The Late Frasnian Kellwasser horizons of the Harz Mountains (Germany): Two oxygen-deficient periods resulting from different mechanisms

Upper Kellwasser carbon isotope excursion pre-dates the F–F boundary in the Upper Devonian Lennard Shelf carbonate system, Canning Basin, Western Australia

“…This hypothesis was similarly suggested for the Upper Kellwasser in the Harz Mountains of Germany by Riquier et al (2006).…”

“…While our geochemical results support a relative increase in marine productivity during the Upper Kellwasser interval, and perhaps to a lesser extent for the Lower Kellwasser, it seems unlikely that (regional) enhanced land-derived nutrient loading was the driving factor. Relatively distal sections, such as those on the lower slope and in the basin (i.e., section VHS of this study; George et al, 2014) are not typically affected by terrestrial influx; productivity blooms are commonly restricted to near-shore environments where the influence of continentally derived material is greatest (Riquier et al, 2006). The lack of active orogenies in Western Australia at this time further decreases the likelihood of extensive nutrient transport.…”

“…Given these threshold values, both paleo-redox proxies indicate low-oxygen levels ( Figure 4) which correspond to the δ 13 C excursions associated with both Kellwasser events noted in this study Elemental ratios of Cu/Al and Ni/Al are reported for their use as reliable indicators of changes in paleo-bioproductivity (e.g. Piper and Perkins, 2004;Riquier et al, 2006;Perkins et al, 2008), particularly in the absence of preserved organic-rich material. While a variety of trace elements behave as micronutrients in oxic marine environments and are deposited in association with the organic carbon flux from surface primary productivity, both nickel and copper may be retained within their host sediments even if the organics are partially or completely remineralized after deposition .…”

“…Paleo-redox data for this time interval are also contradictory: whereas the trace element analyses from most studies have given credence to oceanic anoxia (e.g. Riquier et al, 2006), others infer oxic conditions (e.g. George et al, 2014).…”

Euxinic ocean during the Late Devonian mass extinction inferred from organic compounds

“…Previously, anoxic sea-water condition was considered as the candidate responsible for the F/F mass extinction simply because of the widespread black shale near the boundary worldwide (House, 1985). Both stable carbon and sulfur isotopic signals and trace metal element features indicate that the F/F mass extinction was probably caused by the development of oceanic anoxia (Riquier et al, 2006;Joachimski et al, 2001). However, little has been published on organic geochemical signals across the F/F mass extinction interval.…”