Mass extinctions, climatic and oceanographic changes at the Devonian/Carboniferous boundary

Abstract

A positive carbon isotope excursion is reported for the global Hangenberg Event at the Devonian/Carboniferous boundary, revealed by a correlation of Austrian, Italian, French and German sections using high-resolution conodont biostratigraphy. The $\delta^{13}C_{carb,org}$ excursions indicate global change in the isotopic composition of marine dissolved $HCO_{3}$- and atmospheric $CO_{2}$, which resulted from the increased burial of organic matter by globally widespread black shale deposition during high seawater temperatures, as indicated by $\delta^{18}O_{phosph}$ of conodonts. Low temperatures are recorded in beds overlying the regressive event phase, correlated previously with a glacial episode in Gondwana. Glacially induced sea-level changes were testified by a correlation of Moroccan siliciclastic beds using litho- and ammonoid stratigraphy. The data support the hypothesis that increased $C_{org}$ burial and oceanic anoxia triggered glaciations, eustatic sea-level changes and mass extinctions at the D/C boundary