Anoxic events in the late Frasnian—Causes of the Frasnian-Famennian faunal crisis?

Abstract

Carbon isotope data collected from five Frasnian-Famennian boundary sections in central Europe show two positive δ 13 C excursions in the late Frasnian (∼367 Ma). Both anomalies coincided with the deposition of the bituminous lower and upper Kellwasser horizons. The carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon. A maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late Frasnian transgressive episodes may have induced oceanic oxygen deficits. Variations in the C org burial rates may have resulted in changes in the CO 2 concentrations in the oceans and in the atmosphere, culminating in global climatic changes. We propose that the repeated co-occurrences of sea-level fluctuations, anoxic conditions, and global climatic changes during the late Frasnian would affect especially the subtropical to tropical shallow-water communities and reef ecosystems, which were severely affected during the Frasnian-Famennian faunal crisis.