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

Effects of sulfide minerals on aromatic maturity parameters: Laboratory investigation using micro-scale sealed vessel pyrolysis

Sedimentary organic matter from the Here’s Your Chance (HYC) Pb–Zn–Ag deposit (McArthur Basin, Northern Territory, Australia) displays increased thermal maturity compared to nearby non-mineralised sediments. Micro-scale sealed vessel pyrolysis (MSSVpy) of an immature, organic rich sediment from the host Barney Creek Formation (BCF) was used to simulate the thermal maturation of OM from the HYC deposit, and to assess the effect of sulfide minerals on organic maturation processes. MSSVpy at increasing temperatures (300, 330 and 360 C) resulted in increased methylphenanthrene maturity ratios which were within the range reported for bitumen extracted from HYC sediments. The methylphenanthrene index ratio from MSSVpy of the BCF sample was lower than in HYC, due to a reduced proportion of methylated phenanthrenes. Polycyclic aromatic hydrocarbons with four to six rings were produced in increasing abundance as pyrolysis temperature increased, although they did not approach the levels reported from HYC. Addition of lead sulfide, zinc sulfide and pyrite to the MSSVpy experiments resulted in a reduced response of the methylphenanthrene maturity parameters, possibly due to retardation of methyl-shift and transmethylation reactions

Salinity variations in the northern Coorong Lagoon, South Australia: Significant changes in the ecosystem following human alteration to the natural water regime

European settlement and drought have significantly impacted the hydrology of the Coorong, a shallow coastal lagoon complex in South Australia, which is part of a terminal wetland at the mouth of the River Murray. An increased salinity associated with lower water levels and progressive isolation from ocean flushes contributed to a severe decline in ecological diversity over the past decades. Here we have conducted a molecular and stable isotopic study of a sedimentary core from the northern Coorong Lagoon spanning more than 5000 years to investigate the recent palaeoenvironmental history of the ecosystem. Major alterations were evident in many biogeochemical parameters in sediments deposited after the 1950s coinciding with the beginning of intensified water regulations. The most prominent shift occurred in δ13C profiles of C21–C33n-alkanes from average values of −23.5‰ to an average of −28.2‰.Further changes included decreases in carbon preference index (CPI) and average chain length (ACL) of the n-alkane series as well as significant increases in algal (e.g. C20 HBI, long chain alkenes and C29-alkadiene) and bacterial (e.g. 13C depleted short chain n-alkanes and hopanoids, δ13C: −35.9‰ to −30.1‰) derived hydrocarbons. Long chain n-alkanes with a strong odd/even predominance as observed here are typically attributed to terrigenous plants. In the Coorong however, terrigenous input to sedimentary OM is only minor. Therefore changes in the before mentioned parameters were attributed to a source transition from a major contribution of macrophytes towards predominantly microalgae and bacteria.δD values of C21–C33n-alkanes showed a general trend towards more enriched values in younger sediments, indicating an overall rising salinity. However, the most pronounced positive shift in these profiles again occurred after the 1950s. Altogether this study demonstrates that the recent human induced changes of the Coorong hydrology, compounded by a severe drought led to an increase in salinity and alterations of primary production which have been much more significant than natural variations occurring throughout the Holocene over several thousands of years

Oxygenation in carbonate microbialites and associated facies after the end-Permian mass extinction: Problems and potential solutions

China University of Petroleum (Beijing) Carbonate sediments deposited in normally-oxygenated shallow ocean waters of the latest Permian period, immediately prior to the end-Permian mass extinction, contain well-developed diverse shelly faunas. After the extinction of these skeletal metazoans, the sediments commonly comprise microbialites (regarded by most authors as benthic) and associated facies bearing evidence interpreted by many authors to indicate reduced oxygenation of the shallow ocean waters. However, the evidence of oxygenation state is inconsistent and the sequences have gaps, indicated in the following 5 points: 1) Shelly fossils occur commonly in post-extinction shallow marine limestones, and likely to have been aerated in contact with the atmosphere. Nevertheless, although the largest mass extinction in Earth history may have caused reduced body size in shelly organisms, such reduction is arguably due to environmental stress of lowered oxygenation. Discriminating between these controls remains a challenge. 2) Abundant pyrite framboids in many post-extinction limestones are interpreted by several authors as indicating dysoxic contemporaneous waters, so the organisms that lived there, now shelly fossils, were dysaerobic. However, verification is problematic because pyrite framboids scattered amongst shelly fossils cannot have formed amongst living organisms, which need at least some oxygen; synsedimentary framboid formation requires anoxic conditions in the redox boundary where sulphate-reducing processes work. Thus, framboids and shelly fossils found together means taphonomic mixing of sediments, destroying original depositional relationships so that it is not possible to determine whether the shells were aerobic or dysaerobic prior to sediment mixing. Furthermore, diagenetic growth of framboids is possible, as is import of previously-formed framboids from deeper water during upwelling. Thus, there is no proof of an environmental link between framboid size and occurrence, and contemporaneous oxygenation in these post-extinction shallow water facies, so we question the validity of this model in those facies, but consider that the model is valid for deeper water facies. 3) Some publications provide evidence of oxygenation, from redox-sensitive elements in post-extinction limestones, while others indicate low oxygen conditions. Redox-sensitive geochemistry requires further work to explore this issue at higher resolution of sampling than has been so far applied. 4) Biomarkers recorded in some post-extinction facies contain evidence of anoxic conditions (including green sulphur bacteria) but other examples lack these, which may be indicate fluctuations of water oxygenation. However, a key issue that has not yet been resolved is determination of whether biomarkers were imported into the sites of deposition, for example by upwelling currents, or formed where they are found. Thus, there is currently no verification that biomarkers of low oxygen organisms in shallow water settings actually formed in the places where they are sampled. 5) The common occurrence of small erosion surfaces and stylolites represents loss of evidence, and must be accounted for in future studies. The oxygenation state of post-end-Permian extinction shallow marine facies continues to present a challenge of interpretation, and requires high-resolution sampling and careful attention to small-scale changes, as well as loss of rock through pressure solution, as the next step to resolve the issue

Biomarker distributions and stable isotopes (C, S, H) to establish palaeoenvironmental change related to the end-Permian mass extinction event

Extinction, the irreversible loss of species, is perhaps the most alarming symptom of the ongoing biodiversity crisis. Some of the most significant changes in evolution throughout Earth’s history have coincided with extinction boundary events. In this thesis various organic geochemical (biomarker and stable isotopes) and geological (sedimentology and palaeontology) approaches have been undertaken to examine one of the most significant mass extinction events that occurred during the Late Permian (252 My ago) near to the Permian/Triassic (P/Tr) boundary. In the marine realm 49% of invertebrate families became extinct (equivalent to 80–96% of species loss). However, identifying an ecological crisis and associated extinction interval in any given extinction boundary section can often be difficult.Many different hypotheses have been proposed to explain the end-Permian extinction. The coincidence in timing of the extinction with the massive volcanic eruptions in Siberia has been established. The release of methane and possibly other gases during the volcanic event could have led to global warming. The oceans were oxygen deficient leading to euxinic conditions (with H[subscript]2S as a toxic agent) possibly triggering the extinction. Further, the selectivity of the extinction suggests hypercapnia (high CO[subscript]2) as a kill mechanism. It is widely accepted that the extinction is a “tangled web of causality” with several mechanisms contributing to the biotic crisis.Analyses of molecular fossils (biomarkers) and their stable isotopic compositions provide an alternative tool for identifying mass extinction intervals complimenting bulk stable isotopic data (δ[superscript]34Spyrite, δ[superscript]13Ccarbonate, δ[superscript]13Corg), sedimentological and fossil record data. Only recently have biomarker abundances (and δ[superscript]13C) and changes associated with the end-Permian extinction attracted significant attention. For example, biomarkers ultimately derived from pigments of organisms carrying out anoxygenic photosynthesis (Chlorobiaceae) have been recently reported in several P/Tr sections, providing evidence for widespread photic zone euxinic conditions.The aims of this PhD thesis were (i) to establish the palaeoenvironmental conditions associated with the P/Tr mass extinction event using an integrated biomarker, isotopic (including δD of biomarkers) and sedimentological approach for one section from the northern hemisphere and (ii) to establish whether the biomarker and isotopic signals (including δD of bulk kerogen) observed in several sections from about the globe represent localised environments of deposition and/or are related to global depositional conditions.In Chapter 2 for the first time an integrated study including sedimentological data, biomarker distributions/abundances and selected stable carbon and hydrogen isotopes along with bulk isotopes (δ[superscript]34Spyrite, δ[superscript]13Ccarbonate, δ[superscript]13Corg) for a Late Permian section from Lusitaniadalen, Spitsbergen, Norway has been conducted. These data support a marine transgression and collapse of the marine ecosystem in the Late Permian. Strong evidence for waxing and waning of photic zone euxinic conditions throughout the Late Permian section is provided by Chlorobiaceae-derived biomarkers (including δ[superscript]13C data) and δ[superscript]34Spyrite, suggesting several events of H[subscript]2S outgassing and potentially several pulses of extinction. A rapid decrease in abundance of various land plant biomarkers prior to the marine collapse event suggests a decline in terrestrial organisms during the Late Permian and/or increasing distance from the palaeoshoreline as an effect of sea level rise. Changes in δD of biomarkers also indicate a change in source of OM, microbial diversification and sea level rise. Further, compound specific isotope analysis (CSIA) data of algal and land-plant derived biomarkers, δ[superscript]13Ccarbonate and δ[superscript]13Corg provide strong evidence for synchronous changes in δ[superscript]13C of marine and atmospheric CO[subscript]2, attributed to a [superscript]13C-depleted source. The source could either be associated with isotopically depleted methane released from the melting of gas clathrates and/or from respired OM, due to the collapse of the marine ecosystem.In Chapter 3 δD of kerogen (δDkerogen) for three P/Tr sequences (Hovea#3, Perth Basin, Western Australia; Schuchert Dal section, Jameson’s Land, East Greenland and Lusitaniadalen, Spitsbergen) have been measured and compared with δ[superscript]34S of total reduced inorganic sulfur (δ[superscript]34Spyrite) of all three sections and for one sample set δ[superscript]13C of carbonate (δ[superscript]13Ccarbonate) to establish (i) similarities between the sections and (ii) evaluate whether these signals are local or global. Stable isotope shifts occur for all localities either at the P/Tr transition (Western Australia) or coinciding with the marine ecosystem collapse (Spitsbergen and East Greenland). δDkerogen reflects OM/kerogen type. 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 of biomarkers (Chapter 2). The negative shifts in δ[superscript]13Ccarbonate (primary) and δ[superscript]13Ckerogen are attributed to the release of [superscript]13C-depleted carbon into the atmosphere, whereas the isotopic excursions in δ[superscript]34Spyrite relate to global palaeoredox changes. However, the global synchronous shifts in δDkerogen, δ[superscript]34Spyrite and δ[superscript]13Ckerogen for all sections suggest a relation between the sulfur, carbon and hydrogen cycles.In Chapter 4 the abundances of several polycyclic aromatic hydrocarbons (PAHs) throughout three P/Tr sections from the Global Stratotype Section and Point (GSSP) in Meishan (South China), Kap Stosch Area (East Greenland) and Peace River Basin (Western Canada) were evaluated. The PAHs dibenzothiophene and dibenzofuran were found to decrease in abundance just before or shortly after the P/Tr boundary in all three sections, supporting the hypotheses of a worldwide decrease in preservation of terrestrial OM. Perylene was observed in high abundance at the onset of the main extinction horizon (at bed 25) in Meishan and has been attributed to a wood degrading fungal source, consistent with the demise of land plants. Frequently occurring forest fire events are also evident from the abundance of several combustion-derived PAHs showing independent patterns in all sections. The coincidence of high abundances of combustion markers occurring simultaneous with ash beds in Meishan section indicates an origin related to the Late Permian and Early Triassic volcanic eruptions in Siberia and China.In Chapter 5 an evaluation of selected biomarker maturity parameters [methylnaphthalene ratio (MNR), methylphenanthrene index (MPI-1), C27 diasterane/sterane ratio and Ts/(Ts+Tm) ratio] has been conducted for a number of P/Tr samples (Western Australia, East Greenland and Spitsbergen). Differences in these parameters have been observed between freely extractable bitumens from sedimentary rocks (Bitumen I) and bitumens comprising hydrocarbons closely related to the kerogen/mineral matrix (Bitumen II). Further, a distinct connection between these differences and the clay/TOC ratio of the sediments has been made. The information on thermal maturity that is preserved within Bitumen II could be of significance in petroleum exploration studies, as the original thermal maturity signal of Bitumen I may be overprinted by migrated bitumen