Cenomanian-Turonian composite delta C-13 curve for Western and Central Europe: the role of organic and inorganic carbon fluxes

Detailed delta(13)C stratigraphies have been published recently for several Cenomanian-Turonian pelagic sections of southern England, and the Lower Sa xony basin of Germany. The observed changes in the delta(13)C record provid e a useful tool for high-resolution stratigraphic correlation, and are used here to create a composite Cenomanian-Turonian delta(13)C 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 th e smoothed composite delta(13)C profile varies on time scales of 10(6) year s, and shows stable delta(13)C values through the Lower Cenomanian, an incr ease in the Middle and Upper Cenomanian, with a major positive excursion ar ound the Cenomanian-Turonian boundary, and a decrease through the Lower and Middle Turonian. Short-term fluctuations vary on time scales of 10(5) year s, and dominated the delta(13)C signal in the higher Middle and Upper Turon ian. Changes of the Cenomanian-Turonian delta(13)C record have commonly bee n explained by variations in the organic carbon flux to the sedimentary res ervoir, in response to eustatic sea-level change. However, mass balance con sideration suggests also an influence of carbonate production and burial ra te on the delta(13)C signal. Enhanced inorganic carbon burial increased the ratio of the inorganic to organic carbon fluxes and shifted the C-13/C-12 ratio to more negative values. This pattern may be observed in the Early an d Middle Turonian delta(13)C long-term record, and correlates with the spat ial expansion of pelagic carbonate deposits in epicontinental seas. Short-t erm delta(13)C variations could be either a directly response to short-term sea-level changes, reflecting local conditions in the European epicontinen tal sea, or could represent changes in oceanic C-12 Storage in response to the varying intensity of thermohaline circulation. (C) 2000 Elsevier Scienc e B.V. All rights reserved.