Most abundant Middle Miocene rotaliinas (suborder Rotaliina, Foraminifera) of Kozjansko (Eastern Slovenia) Najpogostej{e srednjemiocenske rotaliine (podred Rotaliina, Foraminifera) Kozjanskega (vzhodna Slovenija)

This research presents the most numerous Middle Miocene foraminifera of the suborder Rotaliina from the Planina syncline in Kozjansko. 85 species and 2 subspecies have been identified. The species that show abundance in samples are: Angulogerina angulosa, Trifarina bradyi, Sphaeroidina bulloides, Cibicidoides ungerianus, Nonion commune, Melonis pompilioides, Pullenia bulloides, Heterolepa dutemplei, Hansenisca soldanii and Hanzawaia boueana.


Introduction
The foraminiferal suborder Rotaliina was established in 1896 by DELAGE & HEROU-ARD as the suborder Rotalidae (renamed in Rotaliina in 1961 by Loeblich and Tappan) (Loeblich & Tappan, 1987). It represents the second largest foraminiferal suborder, comprising 628 genera according to LOEBLICH & TAPPAN (1987). The suborder includes benthic foraminifera with multilocular tests that have a perforated hyaline calcite wall of a lamellar structure. Other test characteristics show great variety; test is typically spiral or may be reduced to triserial, biserial and uniserial growth. Chambers can be simple or subdivided by septulae. The surfa-ce can be smooth, costate, striate, cancellate or papillate. The aperture can be simple or contain internal toothplate or other structures (LOEBLICH & TAPPAN, 1987). A simple to very complex internal canal system may be developed (BILLMAN et al., 1980).
Rotaliinas show a wide tolerance to environment parameters: substrates, water depth, temperature, salinity and availability of food. They also show great variety in their mode of life, being either infaunal, semi-infaunal or epifaunal. In the case of an epifaunal mode they are either sessile attaching to hard substrates or completely mobile on the substrates surface. The strength of the wave action being important, in highenergy environments there is a preference doi:10.5474/geologija. 2007.021 for attachment to hard substrates. Their depth habitat has been shown to range from the shelf (< 180 m) to the abyssal plane (> 4000 m). They are found in water with temperatures ranging from cold to warm. They are euryhaline with specimens being found in brackish (< 32‰), marine (32-37‰) or hypersaline (> 37‰). They exhibit a range of trophic mechanisms: passive suspension feeding, herbivore, detritivore and rarely parasitic (MURRAY, 1991), in shallow nutrient poor waters symbiosis with diatoms has also been identified (BILLMAN et al., 1980;MURRAY, 1991).
Foraminifera of the suborder Rotaliina have existed from the Triassic (LOEBLICH & TAPPAN, 1987). Due to the great diversity, fossil and recent species are recognized globally.
In this research, rotaliinas were studied from six sections; Imenska Gorca, Plohov breg, Javor{ica, Sveta Ana, Trobni Dol and Drensko Rebro (Fig. 1). The investigated area is located mostly on the northern flank of the Planina syncline, only the Drensko Rebro section lies on its southern flank (BUSER, 1977(BUSER, , 1979ANI~I} & JURI{A, 1984 ANI~I} & OGORELEC, 1994/95, 1996; ANI~I} et al .; 2002, 2004). Results show that rotaliinas have great diversity and abundance in the Planina syncline. Previous researches have shown that rotaliinas are numerous also in other Slovenian Middle Miocene sedimentary sequences. Although they represent a significant proportion of foraminiferal assemblages, they have not been described and mostly not imaged in the Slovenian literature previously.

Methods
Six sections within the Planina syncline were selected for the micropalaeontological research: Imenska Gorca, Plohov breg, Ja-vor{ica, Sveta Ana, Trobni Dol and Drensko Rebro (Fig. 1). One hundred and fifty nine samples, consisting of marly calcarenite and marl, were taken. The samples range from the Early Lower Badenian to Early Sarmatian. According to OBLAK (2006), the following foraminiferal biozones are involved in this stratigraphic range: the Lower Badenian Lower Lagenidae and Upper Lagenidae Zones, the Middle Badenian Pseudotriplasia robusta Zone and Uvigerina cf. pygmea Zone, the Upper Badenian Bolivina dilatata Zone and Virgulinella pertusa Zone and the Sarmatian Anomalinoides dividens Zone and Elphidium hauerinum Zone (Tab. 1). The younger Sarmatian Elphidium hauerinum Zone lacks rotaliinas. One hundred and sixteen benthic species were described and classified according to LOE-BLICH & TAPPAN foraminiferal classification (1987). Electron images of spiral, umbilical and side views were taken using the Jeol T330A scanning electron microscope at the Ivan Rakovec Institute of Palaeontology, ZRC SAZU.

Rotaliinas of the investigated area
From 159 Middle Miocene samples taken from all sections, eighty five species and two subspecies of the foraminiferal suborder Rotaliina have been determined:  2003), and in Romania from the Upper Badenian (POPESCU, 1979).
In Slovenia, the fossil specimens of the species have not been determined yet. The species is described and imaged only on recent specimens of the Adriatic Sea (CIMERMAN & LANGER, 1991). Ecolo g y a n d p a l a e o e c o l o g y : Miocene specimens from Romania are recorded from the pelitic facies (POPESCU, 1979 In Slovenia, the fossil species has not been determined yet. Ecol o g y a n d p a l a e o e c o l o g y: The genus Trifarina is infaunal and characteristically found in temperate to cold marine environments of depths ranging from 0 to 400 m; from the shelf to upper bathyal (MURRAY, 1991 In the Central Paratethys, it appears from the Lower Kiscellian to the end of the Badenian (CICHA et al., 1998)   In Slovenia, the species has not been  In Slovenia, the species hasn't been described yet; it was only imaged from the Badenian of the Celje syncline (RIJAVEC, 1978a). It is also noted from Kiscellian to Middle Badenian sediments. It is mentioned as Nonion communis from the Kiscellian of Zasavje (KOLAR, 1978). As   (POPESCU, 1975), and in Poland from the Badenian (SZCZECHURA, 2000) In Slovenia, the species has not been described yet, it is only imaged from the Upper Eocene (Priabonian) of Socka-Dobrna area (northern of Celje; CIMERMAN et al., 2006) and from the Middle Miocene of Slovenske Gorice (RIJAVEC, 1978b). It is also noted from the Lower Egerian to Upper Badenian sediments. It is mentioned from the Lower Egerian of the Celje syncline (RIJAVEC, 1984) and La{ko syncline (RIJAVEC, 1976a(RIJAVEC, , 1984DOZET et al., 1999), from the Upper Egerian of the La-{ko syncline (RIJAVEC, 1977(RIJAVEC, , 1984DOZET et al., 1996DOZET et al., , 1999  Mater i a l: Numerous tests in samples from all six sections (Tab. 2). Descr i p t i o n: Biconvex test is trochospirally enrolled and circular in outline. Spiral side is evolute and weakly convex, rarely high convex; with three to four visible whorls. Umbilical side is involute and highly convex. The last whorl is built of rarely 6 and more frequently of 7-9 chambers that increase slowly in size. They are parallelogram to trapezoidal in shape on the spiral side and triangular on the umbilical side. Sutures are oblique and flush on the spiral side, and straight to curved backward and slightly depressed on the umbilical side. Whorl suture is flush to slightly depressed toward the end of the last whorl. Periphery is subangular and smooth to very slightly lobate in outline toward the latest part of the test. Wall is calcareous, optically granular and coarsely perforate. Surface is smooth. Slitlike interiomarginal aperture is developed on the upper half of the apertural face and extends in a short distance on the spiral side. It is bordered by a lip. Remar k : Specimens of this study show a great variety in convexity of the spiral side. Tests with different degree of convexity were originally described as se- Mate r i a l: Numerous tests in samples from all six sections (Tab. 2). Desc r i p t i o n: Test is trochospirally enrolled, composed of three to four whorls. Whorls enlarge gradually in size. Spiral side is evolute and slightly convex, umbilical side is involute and highly convex.
On the spiral side, the last whorl stands above the level of earlier stage. Equatorial section of the test is circular while the transverse section is conical. Last whorl is built of 9-10 chambers that appear trapezoidal on the spiral side, and triangular on the umbilical side. They enlarge slowly as added. Sutures are straight, oblique and depressed on the spiral side.
On the umbilical side, they are straight, radial and flush; toward the umbilicus they may get incised. Whorl suture is depressed. Umbilicus is wide and deep. Periphery is angular; it is smooth in outline in the early part of the last whorl  1987) and Adriatic Sea (DIECI, 1959).