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1 Department of Earth Sciences, University of Liverpool, Brownlow Street, Liverpool L69 3BX, UK
2 Department of Earth Sciences, Imperial College, South Kensington, London SW7 4BP, UK
3 Department of Palaeontology, Natural History Museum, Cromwell Road, London SW7 5BD, UK
The carbon isotope (
We interpret the increase in background
13C) stratigraphy of the late Lower Cenomanian to early Lower Turonian is presented for three sections (Folkestone in the Anglo-Paris Basin, Wünstorf in the Lower Saxony Basin and Speeton in the Cleveland Basin). The similarity between these isotope curves suggests that they were controlled by synchronous, global processes and can be used for high resolution correlation. Furthermore, sequence stratigraphic analysis of this interval reveals that each isotope excursion is associated with a sequence boundary and/or onlap surface. This is also demonstrated for the whole of the Cenomanian for the section at Speeton. We show that most (if not all) 13C excursions are synchronous within the limits of current stratigraphic resolution. 13C values as representing an increase in the area of ocean floor (specifically continental shelf) available for burial of marine organic carbon caused by the mid-Cretaceous rise in eustatic sea-level. Thus background 13C values may provide an independent method for estimating past eustatic sea-levels. We interpret the sharp 13C excursions as reflecting more rapid changes in the carbon cycle particularly the rate of burial of organic carbon within sediments, and/or of storage in deep and intermediate water masses, at times of rapidly changing sea-level. Carbon excursions may be useful in locating sequence boundaries when other criteria are obscure or lacking.
