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New insights into global carbon cycle disturbances: a shallow marine record of the Middle Oxfordian Excursion (MOxE) in the Lower Saxony Basin

The Oxfordian period is characterized by a long-term (ca. 6 Myrs) trend of increasing stable carbon isotope values, punctuated by three short-lived (ca. <1 Myrs) carbon isotope excursions (CIEs) at the Callovian/Oxfordian boundary, in the lower Oxfordian (Quenstedtoceras mariae ammonite zone), and in the middle Oxfordian (Gregoryceras transversarium ammonite zone), also known as the MOxE. This pattern is evident worldwide in both organic and inorganic carbon (δ13Corg and δ13Ccarb) in terrestrial and shallow marine environments, indicating recurrent global carbon cycle disturbances affecting the entire ocean-atmosphere system. However, previous sedimentological and chemostratigraphic studies on Oxfordian strata in the Lower Saxony Basin (LSB) of northern Germany, have failed to identify the three CIEs cited above, hindering their correlation with the global carbon isotope record. In this study, we provide, for the first time, a high-resolution δ13Ccarb record revealing the MOxE expressed in a positive CIE of 3.8‰. We collected data from drilling core samples of the Korallenoolith Formation in the Konrad 101 borehole, located in the southwestern part of the LSB. This exploration drilling is biostratigraphically well constrained, unlike many other sections in the LSB that are characteristic of shallow tropical marine depositional settings. This particularity enables us to compare the Konrad 101 δ13Ccarb pattern with other localities distributed worldwide incl. Europe, western Asia, and the Gulf of Mexico. Our high-resolution δ13Ccarb reflects a major synchronous change in the exogenic carbon cycle, with no satisfying explanation so far for the triggering mechanisms, in the context of already published datasets.


François-Nicolas Krencker1, Deyan Zhang1, Stefan Huck1, Philipp Ulke1, Michael Schramm2, Ulrich Heimhofer1
1Institute of Geology, Leibniz University Hannover, Germany; 2Federal Institute for Geosciences and Natural Resources, Hannover, Germany
GeoBerlin 2023