Conodont biostratigraphy of the Líšeň Formation at the Mokrá-central quarry
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| Year of publication | 2024 |
| Type | Appeared in Conference without Proceedings |
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| Description | The conodont fauna of the Late Devonian was a highly diverse group of marine animals; however, despite this success, they also suffered from the global paleoenvironmental changes during the Kellwasser and Hangenberg crises (e.g., Kaiser et al. 2016). These rapid paleoenvironmental changes resulted in the evolution of new conodont morphologies that enable their use as index fossils. We studied a new section in the active part of the Mokrá quarry (Moravian karst, Czechia), which exposes Famennian and lower Tournaisian strata of the Líšeň Formation bracketed by both events. Collected conodont associations were assigned to the conodont biozonations sensu Spalletta et al. (2017) and Zhuravlev et al. (2021). The Líšeň Formation in the southern part of the Moravian Karst is represented by the upper carbonate slope Hostěnice facies and the lower slope Horákov facies, with their transition being very complex as both were deformed by the Variscan orogeny (Rez 2011). However, in the Mokrá quarry, a new section was recently uncovered which preserves the transition between both facies in a less deformed manner. The section is in the central part of the quarry and is composed of limestones of the Macocha and Líšeň formations. Ten samples from the Líšeň Formation were analyzed and assigned to conodont biozones ranging from the Famennian Palmatolepis marginifera marginifera to the Tournaisian Siphondella wilberti. The genera identified were Palmatolepis, Polygnathus, Pseudopolygnathus, Bispathodus, Protognathodus, Siphonodella, Branmehla and Mehlina. In addition to identifying conodont biozones, four samples were assigned to conodont biofacies extending from the upper or middle carbonate slope to toe-of-slope or basin deposits. The studied section does not contain a horizon of oolithic ironstones at the base of the Líšeň Formation that were identified by Dvořák et al. (1986); however, it does contain the Devonian/Carboniferous boundary, which Dvořák et al. (1986) only hypothesized. A layer that corresponds to the global anoxic annulata event was identified based on its lithology. Beds of the Hangenberg crisis were previously unknown in the Hostěnice and transitional facies. The layer of dark grey microbial laminite, which represents anachronistic facies showing great environmental stress at the end of the Devonian, was found near the top of the studied section at the Devonian-Carboniferous boundary. |