By Nedelea Emilia-Elena

The evolution of the Paratethys was strongly influenced by temporary connections with the Mediterranean and Indo-Pacific regions during the Middle Miocene (Popescu, 1975; Rögl & Steininger, 1984; Kováč et al., 2007). Radiolarians are particularly important in this context, as they preserved a valuable record of these changes, providing key evidence for reconstructing past marine connections and environmental conditions.

In the Romanian sector of the former Paratethys, the Badenian (16.3-12.8 Ma) is widely regarded as the final marine phase. One of the most distinctive records of this interval is the so-calledRadiolarian Shale Formation (Popescu, 1951, Olteanu, 1951). Later, a series of studies by Paulian Dumitrică provided the first detailed descriptions of the radiolarian and silicoflagellate assemblages recorded within this unit (Dumitrică, 1964, 1965, 2016).

The material presented here comes from the Pietreni area, located in the Getic Depression, southern Romania, where this horizon  is well exposed (Fig. 1). This Upper Badenian (Kossovian) succession consists of finely stratified dark clays interbedded with centimetric to decimetric volcanic tuff layers and contains exceptionally rich siliceous microfossil assemblages.

Figure 1. Geographic location and geological–tectonic setting of the Pietreni section, western Getic Depression, Romania. (A) Geographic position of the investigated section in the Pietreni area (Google Earth image). (B) Simplified tectonic framework of the Getic Depression and adjacent geological units, redrawn after Ghiran et al. (2023) and adapted from Săndulescu (1984) and Schmid et al. (2008). (C) Geological map of the Pietreni area showing the distribution of the main lithostratigraphic units and structural features, redrawn from the Vânturarița Geological Map (1:50,000 scale; Geological Institute of Romania, 1978).

A total of 24 samples were collected and analyzed, revealing a diverse microfauna dominated by radiolarians and accompanied by diatoms. Within this association, spumellarians are the most abundant and taxonomically diverse group, while nassellarians are represented by fewer taxa, many specimens displaying excellent preservation (Figs. 2-3).

Figure 2. A-B.Excentrodiscus grigorei Dumitrică; C. Excentrosphaerella sphaeroconcha Dumitrică; D-F. Didymocyrtis laticonus (Riedel); G-I. Cyphonium virgineum Haeckel.

Figure 3. J-N.Rhopalastrum lagenosum Ehrenberg; O-Q. Schizodiscus disymmetricus (Dogiel); R. Lithopera sp. 

The occurrence of species Didymocyrtis laticonus and Lithopera sp. supports the Late Badenian age for the studied section, corresponding to Zone RN5 (Riedel & Sanfilippo, 1970) emended by Riedel and Sanfilippo (1971, 1978) and Subzone RN5b (Kamikuri, 2022). Furthermore, the radiolarian association identified in the studied section shows strong affinities with radiolarian faunas reported from other localities in Romania and Poland (Dumitrică et al.,1975; Barwicz-Piskorz, 1999).

Beyond their biostratigraphic value, radiolarians provide a glimpse into the environmental conditions that existed during Late Badenian. Their abundance, together with the numerous volcanic tuff layers, points to an increased supply of silica that likely favored the development of siliceous microorganisms, while their stenohaline nature indicates the persistence of normal marine conditions (Dumitrică, 1968).

About the author

Emilia-Elena Nedelea holds a Bachelor’s degree in Geological Engineering and is currently an M.Sc. student in the Sedimentary Basin and Mineral Resources Assessment program at the Faculty of Geology and Geophysics, University of Bucharest. Her research interests focus on Cenozoic radiolarians, particularly those from the Miocene, and their applications in paleoecological and paleogeographic reconstructions.

References

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