Acta Botanica 2-2015.indd ACTA BOT. CROAT. 74 (2), 2015 345 Acta Bot. Croat. 74 (2), 345–361, 2015 CODEN: ABCRA 25 ISSN 0365-0588 eISSN 1847-8476 DOI: 10.1515/botcro-2015-0023 Stratigraphic and taxonomic signifi cance of siliceous microfossils collected from the Turiec Basin, Western Carpathians (Slovakia) NADJA OGNJANOVA-RUMENOVA1*, RADOVAN PIPÍK2 1 Geological Institute, Bulgarian Academy of Sciences, Acad. G. Bonchev str. 24, 1113 Sofi a, Bulgaria 2 Geological Institute, Slovak Academy of Sciences, Ďumbierska 1, 974 01 Banská Bystrica, Slovak Republic Abstract – This study provides the fi rst biostratigraphic data of siliceous microfossils from Turiec Basin, Slovakia. The fossil diatom fl ora consists of 42 species and varieties, belonged to 22 genera. The diatom assemblage studied from the Turiec Basin bears a strong resemblance to assemblages from non-marine diatomaceous sediment of Miocene age from Rüdenschwinden, a village of the eastern slope of the Hohe Rhön (Central Ger- many), non-marine sediments of the early Late Miocene from the village of Szilagy (South Hungary), as well as from Bes Konak Basin, Turkey. The investigated profi le is generally dominated by Alveolophora jouseana. The similarities and differences within the taxono- my of certain species belonging to the genera Aulacoseira, Alveolophora and Miosira are discussed. The accompanying species are species of the genus Fragilaria Lyngbye sensu lato from class Fragilariophyceae. The most interesting taxa belong to the genus Stauro- sirella – S. grunowii, S. leptostauron, S. martyi. Among them are two very unusual taxa identifi ed only to genus. Ecological data for the diatom taxa and the diatom frustules/ chrysophycean stomatocysts ratio are used in an attempt to reconstruct in detail the pal- aeoecological conditions at the time of sediment deposition. Key words: Alveolophora (Bacillariophyceae), biostratigraphy, Late Miocene, palaeo- ecology, siliceous microfossils, Turiec Basin Introduction The Central and South-Eastern European freshwater and brackish systems of the Neo- gene are often chracterised by outstanding endemisms (HARZHAUSER and MANDIC 2008). Neogene non-marine diatoms for this area were documented and illustrated by early work- ers (EHRENBERG 1854, GRUNOW 1882, PANTOCSEK 1892, 1905). During the last decades more of these described diatom taxa have been considered in a stratigraphic context (ŘEHÁKOVÁ * Corresponding author, e-mail: nognjan@geology.bas.bg OGNJANOVA-RUMENOVA N., PIPÍK R. 346 ACTA BOT. CROAT. 74 (2), 2015 1971, 1980, HAJÓS 1985). Recently many papers have appeared on the origin, evolution and phylogeny of lacustrine diatoms during the Neogene period (STACHURA-SUCHOPLES and WIL- LIAMS 2009, WILLIAMS and KOCIOLEK 2010, OGNJANOVA-RUMENOVA and CRAWFORD 2012, KHURSEVICH and KOCIOLEK 2012, etc.). Many of them are concerned with the inventory, de- scription and typifi cation of various diatom species from raw materials, housed in different European diatom collections: Ehrenberg (Berlin), Pantocsek (Budapest), Hustedt (Bremer- haven), Grunow (Vienna), etc. The present paper analysies the non-marine Miocene diatom assemblage present in the sediments of Turiec Basin, Western Carpathian region of Central Europe. Emphasis is given to the centric genera Melosira Agardh, Miosira Krammer, Lange-Bertalot et Schiller and Alveo- lophora Moisseeva et Nevredtinova owing to their stratigraphic importance and diffi cult taxo- nomical problems. Palaeoecological interpretation of the environmental history is also given. Material and methods The Turiec Basin of Slovakia is one of the Western Carpathian intermontane basins that formed during the Middle and early Late Miocene as a results of the Alpine orogeny and its relationship to the Carpathian Mountains (PIPÍK et al. 2012). The sedimentary Neogene fi ll of the basin reaches up to 1,250 m and could have been episodically connected at that time with the back-arc Carpathian ba- sins. The oldest deposits are represented by the Middle Miocene sedimentary, volcano- sedimentary and volcanic andesitic com- plex (PIPÍK et al. 2012). The Turiec Basin fi ll is composed of the Turiec Group with the very complicated positions of various lithostratigraphic units within the Group. Its lithostratigraphy has been redefi ned ac- cording to well preserved fossil leaves, en- demic bivalves, gastropods, and ostracods (KOVÁČ et al. 2011). A total of 20 samples from the area of Tu- riec Basin were analyzed for siliceous micro- fossils: the profi les Martin (49°03’52”N; 18°53’42”E), Socovce (48°57’11”N; 18°51’ 45”E) and Abramová-Kolísky (48°55’47”N; 18°47’09”E) (Fig. 1). Diatom-bearing sed- iments were determined only in the lower- most part of the profi le Abramová-Kolísky on the south-western edge of the Turiec Basin: 6 samples per 0.25 m intervals. The studied sediments belonged to the Abra- mová Member (KOVÁČ et al. 2011), and the geology of the profi le has been accurately described by PIPÍK (2005). 0 5 10 km N Fig. 1. Schematic map of the Turiec Basin in Slovakia with locations of the three sampling stops: Martin (49°03’52”N; 18°53’42”E), Socovce (48°57’11” N; 18°51’45”E) and Abramová-Kolísky (48° 55’47”N; 18°47’09”E). BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 347 The samples for diatom analysis were cleaned according to the method described by OGNJANOVA-RUMENOVA (1991). The relative abundance of diatoms was estimated by Schrad- er’s scale (SCHRADER 1973). Light micrographs were taken with a Nikon DS-Fi 1 camera. For scanning electron microscope (SEM) analyses, samples of cleaned material were dried onto aluminium stubs and coated with gold-palladium. SEM micrographs were provided on a Jeol JSM 5510 using accelerating voltages from 5–10 kV. Ecological spectra were com- posed on the basis of studies of recent diatoms by the method of ABBOTT and VAN LANDING- HAM (1972). The basic environmental factors interpreted in the paleoecological analyses were the active-water reaction (pH), temperature, trophic state, type of habitat and salinity. The percentage ratio of diatom frustules to chrysophycean stomatocysts was applied as an index of trophic status (SMOL 1985). Results Analysis of the diatom fl ora and taxonomical remarks The fossil diatom fl ora consists of only 42 species and varieties of 22 genera (Tab. 1). The classifi cation follows ROUND et al. (1990). The fl ora is almost entirely formed of recent species (85.7%). The taxonomic diversity is very poor. The studied profi le is generally dominated by the centric diatom Alveolophora jouseana (Moiss.) Moiss., hence this species was selected for morphological investigation in light and scanning microscope, due to its stratigraphic im- portance and evolutionary interest. Alveolophora jouseana (Moisseeva) Moisseeva Figs. 5 A–K, 6 A–F, 7 A–H, 8 A–C Melosira jouseana Moisseeva (MOISSEEVA 1971, p. 24, Pl. I, Figs. 1–10) Aulacoseira jouseana (Moisseeva) Moisseeva; (MOISEEVA 1981, p. 125) Alveolophora jouseana (Moisseeva) Moisseeva; (MOISSEEVA and NEVREDTINOVA 1990, p. 542, Pl. I, Figs. 1–10) Miosira jouseana (Moisseeva) Krammer, Lange-Bertalot et Schiller; (KRAMMER et al. 1997, p. 17) Miosira jouseana (Moisseeva) Krammer, Lange-Bertalot et Schiller; (KOZYRENKO et al. 2008, p. 114) Miosira jouseana (Moisseeva) Krammer, Lange-Bertalot et Schiller; (KUZMIN et al. 2009, Pl. 107, Figs. 1–6) Miosira jouseana (Moisseeva) Krammer, Lange-Bertalot et Schiller; (KHURSEVICH and KOCIO LEK 2012, p. 347) Alveolophora jouseana (Moisseeva) Moisseeva; (USOLTSEVA et al. 2013, p. 114) Frustules round in valve view, diameter 7–20 μm. Areolae on the valve face often lo- cated over the entire surface, scattered or isolated as a ring near the margin (Figs. 5 H–K, 6 A–B, C, E). Frustules – short cylinders, 7–10 μm height, with robust costae (3–5 in 10 μm) on the valve mantle. Separating spines pointed (Fig. 7 B). Areolae on the mantle circular, situated in straight rows, 8–12 in 10 μm. Collar short with small ribs, not high (Figs. 7 A–C). Ringleiste varied from deep to shallow, dependent upon the valve diameter (Figs. 5 OGNJANOVA-RUMENOVA N., PIPÍK R. 348 ACTA BOT. CROAT. 74 (2), 2015 Tab. 1. List of diatom taxa from the sediment sequence of the Abramová-Kolísky profi le with their relative abundance. Range: Ol – Oligocene; Mi – Miocene; eMi – Early Miocene; IMi – Late Miocene; PI – Pliocene; ePl – Early Pliocene; Plei – Pleistocene; R – recent. Abundance: 2 – rare; 3 – frequent; 4 – common; 5 – abundant; Ecology: habitat: pl – planktonic; ep – peri- phytic (epiphytic); d – periphytic (deep water form); halobity: hb – halophobous; i – indiffer- ent; hl – halophilous; pH: ac – acidophilic; i – indifferent; alk – alkaliphilic; albnt – alkalibi- ontic; geographical distribution: n-a – north-alpine; c – cosmopolitan; b – boreal; tr – tropical. DIATOMS R A N G E Abundance Ecology B ot to m 2 – 0. 25 m 3 – 0. 25 m 4 – 0. 25 m 5 – 0. 25 m 6 – 0. 25 m H ab ita t H al ob ity pH G eo gr ap hi ca l di str ib ut io n Alveolophora jouseana (Moiss.) Moisseeva, 1990 Mi-Pl 5 5 5 5 5 2 pl Melosira undulata (Ehr.) Kützing, 1844 Mi-R 3 2 2 2 ep i i tr Ellerbeckia kochii (Pant.) Moisseeva, 1992 eMi-lPl 3 3 3 2 3 Aulacoseira granulata (Ehr.) Simonsen, 1979 Ol-R 2 2 3 3 pl i alk c Fragilaria bituminosa Pantoscek, 1889 lMi-Pl 3 3 3 2 2 F. ulna (Nitzsch.) Lange-Bertalot, 1980 Ol-R 2 2 pl i alk c F. heidenii Oestrup, 1910 Pl-R 2 ep i alk n-a Pseudostaurosira brevistriata (Grun.) Williams & Round, 1987 Ol-R 2 ep i alk c Staurosira construens Ehrenberg, 1843 Ol-R 3 3 ep i alk c S. construens var. binodis (Ehr.) Hamilton, 1992 Mi-R 2 ep i alk c S. construens var. venter (Ehr.) Hamilton, 1992 Ol-R 2 3 3 ep i alk c Staurosirella grunowii (Pant.) Morales, Buczkó & Ector, 2013 Mi 2 3 2 S. leptostauron (Ehr.) Williams & Round, 1987 Ol-R 3 2 3 2 d hb alk b S. leptostauron var. dubia (Grun.) Edlund, 1994 Mi-R 3 3 4 ep i i b S. martyi (Hérib.) Morales & Manoylov, 2006 lMi-R 3 3 4 2 ep i alk c S. pinnata (Ehr.)Williams & Round, 1987 Ol-R 3 3 3 2 ep i alk c Staurosirella sp. 1 (= Fragilaria magna Hajós, 1985) Mi 4 3 4 2 3 2 ep Staurosirella sp. 2 2 2 3 2 2 BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 349 DIATOMS R A N G E Abundance Ecology B ot to m 2 – 0. 25 m 3 – 0. 25 m 4 – 0. 25 m 5 – 0. 25 m 6 – 0. 25 m H ab ita t H al ob ity pH G eo gr ap hi ca l di str ib ut io n Cavinula scutelloides (Smith) Lange-Bertalot, 1996 Mi-R 2 2 ep i albnt c Placoneis gastrum (Ehr.) Mereschkowsky, 1903 Mi-R 2 ep i i c P. signata (Hust.) Mayama, 1998 eMi-R 2 d i alk c Placoneis sp. 1 2 Caloneis schumanniana (Grun.) Cleve, 1894 ePl-R 2 2 ep i alk c Diploneis carpathorum (Pant.) Pantocsek, 1913 lMi-ePl 2 2 2 3 D. krammeri Lange-Bertalot & Reichardt, 2004 Mi-R 2 2 2 ep i alk c D. ostracodarum (Pant.) Jovanovska, Nakov & Levkov, 2013 Mi-R 3 2 Diploneis sp. 2 Cocconeis neodiminuta Krammer, 1991 Pl-R 3 2 2 ep i albnt c C. neothumensis Krammer, 1991 Plei-R 2 3 hb alk C. placentula var. euglypta (Ehr.) Grunow, 1884 Mi-R 2 2 ep i alk c Planothidium hauckianum (Grun.) Round & Bukhtiyarova, 1996 Mi-R 2 hl albnt c Eunotia faba Ehrenberg, 1838 eMi-R 2 E. minor (Kütz.) Grunow, 1881 MI-R 2 ep hb ac c Encyonema silesiacum (Bleisch) Mann, 1990 eMi-R 2 ep i i c Amphora buczkoae Levkov, 2009 Mi 2 2 2 2 Gomphonema angustatum (Kütz.) Rabenhorst, 1864 eMi-R 2 ep i alk b Gomphonema sp. 2 Gomphosphenia grovei var. lingulata (Hust.) Lange-Bertalot, 1995 Mi-R 2 Epithemia cistula (Ehr.) Ralfs in Pritchard, 1861 Mi-R 2 E. turgida (Ehr.) Kützing, 1844 Mi-R 2 ep i albnt c Surirella linearis W.Smith, 1853 Plei-R 2 d i i c OGNJANOVA-RUMENOVA N., PIPÍK R. 350 ACTA BOT. CROAT. 74 (2), 2015 L, 8 A–C). Rimoportulae not observed in SEM, as frustules were more or less dissolved, but the channels of the rimoportulae was oblique and passed through the Ringleiste visible in LM (Fig. 5 L). Alveolae with a complex structure (3–5 in 10 μm) (Figs. 7 F–H). The specimens of Alveolophora jouseana from the Abramová-Kolísky profi le show slight differences in valve dimensions (the range of the height is 7–10 μm) relatively to those given in MOISSEEVA (1971). Despite these differences we feel confi dent in assigning all specimens we observed to the same taxon. According to USOLTSEVA et al. (2013) the genus Alveolophora had a restricted distribu- tion, found only in fossil localities in Asia and the Russian Far East, but in KHURSEVICH and KOCIOLEK (2012) the known stratigraphic range is from Oligocene (Czech – North Bohe- mia), Late Oligocene – Early Miocene (Sea of Japan), Early to Middle Miocene (Russia – Transbaikal area, Primorye), Middle Miocene (Belarus), Late Miocene (Bulgaria, West Ka- mchatka, Lake Baikal – bottom sediments). The accompanying species are from the genus Fragilaria Lyngb. sensu lato (class Frag- ilariophyceae). The most interesting taxa are those that now belong to the genus Staurosire- lla – S. grunowii (Pant.) Morales, Buczkó, Ector, S. leptostauron (Ehr.) Williams et Round, S. martyi (Herib.) Morales et Manoylov. Alongside these are two very unusual forms that can be identifi ed to genus level only (Figs. 9 E–H. 10 A–C). Staurosirella sp. 1 has valves with rhomboid to lanceolate shape, with broadly rounded apices. The central sternum is wide with lanceolate form. The valve dimensions are: length 13–45 μm, width 8–20 μm, striae 3–5 in 10 μm, parallel to slightly radial towards the apices. Apical pore fi elds are present at both apices, consisting of several rows of round poroids. A similar Fragilaria complex was determined by HAJÓS (1985) in Miocene sediments, Hungary, where she de- scribed the new species Fragilaria magna Hajós – extremely similar to Staurosirella sp. 1. Fragilaria magna was invalidly published as it lacked any description and was accompa- nied by only a few illustrations. Diatom biostratigraphy The results of diatom analysis have been synthesized in the form of a diagram of the species attaining relative abundance 4–5 according to Schrader’s scale in at least one sam- ple (Fig. 2). One assemblage was distinguished in the development of the diatom fl ora in the investi- gated profi le. In the lowermost part of the microlaminated sequence (bottom-sample 3) the diatom fl ora was rich and variable. This was the association of Alveolophora jouseana, Au- lacoseira granulata and Ellerbeckia kochii. More of the frustules were joined into short chains. The class Coscinodiscohyceae was represented also by Melosira undulata as sub- dominant species. The lower diversity and abundance of the assemblage was observed above this interval (samples 4–6). Several extinct species of stratigraphic interest were detected: Alveolophora jouseana (Moiss.) Moiss., Fragilaria bituminosa Pant., Staurosirella grunowii (Pant.) Morales, Bu- czkó & Ector, Staurosirella sp. 1 (= Fragilaria magna Hajós), Diploneis carpathorum (Pant.) Pant., and Amphora buczkoae Levkov. They can be considered as biostratigraphic markers for the beginning of the Late Miocene age (Late Pannonian s. str.) (HAJÓS 1985). BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 351 Ecological analysis of the diatom fl ora Ecological spectra were established for 28 taxa (66.7% of the determined diatom taxa). The results of ecological analysis are presented in the histograms (Fig. 3). Fig. 2. Diatom diagram from a profi le near the village of Abramová-Kolísky, showing the succes- sion of the most common taxa. Fig. 3. Percentage ratio of the ecological groups diatoms. pH spectrum: 1 – acidophilic, 2 – indiffer- ent, 3 – alkaliphilic, 4 – alkalibiontic; »Habitat« spectrum: 1 – planktonic, 2 – periphytic (deep water forms), 3 – periphytic (epiphytic); Halobion spectrum: 1 – halophobous, 2 – in- different, 3 – halophilous; Geographical distribution: 1 – tropical forms; 2 – boreal forms, 3 – cosmopolitans, 4 – north-alpine forms. OGNJANOVA-RUMENOVA N., PIPÍK R. 352 ACTA BOT. CROAT. 74 (2), 2015 Planktonic species formed 15.4–50% of the assemblage, especially in the uppermost part of the profi le, where Alveolophora jouseana showed a massive appearance. Periphytic forms predominated, with epiphytic ones ranging from 50 to 78.9%, and benthic deep wa- ter forms ranging from 5.3 to 25%. With respect to salinity, the oligohalobous indifferent species prevailed in the assem- blage, ranging from 50 to 100%, with halophobous taxa accounting for 5.9 to 50%, while halophilous taxa (5.3%) were less abundant. Staurosirella leptostauron was a transient sub- dominant species of the halophobous group. In relation to pH of the water, the content of alkaliphilic species ranged between 50 and 70.6%, and of indifferent ones between 15.8 and 50%. These two groups strongly domi- nated in the diatom fl ora. The content of acidobiontic forms ranged from 0–5.2%, and of alkalibiontic forms from 0–20%. Only one acidophilic species was present: Eunotia minor. In biogeographical distribution, the abundance of cosmopolitan taxa predominated in the assemblage (72.2 to 100%), followed by boreal (11.8 to 50%), tropical (5.6 to 50%), and north-alpine (only 5.6%). Relative proportions of diatom frustules and chrysophycean stomatocysts Tracing the ratio of diatom frustules/chrysophycean stomatocysts only one peak in the development of the latter was determined (Fig. 4). Chrysophycean stomatocysts were most abundant at 1.00 m (22%); at the top of the profi le there were only a few diatom frustules and the chrysophycean stomatocysts disappeared. Fig. 4. Percentage ratio of the diatom frustules/chrysophycean stomatocysts. BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 353 Discussion This study integrates our work on diatom biostratigraphy. The dominant complex from the sediments of Turiec Basin is comprised of variable roughly silicifi ed frustules of Alveo- lophora jouseana. During recent decades this species has been placed in various genera: Melosira Ag., Alveolophora Moiss. et Nevretd., Miosira Krammer, Lange-Bertalot et Fig. 5. Alveolophora jouseana (Moiss.) Moiss., light microscope images (A–L): external view of mantle (A–G), external view of valve face showing areolae position (H–K), external view of valve from the Ringleiste with channels of rimoportulae (L). OGNJANOVA-RUMENOVA N., PIPÍK R. 354 ACTA BOT. CROAT. 74 (2), 2015 Schiller and again Alveolophora. Pertinent taxonomic and morphological data for this tax- on, the dominant diatom species, are reviewed and discussed. Melosira jouseana Moisseeva was described from non-marine Miocene sediments from the Russian Far East (MOISSEEVA 1971). It was subsequently transferred by MOISSEEVA to the genus Aulacoseira Thwaites (DAVIDOVA and MOISSEEVA 1988) and then to a newly described genus – Alveolophora Moisseeva et Nevredtinova, which was introduced to a new family Aulacoseiraceae (MOISSEEVA and NEVREDTINOVA 1990). Fig. 6. Alveolophora jouseana (Moiss.) Moiss., scanning electron microscope images (A–F): exter- n al valvae face view (A–B, C, E), internal view of valve showing the Ringleiste (D, F). BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 355 In 1997, KRAMMER et al. described the new genus Miosira Krammer, Lange-Bertalot et Schiller from non-marine diatomaceous sediments of Miocene age from Rüdenschwinden – a village of the eastern slope of the Hohe Rhön (Central Germany). In this study Alveo- lophora jouseana was transferred to Miosira jouseana (Moiss.) Krammer, Lange-Bertalot et Schiller. This new name has been cited in several publications without any further de- scriptions (KOZYRENKO et al. 2008, KUZMIN et al. 2009, KHURSEVICH and KOCIOLEK 2012). Fig. 7. Alveolophora jouseana (Moiss.) Moiss., scanning electron microscope images (A–H): exter- nal view of mantle (A, C), external view of mantle showing separating spines (B), internal view of valvae showing the Ringleiste (E), internal view showing valve with costae (F–H). OGNJANOVA-RUMENOVA N., PIPÍK R. 356 ACTA BOT. CROAT. 74 (2), 2015 KRAMMER et al. (1997) showed that Miosira lacked rimoportulae and the type species pos- sesses triangulate forms, features that make it different from all other species in Alveo- lophora. Similar triangulate forms were also established in abundant quantities from the Miocene sediments of Bes Konak Basin, Turkey (SERVANT-VILDARY et al. 1986). EDGAR and THERIOT (2004) suggested that the phylogeny of Aulacoseira may include Miosira, they noted that Aulacoseira sensu lato was a monophyletic group, then that Miosira must be in- cluded in Aulacoseira, and they provided some evidence to support this systematic place- ment. Recently three new species of genus Alveolophora were described from North Amer- ica (USOLTSEVA et al. 2013). Comparison of the frustules morphology with the known members of the genera Melosira/Alveolophora/Miosira supported our decision to name the most abundant centric form from the investigated profi le in Turiec Basin Alveolophora jouseana (Moiss.) Moiss.: these specimens possess the channels of the rimoportulae (Fig. 5 L), as well as complex alveolar structure on the internal surface of the valve mantle (Figs. 7 F–H). Our observations suggest that there may be several fossil species of the genus Mio- sira/Alveolophora but their taxonomy is far from being clear. Several extinct species of stratigraphic interest are detected in the established diatom thanatocoenosis: Alveolophora jouseana (Moiss.) Moiss., Fragilaria bituminosa Pant., Staurosirella grunowii (Pant.) Morales, Buczkó & Ector, Staurosirella sp. 1 (= Fragilaria magna Hajós), Diploneis carpathorum (Pant.) Pant., and Amphora buczkoae Levkov. They can be considered as biostratigraphic markers for the beginning of the Late Miocene (Late Fig. 8. Scanning electron microscope images (A–D): Alveolophora jouseana (Moiss.) Moiss., inter- nal valve view showing different stages of dissoluted Ringleiste (A–C), Melosira undulata (Ehr.) Kütz., external valve view (D). BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 357 Pannonian s. str.) age. The diatom assemblage studied from the Turiec Basin bears a strong resemblance to assemblages from the non-marine diatomaceous sediment of Miocene age from Rüdenschwinden, a village of the eastern slope of the Hohe Rhön (Central Germany) (SCHILLER 1994), non-marine sediments of early Late Miocene from the village of Szilagy Fig. 9. Light microscope images (A–S): Ellerbeckia kochii (Pant.) Moiss. (A), Melosira undulata (Ehr.) Kütz. (B–D), Staurosirella sp. 1 (E–H), Staurosirella leptostauron var. dubia (Grun.) Edlund (I), Staurosirella leptostauron (Ehr.) Williams et Round (J–M, O–S), Staurosirella martyi (Hérib.) Morales et Manoylov (N). OGNJANOVA-RUMENOVA N., PIPÍK R. 358 ACTA BOT. CROAT. 74 (2), 2015 (South Hungary) (HAJÓS 1985), as well as from Bes Konak Basin, Turkey (SERVANT-VILDARY et al. 1986). The above diatom assemblage shows strong differences to the Neogene diatom assemblages from the Balkan Peninsula (OGNJANOVA-RUMENOVA 2000, 2006). The long-lived Turiec Basin was a large lake system with local development of alluvial fans, swamps and deep water areas (PIPÍK et al. 2012). According to the siliceous microfos- sils (diatoms and chrysophycean stomatocysts) the lake was large and the periphytic sub- dominants confi rmed the development of a shallow littoral zone. The salt content ranged between 0.2–0.3‰. The active water reaction was neutral to slightly alkaline which corre- sponds to the results from geochemistry of the sediments. The temperature of the lake water was similar to those from the subtropical areas; a few tropical elements were presented. Further data could be derived from chrysophycean stomatocysts, which were common in the uppermost level of the sedimentary sequence, forming 22% of the total diatom-cyst as- semblage. These organisms have been most abundant in low productivity lakes with cir- Fig. 10. Scanning electron microscope images (A–F): Staurosirella sp. 1, internal valve view (A–B), Staurosirella sp. 1, external valve view (C), Staurosirella leptostauron (Ehr.) Williams et Round, internal valve view (D–E), Staurosirella martyi (Hérib.) Morales et Manoylov (F). BIOSTRATIGRAPHIC DATA OF SILICEOUS MICROFOSSILS FROM THE TURIEC BASIN ACTA BOT. CROAT. 74 (2), 2015 359 cum-neutral pH, low alkalinity and low phosphorus (OGNJANOVA-RUMENOVA 2005). The ra- tios thus document a period of oligotrophic conditions. Conclusions This paper presents the fi rst biostratigraphic data of siliceous microfossils from Turiec Basin, Slovakia. The fossil diatom fl ora consists of 42 species and varieties, belonging to 22 genera. The investigated profi le is generally dominated by Alveolophora jouseana, and the subdominants belong to the genus Staurosirella. The established biostratigraphic dia- tom marker species suggest the beginning of the Late Miocene. The results of the diatom analysis imply the existence of a large, alkaline shallow lake in Turiec Basin, which belonged to the subtropical climate area at the beginning of the early Late Miocene. Acknowledgments The manuscript was prepared with the help of bilateral agreements between the Bulgar- ian and Slovak Academies of Science: Joint Research project: BAS-SAS (2012–2014) »Os- tracod-Diatomaceae paleoecologic and isotopic inference model for the Neogene freshwa- ter and brackish lakes«. We also thank the Synthesys project HU–TAF–3690. Project FP 6 (Structuring the European Research Area Programme, http://www.synthesys.info/), Natural History Museum, Budapest, Hungary. References ABBOTT, W., H., VAN LANDINGHAM, S., 1972: Micropaleontology and paleoecology of Mio- cene non-marine diatoms from Harper District, Malheur Country, Oregon. Nova Hed- wigia 23, 847–90. DAVIDOVA, N., MOISSEEVA, A., 1992: Genus Aulacoseira Thw. In: GLESER, S., MAKAROVA, I., MOISSEEVA, A., NIKOLAEV, V. 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