127 research outputs found

    NGF Abstracts and Proceedings

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    Investigating the relationship between magnetisation and oil geochemistry

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    A relationship between hydrocarbons and their magnetic signatures has previously been alluded to but this is the first study to combine extensive geochemical and magnetic data of hydrocarbon-associated samples. A detailed study is reported that identifies a definitive connection between magnetic mineralogy and oil biodegradation within samples from Colombia, Canada, Indonesia and the UK. Geochemical data revealed that all the oil samples were derived from mature type-II kerogen deposited in oxygen-poor environments allowing for an investigation into biodegradation. Biodegradation is the decrease of oil quality through the conversion of aliphatic hydrocarbons to polar constituents through the activity of bacteria. The percentage of oil components and the biodegradation state of the samples were compared to the magnetic susceptibility and magnetic mineralogy. A distinct decrease in magnetic susceptibility was correlated to decreasing oil quality as well as extractable organic matter percentages, which cannot be rejected at 99% confidence. Further magnetic characterisation revealed that the high quality oils were dominated by pseudo-single domain grains of magnetite and the lower quality oils by larger pseudo-single domain to multi domain grains of magnetite and hematite; with decreasing oil quality there is a progressive dominance of multi domain magnetite as well as the appearance of hematite. It is concluded that biodegradation is a dual process, firstly, removing aliphatic hydrocarbons reducing oil quality and secondly, both creating and destroying magnetic signatures. This complex relationship may explain why controversy existed in the past when studying hydrocarbon associated anomalies. Remagnetisation due to hydrocarbon infiltration is also reported within the Wessex Basin, UK. Palaeodirectional data from Mupe Bay revealed oil migration was initiated in the Early Cretaceous and a two-phase staining model is correct. These findings reinforce the importance of bacteria within petroleum systems as well as providing a platform for the use of magnetisation as a hydrocarbon proxy

    Geology, geochemistry and petrology of the Foss stratiform barite - base metal deposit and adjacent Dalradian metasediments, near Aberfeldy, Scotland

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    2 volsAvailable from British Library Document Supply Centre- DSC:D66694/86 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

    Michigan Geology: A Bibliography, March 2016

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    The Michigan Geological Survey produced a historic Index of Michigan Geology with an extensive bibliography in 1956. This current bibliography is an update of the bibliography in the Martin and Straight compilation. It is not comprehensive, but provides a starting place for anyone interested in Michigan Geology. The Michigan Geological Survey plans to update this bibliography periodically with newly published citations as well as other older citations we find

    Michigan Geology: A Bibliography, March 2016

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    The Michigan Geological Survey produced a historic Index of Michigan Geology with an extensive bibliography in 1956. This current bibliography is an update of the bibliography in the Martin and Straight compilation. It is not comprehensive, but provides a starting place for anyone interested in Michigan Geology. The Michigan Geological Survey plans to update this bibliography periodically with newly published citations as well as other older citations we find

    GAC-MAC-SGA 2023 Sudbury Meeting: Abstracts, Volume 46

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    Mechanisms and biogeochemical implications of Cenomanian/Turonian black shale formation in North Africa:An integrated geochemical, millennial-scale study from theTarfaya-LaAyoune Basin in SW Morocco

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    Cenomanian/Turonian (C/T; ~94 Ma ago) black shale successions from various N African basins, in particular from the Tarfaya-LaAyoune Basin (SW Morocco), have been studied in great detail using data from the field (including gamma-ray resistivity logging), sedimentology and advanced geochemical trace metal, biomarker and stable isotope methods. Deposition of these black shale units in most of the region was restricted to a short time envelope termed the C/T oceanic anoxic event (OAE2). During this short period, a favourable combination of factors existed which led to the development of exceptionally strong oxygen-deficiency in the N African Tethys and in particular in the southern proto-North Atlantic oceans. The C/T black shales in N Africa are laterally discontinuous and their distribution and thickness were controlled by the palaeorelief. The thickest and regionally most extensive C/T organic-rich shales in N Africa occur in Morocco namely in the Atlantic Tarfaya-LaAyoune Basin. The laminated biogenic sediments from this NW African shallow marine basin were deposited with very high sedimentation rates (av. 5-10 cm/ka) enabling the investigation of mid-Cretaceous paleoceanographic events at high temporal resolution with respect to rapid climate change and associated hydrocarbon source-rock formation. The low level of thermal maturity and the high degree of sulphurisation of the organic matter (kerogen) makes these black shale successions suitable for advanced inorganic and organic geochemical investigations
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