The wider context of the Lower Jurassic Toarcian oceanic anoxic event in Yorkshire coastal outcrops,UK |
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| Authors: | Nicolas Thibault Micha Ruhl Clemens V Ullmann Christoph Korte David B Kemp Darren R Gröcke Stephen P Hesselbo |
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| Institution: | 1. Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark;2. Department of Earth Sciences, University of Oxford,South Parks Road, Oxford OX1 3AN, UK;3. University of Exeter, Camborne School of Mines & Environment and Sustainability Institute, Penryn Campus, Penryn, Cornwall TR10 9FE, UK;4. School of Geosciences, University of Aberdeen, Aberdeen, AB24 3UE, UK;5. Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK |
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| Abstract: | The Toarcian Oceanic Anoxic Event (T-OAE, ～183 Ma) was characterized by enhanced carbon burial, a prominent negative carbon-isotope excursion (CIE) in marine carbonate and organic matter, and numerous geochemical anomalies. A precursor excursion has also been documented at the Pliensbachian/Toarcian boundary, but its possible causes are less constrained. The T-OAE is intensively studied in the Cleveland Basin, Yorkshire, UK, whose sedimentary deposits have been litho-, bio- and chemostratigraphically characterised. Here, we present new elemental data produced by hand-held X-ray fluorescence analysis to test the expression of redox-sensitive trace metals and detrital elements across the upper Pliensbachian to mid-Toarcian of the Cleveland Basin. Detrital elemental concentrations (Al, Si, Ti, Zr) are used as proxies for siliciclastic grain content and thus, sea-level change, which match previous sequence stratigraphic interpretations from the Cleveland Basin. The timescale of the event is debated, though our new elemental proxies of relative sea level change show evidence for a cyclicity of 350 cm that may be indicative of ～405 kyr eccentricity cycles in Yorkshire. Trends in total organic carbon and redox-sensitive elements (S, Fe, Mo, As) confirm scenarios of widespread ocean deoxygenation across the T-OAE. The correlation of comparable trends in Mo across the T-OAE in Yorkshire and the Paris Basin suggests a similar oceanic drawdown of this element accompanying widespread anoxia in the two basins. Data from Yorkshire point to a transgressive trend at the time of the Mo drawdown, which contradicts the “basin restriction” model for the euxinic conditions that characterise the CIE interval. |
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| Keywords: | Euxinia Mo drawdown Cyclostratigraphy Sea level |
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