| The carbonate clumped isotope thermometer is based on an isotope exchange reaction that promotes 'clumping' of heavy isotopes into a single carbonate ion as temperature decreases. This proxy has great potential for advancing our understanding of the evolution of Earth's surface and its changing climate as, unlike the traditional oxygen isotope paleothermometer, it is independent from the water in which the carbonate precipitated.;We develop and modify existing methodologies of this new proxy and demonstrate a precision +/- 0.005‰ for Delta47.;We present a new approach to standardizing Delta47 by referencing data to theoretical predictions of the abundances of isotopologues of CO 2. Using this reference frame, we achieve inter-laboratory reproducibility of +/- 0.01‰, and revise paleotemperature scales that should be used to convert carbonate clumped isotope signatures to temperature.;To assess the integrity of the proxy over long timescales and the effect of closed system burial diagenesis, we measure the clumped isotopic signature of carbonatites. Pristine carbonatites suggest free exchange of carbon and oxygen atoms within the carbonate lattice occurs at high temperatures, but there is no systematic trend in the clumped isotope signature of pristine carbonatites with age. We conclude that their solid-state re-ordering is sufficiently slow to enable the use of the proxy on timescales of 108 years, but that diagenetic resetting can still occur, even without bulk recrystallization.;We apply the proxy to the Late Cretaceous to determine the temperature and oxygen isotopic composition of the Western Interior Seaway. Using a vital effect correction based on measuring modern nautilus, we reconstruct temperatures to within a range of 15 to 20°C, which agrees with previous estimates from general circulation models and other proxies. The delta18O of the seaway is similar to the ice-free global ocean average, whereas a freshwater environment records significantly more depleted water. We see evidence for cooling in the seaway between the Late Campanian and Maastrichtian.;Carbonate clumped isotope thermometry has also been applied to soil and lacustrine carbonate from the Tibetan plateau to assess the timing of uplift, and to Holocene lake sediments from Lake Turkana, Kenya. |
