A tropically hot mid-Cretaceous North American Western Interior Seaway

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

Automated summary

The mid-Cretaceous thermal maximum is considered one of the warmest periods in Earth's history, accompanied by significant paleoceanographic changes and the formation of epicontinental seaways. Analyzing Cenomanian oyster fossils revealed extreme mid-latitude warmth in North America, providing insights into Late Cretaceous temperature trends. The findings highlight the potential of clumped isotope paleotemperatures in resolving upper thermal limits of Phanerozoic greenhouse climates.