Biomarker distributions and their stable isotopes in marine Permian/Triassic sections from around the globe

A compound specific isotope approach using biomarkers associated with the event from P/Tr sections from around the globe ( Western Australia, Eastern Greenland and Kashmir-Tibet) is in progress. Gradual changes in 13C/12C of dissolved inorganic carbon in the marine realm appeared to have occurred perhaps over several million years before the end of the Permian. It appears in many cases (but not all) that isotopic trends are not just simple records of changes in 13C/12C of carbon reservoirs, since some trends are consistent with a palynofacies change from charcoal-wood to algal-amorphous dominated organic matter, respectively. In contrast, 13C/12C of the molecular fossils such as pristane and phytane can represent robust proxies for the isotopic composition of phytoplanktonic organic matter inputs, and/or an increase in stratification towards the Triassic causing enhanced recycling of 13C-depleted CO2. C14-C18 n-alkyl carbon chains have multiple inputs, comprising phytoplankton and heterotrophs. If derived from phytoplankon, the isoprenoids are depleted in 13C compared to the co-occurring isoprenoids by ca. 1.5 per mil There is also independent evidence such as the abundance and d 13 C of porphyrins, the abundance and 13C/12C of selected polycyclic aromatic hydrocarbons for high algal productivity in the Triassic. 13C/12C of higher plant and phytoplankton biomarkers, and carbonates in the P-Tr section from Eastern Greenland show similar isotopic changes across the P-Tr transition indicating a global disruption to the carbon cycle. This data provides further evidence for a switch in the mode (or extent) of organic carbon remineralisation at the P-Tr transition.

Personnel

K. Grice, R. Twitchett, C.B. Foster, R.E. Summons

Funding

ARC (QEII), MIT was supported by the NASA Exobiology grant NAG5-1236.

Collaborators

Plymouth University ( UK), Geoscience Australia ( Canberra), MIT ( USA),