An Integrated Stratigraphy of the Frasnian-Famennian Boundary Interval (Late Devonian) in the Moravian Karst (Czech Republic) and Kellerwald (Germany)

Abstract

Rapid and profound changes in Earth surface environments and biota across the Frasnian-Famennian (Fr-Fa) boundary are well known and related to one of the five most severe mass extinction events in Earth history. Here, we present sedimentological, biostratigraphical, petrophysical (gamma-ray spectrometry, magnetic susceptibility) and geochemical (X-ray fluorescence) data from environmentally distinct sections in the Moravian Karst (Czech Republic) and compare them with the Steinbruch Schmidt section in the Kellerwald (Rheinisches Schiefergebirge, Germany). Both areas were located at the southern margin of Laurussia. The studied sections span the interval from the Lower or Upper rhenana to the Palmatolepis minuta minuta or younger conodont zones and the foraminiferal Eonodosaria evlanensis Zone and Eonodosaria evlanensis-Quasiendothyra communis Interzone including high resolution biozonation of the Fr-Fa boundary interval. In the Moravian Karst pure limestone facies of an inclined carbonate ramp reflect the worldwide trend in the widespread occurrence of calcimicrobes during upper Frasnian and lower Famennian. Geochemical and petrophysical data show a decrease in grain size of the siliciclastic supply and carbonate productivity in the Kellwasser Event intervals probably due to a deepening and correlate with maximum flooding surfaces and highstand system tracts in the Steinbruch Schmidt. Certain differences in some geochemical proxies between the Moravian Karst and Steinbruch Schmidt are due to lower carbonate dilution of the latter. Significant Zr, TiO 2 , Mn or Fe 2 O 3 enrichments may indicate the influence of volcanic sources in the studied Moravian Karst Fr-Fa sections.

Phosphorus-cycle disturbances during the Late Devonian anoxic events

“…The fossiliferous, bioturbated, carbonate-rich strata that envelope the Kellwasser horizons at Steinbruch Schmidt are interpreted as recording oxygenated marine conditions, and whilst it is accepted that the Kellwasser horizons mark times of a more oxygen-depleted water column, the degree of anoxia remains less clear. V/Cr and Th/U ratios from the Kellwasser horizons suggest that at least dysoxic conditions developed, but that sustained anoxia/euxinia probably did not (Pujol et al, 2006;Weiner et al, 2017). This conclusion is supported by ostracod fauna within the UKW Level, which also indicate variable degrees of oxygenation and that truly anoxic conditions were no more than intermittent (Casier and Lethiers, 1998).…”

“…These pelagic sediments were deposited on a submarine rise that was part of a large carbonate platform in northeastern Laurentia (also referred to as the southeastern part of Laurussia), indicating an environment distal from the palaeoshoreline (Meischner, 1971;Devleeschouwer et al, 2002). A minimal influx of detrital terrigenous material to this location is further suggested by decreased Ti/Al, Si/Al, and Zr/Rb ratios within the Kellwasser strata (Pujol et al, 2006;Weiner et al, 2017;and supplementary information therein), and potentially supported by a relatively low kaolinite/illite clay composition (Devleeschouwer et al, 2002).…”

“…Alternatively, it has been proposed that an increase in continental weathering rates and associated runoff of terrigenous nutrients stimulated the enhanced primary productivity and subsequent marine anoxia (e.g., Wilder, 1994;Algeo and Scheckler, 1998;Averbuch et al, 2005). Increased terrestrial runoff associated with enhanced continental weathering during the Devonian crises has been documented by a number of proxies (e.g., strontium-isotopes, Chen et al, 2005; osmium-isotopes, Percival et al, 2019; silicon/aluminum (Si/Al), titanium/aluminium (Ti/Al), and zirconium/rubidium (Zr/Rb) ratios, Racki et al, 2002;Pujol et al, 2006;Riquier et al, 2006;Weiner et al, 2017;Paschall et al, 2019), with evidence of soil erosion and wildfires from organic-geochemistry studies further highlighting the contribution of terrestrial matter to the marine realm (Marynowski et al, 2012;Kaiho et al, 2013;Rimmer et al, 2015). Here, the distribution of nutrients in marine shelf basins during Late Devonian anoxic events, as well as their potential source, is further investigated, using phosphorus as a tracer of nutrient influx and recycling at a number of new records of Upper Devonian strata with a wide palaeogeographical coverage.…”

Mercury enrichments and the Frasnian-Famennian biotic crisis: A volcanic trigger proved?

“…Therefore, there a several candidates for an F-F volcanic "smoking gun" although geochronological dating needs considerable improvement. Geochemical proxies documented hitherto from several F-F sections, including Zr/Al and Sr isotopes (Racki et al, 2002;Chen et al, 2005;Pujol et al, 2006;Weiner et al, 2017), and mineralogical data , are additional but far from conclusive evidence. Thus, the emergence of Hg chemostratigraphy as a reliable proxy for the occurrence of major volcanic events during mass extinction episodes.…”

Exceptional Late Devonian arthropods document the origin of decapod crustaceans

“…In the Hády quarry, Late Frasnian pure massive limestones of the Macocha Formation are overlain by the latest Frasnian to late Famennian nodular to well bedded limestones of the Líšeň Formation (electronic supplementary material, figure S1). A drowning of the Frasnian outer ramp and transition to an Famennian hemipelagic slope environment with turbiditic influence is recorded in the studied section [15,16,17]). Angustidontid-bearing bed is one of the calcareous shale intercalations, which alternate with platy calcilutites and occasional banks of medium-grained calcirudites (electronic supplementary material, figure S1).…”