Basin. This interval is globally correlated by the negative-trending limb of an excursion of δ¹³C known as the Steptoean Positive Isotopic Carbon Excursion. The deep-water equivalent of the Sneakover Limestone in eastern Nevada is the Barton Canyon Member of the Windfall Formation. It also is cyclic, but overlying strata of the Catlin Member of the Windfall Formation consists of carbonate turbidite deposits. This study focuses on cyclicity within the Sneakover and Barton Canyon limestones and anomalous depositional environment of the Catlin Member above, interpreted as a drowning unconformity. This raises two questions: what is the isotopic signature of a drowning unconformity? What are the potential causes of the unconformity? Seven sections were measured, described, and logged for gamma-ray profiles to create a sequence stratigraphic framework for the Sneakover Limestone and correlates. These methods allow for high-resolution correlation of sections and identification of sequence-stratigraphic surfaces. Combining this data with C data from overlying deep-water turbidities will help to understand limitations on accumulation of cycles where carbonate productivity is curtailed from subsidence and eustatic rise.