International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Foraminiferal species diversity in the Central Paratethys — a reflection of global or local events?

Pages: 71 - 85


Abstract: The stratigraphical ranges of the Eocene–Sarmatian Central Paratethys Foraminifera were used to calculate their species diversity (=the number of foraminiferal species in a certain time interval). Species diversity was evaluated separately for benthic and planktonic Foraminifera, agglutinated and porcellanaceous foraminifers, lagenids, oxyphilic, dysoxic and euryhaline species. In the Central Paratethys basins, six foraminiferal species diversity events were defined: (i) The Egerian species diversity maximum was reached by progressive growth in the number of foraminiferal species during approximately 15 Myr from the Early Eocene to the Egerian. (ii) The Egerian and Egerian/Eggenburgian extinction event interrupted the growth of species diversity. The beginning of extinction was approximately isochronous with the acme of small-sized reticulofenestras (calcareous nannoplankton) which are considered to be an indicator of warm water with low nutrient concentrations; (iii) The Ottnangian species diversity minimum is the consequence of a minimum number of foraminiferal FOs during the Eggenburgian and the Ottnangian (3 Myr). This was caused by isolation of the Paratethys and the progressive decrease of salinity and oxygen content during the Ottnangian. (iv) The Early Badenian species diversity maximum followed an abrupt increase in species diversity of benthic Foraminifera at the Karpatian/Badenian boundary as a consequence of a large transgression and the establishment of fully marine conditions in nearly the whole territory. Diversity of the planktonic assemblages increased gradually in the Karpatian (1.1 Myr) as a result of the opening of new sea-ways. (v) Extinction at the Badenian/Sarmatian boundary indicates rapid shift of paleoenvironmental parameters. (vi) The number of Sarmatian species represents only 29 % of the Egerian species. The composition of assemblages changed and shifted to endemic, euryhaline species. These changes can be clearly correlated with the isolation and vanishing of the Central Paratethys basins. It is suggested that foraminiferal species diversity in the intracontinental Central Paratethys basins was controlled mainly by regional paleogeographic communication/isolation events which may be influenced by global sea-level changes and partly by regional paleoenvironmental changes influenced by global climate changes.

Keywords: Oligocene, Miocene, Central Paratethys, paleoenvironment, paleogeography, species diversity, Foraminifera

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