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Depleted oil and gas fields constitute potentially important storage sites for CO2 in the subsurface, but large-scale injection of supercritical (sc) CO2 in chalk has not yet been attempted. One of the risks is the adverse effect of the substantial amount of remaining oil in the chalk reservoirs on scCO2 injection. In order to counter an undesired effect on injectivity, a fundamental understanding of the spatial distribution and quantity of the movable, semi-movable, and non-movable oil, and solid bitumen/asphaltenes fractions of the remaining oil is critical. In this study a combination of organic geochemistry (gas chromatography of the saturated fraction and programmed pyrolysis), and reflected light microscopy was applied to evaluate and measure the spatial distribution, volume, and saturation of different oil fractions in a well-defined reservoir interval of a waterflooded Maastrichtian chalk reservoir in the Danish Central Graben, North Sea. A total of 127 samples from a slightly deviated vertical well and two ∼5 km-long horizontal wells from the Halfdan and Dan fields were analyzed. An original uneven distribution of oil saturation and composition or different production efficiency of different levels in the reservoir may account for variations in the total oil and oil fraction saturations. Gas chromatography shows that the solvent extractable oil is quite similar in composition, characterized by a dominance of polar compounds and a high content of asphaltenes. Extended slow heating (ESH) pyrolysis reveals that most of the remaining oil saturation consists of semi-movable oil and total non-movable oil (non-movable oil plus solid bitumen/asphaltenes). Reduced oil gravity values (API) are related to evaporation loss of the lightest hydrocarbon fraction during core storage and increase of the relative proportion of the heavier oil fractions by waterflooding during production. Microscopy disclosed three forms of oil: i) Patchy d

The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (T-J) boundary (~201.3 Ma). CAMP emissions have been invoked as the main trigger for the formation of abnormal pollen and spores during the end-Triassic crisis that may have led to forest dieback and proliferation of pioneer species. Proposed scenarios include extensive climate change leading to wildfire activity, acid rain, and increased UV-B radiation due to ozone depletion. More recently, volcanogenic mercury (Hg) has been implicated in the occurrence of mutations in fern spores. However, Hg-dynamics in deep-time remain poorly understood and require further examination. Here, we explore a new long-term (Rhaetian to Sinemurian) bulk Hg-concentration record combined with Hg-isotope data to understand the link between floral turnovers and the Hg-cycle. Shallow marine sediments sampled from the Schandelah-1 core in northern Germany contain a record of cyclical shifts in malformed fern spores coinciding with fluctuations in carbon isotopes, increased levels of weathering, and Hg-enrichments. Similarly, increased mutagenic spore abundances with accompanying Hg-isotope records confirm the volcanogenic origin of Hg at the T-J boundary, showing a sharp positive excursion in mass-independent fractionation (MIF) of odd-numbered Hg-isotopes. Hettangian cyclicity is clearly reflected in the Hg-isotopic signals, showing positive excursions in mass-dependent/independent fractionation records (d202Hg and D199Hg) during periods of sedimentary Hg-enrichment. In addition, the Hettangian Hg-isotopic signature clearly deviates from Rhaetian signatures, which hints at climate-controlled mechanisms being responsible. Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the T-J boundary interval in multiple sites across the globe. In contrast, the origin of

The organic matter content of marine sediments is often used to infer past changes in ocean conditions. However, the organic carbon pool preserved in coastal sediments is a complex mixture derived from different sources and may not reflect in situ processes. In this study, we combine taxonomic identification of reworked palynomorphs with pyrolysis organic geochemistry and reflected-light organic petrographic microscopy to investigate the provenance, composition and preservation of organic matter in a marine sediment core retrieved from the NE Greenland shelf. Our study reveals continuous yet variable input of land-derived organic carbon to the marine environment throughout the late Younger Dryas–Holocene, with the highest input of inert carbon in the late Younger Dryas. Although the sediments contain some recent marine palynomorphs, there is no other evidence of fresh marine organic carbon. In contrast, our results indicate that these shelf sediments represent a significant sink of recycled organic carbon. The results of pyrolysis geochemistry revealed that ~90% of the total organic carbon in the sediments is inert. The organic petrography analyses revealed that >70–84% of the organic carbon in the sediment core is terrigenous. Reworked dinoflagellate cysts showed a continuous provenance of Cretaceous land-derived material, most likely from the nearby Clavering Island. Our study points to the importance of constraining the organic matter origin, composition and preservation in marine sediments to achieve more accurate palaeoenvironmental reconstructions based on organic proxies.