The influence of the Late Devonian Kellwasser events on deep-water ecosystems: Evidence from palaeontological and geochemical records from South China

The Late Devonian Frasnian-Famennian (F-F) event, consisting of the Lower and Upper Kellwasser events, had a severe impact on shallow-water ecosystems, while the effect on deep-water ecosystems is ambiguous. In order to recognize the Kellwasser events and to evaluate their influences on the deep-water ecosystems, a newly refined conodont biostratigraphic framework spanning the Lower Palmatolepis rhenana Zone to the Pa. delicatula platys Zone has been established in the Nandong section (basinal facies), Guangxi, South China. The Upper Devonian Lower and Upper Kellwasser horizons (LKH and UKH) have been recognized in the deep-water facies on the basis of lithological variations, biological turnovers, and positive carbon isotope (δ13Ccarb) excursions. The LKH is characterized by the enrichment of marine nektonic communities (e.g. conodonts, homoctenids, and entomozoacean ostracods), whereas the top of the UKH is barren of fossil organisms, suggesting that the Upper Kellwasser event had a more severe effect on nekton than the Lower Kellwasser event. The Upper Kellwasser (UK) δ13Ccarb positive excursion lags behind the enrichment of Cu, Ni, Mo and V, indicating that the UK δ13Ccarb positive excursion was probably related to elevated primary productivity, which induced oxygen depletion in the water column. The UK δ13Ccarb positive excursion peak prior to the F-F boundary indicates a more limited effect of riverine influx on the deep-water setting, which suggests that the regional palaeogeographic configuration played an important role in the carbon cycle.