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A Callovian-Kimmeridgian stable isotope record from Staffin Bay, Isle of Skye, UK: implications for the ocean-atmosphere system

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Nunn E. , Price G. , Hart M. , Page K. , Leng M.

tom Vol. 4, no. 1

198-198

The Staffin Bay section in the Isle of Skye, UK is one of the most stratigraphically complete Oxfordian sections in Europe. This contribution presents the first high-resolution stable isotope record of this Middle Callovian to Early Kimmeridgian succession. The isotope record includes both terrestrial and marine data that were obtained from microscopic wood debris and belemnites respectively. The organic carbon-isotope record was derived from organic rich sediment samples taken almost entirely from the Staffin Shale Formation. This formation is largely represented by a series of isolated foreshore exposures dominated by mudrocks that were deposited in a predominantly offshore marine environment. Over 200 sediment samples were analysed from the 150 m section. The concurrent ä13C marine carbonate curve was produced using belemnites collected from the same formation. Approximately 200 belemnite horizons were sampled. The organic carbon-isotope data show a broad Lower to Middle Oxfordian positive carbon isotope excursion from the Mariae to Tenuiserratum Zone, with maximum values occurring in the Cordatum Zone. This is followed by a return to pre-excursion values continuing into the Early Kimmeridgian Cymodoce Zone. A brief negative excursion (of ~2‰) is also identified near the Densiplicatum-Tenuiserratum zones boundary. Rock-eval analysis confirms that the organic matter is predominantly terrestrial in origin. The concurrent ä13C marine carbonate curve derived from belemnites shows a broadly similar trend. This suggests that the positive carbon-isotope excursion recorded here may have affected the global carbon reservoir (i.e. the whole ocean-atmosphere system). The carbon-isotope record derived from this section appears to be generally consistent with Oxfordian Tethyan records (e.g. Wierzbowski 2002, 2004) and a preliminary study of the Staffin Bay area by Pearce et al. (2005).