Bedrock Geology Map of the Naomi Peak 7.5\u27 Quadangle, Cache County, Utah and Novel Age Constraints on its Cambrian Strata

Geologists use various “rock-clocks” in order to interpret the timing and tempo of events in Earth’s history. These include global geochemical events in the oceans (chemostratigraphy), the evolution of certain fossil species (trilobite biostratigraphy), and the radiogenic decay of uranium to lead in certain mineral such as zircon (U-Pb geochronology). Integrating these methods in the stratigraphic record in one location can provide a well-constrained timeline for a select part of the Geologic, or Deep Time, record. This technique is especially important in the Cambrian Period (538.8 to 486.9 million years; Ma), which sets the stage for life today with the rise of animals including familiar groups like arthropods. The Naomi Peak 7.5’ Quadrangle, situated in the Bear River Range, Northern Utah boasts a largely unstudied yet well-preserved and exposed package of sedimentary rocks, with an unusually thick succession of Cambrian strata. We present an updated bedrock geology map of the Naomi Peak Quadrangle, which provides greater detail regarding the character of the sedimentary succession of the rocks in the map area and reveals small, previously unmapped faults. We use these strata as a living laboratory to test the integration and calibration of traditional rock-clocks and have refined the biostratigraphy of several map units. We build upon previous work in the area by integrating trilobite biostratratigraphy and chemostratigraphy of a prominent oceanic geochemical event called the Steptoean Positive Isotopic Carbon Excursion (SPICE), which provides the first useful age constraint ≤494.4 ± 0.5 Ma. This requires boundaries of the late Cambrian Time Scale to become younger by several millions of years. Dating the SPICE and associated trilobite biozones is key to understanding patterns in evolution and environmental changes due to variations in the ancient carbon cycle, which will be important to understanding the effects of a rapidly changing carbon cycle in the modern