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Research Article |
1 School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK
2 Present address: Department for Applied and Analytical Palaeontology, Institute for Geosciences, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher-Weg 21, 55128 Mainz, Germany
3 NERC Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
4 School of Geography, University of Nottingham, Nottingham NG7 2RD, UK
*Corresponding author (e-mail: nunn{at}uni-mainz.de)
Supplementary material: Isotopic and geochemical data are available at http://www.geolsoc.org.uk/SUP18339.
The stable isotope data presented here significantly extend and expand upon previous isotopic investigations of the Middle to Late Jurassic interval. The belemnite samples collected from the Staffin Bay and Staffin Shale formations from the Isle of Skye, Scotland, yielded oxygen isotope values consistent with Callovian–Kimmeridgian palaeotemperatures of 6.7–20.6 °C. The carbon isotope data comprise one of the first moderately high-resolution investigations of the relationship between terrestrial 
13Corg (predominantly fossil wood debris) and marine 13Ccarb (belemnites) as derived from a geologically coeval record. The Staffin Bay data reveal a broad Early to Mid-Oxfordian positive carbon isotope excursion. The excursion maximum occurs in the cordatum Zone (British Boreal ammonite zonation), although high values persist into the tenuiserratum Zone. The correspondence between the marine and terrestrial records indicates a strong coupling of the ocean–atmosphere system and suggests that the total exchangeable carbon reservoir would have been affected at this time. The Mid-Oxfordian negative carbon isotope excursions identified in published Tethyan records and commonly attributed to methane release are not recorded in the Staffin Bay data, which may suggest that the Tethyan excursions do not represent fluctuations in the global carbon reservoir and that the fidelity of the methane hypothesis should be re-evaluated.
