The Sheep Pass Formation type section in east-central Nevada preserves lacustrine (lake), palustrine (wetland), and microbialite carbonates deposited within a high-elevation lake basin between the latest Cretaceous and middle Eocene. This interval spans a pivotal time in geologic history; it encompasses the Cretaceous-Paleogene (K-Pg) mass extinction, as well as long-term greenhouse conditions and rapid warming events that serve as some of our best analogs for future climate change under un-mitigated anthropogenic warming. Understanding terrestrial records from this time contributes an invaluable perspective beyond the better-constrained marine realm. However, continental settings are complex and variable, requiring a diverse range of paleoenvironmental proxies and settings to holistically describe this climate response on land.

Characterizing the carbonate sedimentology and stable isotope geochemistry of the Sheep Pass Formation type section has the potential to provide a nuanced record of environmental change in a high-elevation setting during this crucial past climate interval. My dissertation work combines transmitted light and cathodoluminescence petrography, X-ray diffraction mineralogy, and various stable isotope geochemistry tools (δ¹³C, δ¹⁸O, and Δ₄₇) to describe the paleoenvironmental trends preserved in the Sheep Pass Basin. I find that the Sheep Pass Formation type section preserves a dynamic and sensitive lake basin due to its small size, with evidence that microbialites – lithified microbial mats – thrived in place of a more complex metazoan food web. I also find sedimentological and geochemical evidence for the potential expression of both long-term and short-term global climate signals, including warming from the late Paleocene to early Eocene, as well as abrupt climate transitions like the K-Pg boundary and early Paleogene hyperthermal climate events. Lastly, carbonate microbialites from the Sheep Pass Formation type section preserve geochemical evidence for local-scale photosynthetic carbon cycling, similar to both modern and modeled observations. In full, this work highlights that the careful characterization of ancient carbonates from the Sheep Pass Formation type section reveals a new and unique record of global- and local-scale environmental change during an important geologic climate interval.