Publication details
Famennian sea-level changes recorded in the carbonate turbidites of the Líšeň Formation, Moravo-Silesian Zone, Czech Republic
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| Year of publication | 2024 |
| Type | Conference abstract |
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| Description | The southern part of the Moravian Karst, Czech Republic, features well-preserved Devonian and Mississippian carbonate sequences of the SE margin of Laurussia. The shallow-marine Macocha Formation (Eifelian to Frasnian) is overlain by slope carbonates of the Líšeň Formation (Frasnian to Viséan). This study provides interpretation of relative sea-level changes recorded in the carbonate turbiditic succession of the Líšeň Formation (Hády-Říčka Limestone) exposed in the Hády quarry, in the outskirt of the city of Brno. The studied section is 113 m thick and exposes a lower to upper Famennian succession, which was documented using conodont biostratigraphy, bed-by-bed facies logging, and gamma-ray spectrometry. In total, 22 samples for conodont biostratigraphy were extracted and conodonts of the genera Palmatolepis, Polygnathus, Bispathodus, Mehlina, Branmehla, and Icriodus were documented. The stratigraphical range of the studied section is between the Palmatolepis minuta minuta (lower Famennian) and the Bispathodus costatus (upper Famennian) conodont zones. The polygnathid-icriodid, palamatolepid-polygnathid and palmatolepid conodont biofacies were identified in the studied samples. Based on sedimentary textures and structures, eight lithofacies were defined: calcareous black shales (LF1), marls (LF3), and marls with calcilutite nodules (LF4) interpreted as slope hemipelagic sediments; silty shales (LF2), calcilutites to calcisiltites (LF5), calcisiltites to very fine calciarenites (LF6b), and fine- to coarse-grained calciarenites (LF7) interpreted as distal to relatively proximal turbidites; thin-bedded calcisiltites to very fine calciarenites (LF6a) and limestone breccias (LF8) interpreted as storm deposits of the middle carbonate ramp. In the earliest Famennian, deposition took place in the middle carbonate ramp, which was drowned during the Palmatolepis minuta minuta and Palmatolepis crepida zones, and the depositional environment shifted into the lower part or even base of the carbonate slope. The lower slope deposition continued until the Palmatolepis marginifera marginifera Zone. The depositional environment gradually passed into the middle to upper part of the carbonate slope during the middle Famennian, between the Palmatolepis marginifera marginifera and Palmatolepis gracilis manca zones. A following progradation of calciturbidite system during the late Famennian is documented by facies stacking pattern and decreasing gamma-ray spectrometry determined K and Th concentrations, reflecting dilution of fine grained clastic material by increasing carbonate content. The most proximal calciturbidites were deposited between the Palmatolepis gracilis expansa and Bispathodus costatus zones. When compared with the Famennian T-R cycles (Becker et al., 2020), the drowning of the carbonate platform, and subsequent lower slope deposition, correlates well with global sea-level rise during the early Famennian. Likewise, the gradual transition into the proximal facies correlates with the sea-level fall during the middle to late Famennian. |