Mississippian δ13Ccarb and conodont apatite δ18O records — Their relation to the Late Palaeozoic Glaciation

Carbon isotopes of whole rock carbonates and oxygen isotopes of conodont apatite from Late Devonian to Early Pennsylvanian sections in Europe and Laurentia were measured in order to reconstruct variations in the carbon cycle, marine palaeotemperature, and ice volume during the Mississippian. Conodont apatite δ18O values show two major positive shifts of + 2‰ and + 1.5‰ V-SMOW in the late Tournaisian and Serpukhovian, respectively, that are interpreted to reflect climatic cooling and changes in ice volume. Carbon isotope ratios of inorganic and organic carbon show a major positive excursion with an amplitude of + 6.5‰ V-PDB in the Tournaisian and a positive shift of up to + 5‰ V-PDB in the Serpukhovian. The positive δ13C excursions coincide with the deposition of organic carbon-rich black shales which indicate that organic carbon burial, lowering of atmospheric pCO2, and climatic cooling may have occurred during these time intervals. However, while in the Tournaisian the positive shifts in δ18Oapatite and δ13C coincide, in the Serpukhovian the positive shift in δ18Oapatite precedes the positive shift in δ13C and raises the question as to whether changes in the global carbon cycle were the ultimate cause of the inferred climatic changes. The conodont apatite δ18O values suggest that a first major cooling and potential glaciation event occurred in the Tournaisian with ice masses persisting into the Visean. The second glaciation event occurred in the Serpukhovian and culminated in the first glacial maximum of the Late Palaeozoic Glaciation.