Systematics and biostratigraphy of Oligocene ( Rupelian-Early Chattian ) foraminifera from lagoonal-very shallow water limestone in the eastern Sivas Basin ( central Turkey )

The aim of the present work is to describe the Oligocene (Rupelian-early Chattian) shallow water larger foraminifera from central Turkey (Sivas Basin). Among them is a new miliolid genus, Sivasina n. gen. SİREL & ÖZGEN-ERDEM (type species Sivasina egribucakensis n. gen. n. sp. SİREL & ÖZGEN-ERDEM), which occurs in the Eğribucak, Bakımlı, Tuzlagözü and Çaygören sections (E of Sivas). One new Rupelian-early Chattian lagoonal very shallow water peneroplid species Peneroplis fl abelliformis n. sp. SİREL & ÖZGEN-ERDEM from the Eğribucak, Tuzlagözü and Çaygören sections and Rupelian lagoonal two new peneroplid species Coscinospira sivasensis n. sp. SİREL & ÖZGEN-ERDEM, Coscinospira elongata n. sp. SİREL & ÖZGEN-ERDEM from the Eğribucak section (E of Sivas), two new Rupelian very shallow water alveolinid species Praebullalveolina oligocenica n. sp. SİREL & ÖZGEN-ERDEM and Praebullalveolina minuta n. sp. SİREL & ÖZGEN-ERDEM from the Bakımlı section are described and fi gured. Furthermore, details on several already known Oligocene species are given (soritids: Praearchaias diyarbakirensis SİREL, Praearchaias minimus SİREL, Archaias kirkukensis HENSON, Archaias asmaricus SMOUT & EAMES; austrotrillinids: Austrotrillina brunni MARIE). In addition, the biostratigraphy of four studied sections is discussed.


INTRODUCTION
The Scientifi c and Technological Research Council of Turkey (Tübitak) project on the Stratigraphy, Sedimentology and Basin Development in the Oligocene-Miocene of Sivas Basin was carried out in 2009-2012 by the Department of Geological Engineering of Cumhuriyet (Sivas), at the universities of Ankara, Hacettepe (Ankara), Dumlupınar (Kütahya), Ege (İzmir) and Onsekizmart (Çanakkale) and at the Geological Mapping Department of MTA.The Oligocene (Rupelian-early Chattian) lagoonal-very shallow water larger foraminifera, including alveolinids, soritids, penero-plids, austrotrillinids and miliolids and their biostratigraphy were investigated as a part of this project.
According to our current knowledge marine sediments of Danian-Bartonian age are very widespread in the territory of Turkey.On the contrary, continental deposits are observed mostly after Bartonian stage at the Çankırı, Sivas and similar basins, as well as those of Oligocene age.Throughout the Mediterranean region, at the end of Bartonian or at the beginning of Priabonian, important paleogeographic, sedimentary and faunal (particularly in benthic foraminifera) changes occurred.These may be connected with tectonic movements (particularly orogeny) causing major regressions.These changes are refl ected in different ways in the study area, resulting in different facies developments benthic foraminiferal assemblages.The lagoonal, very shallow to and shallow water limestones in the Eğribucak, Bakımlı, Tuzlagözü and Çaygören sections and few spot samples from the eastern Sivas basin yielded several new peneroplid, alveolinid, miliolid and known austrotrillinid and soritid species which are here described and fi gured.
Throughout the Mediterranean region, the very shallow water marine environments with porcellaneous foraminifera are virtually absent in the depositional sequences of Oligocene age.As yet, these depositional environments have been recorded from the Middle-East, Iran and Iraq by HEN In Turkey, interesting Early Oligocene very shallow water marine spot limestone samples with porcellaneous foraminifera (mainly soritids, miliolids, peneroplids and austrotrillinids species) have previously been reported from the Kırkbini village, SW Diyarbakır, southern Turkey by SİREL (1996) and Rupelian-early Chattian very shallow water marine limestone sequence with soritids, miliolids and austrotrillinids species from the Develi village, W of Malatya, E Turkey by SİREL (2003, Figs.4,14).In the studied area, interesting Rupelian-early Chattian lagoonal, four very shallow and shallow water lithologic successions were investigated with special reference to the description of the porcellaneous foraminiferal species and their biostratigraphy.They were measured from different localities of the eastern Sivas basin, eastern part of Central Turkey (Fig. 1) as follows.
The Eğribucak section, located near the Eğribucak village (E of Sivas) (Fig. 2), is the type locality of several new foraminiferal taxa, namely, the new miliolid genus Sivasina Another interesting succesion, here referred to as the Bakımlı section (Fig. 3) (samples Bak. 1 to 21) is situated southeast of the Bakımlı village, E of Sivas.The sandy limestone and limestone beds ranging from 15 to 21 are the type locality of P. oligocenica n. sp. and P. minuta n. sp.Two additional known Rupelian soritid species P. diyarbakirensis SİREL and P. minimus SİREL (SİREL, 1996, Pl.I and SİREL, 2003, Fig. 14) co-occur with the two new alveolinid species.The Tuzlagözü section (Fig. 4) is an interesting succesion for the shallow/very shallow water Oligocene foraminifera, located SE of Tuzlagözü village, E of Sivas.The very shallow water limestone samples ranging from Tzg. 1 to Tzg.  (SBZ 23).The stratigraphic distributions in the studied sections of the here described Rupelian-early Chattian lagoonal-very shallow water foraminiferal species can be correlated with the shallow benthic zones of CAHUZAC & POIGNANT (1997) and be referred to lagoonal-very shallow water environments.
The description of the new foraminiferal taxa and the already known Oligocene species is by E. SİREL and N. ÖZGEN-ERDEM, as well as the interpretation of their structural elements, given in Fig. 6.The Eğribucak (Fig. 2), Bakımlı (Fig. 3), Tuzlagözü (Fig. 4) and Çaygören (Fig. 5) sections were measured by N. ÖZGEN-ERDEM and Ö. KANGAL.The Chattian and Miocene miogypsinid and other foraminiferal species are out of the scope of present study.
All the random and oriented thin sections of the foraminiferal species described and fi gured in this paper are deposited in the collection of Cumhuriyet University (Sivas, Turkey), under the labels shown in Pls.I-XI.

STUDIED SECTIONS
In this chapter, the lithostratigraphic and biostratigraphic features of the studied sections (Figs.2-5) are summarized.The benthic foraminiferal biozones in the lithologic successions listed above are largely based on the SBZ zonation by CAHUZAC & POIGNANT (1997).The stratigraphic and environmental distributions of the Oligocene lagoonal, very shallow and shallow water foraminiferal species are shown in Figs.7 and 8, respectively.
The lithologic units and their foraminiferal content are given in Fig. 2.

Biostratigraphy
The following biostratigraphic benthic biozones are recognized in the Eğribucak succession.
SBZ 21-22 (Rupelian-early Chattian): The fi rst biostratigraphic unit ranging from Eb. 11 to Eb. 33 is defi ned by the fi rst and the last occurrences of S. egribucakensis.n.gen.n. sp.The fi rst appearance of M. borodinensis and M. cf.complanata defi nes the upper boundary of the unit.The occurrence of the lagoonal peneroplid species P. fl abelliformis n. sp, C. sivasensis n. sp., C. elongata n. sp. and known peneroplid species P. evolutus is recognized in the basal level of this zone (Fig. 2).
SBZ 23 (late Chattian): The unit ranging from Eb. 34 to Eb. 37 is characterized by the presence of M. borodinensis and M. cf.complanata.

Bakımlı section
This is the most representative succession in the territory of Turkey as regards the Rupelian very shallow water limestone with the new alveolinid species Praebullalveolina oligocenica and P. minuta.The outcrop (Fig. 3) is situated 2 km SE of Bakımlı village, SE Hafi k, NE Sivas (map reference İ38, coordinates 39°17'78''N; 37°29'13.11''E).The Eocene sequence ranging from Bak. 1 to Bak. 13 is composed of alternation of marl, sandstone and sandy limestone beds.The second lithostratigraphic unit ranging from Bak. 14 to Bak.21 consists of very shallow water marine limestone with benthic foraminiferal species of Rupelian age (SBZ 21).The third lithostratigraphic unit, which is composed of sandstone and siltstone (Fig. 3), was likely deposited in a continental environment.
The lithologic units and their very shallow/shallow water benthic and planktonic (determined by Dr. Aynur HAKYEMEZ) foraminiferal species are given in Fig. 3.

Tuzlagözü section
A further interesting Oligocene succession (Fig. 4) with peneroplids, soritids, miliolids and miogypsinids species is situ-   ated near the Tuzlagözü village, S Zara town, E of Sivas (map references İ38; coordinate 39°42'45''N; 37°40' 41.23''E).The section commences with limestone and ends with marl beds of early Miocene age (Fig. 4).The lower part of the Tuzlagözü succession that ranges from sample Tzg. 1 to sample Tzg. 5 deposited in very shallow water marine environment with peneroplids, soritids and miliolids species of Rupelian-early Chattian age, as opposed to the upper part of the sequence, in which the algal limestone with miogypsinid species are developed in a deeper, shallow water environment.
The lithologic units and their very shallow/shallow water foraminiferal species are given in Fig. 4.

Biostratigraphy
The following benthic biozones are recognized in the lithologic succession of the Tuzlagözü section.

Çaygören section
The studied section (Fig. 5) is located 10 km SE of Çaygören village, E Sivas (map references İ 38, coordinates 39°44' 26.92''N; 37°16'07.94''E).The fi rst lithostratigraphic unit, ranging from Buc. 1 to Buc. 12, consists of alternating sandstone, marl and sandy limestone with soritids, miliolids and peneroplids species of Rupelian-early Chattian age, which indicate a very shallow water marine environment for this unit.The shallow water marine algal limestone with miogypsinids of late Chattian age is found at the top of the Çaygören section.
The lithologic units and their very shallow/shallow foraminiferal species are given in Fig. 5.

Biostratigraphy
The following two biostratigraphic units are recognized in the Çaygören succession (Fig. 5).

SBZ 23 (Late Chattian):
The fi rst and the last occurrence of M. borodinensis defi ne the lower and upper boundaries of this zone, respectively.The occurrence of Postmiogypsinella sp. and Marasella sp. in the unit is noteworthy, and thus this foraminiferal assemblage can be correlated with the late Chattian assemblages described by SİREL & IŞIK (2011) and SİREL & GEDİK (2011).Paratypes: Illustrated in Pl.I, fi gs.1-14; Pl.II, fi gs.1,2; Fig. 6 A-C; labels indicated in Pl.I and II and Fig. 6.

SYSTEMATIC PALEONTOLOGY
Material: More than 120 specimens in equatorial, subequatorial and axial sections from the type locality.
Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).
Type level: Rupelian-early Chattian (SBZ 21-22).Description: The porcellaneous, calcareous test of the new species is composed of three growth stages, namely, small and arcuate early chambers are lined up in two planispiral-involute whorls, later low and broad chambers fl aring and arranged in peneropline and fl abelliform mode, senile chambers become cyclical (Pl.I, fi g. 12; Figs.6A, B).Diameter of the spheric protoconch ranges from 0.05 to 0.08 mm.The connection between the early planispiral chambers is provided by single intercameral foramen (Fig. 6A), whereas the aperture is composed of two rows of foramina in the fl abelliform chambers (Figs.6A, C).The largest diameters of the planispiral and cyclical stages reach 0.47 mm and 1.8 mm (measured from Pl. I, fi gs.7 and 12), respectively.The early planispiral-involute stage forms a swollen central boss on both sides of the test (Pl.I, fi gs.[10][11][12]. Remarks: A fl abelliform-cyclical form was fi rst described and fi gured as Peneroplis damesini HENSON from the late Eocene of Iraq by HENSON (1950, p.34-35, Pl. 4, fi gs.2,3,6; Pl. 5, fi g. 1).Unfortunately, the embryonic and nepionic stages (planispiral-involute chambers) have not been described adequately in the original defi nition of P. damesini.However, the new species differs from P. damesini in its smaller test and developed broad fl abelliform chambers.P. fl abelliformis n. sp.differs from the Oligocene specimens determined as P.cf.damesini HENSON by HOT-TINGER (1963, p. 968, Pl.III, fi gs. 7, 8; text fi gs.q-r) in possessing a larger test, broader fl abelliform chambers and cyclical chambers.The new species is distinguished from the late Eocene species indicated as P. cf. damesini HEN-SON by SİREL & ACAR (1982, Pl. 5, fi gs. 4, 7-9) in having a larger test, well-developed fl abelliform and cyclical chambers.
Stratigraphic and geographic distribution: The new species occurs in the lagoonal-very shallow argillaceous limestone of the Eğribucak section (Fig. 2) and in the very shallow water marine limestone of the Tuzlagözü (Fig. 4) and Çaygören (Fig. 5) sections.The very shallow water limestones with new species underlie algal limestone beds with M. borodinensis and M.cf.complanatus of late Chattian age on the one hand, and it is associated in the very shallow water limestone of the Tuzlagözü section (Fig. 4) with P. diyarbakirensis, P. cf. minimus of Rupelian age (SİREL, 1996) on the other hand.Therefore, the stratigraphic range of the new species is interpreted as Rupelian-early Chattian (SBZ 21-22).Description: Compressed small test is composed of two stages.The early stage is enrolled planispirally and involute with numerous low arched chambers, later adult chambers are uncoiled and arranged in fl aring peneropliform pattern (Pl.II, fi gs.5,10,11).The diameter of the planispiral early stage ranges from 0.25 to 0.43 mm and the longitudinal diameter of the adult test from 0.68 to 1 mm.The interior of the chamber is undivided.The connection of the planispiral early chambers is provided by a single intercameral foramen, whereas the connection between the adult chambers is provided by the numerous openings (Fig. 6F).
Remarks: The peneroplid specimens illustrated in Pl.II, fi gs.3-11 resemble the Oligocene-Aquitanian specimens described as Peneroplis sp. by AMIRSHAHKARAMI & TAHERI (2010, pl. 7, fi g. 1).The specimens described here are poorly sectioned, so the apertural face cannot be investigated in detail.Therefore we cannot decide whether they belong to Peneroplis de MONTFORT or Laevipeneroplis SULC.For the time being, they are referred to as Peneroplis sp.
Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).
Type level: Rupelian (SBZ 21).Description: Both generations have a large, operculiniform (Pl.II, fi gs. 12, 14, 17) or short crosier-shaped test with imperforate, calcareous, porcellaneous wall.The diameter of the planispiral early stage ranges from 0.83 to 1.16 mm in megalospheric forms, and from 0.8 to 1.1 mm in microspheric forms.The relatively large, spheric megalosphere (0.083-0.100 mm in diameter) is followed by planispiral arcuate early chambers increasing suddenly in size in the last whorl (Pl.II, fi gs. 12, 14, 15, 17).There are 39 planispiral chambers in an equatorial section of 1.16 mm in diameter that are arranged in the three whorls (Pl.II, fi g. 18).Later few adult chambers start to uncoil.Microspheric forms are rather rare in respect to the megalospheric forms.The small, spheric microsphere (about 0.030 mm in diameter) is followed by arcuate early chambers, planispirally arranged.There are 34 and 37 planispiral early chambers in an equa-torial section measured 0.76 mm (Pl.II, fi g. 15) and 1 mm in diameter (Pl.II, fi g. 17), respectively.Later chambers tend to uncoil (Pl.II, fi gs. 12, 14-18) with cribrate aperture.
Stratigraphic and geographic distribution: The new species C. sivasensis n. sp. and C. elongata n. sp. are frequent in the clayey lagoonal limestone of the Eğribucak (Fig. 2) in association with P. fl abelliformis n. sp., Peneroplis sp. and S. egribucakensis n. gen.n. sp.This lagoonal limestone with C. sivasensis n. sp. and C. elongata n. sp.lies in the lower level of SBZ 21-22, therefore the stratigraphic range of these two species of Coscinospira is considered as Rupelian.Paratypes: Illustrated in Pl.III, fi gs.7-9, 11-13; labels are given in the Pl.III.
Material: Fifty-fi ve specimens in random sections from the Eğribucak section (Fig. 2).
Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).
Remarks: It is distinguished from the type species of the genus, C. hemprichii, in its larger test and longer biserial stage.The new species differs from C. sivasensis n. sp. in possessing smaller early planispiral and longer uniserial stages.
Material: 140 specimens in random sections from the Eğribucak section (Fig. 2) Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).
Type level: Rupelian-early Chattian (SBZ 21-22).Description: Both generations have an infl ated, biumbilicate lenticular test with tremataphorid aperture.Diameter of the test ranges from 0.66 to 0.9 mm in the megalospheric form and from 1to 2 mm in the microspheric form.
Remarks: Similarities and differences between S. egribucakensis n. gen.n. sp and other species are given in the differential diagnosis of the new genus.

Stratigraphic and geographic distribution:
This new miliolid species occurs in the lagoonal restricted marine limestone-very shallow water marine limestone of all studied sections (Figs 2-5).
The interesting Oligocene (Rupelian-early Chattian) lagoonal-very shallow water marine succession crops out in the vicinity of Eğribucak village (E Sivas).As seen in Eğribucak section (Fig. 2), the Oligocene (Rupelian-early Chattian) sequence is composed of various lithologic units.The basal lagoonal argillaceous limestone with S. egribucakensis n. gen.n. sp P. fl abelliformis n. sp., Peneroplis sp., C. sivasensis n. sp and C. elongata n. sp that lies between gypsum beds is noteworthy.On the other hand, S. egribucakensis n. gen.n. sp. was observed in the upper part of the Rupelian-early Chattian sequence along with peneroplids and miliolids species (see Fig. 2).This species occurs also in the very shallow water marine limestone of the Bakımlı section (Fig. 3), associated with the soritid species P. diyarbakirensis, P. minimus and the new alveolinid species P. oligocenica n. sp. and P. minuta n. sp. of Rupelian age.Additional very shallow water foraminiferal species, A. kirkukensis, A. brunni and miliolids, occur in this biostratigraphic unit SBZ 21 (Rupelian).
Remark: In the original defi nition of Praebullalveolina, two rows of alveoli connected with two rows of secondary apertures have previously been reported as a diagnostic characteristic of the genus by SİREL & ACAR (1982, p. 823-824).This Late Eocene-Early Oligocene alveolinid genus has defi nitely one row of main and secondary apertures.The undivided early stage consists of two cycles of quinqueloculine and later one cycle of triloculine chambers, that are well recognizable in the microspheric form.In addition, the supplementary chamberlets are present in the adult planispiral chambers.Material: 65 specimens in random sections from the Bakımlı section, (Fig. 3).
Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).

Description:
The specimens with coarser structure have a slightly nautiloid test (Pl.VII, fi gs.3,4).The axial and equatorial diameters range from 0.6 to 0.83 mm and from 0.83 to 1.05 mm, respectively.The new species has characteristically larger divided chambers when compared with the type species P. afyonica and the new species P. minuta n. sp.In well-preserved microspheric specimens, the very small protoconch is followed by two or possibly more cycles of quinqueloculine undivided early chambers (Pl.VII, fi g. 1; Pl.VIII, fi g. 1).Later undivided chambers are lined up in triloculine pattern (Pl.VII, fi g. 1; Pl.VIII, fi g. 1) and the adult divided planispiral chambers that are characteristically broad and infl ated arranged in the planispiral whorls.The height of the planispiral chambers increases fi rst gradually from the undivided triloculine chambers towards the last whorl (Pl.VII, fi g. 1; Pl.VIII, fi g. 1), then suddenly in height and length in the last whorl.There are eight divided chambers in the last whorl of the equatorial section, measuring 1 mm in diameter (Pl.VII, fi g. 1) Remarks: The new species differs from the type species of the genus P. afyonica in its larger test with larger divided planispiral chambers (Pl.VII, fi gs.1-2; Pl.VIII, fi gs.1-2).
In the holotype of P. oligocenica n. sp.there are eight divided chambers in the last whorl at an equatorial diameter of 1 mm (Pl.VII, fi g. 1), whereas in P. afyonica there are 15 divided lower and smaller chambers in the last whorl at an equatorial diameter of 0.92 mm (SİREL & ACAR 1982, Pl.I, fi gs.1,5).In addition, the chamberlets of P. oligocenica n. sp. are larger than the chamberlets of P. afyonica.The new species P. minuta n. sp.differs from P. oligocenica n. sp. in possessing smaller test with lower and narrower, numerous divided adult chambers with smaller chamberlets (Pl.VIII, fi gs.4,8).Thus, the very shallow water marine limestone sequence (Fig. 3) located near Bakımlı village (E Sivas) is particularly interesting, because here the two new species of Praebullalveolina appear together with P. diyarbakirensis, P. minimus and other taxa (see Fig. 3) of Rupelian age (SİREL, 1996).Material: 60 specimens in oriented and random sections from the Bakımlı section.
Depository: Holotype and paratypes are deposited in the collection of Cumhuriyet University (Sivas, Central Turkey).
Type level: Early Rupelian (SBZ 21).Description: The investigated specimens have a subspheric small test with imperforate, calcareous, porcellaneous wall.The axial and equatorial diameters range from 0.61 to 0.66 mm and from 0.70 to 0.78 mm, respectively.The test of the new species is composed of characteristically numerous narrow and low planispiral adult chambers with small chamberlets when compared with P. afyonica and P. oligo-  cenica n. sp.In some sections, the very small protoconch is followed by two cycles of undivided quinqueloculine early chambers (Pl.VIII, fi g. 6), and later undivided chambers arranged in triloculine pattern as in P. oligocenica n. sp.(Pl.VIII, fi gs.6, 8).The adult chambers are lined up in planispiral mode and divided into numerous chamberlets by septula.The height of the planispiral whorls increases gradually towards the last whorl.There are 14 divided planispiral chambers in the last whorl (holotype, Pl.VIII, fi g. 4) measuring 0.78 mm in diameter.

Description:
The species has a discoidal test with swollen central boss.The diameter of the test ranges from 2.56 to 3.06 mm.The very small microsphere is followed by small undivided, arcuate chambers lined up in a planispiral pattern for one and half whorls, later divided chambers with interseptal partitions arranged in a cyclical mode (Pl.IX, fi gs. 1, 3-8).

Stratigraphic and geographic distribution:
The species was reported from the late Oligocene of the type locality, Kerkük, Iraq by HENSON (1950, p. 43).It has been found in the Oligocene of Sivas, Central Turkey, by TUR-NOVSKY (1955) and VAN BELLEN (1956)

Description:
The defi nition of this species is based on the holotype of A. asmaricus (SMOUT & EAMES 1958, Pl. 41, fi g. 7).The species has an infl ated lenticular test with rounded periphery.The thickness of the swollen central part decreases toward the periphery (Pl.IX, fi gs.[10][11][12][13][14][15][16].The diameter of the test ranges from 1.66 to 2.33 mm, the central thickness from 0.73 to 0.83 mm and the peripheral thickness 0.33 to 0.43 mm.The protoconch is very small, followed by few undivided, arcuate small chambers (Pl.IX, fi gs. 10, 11); later divided chambers are arranged in planispiral-involute mode (Pl.IX, fi g. 9) and the following cyclical adult chambers are divided by thin interseptal partitions into numerous small chamberlets.

Stratigraphic and geographic distribution:
This species is found in the very shallow water marine limestone of the Tuzlagözü section (Fig. 4

Description:
The megalospheric test has an infl ated lenticular shape with imperforate, calcareous porcellaneous wall.The diameter of the test ranges from 1.6 to 2.6 mm and the thickness from 0.48 to 0.8 mm.The large, spherical megalosphere (about 0.160 mm in diameter) is followed by a semilunar second chamber (Pl.X, fi g. 4), later by few undivided arcuate chambers and the last divided chambers of the adult stage are arranged in a planispiral-involute mode throughout ontogeny (Pl.X, fi gs.3,4).The chambers are divided by complete or incomplete interseptal pillars (Pl.X, fi gs. 4, 7).
Stratigraphic and geographic distribution: This early Oligocene (Rupelian) species is found in the very shallow water marine limestone of the Bakımlı section (Fig. 3) with the two new species, P. oligocenica n. sp. and P. minuta n. sp.It is found in the lower part of SBZ 21-22 in the Tuzlagözü section with additional foraminiferal species (see Fig. 4).8-12, 17, 18. Description: Small, infl ated lenticular test with imperforate, calcareous, porcellaneous wall.The diameter of the test ranges from 0.8 to 1.3 mm and the thickness from 0.36 to 0.75 mm.The small, spheric megalosphere (0.08-0.13 mm in diameter) is followed by a semilunar second chamber (Pl.X, fi gs. 8, 10, 13) and few undivided arcuate small chambers (Pl.X, fi g. 9), later subrectangular adult chambers by interseptal pillars (Pl.X, fi g. 9) are lined up in planispiralinvolute whorls throughout ontogeny.

Description:
The test is small and the peripheral margin is rounded.The transverse diameter of the test ranges from 0.88 to 1.19 mm, the longitudinal diameter from 1 to 1.27 mm.The spheric megalosphere (0.100-0.138 mm in diameter) is followed by small undivided chambers arranged in probably triloculine mode (Pl.XI, fi gs.2-6, 9, 11, 12, 14).Later adult chambers with fi ne subepidermal partitions are also lined up in triloculine pattern (Pl.XI, fi gs.3,12).Two types of subepidermal partitions form small alveolar compartments (Pl.XI, fi gs.16,20).

Figure 2 :
Figure 2: Stratigraphic distribution of the foraminiferal species in the Eğribucak section.

Figure 3 :
Figure 3: Stratigraphic distribution of the foraminiferal species in the Bakımlı section.

Figure 4 :
Figure 4: Stratigraphic distribution of the foraminiferal species in the Tuzlagözü section.

Figure 5 :
Figure 5: Stratigraphic distribution of the foraminiferal species in the Çaygören section.
Stratigraphic and geographic distribution: Until 1998, the alveolinid genus Praebullalveolina (type species P. afyonica) was considered as a marker species of the Priabonian very shallow environment in the Mediterranean region by SİREL & ACAR (1982) and SERRA-KIEL et al. (1998).The fi rst occurrence of Praebullalveolina at the Priabonian/Oligocene boundary was reported from the Priabona region (Italy) by BARBIN et al. (1998).This biostratigraphic age concerning Praebullalveolina was constrained by the presence of the associated early Rupelian foraminiferal species P. delicata and Austrotrillina paucialveolata GRIMS-DALE by BARBIN et al. (1998, p. 143).

Figure 7 :
Figure 7: Stratigraphic distribution of the Oligocene lagoonal-very shallow and shallow water foraminiferal species of the studied sections in the benthic biozonation of CAHUZAC & POIGNANT (1997).

Figure 8 :
Figure 8: Distribution of the larger benthic foraminiferal species in the lagoonal-very shallow-shallow marine environments of studied sections.

:
P. minuta n. sp.differs from P. afyonica and P. oligocenica n. sp. in having smaller test, lower and narrower chambers with small chamberlets.Its stratigraphic range and geographic distribution of P. minuta n. sp.coincide with those of P. oligocenica n. sp.