Significance of δD_(kerogen), δ~(13)C_(kerogen) and δ~(34)S_(pyrite) from several Permian/Triassic (P/Tr) sections

摘要

For the first time we report δD of kerogen (δD_(kerogen)) for three Permian-Triassic (P-Tr) sequences (Hovea#3, Perth Basin, Western Australia; Jameson Land, East Greenland and Lusitaniadalen, Spitsbergen). We have compared δD_(kerogen) with δ~(13)C of kerogen (δ~(13)C_(kerogen)) and δ~(34)S of total reduced inorganic sulfur (TRIS, essentially pyrite; δ~(34)S_(pyrite)) of all the sections and for one sample set with δ~(13)C of carbonate (δ~(13)C_(carbonate)) to establish (i) similarities between the sections and (ii) evaluate whether these signals are local and/or global. Stable isotope shifts occur for all three sample sets either at the P-Tr transition (Western Australia) or coinciding with the marine ecosystem collapse (Spitsbergen and East Greenland) δD_(kerogen) reflects organic matter (OM)/ kerogen type and is not sensitive to the low level of thermal maturation. Reliable palaeoenvironmental information in terms of the use of δD can therefore only be obtained for the P-Tr transition from hydrogen compound-specific isotope analyses (CSIA) of biomarkers (Nabbefeld et al., 2010b). The negative shifts in δ~(13)C_(carbonate) (primary) and δ~(13)C_(kerogen) are attributed to the release of ~(13)C-depleted carbon into the atmosphere, whereas the isotopic excursions in δ~(34)S_(pyrite) relate to palaeoredox changes. However, the global coincidence in timing of the shifts in δD_(kerogen), δ~(34)S_(pyrite) and δ~(13)C_(kerogen) suggests a relation between the sulfur, carbon and hydrogen cycles. The negative shifts in δ~(13)C_(carbonate) (primary) are in general attributed to the release of ~(13)C-depleted source of carbon into the oceans and atmosphere, whereas δ~(13)C_(kerogen) can reflect the latter in certain cases, but can also be superimposed by varying sources of OM/kerogen type. Isotopic excursions in δ~(34)S_(pyrite) relate to global changes in the palaeoredox conditions that affect sulfur cycling in the ancient seas.