Publication details
The disaster fauna of the Devonian-Carboniferous biotic crisis preserved in microbial limestones from the Moravian Karts, Czech Republic
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| Year of publication | 2022 |
| Type | Conference abstract |
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| Description | The Hangenberg Biotic Crisis at the Devonian/Carboniferous boundary can be regarded as a first order mass extinction; however, the overall palaeobiodiversity loss estimations show that its consequences were milder than those of the other “Big Five” mass extinctions. The record of the Hangenberg Biotic Crisis can be subdivided into three intervals, comprising the hypoxic Hangenberg Black Shale Event (the main mass extinction phase), the regressive Hangenberg Sandstone Event, and the Stockum Limestone Event. The complete succession of the Hangenberg biocrisis is recorded in the Líšeň Fm in the Moravian Karst, north-east to Brno city, Czechia. The Moravian Karst is outcrop of the Palaeozoic sedimentary cover of the Brunovistulian Terrane (southern Laurussian margin during Devonian and early Carboniferous). The Hangenberg Black Shale Event is represented by peculiar laminated limestone (“laminite”) which is well exposed in Brno-Líšeň and its vicinity. The laminite is approximately 0.5 to 1.0 m thick dark grey microbial bindstone, intercalated by thin turbiditic layers (peloidal grainstone and bioclastic packstone). The microbial origin of the bindstone has been revealed by petrographic study as well as by its geochemical (REE) signature, and represents anachronistic facies related to the mass extinction (Kalvoda et al. 2018). The laminite yielded low-diversity macrofaunal association at two sites in the Brno-Líšeň (Říčka Brook Valley and Líšeň-Hřbitov). The most abundant macrofossils are ammonoids and bivalves. The determinable ammonoids belong to the clymeniid species Postclymenia cf. evoluta. Isolated articulated jaws of this cephalopod are highly abundant in several levels of the laminite, as well as dissolved and compacted conchs. Additionally, a single conch of undeterminable tornoceratid goniatite has been found. Bivalves are articulated and belong to Guerichia sp., and probably also to other taxa. Besides these mollusks, also bryozoan colony encrusting Postlymenia conch, single complete carapace of thylacocephalan arthropod Concavicaris sp., and undeterminable ichthyoliths have been found. Deposits of the Hangenberg Black Shale Event are usually fossil free worldwide; therefore, fossiliferous rocks from this time interval are rare and highly important. The macrofossils association with gueirichids and Postclymenia cf. evoluta has been reported from the type litostratigraphic unit of the event, the Hangenberg Black Shale from the Rhenish Slate Mts. (Laurussia; Becker et al. 2021). The association highly similar to the Moravian one has been documented from the Hangenberg Black Shale equivalent in the Ma’der region, Morocco (Gondwana; Klug et al. 2016), involving also ammonoids encrusted by bryozoan colonies and ichthyolites. This low-diversity association represents cosmopolitan disaster fauna with predominance of nektonic groups, due to the global benthic dysoxia, symptomatic for the Hangenberg Black Shale Event. Abundant occurrence of gueirichid bivalves could be related to short episodes of oxygenation triggered by turbiditic currents (Kalvoda et al. 2018, Kumpan et al. 2019), or to their possible pseudoplanktic lifestyle. Conspicuous is abundant occurrence of cephalopod jaws in the Moravian Karst and Ma’der. Anaptychi are well known from the Frasnian, but the Famennian cephalopod jaws record is very scarce, restricted to Ohio (Frye and Feldmann, 1991), lower part of the upper Famennian in the Rhenish Massif (Korn 1994), and Ma’der only (Klug et al. 2016). The reported jaws from the Moravian Karst are the first Laurassian record from the uppermost Famennian. |
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