explain explain the multi- Myr lag between the δ C excursion and global cooling. We use planktic foraminiferal B/Ca, 11 13 δ B, δ C, and Mg/Ca to reconstruct surface ocean carbonate chemistry and temperature. We propose that the MCOwas associated with elevated oceanic dissolved inorganic carbon caused by volcanic degassing, global warming, and sea-level rise. A key negative feedback of this warm climate was the organic carbon burial on drowned continental shelves.

Sośnicka, M., Lüders, V., 2020. Fluid inclusion evidence for low-temperature thermochemical sulfate reduction (TSR) of dry coal gas in Upper Permian carbonate reservoirs (Zechstein, Ca2) in the North German Basin. Chemical Geology 534, 119453.

http://www.sciencedirect.com/science/article/pii/S0009254119305820 Upper Permian Zechstein carbonate Ca2 gas reservoirs in the southern part of the Pompeckj Block in the North German Basin locally contain up to 36 vol% hydrogen sulfide (H S) produced by thermochemical sulfate 2 reduction (TSR). TSR was triggered by migration of dry to extremely dry coal gas from Upper Carboniferous into the Zechstein carbonate reservoirs. Methane reacted with dissolved sulfate at temperatures of <150 °C, as inferred from fluid inclusions hosted in fracture-filling minerals and cements in the carbonate reservoir rocks. Such low temperatures for methane-dominated TSR are unique and were not observed so far, as it was widely believed that alteration of super dry methane requires much higher temperatures. Here we present detailed compositional and carbon isotope data of reservoir gases as well as those of gases trapped in fluid inclusions hosted in cements and fracture-filling minerals in Zechstein Ca2 carbonate reservoir rocks. We constrained the P-T conditions of gas entrapment, hydrocarbon reactivity and the lower temperature limit for TSR. The results of this study decipher three major stages of gas migration in the Pompeckj Block. Stage I commenced in the Late Triassic during burial when Zechstein Ca2 reservoirs were charged with dry CH - 4 CO ± N gas sourced from mature Upper Carboniferous coals. Burial continued through the Jurassic and 2 2 caused alteration of Ca2 reservoir gas by sulfate reduction reactions due to increasing temperatures. Entrapment of CH -H S-CO -N gases in fluid inclusions, hosted in cements and fracture-filling minerals, occurred at 4 2 2 2 temperatures between 100 and 152 °C and was related to Stage II uplift in the Early Lower Cretaceous. In the Late Cretaceous (Stage III) deep burial of the Pompeckj Block led to charge of the Zechstein Ca2 carbonate reservoirs with Upper Carboniferous-derived CH -CO ± N ±C coal gas and/or dilution of existing reservoir 4 2 2 2+ 13 gas at temperatures of 144 -167 °C. Highly variable δ C values from -18.7 to -8.7‰ and very negative CH4 13 13 δ C values (-22.4 to -18.9‰) of H S-rich fluid inclusion gases as well as negative δ C values (-10.4 to CO2 2 -4.6‰) of host calcites reveal compelling evidence for participation of methane in TSR. Fluid inclusions imply that CH -dominated TSR proceeded at T of 135 °C in the presence of catalyzers such as H S and dissolved 4 min 2 2+ Mg . This study demonstrates that fluid inclusions serve as an excellent and accurate tool for tracing H S 2 concentrations in hydrocarbon gases through time and space, which is not possible using the present-day compositions of natural reservoir gases. It also contributes to the understanding of carbonate reservoir-hosted hydrocarbon-bearing fluid systems and processes that significantly control the quality of reservoir gases.

Spaak, G., Edwards, D.S., Grosjean, E., Scarlett, A.G., Rollet, N., Grice, K., 2020. Identifying multiple sources of petroleum fluids in Browse Basin accumulations using semi-volatile compounds. Marine and Petroleum Geology 113, 104091.

http://www.sciencedirect.com/science/article/pii/S0264817219305276 Hydrocarbon fluid correlation studies often rely on compounds that are source-specific, but only represent a minor fraction of the bulk fluid (e.g. steranes). The correlation in the present study utilises compounds that represent a significant proportion of the bulk fluid (semi-volatile aromatics (SVA)) and diamondoids. Comprehensive two dimensional gas chromatography coupled to time-of- flight mass spectrometry (GC × GC - TOFMS) was used to analyse diamondoids and SVA in whole oil/condensate samples from the Browse Basin, North West Shelf, Australia. Together with aromatic maturity ratios and the stable carbon isotopic composition for selected diamondoids and alkylbenzenes, these analyses demonstrate that numerous accumulations within