Publication details

The earliest Badenian Planostegina bloom deposit: reflection of an unusual environment in the westernmost Carpathian Foredeep (Czech Republic)

Authors

KOPECKÁ Jitka HOLCOVÁ Katarina NEHYBA Slavomír HLADILOVÁ Šárka BRZOBOHATÝ Rostislav BITNER Maria Aleksandra

Year of publication 2018
Type Article in Periodical
Magazine / Source Geological Quarterly
MU Faculty or unit

Faculty of Science

Citation
Web http://dx.doi.org/10.7306/gq.1398
Doi http://dx.doi.org/10.7306/gq.1398
Keywords Middle Miocene-Central Paratethys-siliciclastic sedimentation-carbonate sedimentation- large benthic foraminifera-palaeoecology
Description The Miocene sedimentation history of the Brus denudation relict (the western part of the Carpathian Foredeep, Czech Republic) has been inferred from 20 m of silt/siltstones, sand/sand stones and limestones penetrated by the Brus-1 borehole. Detailed multiproxy lithofacies and biofacies analyses have allowed facies and palaeoenvironment interpretations. The presence of molluscs, brachiopods and fish fauna, as well as large benthic and epiphytic foraminifera indicates a generally shallow, subtropical, marine environment. Despite the scarcity of biostratigraphical markers, the section can be correlated with the lower most Badenian (~15–16 Ma). In the siltstones in the lower part of the borehole, there are abundant low-salinity foraminifera, which may indicate increased rain fall. Linked to this is the nutrient enrichment of the sea bottom water inferred from the presence of the high-nutrient taxa accompanied by abundant calcareous nannoplankton eutrophic taxa such as Coccolithus pelagicus and eutrophic planktonic foraminifera of the Globigerina bulloides/praebulloides group. The main Planostegina bloom was recorded in a sandstone in the interval 12.5–7 m, and was not influenced by a shift from high-organic content Valvulineria assemblage of small foraminifera to an epiphytic one. The boundary between siliciclastic and carbonate sedimentation (7.5 m) shows a drop in K and Th concentrations, and in the Th/U ratio, but a rise in the Th/K ratio. This change in radioactive element content may generally indicate a significant decrease in terrestrial sediment input which is further supported by the on set of limestone deposition. Reversal of the deposition regime and a decrease of clastic input into the basin may be related to the changing of the precipitation régime, probably triggered by orbitally-forced cyclicity.

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