CENTRAL NORTH AMERICAN RECORD OF THE GLOBAL HANGENBERG CARBON ISOTOPE EXCURSION IN AN EPEIRIC SEA SETTING: VARIATIONS IN CARBONATE PRODUCTION AND ORGANIC CARBON BURIAL DURING THE LATE FAMENNIAN

Marine carbonates from the Late Famennian (Louisiana Limestone) of the mid-continent of North America were examined for carbon isotope (δ 13C carb) stratigraphy in order to constrain more precisely the timing of the Hangenberg Excursion. Three outcrops in northeast Missouri and a core from southeast Iowa containing biostratigraphically significant conodont faunas record the latest Famennian (Hangenberg) positive carbon isotope excursion with values in excess of +6‰ (VPDB). The term “Hangenberg” is applied to the Late Famennian δ 13C isotope excursion that acheived peak δ 13C values immediately following the marine biotic crisis referred to as the Hangenberg Event, which affected ammonoids, conodonts, brachiopods, and other elements of the marine biota. The first report of a late Famennian positive carbon isotope excursion from the Louisiana Limestone correlated the shift with the Hangenberg Black Shale of Europe. However, the Louisiana post-dates the Middle Siphonodella praesulcata Zone Hangenberg Black Shale interval by one conodont zone.

Our data are consistent with recently reported isotopic records in Germany and Morocco and demonstrate that the Hangenberg δ 13C (carb) excursion began in the upper part of the Middle S. praesulcata Zone with peak values in the Upper S. praesulcata Zone. We conclude that black shale deposition in epeiric sea settings ended at the onset of the global excursion. The Hangenberg Excursion is coincident with expansion of carbonate platforms in epeiric sea settings and is a pattern similar to that which has emerged in studies of Silurian and other Paleozoic excursions.