Journal of Conference Abstracts

Calciturbidite Composition with a Special View to Conodont Elements: A Case Study from Late Devonian to Early Carboniferous Carbonates of Moravia, Czech Republic

Ondøej Bábek (babek@prfnw.upol.cz)¹ & Jiøí Kalvoda (dino@gap.muni.cz)²

¹ Palacky University of Olomouc, Department of Geology, tø. Svobody 26, Olomouc, Czech Republic

² Masaryk University of Brno, Department of Geology and Paleontology, Kotláøská 2, Brno, Czech Republic

Conodont biofacies concept is a powerful tool in paleoenvironment analysis, event stratigraphy and even in reconstruction of eustatic sea-level curves. However, as some of the conodont workers do claim, in apparently reworked beds such as calciturbidites and carbonate storm beds, conodont assemblages from different paleoecologic niches may be mixed in so far as they do not fit any of the existing biofacies models.

Conodont assemblages from the Late Famennian to Middle Tournaisian deep-water carbonates of Moravia, Czech Republic, offered a good opportunity to compare their compositional variations and grain-size properties with similar features of their source rocks. Detailed facies analysis and point-counting analysis revealed several basic carbonate facies types: Facies 1 - pelagic-hemipelagic carbonates, Facies 2 - low density turbidity current deposits, Facies 3 - high density turbidity current deposits, and Facies 4 - bottom current deposits and/or winnowed pelagic carbonates. The conodont assemblages were analysed with respect to their compositional variations, grain-size properties, fragmentation and evidential reworking of stratigraphically older taxa.

The features of conodont assemblages showed to be strongly dependent on facies type of their host rock. Typically, the pelagic - hemipelagic carbonates of Facies 1 yielded poorly sorted, pelagic assemblages, that fit the previously published pelagic conodont biofacies concepts, with only a minor degree of fragmentation. The normal calciturbidites of Facies 2 showed a moderate degree of conodont element fragmentation, poor- to moderate sorting and mixing of elements from both deep-water- and shallow-water paleoecologic settings. The coarse-grained calciturbidites of Facies 3 yielded strongly fragmented and poorly sorted conodont assemblages composed of mixed shallow-water- and deep-water derived elements. The bottom current deposits and/or winnowed pelagic carbonates of Facies 4 yielded well- to very-well sorted, pelagic conodont assemblages with only a minor degree of fragmentation.

In calciturbidite successions, the conodont assemblages, in particular those separated from the normal calciturbidites of Facies 2, showed to be useful indicators of variations in exposure and flooding of their source area. Our preliminary results from the Late Devonian to Early Carboniferous calciturbidite succession in Lesní lom, Moravia, indicate that during sea-level highstands, the input of relatively shallow-water, platform interior- and platform margin conodont elements is increasing significantly while during lowstands, epipelagic- and deep-water conodonts are predominating. In this respect the conodonts may be as useful as carbonate constituents in stratigraphic considerations. In slightly metamorphosed, recrystallized carbonate successions where carbonate constituent analysis may be complicated, if possible at all, the conodonts may be still preserved to serve as alternative environment markers.

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