Multiple S-isotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction

Global fossil data show that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale at the end of the Permian. Many hypotheses have been proposed to explain this extinction and yet still remain greatly debated. Here, we report analyses of all four sulphur isotopes (32S, 33S, 34S and 36S) for pyrites in sedimentary rocks from the Meishan section in South China. We observe a sulphur isotope signal (negative δ34S with negative Δ33S) that may have resulted from limitation of sulphate supply, which may be linked to a near shutdown of bioturbation during shoaling of anoxic water. These results indicate that episodic shoaling of anoxic water may have contributed to the profound biodiversity crisis before the final catastrophe. Our data suggest a prolonged deterioration of oceanic environments during the Late Permian mass extinction

Vascular plant biomarker distributions and stable carbon isotopic signatures from the Middle and Upper Jurassic (Callovian-Kimmeridgian) strata of Staffin Bay, Isle of Skye, northwest Scotland

The molecular and stable carbon isotopic composition of higher plant biomarkers was investigated in Middle to Upper Jurassic strata of the Isle of Skye, northwest Scotland. Aromatic hydrocarbons diagnostic of vascular plants were detected in each of nineteen sedimentary rock samples from the Early Callovian to Early Kimmeridgian interval, a succession rich in fossil fauna including ammonites that define its constituent chronozones. The higher plant parameter (HPP) and higher plant fingerprint (HPF) calculated from the relative abundance of retene, cadalene and 6-isopropyl-1-isohexyl-2-methylnaphthalene (ip-iHMN) exhibit several large fluctuations throughout the Skye succession studied. These molecular profiles contrast with both (1) the more uniform profiles previously observed in Jurassic successions, putatively of the same age, from other palaeogeographical settings, including the Carnarvon Basin, Western Australia and (2) the steady rise in global sea level during this interval. This suggests that the HPF profiles of Jurassic marine successions may not be reliable indicators of global climate change. Our results indicate that other factors such as local tectonism, resulting in changes to the relief and landscape of the hinterland, likely influenced the palaeoflora and the mode of transport of its detritus into adjacent marine depocentres. However, the Skye succession showed similar d13C profiles of total organic carbon (TOC; comprising mainly fossil wood), the vascular plant biomarker retene and a predominant phytoplanktonic biomarker (phytane). The apparent isotopic relationship between terrigenous and marine-derived biomarkers supports a strong coupling of the atmosphere and ocean. The maximum isotopic excursion occurs in the Cardioceras cordatum ammonite biozone of the Early to Middle Oxfordian, which may be indicative of changes in atmospheric and oceanic levels of CO2

Disentangling Diagenesis From the Rock Record: An Example From the Permo-Triassic Wordie Creek Formation, East Greenland

The measurement of isotope ratios in sedimentary rocks deposited over geological time can 6 provide key insights to past environmental change over important intervals in the past. However, it is 7 important to be aware that secondary alteration can overprint the original isotopic records. We demonstrate 8 this principle using high-resolution carbon, sulfur, and oxygen isotope measurements in organic carbon, 9 pyrite, and carbonate minerals (d 10 13Corg, d34Spyr, d34SCAS, d13Ccarb, and d18Ocarb) and kerogen analyses (HI and OI) from the Wordie Creek Formation, East Greenland. These sediments were initially deposited across the 11 Permo-Triassic transition, but as we will show, the carbonate record has been altered by interaction with 12 meteoric water significantly after initial deposition. Comparison of the better preserved organic carbon and 13 pyrite records with a proximal Permo-Triassic sequence reveals significant pyrite-sulfur isotope variability 14 across the Permo-Triassic transition. This regional heterogeneity argues against basin-wide euxinia and 15 instead suggests localized changes in sulfur fractionation in response to variations in organic carbon flux. 16 This hypothesis can be used to explain seemingly inconsistent regional trends in other sulfur isotopes across 17 the Permo-Triassic transition