A tropically hot mid-Cretaceous North American Western Interior Seaway

Abstract The mid-Cretaceous thermal maximum (KTM) during Cenomanian to Santonian times from ca. 100 83 Ma is considered among Earth's warmest sustained intervals of the Phanerozoic. time interval also characterized by major paleoceanographic changes in form an oceanic anoxic event and flooding epicontinental seaways, such as Western Interior Seaway North America. We report carbonate clumped isotope (?47) paleotemperatures (T?47) KTM measured oyster fossils Seaway. Following screening specimens for diagenesis exclusion geographic zones with evidence consistent solid-state ?47 reordering, a mean T?47 28–34 °C (95% confidence standard error mean) primary calcite quantifies extreme mid-latitude warmth When combined existing Campanian Maastrichtian marine records, new data constrain Late Cretaceous temperature trends underlying evolution American faunal stratigraphic records. These peak highlight potential this proxy quantitatively resolve upper limits Phanerozoic greenhouse climates.