Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Lower Permian lacustrine limestones in the western part of the Krkonoše Piedmont Basin, locality Tatobity (Rotliegend)
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The studied Lower Permian limestones (Chotěvice Formation were found in the western part of the Krkonoše Piedmont Basin (the Tatobity section) in the sequence of lacustrine fine grained sediments - red brown mudstones and siltstones with admixture of carbonates. The limestones are of micritic up to sparitic character with ostracods, small fish bones and coprolites enclosing fish fragments (bones and scales). These rocks show sporadic bioturbated structures. Quartz grains, albite, micas, hematite matrix and cement form the infilling of bioturbations. Limestones matrix consists of micritic calcite with low content of Mg. Crystals of secondary calcite also occur in the matrix overprinting locally the primary lamination, but the bedding of outcropping limestones is preserved. Coprolites are maximum 4 cm long, and are flattened pararelly with bedding. Macroscopically are coprolites (easily recognizable, because of their white colour and often red (hematite) rims. In microscope, the coprolite matrix is formed by hydroxyapatite locally replaced by calcite. The matrix consists of microcrystalline tricalcium phosphate with numerous voids which are considered to be products of spherical bacterias in excrements full of gas. Coprolites are probably products of Permian predatory fishes activities. Bioturbation structures are ascribed to water plant roots in a shallow calm lake. The deformation of roots, ostracods, and also the occurrence of numerous stylolites were caused by compaction of the sediment during diagenetic processes. The newly discovered and described locality of limestones with organic material near Tatobity confirmed the extent of the Rotliegend lake horizon in the western part of the Krkonoše Piedmont Basin. This horizon of light-grey limestones at Tatobity section macroscopically and even microscopically (with the exception of the presence of coprolites) does not differ from similar lacustrine horizons in the underlying Prosečné Formation (Čáp 2010).References
