Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Rostroconchs from Devonian sediments of the Moravo-Silesian Basin


Hedvika Weinerová, Tomáš Weiner, Jindřich Hladil

Geoscience Research Reports 50, 2017, pages 153–157
Map sheets: Bruntál (15-31)

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Published online: 29 June 2017

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To date, the rostroconch macrofossils have not been known from the Devonian sequences of the Moravo-Silesian Basin, and specimens in thin sections were overlooked or treated as enigmatic microfossils. This paper focuses on rostroconchs in thin sections from four localities with various facies development in the time interval from Eifelian to Famennian. The Horní Benešov ore mine is a locality with the Drahany (basinal) facies development. Here, the rostroconch was recorded in an uppermost Eifelian calciturbidite breccia from steep slope of a guyot. This intraclastic-bioclastic packstone/rudstone contains styliolinids with common calcite aureols, crinoids, algal, coral and trilobite fragments. The Křtiny Brook valley, Lesní lom Quarry and Šumbera section represent sites with Moravian Karst (platform) facies development. Rostroconch from the Křtiny Brook valley came from the upper Givetian tempestites represented by packstones with resedimented micritized grains, foraminifers, amphiporids, stachyodids, and tabulate corals. Rostroconch from the Lesní lom Quarry section (carbonate ramp depositional environment) is Frasnian in age and comes from wackestone/packestone with microbial clotted structure, peloids, crinoids, foraminifers, calcispheres, microproblematics, ostracods, trilobites, and bioclasts with micrite envelopes. Sample from the Šumbera section (carbonate ramp depositional environment) was obtained from Famennian peloidal/intraclastic/bioclastic grainstone with girvanellids, crinoids and brachiopods. Rostroconchs from the Devonian of the Moravo-Silesian Basin possess at least two distinguishable shell layers. The outer shell layer is beige to brownish, and forms also surface sculpture and distinct internal ribs. Especially at internal ribs, fine prismatic microstructure and growth bands are visible. Such a very good preservation might indicate original calcite mineralogy and/or former admixture of possible organic or phosphate ligands. The inner shell layer consisted of aragonite and was commonly dissolved before its replacement by sparry calcite cement.


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