ABSTRACTStudies on Cretaceous pelagic limestones have shown a close correspondence between putative sea‐level curves and the carbon‐isotope profile, suggesting a possible relationship between the two phenomena. Such a relationship could relate to shelf‐sea area governing the global burial rate of organic carbon which, in turn, controls the13C/12C ratio of dissolved inorganic carbon in the oceanic reservoir. In order to see whether or not this relationship might be of more general applicability, the major mid‐Oxfordian (Jurassic) transgression is documented to zonal level and appropriate carbon‐isotope data are presented. Although the applicability of ammonite zonation to the mid Oxfordian is problematic on a regional scale, a clear δ13C excursion is present in thetrunsversariurnZone, which is coincident with regional overstep and/or evidence of shoreline retreat and/or evidence of bathymetric deepening in Europe and elsewhere. The use of the carbon‐isotope curve as a proxy for shelf‐sea area or relative sea level is worthy of furth