Paper No. 9
Presentation Time: 3:55 PM
CARBONATE CLUMPED ISOTOPE THERMOMETRY OF FOSSIL BONE AND DENTIN: PROSPECTS FOR USE AS A GROUND TEMPERATURE THERMOMETER
SUAREZ, Marina B., Earth and Planetary Sciences, Johns Hopkins University, 301 Olin Hall, 3400 N. Charles St, Baltimore, MD 21218 and PASSEY, Benjamin H., Earth and Planetary Sciences, Johns Hopkins University, 301 Olin Hall, 3400 North Charles Street, Baltimore, MD 21218, marinabsuarez@gmail.com
It is generally accepted that tooth enamel is a reliable recorder of stable isotopes as they relate to biology and environment of fossil animals, whereas less crystalline phases like bone and dentin are susceptible to isotopic alteration during diagenesis. However, it has been suggested that early bone diagenesis often occurs at time scales similar to soil formation, and therefore that isotopes in bone may record aspects of the soil environment relating to paleoenvironment. Such a tool would be valuable in settings where pedogenic carbonates are not present but where vertebrate fossils are abundant. Here we utilize carbonate clumped isotope thermometery to assess temperatures recorded in the carbonate component of fossil bone and dentine ranging in age from Pleistocene to Cretaceous. We analyzed Pleistocene mammal bones from a range in latitudes (and hence ground temperatures) to assess the hypothesis that early diagenesis reliably resets clumped isotope temperatures to local ground temperatures. We find that the lowest clumped isotope temperatures occur at the highest latitudes, but that large deviations from the isotope temperature vs. ground temperature 1:1 line are common. For example, clumped isotope temperatures from Alaska range from 41±2°C to 22±2°C suggesting that bone preserves temperatures ranging from mammalian body temperature (~38°C) to values ~25°C warmer than early burial temperature (<0°C).
To assess a longer term resistance to diagenesis, we analyzed fossil bone from older strata. Bone from the Cretaceous Cedar Mountain Formation yields apparent temperatures of 50–60°C that approach maximum burial temperatures. Bone from the Eocene Willwood Formation yields ~40°C, similar to temperatures observed for paleosol carbonates, but cooler than sparry calcite infill of bone (54°C to 60°C). Miocene bone from the Chinese Loess Plateau on the other hand yields temperatures warmer than paleosol carbonates (~34°C, versus 18°C). These results suggest that carbonate clumped isotope temperatures of bone and dentin reflect complex factors unique to each setting, including fossilization environment, rate of fossilization, and burial history, and that only special circumstances will permit the use of bone clumped isotopes as a straightforward climatic paleothermometer.
