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.
Bibliographical noteThe authors warmly thank Mads E. Jelby and Anders L. Ebbesen for help in collecting samples in the field. NT is thankful to Christian Bjerrum for use of the HH-XRF gun and fruitful discussions on calibration of the device, to Samer Bou Daher for fruitful discussions on organic geochemistry and to Michaël Hermoso for fruitful discussion on the Sancerre-Couy data and geochemistry of the Toarcian event. The Carlsberg Foundation (project 2011-01-0737 to CK) and the Danish Council for Independent Research-Natural Sciences (project 09-072715 to CK) are acknowledged for contributions to financing this project. This manuscript strongly benefited from high-quality reviews and many constructive comments of Mathieu Martinez and an anonymous reviewer. Many thanks to Raven Hall for a fantastic view and for their food of a high standard that contradicted the French opinion on English cuisine.
- Mo drawdown
- Sea level