First high-resolution shallow-marine bulk-carbonate record of the Middle Oxfordian Event in the Sub-Boreal Realm, Lower Saxony Basin, Germany

The Oxfordian is characterized by two pronounced ca. 2‰ positive carbon isotope excursions (CIE) within the Lower and Middle Oxfordian referred as the EOxE and the MOxE, respectively. The EOxE and MOxE have been recorded from various marine and terrestrial organic and inorganic substrates and represent “shorter-term” (<1 Myr) variations modulating the prolonged uppermost Callovian–Middle Oxfordian carbon isotope increasing values. These chemostratigraphic markers have been interpreted to reflect climate fluctuations, changes in marine carbonate production, and long-term sea-level rise. A new high-resolution inorganic δ13Ccarb record from bulk-carbonate, is obtained from a scientific borehole (Konrad 101 core) located in the Lower Saxony Basin (LSB) and allow the recognition of the MOxE. In its counterpart, the EOxE is missing from the record due to a stratigraphic hiatus in the core, which is potentially associated with the well-documented sea-level lowstand characterizing the Callovian/Oxfordian transition. The MOxE record is interpreted to reflect synchronous changes in the global marine dissolved inorganic carbon pool, probably in response of weakening of shelf current intensity along the northern Tethyan margin and a sea-level rise, so it is linked to regionally enhanced organic carbon burial or increased carbonate carbon accumulation. This is the first high-resolution bulk-carbonate record of the MOxE within shallow-marine carbonate Sub-Boreal Realm. Our dataset emphasizes the global significance of the Middle Oxfordian carbon-cycle disturbance and confirms its recognition as a chemostratigraphic reference marker.