C-isotope geochemistry – tool for chemostratigraphy and carbon cycle history

Abstract

Chemostratigraphy uses chemical fingerprints stored in sediments and sedimentary rocks for stratigraphic correlation. Stable carbon isotope signatures fixed in sedimentary inorganic and organic matter are among the most powerful proxies used in chemostratigraphy. Carbon isotope records provide information on both stratigraphy and on the history of the global carbon cycle, as documented in early studies which were focusing on Cretaceous C-isotope records 8e.g. (Scholle & Arthur, 1980). The Mesozoic C-isotope record is punctuated by repeated negative and positive carbon isotope anomalies with amplitudes reaching several permil. Globally identified negative carbon isotope spikes in the carbonate and organic carbon isotope records at the Permo-Triassic Boundary (e.g. Oberhänsli et al., 1989), at the Triassic-Jurassic boundary (e.g. Galli et al., 2005), in the Toarcian (e.g. Hesselbo et al., 2000) and Aptian (e.g. Menegatti et al., 1998) and at the Paleocene –Eocene Boundary (e.g. Röhl et al., 2007) correspond to major perturbations of the carbon cycle, possibly triggered by sudden release of carbon dioxide and/or methane from volcanic or gas hydrate sources. These negative spikes in the carbon isotope record serves as excellent stratigraphic marker. Positive carbon isotope excursions with a duration of up to millions of years record the response of the biosphere to carbon cycle perturbation. Increased organic carbon burial rates contribute to climate stabilization after times of rapid injection of carbon dioxide into the atmosphere (negative spikes). Positive excursions provide stratigraphic information, which can be used for establishment of accurate age models in earth history. Keywords: Carbon isotopes, chemostratigraphy, carbon cycle, Mesozoic