How Hot Is Too Hot? Disentangling Mid‐Cretaceous Hothouse Paleoclimate From Diagenesis

Abstract

The Cretaceous was a time of highly active tectonism, including the ongoing breakup of supercontinent Pangaea and increased seafloor spreading rates, as well as of greenhouse climate, including elevated global temperatures and a reduced equator-to-poles temperature gradient (

Hot Rocks: Interpreting Extremes of Earth Surface Temperatures From the Geologic Record

“…This requires both field and microscopic observations of sedimentary relationships, structures, and microfacies. Fetrow et al (2022) and a prior study (Fetrow et al, 2020) provide detailed description of the relationships between the complex types of continental carbonates present in the Cretaceous Newark Canyon Formation (NCF), Nevada. The carbonates can be categorized in one of the three categories: pedogenic carbonates, palustrine carbonates, and lacustrine carbonates.…”

“…Fetrow et al. (2022) provide an example of the wide‐ranging effort needed to put clumped isotope‐derived temperatures into context. It starts with an understanding of depositional setting.…”

“…“Bare‐skin” temperatures influence by direct radiative heating can provide explanations for many of these hot temperature, but they are not useful for paleoclimate studies (other than providing some potential seasonal limits for flora and fauna as Fetrow et al. (2022) point out). Meanwhile, warm season biases in carbonate precipitation in soils and lacustrine carbonates provide a partial explanation for why some paleoclimate data do not match climate model data, but it also provides implications for being able to truly determine just how hot Greenhouse Earth could get.…”

“…Diagenetic alteration must also be evaluated. Again, Fetrow et al (2022) conducted a detailed examination of isotope data and investigation of burial history of the sedimentary package. Fetrow et al utilize both the carbon and oxygen isotope value of the carbonates, their clumped isotope derived temperature and the water isotope value calculated to examine different potential diagenetic trends.…”

“…Another advantage to the clumped isotope paleothermometer is the ability to calculate water isotope values. On this front, Fetrow et al (2022) provide an intriguing result. Water isotope values for the lower palustrine facies of the NCF and upper lacustrine facies of the NCF range from −2.97 to +2.71‰.…”