Cenomanian–Turonian composite δ13C curve for Western and Central Europe: the role of organic and inorganic carbon fluxes

Detailed δ13C stratigraphies have been published recently for several Cenomanian–Turonian pelagic sections of southern England, and the Lower Saxony basin of Germany. The observed changes in the δ13C record provide a useful tool for high-resolution stratigraphic correlation, and are used here to create a composite Cenomanian–Turonian δ13C curve in a time-related framework. A best fit curve to 673 carbon isotope data is provided using the LOWESS regression scatterplot smoother. The long-term trend of the smoothed composite δ13C profile varies on time scales of 106 years, and shows stable δ13C values through the Lower Cenomanian, an increase in the Middle and Upper Cenomanian, with a major positive excursion around the Cenomanian–Turonian boundary, and a decrease through the Lower and Middle Turonian. Short-term fluctuations vary on time scales of 105 years, and dominated the δ13C signal in the higher Middle and Upper Turonian. Changes of the Cenomanian–Turonian δ13C record have commonly been explained by variations in the organic carbon flux to the sedimentary reservoir, in response to eustatic sea-level change. However, mass balance consideration suggests also an influence of carbonate production and burial rate on the δ13C signal. Enhanced inorganic carbon burial increased the ratio of the inorganic to organic carbon fluxes and shifted the 13C/12C ratio to more negative values. This pattern may be observed in the Early and Middle Turonian δ13C long-term record, and correlates with the spatial expansion of pelagic carbonate deposits in epicontinental seas. Short-term δ13C variations could be either a directly response to short-term sea-level changes, reflecting local conditions in the European epicontinental sea, or could represent changes in oceanic 12C storage in response to the varying intensity of thermohaline circulation.