GEOLOGIJA 48/2, 211–223, Ljubljana 2005 Badenian discoasters from the section in Lenart (Northeast Slovenia, Central Paratethys) Badenijski diskoastri v profilu pri Lenartu (severovzhodna Slovenija, Centralna Paratetida) Milo{ BARTOL & Jernej PAV[I^ Naravoslovnotehni{ka fakulteta, Oddelek za geologijo, Katedra za paleontologijo in stratigrafijo, A{ker~eva 2, SI-1000 Ljubljana, milos.bartol@gmail.com jernej.pavsic@ff.uni-lj.si Key words: Slovenske gorice, Eastern Sovenia, Central Paratethys, Miocene, Badenian, nanoplankton, discoasters, paleoecology Klju~ne besede: Slovenske gorice, vzhodna Slovenija, Centralna Paratetida, miocen, badenij, nanoplankton, diskoastri, paleoekologija Abstract In Slovenske gorice, south of Lenart, a 20 m profile of Middle Miocene strata has been exposed. During previous research numerous discoasters have been found among other coccoliths. In Slovenia Miocene discoasters have only been found in Badenian sediments in Slovenske gorice and they are particularly useful for paleoecological reconstructions. Additional samples were taken from three selected sections in the middle part of the profile, targeting strata with the greatest abundance of discoasters. In two of the three examined sections 9 species of discoasters were identified, the most abundant being D. exilis and D. variabilis. Even though warm water species were found in samples from all three sections, discoasters only occured in two short intervals. This pattern is not a result of temperature changes and is in our opinion connected with the changes in nutrient levels of seawater. Kratka vsebina Ju‘no od Lenarta v Slovenskih goricah izdanja pribli‘no 20 m visok profil srednjemi-ocenskih plasti. V srednjem delu profila so bili med predhodnimi raziskavami poleg drugih kokolitov najdeni tudi {tevilni diskoastri. Miocenski diskoastri se v Sloveniji pojavljajo le v badenijskih plasteh v Slovenskih goricah, zato so posebej zanimivi za paleoekolo{ko interpretacijo. Trije kraj{i profili, kjer se je v predhodni raziskavi pojavljalo najve~ dis-koastrov, so bili ponovno podrobno vzor~eni. V dveh od treh vzor~enih profilov je bilo dolo~enih 9 vrst diskoastrov od katerih se mno‘i~no pojavljata Discoater exilis in D. valiabilis. ^eprav so vrste, zna~ilne za toplo morje prisotne v vseh treh profilih, je pojavljanje diskoastrov omejeno na dva kratka intervala. Vzorec pojavljanja diskoastrov ni rezultat temperaturnih sprememb, temve~ je, po na{em mnenju, povezan s spremembami koli~ine hranil v vodi. Introduction uth side of Lenart during construction works (Figure 1). The profile was sampled and on The research of Badenian nanoplankton the basis of nanoplankton assemblage it was in the territory of Slovenske gorice begun a established that the sediments are of Bade- few years ago, when a large profile of clastic nian age. In the lower part of the sequence Miocene strata has been exposed on the so- poorly preserved shells of eutecosomate pte- 212 Fig. 1. Location map of the investigated section Sl. 1. Karta s polo‘ajem obravnavanega profila ropods belonging to the species Vaginella austriaca were found in great numbers, further confirming Badenian age (Pav{i~, 2002). Upper parts of the sequence contain nodules of lithothamniens and sandstone inclusions, which become more frequent in the upward direction. In the uppermost part of the sequence the sandy marlstone contains fossilized plant particles and parts of fish scales and bones. In some parts poorly preserved remains of linear and spiral eutecosomate ptero-pods were identified (Pav{i~, 2002). Discoasters have been found in the middle part of the sequence. Those were the first discoasters of Miocene age to be found in Slovenia. We were interested why disco-asters are only present in this area and furthermore why they are present in some samples and absent in others, this pattern lacking any association with lithologic changes within the sequence. Methods and materials Additional samples were taken from selected sections of the previously examined profile. We targeted the parts of the sequence in which the presence of discoasters was found to be the most significant. Continuous sampling of long sequences within the Ba-denian strata was impeded by the presence of dense vegetation. For that reason we were compelled to take samples from three separate sections in close proximity. Those sections were sampled in detail at 2, 5 and 10 cm intervals. In this manner we sampled approximately 7 m of marlstone beds in the cen- Milo{ Bartol & Jernej Pav{i~ tral part of the previously examined profile (Figure 2). The sampled sequences consist mainly of grey marlstone, weathering to brown on the surface. Samples were collected from unwe-athered marlstone. The interval we examined is a compound of three short sections. In the first section - A - 40 samples were collected at 10 cm intervals (LR 1-40), in the second section - B - 46 samples were collected at 5 cm intervals (LE 1-46) and in the third section - C - 50 samples were taken at 2 cm intervals (LJ 1-50). Sequence C is the part of the profile which contained the greatest quantity of discoasters in previous examination. Marlstone dust was scraped directly onto a glass slide, distilled water was added. Glass slides were then dried on a hotplate and fixed with Canada balsam. Slides were examined under Zeiss MC 80 DX LM with an oil immersion objective of 100 x with a total magnification of 1000 x. We examined one sample (LR-34), which contained diverse and well preserved fossil coccoliths, with a JE-OL SEM. Nanoplankton species were identified. Dis-coasters (Discoaster spp.) and coccoliths belonging to the species Coccolithus pelagicus and Helicosphaera carteri were counted. Complete coccoliths and fragments, sufficiently preserved for identification, were counted until minimum of 500. Double counting was avoided by means of zigzag motion along the 22 x 22 mm cover slip. The abundance of sphenoliths (Sphenolithus spp.) was semi quantitatively analysed and rated into 4 different categories according to their abundance. Calcareous nanoplankton in the samples is relatively well preserved and complete by our appreciation. Considering the level of preservation we believe, that selective dissolution of nanofossils did not take place. Results 153 samples from 3 proximal profiles were thoroughly examined. Apart from identification of all present species, abundance of four taxa was studied in detail: genus Discoaster, Coccolithus pelagicus, Helicosphaera carteri and genus Sphenolithus. We were interested in their relative abundance and interdependence. Badenian discoasters from the section in Lenart (Northeast Slovenia, Central Paratethys) 213 Fig. 2. Schematic section of the Badenian strata and distribution of discoasters in Lenart Sl. 2. Shematski profil badenijskih plasti in raz{irjenost diskoastrov v Lenartu 38 214 Milo{ Bartol & Jernej Pav{i~ Discoasters were absent from the majority of samples, but two culminations in their abundance were noticed. The first was located near the top of the section A (samples LR 32-40) and the other in the upper half of the section B (samples 21-35). Disco-asters from section A are in a good state of preservation, while those from B are in a considerably poorer state of preservation, relative to the discoasters from A and to the other species present in the samples from the section B. In total 31 species and 2 genera were identified (Table 1). 12 species are present in all three sections. The dominating species are Coccolithus pelagicus and Helicosphaera carteri, the first one being more frequent in nearly all the samples examined. Two small (>5µm) Reticulofenestra species were also found to be common in the samples from all SPECIES - VRSTE \SECTION - PROFIL A B C Coccolithus pelagicilS (Wallich, 1871) Schiller, 1930 X X X Helicosphaera carteri (Wallich, 1877) Kamptner, 1954 X X X Sphenolithus moriformis (Brönnimann & Stradner, 1960) Bramlette & Wilcoxon, 1967 X X X Cyclicargolithus floridanUS (Roth & Hay, 1967) Bukry, 1971 X X X Reticulofenestra minuta Roth, 1970 X X X Reticulfenestra haquü Backman, 1978 X X X Reticulofenestra pseudoumbilica (media) (Gartner, 1967) Gartner, 1969 X X X Geminilithella rotula (Kamptnerl956) Backman 1980 X X X Rhabdosphaera Sicca Stradner & Bachmann et al. 1963 X X X Pontosphaera multipara (Kamptner, 1948) Roth, 1970 X X X HohdiSCOlithuS macroporUS (Deilandre & Fert, 1954) Roth, 1970 X X X Calcidiscus premacintyrei Theodoridis, 1984 X X X Pontosphaera discopora Schiller, 1925 X X Coronocyclus prionion (Deflandre & Fert, 1954) Stradner & Edwards, 1968 X X CalcidisCUS leptoporus (Murray & Blackman, 1898) Loeblich & Tappan, 1978 X Thoracosphaera saxea stradner, 1961 X X Thoracosphaera heimii (Lohmann, 1919) Kamptner, 1941 X Sphenolithus heteromorphus Deflandre, 1953 X X Helicosphaera walbersdorfensis Müller, 1974 X Helicosphaera waltrans Theodoridis, 1984 X Helicosphaera intermedia Martini, 1965 X X Lithostromation perdurum Deflandre, 1942 X X DisCOaSter variabilis Martini & Bramlette, 1963 X o Discoaster exilis Martini & Bramlette, 1963 X o Discoaster adamantheus Bramlette & wilcoxon, 1967 X Discoaster cf. brouweri Tan, 1927 emend. Bramlette & Riedel, 1954 X Discoaster formOSUS Martini & Worsley, 1971 X DisCOaSter mUSiCUS Stradner, 1959 X Discoaster moorei Bukry, 1971 X Discoaster tanii Bramlette & Riedel, 1954 0 Discoaster deflandrei Bramlette & Riedel, 1954 0 Discoaster sp. o Micrantholithus sp. X Catinaster sp. X Table 1. Calcareous nanoplankton species and their presence in sections A, B and C. Species with stratigraphic relevance are marked with bold letters. Species considered not autochthonous are marked o. Tabela 1. Vrste kalcitnega nanoplanktona in njihova pogostnost v profilih A, B in C. Stratigrafsko pomembne vrste so ozna~ene z odebeljenimi znaki. Presedimentirane vrste so ozna~ene z o. Badenian discoasters from the section in Lenart three sections. Diversity of assemblage is highest in the samples from section A, where all 31 identified species are present. Genus Discoaster is represented by 9 species, the most common being D. variabilis, D. exilis, D. adamantheus and D. formosus. In the samples from section B, where discoasters were found, their presence is less pronounced, and they are in a poorer state of preservation compared to the rest of the assemblage. The genus Sphenolithus is represented by two species: S. moriformis and S. hetero-morphus. A large majority of all sphenoliths we found belong to the first of the two. S. heteromorphus sphenoliths are rare in sections A and B and absent in section C. Sphenoliths are common in sections B and C (1-10 sphenoliths / field of view), and abundant in the lower part of section B (>10 sphenoliths / field of view). The samples taken from section A contain fewer spheno-liths. They are present in all examined samples, but are rare (1 sphenolith / 1-10 fields of view) or very rare (<1 sphenolith / 10 fields of view). The composition of nanoplankton assemblage differs considerably between section A and sections B and C. Samples from section A (LR 1-40) exhibit greater diversity of species and they contain fewer sphenoliths. In the samples taken from the upper portion of the section A a considerable share of dis-coasters was observed among other cocco-liths. Discussion The presence of Cyclicargolithus florida-nus and the absence of Helicosphaera am-pliaperta enables us to place section C into biozone NN 5 or NN 6. The absence of Sphe-nolithus heteromorphus would imply the age correspondent to the upper part of NN 6. As this species is rare in other sections as well its absence could be attributed to extreme rarity. Moreover in the Mediterranean, intervals of temporary absence of this species are known (F o r n aciari et al., 1996). For that reason we can not give a more precise stratigraphic position of the section C based only on the absence of S. heteromorphus. Samples from section B contain cocco-liths belonging to species S. heteromorphus, (Northeast Slovenia, Central Paratethys) 215 D. exilis and D. variabilis as well as Cy. floridanus. All listed species are characteristic of biozones NN 5 and the lower part of NN 6. The most accurate stratigraphic position can be given for section A. Apart from all the species mentioned above, the samples LR contain D. formosus and D. musicus, stratigraphic markers of biozone NN 5 (Perch-Nielsen, 1985; Bown, 1999) and D. moorei, characteristic of the same biozone (Bukry, 1971). The presence of Heli-cosphaera species enables us to narrow the interval further: H. intermedia, H. waltrans and H. walbersdorfensis only coexist in a short interval in the upper part of the biozone NN 5 (B o w n , 1999). The first occurrence of the species Cocco-lithus pelagicus is known from the Lower Paleogene in equatorial latitude. Today it can be found in the polar and sub polar environments of the Northern hemisphere. It is most common in the North Atlantic (Sato et al., 2004). But the species is also known from certain subtropical environments. It has been found in the shelf area along the Portuguese coast (Cachão & Mo-it a , 2000), J Africa (Baumann, 2004), Tasmania and New Zealand (Ziveri et al., 2004). In Western Iberia optimal temperature for its growth has been established at 16 °C (Cachão & Moita, 2000). Ziveri et al. (2004) report, that only the large form (or a sibling species) can be found in subtropical environments while the more common, small form (or species), only lives in cold water. The small form of Coccolithus pelagi-cus can therefore be used as an indicator of cold water. In the Middle Miocene the paleoecologi-cal preferences of Coccolithus pelagicus were significantly different. The range of the species was far wider than it is today. The small coccolith variety can only withstand temperatures up to 14 °C, whereas it has been found in Middle Miocene sediments from equatorial latitude (Bukry, 1981). Coccolithus pelagicus from the Badenian can therefore not be used as an indicator of cold water. The presence of discoasters in the sediment is a characteristic of warm low-nutrient sea environment (C h a p m a n & C h e p -stow -Lusty, 1997). Badenian was a relatively warm period, so we would expect 216 consistent presence of discoasters in all the sections we have examined. Nevertheless discoasters were only found in short intervals and were absent from the majority of samples. According to the state of preservation we believe that the dicoasters found in the samples from section A are autochthonous. We can not be sure of that in the case of discoasters found in section B, as they are in a poorer state of preservation than the accompanying assemblage. The assemblage in section B is much more similar to that in section C than assemblage in section A (apart from containing discoasters of course). This again implies that discoasters in the profile B are not autochthonous. During the Badenian, the 6 Ma period of the Miocene climatic optimum came to an end (Jiminez-Moreno, 2005). Mean annual precipitation values dropped in the Ba-denian, and seasonality of precipitation increased at the base and in the middle Badenian. Dry periods lasted up to six months (Böhme, 2003). Temperatures stayed high until the end of Badenian. On the basis of palynological analysis an estimate of mean annual temperature of 16–20 °C has been made (Jiminez-Moreno et al., 2005) while a study of ectotermic vertebrates, plants and bauxite yielded an estimate of 17.4–22 °C (Böhme, 2003). The threshold temperature for discoasters – 14 °C (Chapman & Chepstow-Lusty, 1997) was not exceeded until the end of Badenian. Isotope record of pectinid and brachiopod shells from the Styrian basin indicates significant seawater temperature fluctuation, yet warm climate until 14.2 (+/- 0.1) Ma (Bojar, 2003). According to this the cooling of seawater was somewhat earlier than the cooling of the climate in Central Europe dated between 13.5 and 14 Ma by Böhme (2003). Species of the genus Helicosphaera are most common in hemipelagic environments, their presence usually marks the areas of upwelling (Perch-Nielsen , 1985). Contrary to this discoasters prefer pelagic low-nutrient environments (Chapman, Chep-stow -Lusty, 1997). Those ecological preferences are in accordance with the pattern of fluctuations in abundance of the mentioned genera observed in section A. In the upper portion of this section the abundance of discoasters increases. This occurrence coincides with a significant drop in Milo{ Bartol & Jernej Pav{i~ the abundance of helicoliths belonging to the species H. carteri. This incident is a clear indication of a transition from high-nutrient to low-nutrient environment. No similar event can be observed in section B. Lithostromation is a genus lacking strati-graphic value, nevertheless its paleoecologic preference for hemipelagic environments is known. It is usually not found in sediments deposited far from the shore. The same is presumed for the entire family Pontospha-eraceae (Perch-Nielsen, 1985). Representatives of the genus Pontosphaera are consistently present throughout the studied material, while Lithostromation perdurum was found in a few samples from sections A and C. Discoaster and Thoracosphaera are characteristic for pelagic environments. The first of the two is present only in short intervals, the presence of the other is more consistent, but it is very rare. Nanofossils from all three profiles indicate deposition in a warm epicontinental sea. Sections B and C contain common to abundant sphenoliths. The samples from section A contain fewer sphenolits, but exhibit high assemblage diversity, characteristic of tropical and subtropical environments. Some contain discoasters, indicative of warm water as well as sphenoliths (Perch-Niels e n , 1985; Bown , 1999). The absence of discoasters can therefore not be attributed to low temperatures. The changes of nano-plankton assemblage composition can neither be explained by seasonal dynamics, as we frequently find species specific for different seasons according to Beaufort (2001) in a single sample. Apart from surface water temperature the presence of nutrients in seawater is the most significant factor governing the composition of nanoplankton assemblages. Discoasters are typical of low-nutrient waters. Chapman and Chepstow-Lusty (1997) describe a correspondence between an increase in diatom abundance and decrease in discoaster abundance. Diatoms are characteristic of high-nutrient waters. Influx of land-derived detritus has a major effect on the nutrient levels in epicontinental seas and it depends largely on precipitation. Böhme (2003) writes about climatic changes taking place in Badenian in Central Europe. The results of a study concerning fossil vertebra- Badenian discoasters from the section in Lenart te species and the changes of their ranges indicate a seasonal character of precipitation in the lower Badenian and increasingly dry climate on the transition from lower to middle Badenian. The stratigraphic correlation of that transition would coincide with the upper half of NN 5 (S t e i n i n g e r et al., 1976), the time when sediments sampled in section A were deposited. Moreover the paly-nological study of Paratethys deposits (J i -minez-Moreno et al., 2005) indicates a drop of mean annual precipitation in the Badenian. The reduction in the amount of precipitation could lead to the establishment of low-nutrient environment in the surface waters of Paratethys. This would create conditions that meet the paleoecological requirements of discoasters. On the contrary the increase in the amount of precipitation would cause more nutrients to be washed into the sea and produce a high-nutrient environment, favouring the thriving of genera Sphenolithus and Helicosphaera. The sudden appearance and disappearance of disco-asters could therefore be attributed to the variations in the amount of precipitation leading to changes in nutrient levels of seawa-ter. An influx of nutrients can cause a competitive exclusion or a local extinction event of Discoaster species. Recolonisation in favourable conditions would cause the reappearance of discoasters. This would only be only possible if connections with the surrounding seas existed. In the analysed time interval a connection between the Paratethys and the Mediterranean is known to exist, but is gradually fading. On the basis of a study concerning diatoms Horvat (2004) concludes, that a connection between the Paratethys and the Mediterranean persisted until the end of Badenian. The connection between the Eastern Paratethys and the Indian Ocean in the Badenian is uncertain (B i c c h i et al., 2003). Conclusions The studied fossil material was deposited in a warm hemipelagic sea environment. Dis-coasters, characteristic of low-nutrient pelagic environments have been found in two short intervals, but are, by our appreciation, only autochthonous in one. The pattern of (Northeast Slovenia, Central Paratethys) 217 changes in their abundance is not a consequence of temperature changes, as warm water species were found in all sections. On the grounds of nanoplankton assemblage we are of the opinion that the observed changes are due to fluctuations in nutrient levels of se-awater. A clear indication of such events taking place is a coinciding drop in Heli-cosphaera carteri abundance and an increase in the abundance of discoasters in section A. Variation in the amount of precipitation, known to coincide with the studied interval, provides the most plansible reason for fluctuations in nutrient levels. Acknowledgements The authors would like to thank dr. A. Horvat for critical reviews and constructive comments that greatly improved the manuscript, M. Grm for elaborating the figures and M. Gole‘ for much needed help with the use of JEOL SEM at ZRMK in Ljubljana. Badenijski diskoastri v profilu Lenart (severovzhodna Slovenija, Centralna Paratetida) Uvod S prou~evanjem badenijskega nanoplank-tona na obmo~ju Slovenskih goric smo za~e-li pred leti, ko se je ob priliki gradnje stanovanjskega naselja odprl dalj{i geolo{ki profil na ju‘nem obrobju Lenarta (slika 1). Profil smo podrobno posneli in mu na podlagi na-noplanktonskih vrst dolo~ili badenijsko starost. V spodnjem delu profila smo na{li tudi ve~je {tevilo slab{e ohranjenih ostankov ev-tekosomatnih pteropodov vrste Vaginella austiriaca, ki badenijsko starost {e dodatno potrjujejo (Pav{i~, 2002). V zgornjih delih obravnavanih profilov se pojavljajo le~e li-totamnij in posamezne plasti pe{~enjaka, ki postajajo navzgor vse gostej{e. V najvi{jem delu profila so v pe{~enem laporovcu tudi posamezni rastlinski ostanki in ostanki ribjih skeletov in lusk. Ponekod se pojavljajo tudi slabo ohranjeni ostanki ravnih evteko-somatnih in spiralno zavitih pteropodov (Pav{i~ , 2002). 218 Milo{ Bartol & Jernej Pav{i~ V vzorcih smo prvi~ v Sloveniji na{li mi-ocenske diskoastre, ki se pojavljajo le v do-lo~enih delih sklenjenega profila. Prav prisotnost diskoastrov je bila za nas posebno zanimiva, saj se ne pojavljajo v vseh vzorcih. Zanimalo nas je zakaj se diskoastri pojavljajo le na tem obmo~ju in kaj je povzro~ilo neenakomeren na~in pojavljanja disko-astrov, saj njihova prisotnost oziroma odsotnost ne sovpadata z litolo{kimi spremembami v profilu. Metodika dela Za dodatno vzor~evanje smo se odlo~ili na mestih, kjer smo v predhodnih raziskavah naleteli na pove~ano {tevilo diskoastrov. Kontinuirano vzor~evanje dalj{ih profilov v badenijskih plasteh ovira mo~na pora{~e-nost terena. Zato smo bili prisiljeni sestaviti dalj{i profil na treh bli‘njih, vendar lo~enih odsekih. Posamezne odseke profila smo podrobno vzor~evali tako, da smo vzorce pobi- rali na 2, 5 in 10 cm. Na ta na~in smo obdelali okoli 7 metrov profila laporovca v osrednjem delu znanega profila (slika 2). V omenjenih profilih nastopa v glavnem siv laporovec, ki na povr{ini rjavo prepereva. Vzor~evali smo v sve‘ih nepreperelih delih. Prou~evani interval laporovca je sestavljen iz treh kraj{ih profilov. Prvi interval - A -sestavlja 40 vzorcev, pobranih na 10cm (LR 1-40), drugi del - B - sestavlja 46 vzorcev, pobranih na 5cm (LE 1-46), tretji del - C - pa sestavlja 50 vzorcev, pobranih na 2cm (LJ 1-50). V tem delu smo v prej{njih raziskavah na{li najve~jo gostoto diskoastrov. Preparate za prou~evanje kalcitnega na-noplanktona smo izdelali po standardni metodi direktnega razmaza laporov~evega prahu. Nanoplankton smo opazovali pod opti~nim mikroskopom Zeiss MC 80 DX LM z imerzijskim objektivom pri 1000 x pove~a-vi. Iz vzorca z odli~no ohranjenim fosilnim materialom (LR-34) je bilo izdelanih in pregledanih ve~ preparatov za vrsti~ni elektronski mikroskop (JEOL SEM). Plate 1 Tabla 1 I Discoaster exilis Martini & Bramlette, 1963; sample, vzorec LR-34 JEOL- SEM. Discoaster exilis Martini & Bramlette, 1963; sample, vzorec LR-34, JEOL SEM. 3 Discoaster variabilis Martini & Bramlette, 1963; sample, vzorec LR-34, JEOL SEM. 4 Discoaster formosus Martini & Worsley, 1971; sample, vzorec LR-34, JEOL SEM. 5 Discoaster adamantheus Bramlette & Wilcoxon, 1967; sample, vzorec LR-34, , JEOL SEM 6 Discoaster variabilis Martini & Bramlette, 1963; sample, vzorec LR-34, JEOL SEM 7 Discoaster adamantheus Bramlette & Wilcoxon, 1967; sample, vzorec LR-34, JEOL SEM 8 Discoaster variabilis Martini & Bramlette, 1963; sample, vzorec LR-34, JEOL SEM 9 Discoaster sp.; sample, vzorec LR-32, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli 10 Pontosphaera dicopora Schiller, 1925, sample, vzorec LR-22, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli II Sphenolithus moriformis (Brönnimann & Stradner, 1960) Bramlette & Wilcoxon, 1967; sample, vzorec LJ-41, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli 12 Discoaster adamantheus Bramlette & Wilcoxon, 1967; sample, vzorec LR-33, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli 13 Thoracosphaera heimii (Lohman, 1919) Kamptner, 1941; sample LR-25, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli 14 Helicosphaera walbersdorfensis Müller, 1974; sample LR-17, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli 15 Helicosphaera intermedia Martini, 1965; sample, vzorci LR-11, light micrograph, opti~ni mikroskop, 1000x, crossed nicols, navzkri`ni nikoli Badenian discoasters from the section in Lenart (Northeast Slovenia, Central Paratethys) 219 220 Nanoplankton smo statisti~no obdelali. [teli smo rodove, poleg diskoastrov (Discoaster spp.) {e primerke Coccolithus pelagi-cus in Helicosphaera carteri. Upo{tevali smo cele primerke, oziroma dolo~ljive fragmente do skupnega {tevila 500 primerkov. Podvajanju smo se izognili s cik-cakasto obdelavo preparata na polju 22 x 22 milimetrov. Skupno smo pre{teli omenjene rodove iz 153 vzorcev, poleg vzorcev iz omenjenih treh intervalov {e sonda‘ne vzorce, pobrane v neenakomernih presledkih vzdol‘ celotnega profila (L 1-17). Semikvantitativno smo analizirali tudi pogostnost sfenolitov (Spheno-lithus spp.). Kalcitni nanoplankton je v preparatih razmeroma dobro ohranjen in po na{i oceni popoln. Glede na stopnjo ohranjenosti menimo, da ni pri{lo do selektivnega raztapljanja fosilne zdru‘be. Rezultati Detajlno smo pregledali 153 vzorcev v sestavljenem profilu, ki po predhodnih podrobnih biostratigrafskih raziskavah na osnovi kalcitnega nanoplanktona in evteko-somatnih pteropodov pripada badenijski bioconi NN5 (Pav{i~, 2002). Poleg splo-{nega pregleda nanoplanktonske flore smo posebno pozornost namenili {tirim takso-nom: rod Sphenolithus, rod Discoaster, He-licosphaera carteri in Coccolithus pelagicus. Zanimala nas je njihova pogostnost in medsebojna odvisnost. Na{o pozornost so pritegnili nekateri vi-{ki v pojavljanju diskoastrov glede na si-cer{njo bolj ali manj konstantno odsotnost. Vi{ke smo opazili v dveh nivojih: v profilu A, vzorci LR 32-40, in manj{i vi{ek v profilu B, vzorci LE 21-35 (slika 2). V profilu A so diskoastri zelo dobro ohranjeni, tisti iz profila B pa so v bistveno slab{em stanju. V pregledanem materialu smo dolo~ili 31 vrst in 2 rodova (tabela 1). 12 vrst se pojavlja v vseh vzorcih. Prevladujo~i vrsti sta Coccolithus pelagicus in Helicosphaera car-teri, od katerih je prva praviloma pogost-nej{a. Pogostni sta tudi vrsti rodu Reticulo-fenestra z majhnimi (<5µm) kokoliti in vrsta Sphenolithus moriformis v vzorcih iz profilov B in C. Najve~ja je vrstna pestrost v vzorcih iz profila A, kjer se pojavlja vseh 31 identificiranih vrst. Rod Discoaster je v tem Milo{ Bartol & Jernej Pav{i~ profilu zastopan z 9 vrstami, od katerih so najpogostnej{e D. variabilis, D. exilis, D. adamantheus in D. formosus. V profilu B se pojavljajo diskoastri v precej skromnej{em {tevilu, pa tudi njihova ohranjenost praviloma ne dopu{~a identifikacije vrst. Primerki, ki jih je mogo~e identificirati pripadajo vrstama D. exilis in D. variabilis, v splo{nem pa so slab{e ohranjeni tako od diskoastrov v profili A, kot od spremljujo~e zdru‘be. Rod Sphenolithus je zastopan z vrstama S. moriformis in S. heteromorphus. Prva od obeh je veliko pogostnej{a, predstavlja ve~i-no opa‘enih sfenolitov in se pojavlja v vseh treh profilih. Vrsta S. heteromorphus je bistveno redkej{a, pojavlja se v profilih A in B, ne pa tudi v C. V profilih B in C so sfenoliti pogostni (1-10 sfenolitov na vidno polje), v spodnjem delu profila B pa zelo pogostni (>10 sfenolitov na vidno poje). Vzorci iz profila A vsebujejo bistveno manj sfenolitov. Ti se sicer pojavljajo v vseh pregledanih vzorcih, a so redki (1 sfenolit na 1-10 vidnih polj) ali pa zelo redki (<1 sfenolit na 10 vidnih polj). Profil A se po nanoflori v veliki meri razlikuje od ostalih dveh. V vzorcih LR je opaziti ve~jo vrstno pestrost, izrazito manj{o prisotnost sfenolitov in v zgornjem delu pojav opaznega dele‘a diskoastrov. Diskusija Profil C lahko na podlagi prisotnosti vrste Cyclicargolithus floridanus in odsotnosti vrste Helicosphaera ampliaperta umestimo v biocono NN 5 ali spodnji del NN 6. Isto starost lahko pripi{emo profilu B, kjer se pojavljajo tudi S. heteromorphus, D. exilis in D. variabilis, vrste, ki potrjujejo omenjeni interval, a ga ne opredeljujejo natan~neje. Najnatan~neje je mogo~e datirati profil C, kjer se pojavljajo mnoge stratigrafsko pomembne vrste. Razen vseh zgoraj omenjenih vrst vsebujejo vzorci LR tudi D. formosus in D. musicus, ki ozna~ujeta biocono NN 5 (Perch-Nielsen, 1985; Bown, 1999) ter za isto biocono zna~ilni D. moorei (B u k r y , 1971). Glede na prisotnost vrst rodu Heli-cosphaera lahko nastanek sedimentov dolo-~imo {e natan~neje: vrste H. intermedia, H. waltrans in H. walbersdorfensis soobstajajo le v zgornji polovici NN5 (Bown , 1999). Badenian discoasters from the section in Lenart Vrsta Coccolithus pelagicus se pojavi v spodnjem paleogenu v ekvatorialnem ob-mo~ju. Danes jo najdemo v subpolarnih in polarnih vodah S poloble, predvsem v Atlantiku (S a t o et al., 2004). Coccolithus pelagi-cus pa se pojavlja tudi v subtropskih vodah. Prisoten je v {elfnih vodah ob portugalski obali. O pojavljanju vrste poro~ajo tudi z obal Ju‘ne Afrike (Baumann, 2004), Ta-smanije in Nove Zelandije (Ziveri et al., 2004). Ob portugalski obali vrsta uspeva pri temperaturah med 15 in 19 °C, optimalno pri 16 °C (Cachao & Moita, 2000). V sub-tropskih vodah se najverjetneje pojavlja samo ve~ja od dveh sestrskih vrst, ki sta mor-folo{ko skoraj identi~ni, a imata precej razli~ni ekolo{ki valenci (Z i v e r i et al., 2004). Recentni C. pelagicus upravi~eno slu-‘i kot indikator hladnih povr{inskih voda, a le pri podvrsti (oziroma vrsti) s kokoliti, manj{imi od 10 µm. V srednjem miocenu pa je bila situacija precej druga~na. Areal vrste Coccolithus pe-lagicus je bil veliko ve~ji od dana{njega. Vrsta z manj{imi kokoliti danes tolerira le temperature do 14AC, takrat pa je uspevala tudi na ekvatorialnem obmo~ju (Bukry, 1981). Uporaba badenijskih fosilnih ostankov C. pelagicus za indikatorje hladnih povr{inskih voda je torej vpra{ljiva. Prisotnost vrst rodu Discoaster v sedi-mentu ka‘e na toplo oligotrofno morsko okolje (Chapman & Chepstow-Lusty, 1997). Badenij je bil razmeroma toplo obdobje, zato bi pri~akovali konsistentno prisotnost diskoastrov v morskih sedimentih. V nasprotju s pri~akovanji so bili najdeni le v dolo~enih plasteh, v ve~ini pregledanih vzorcev pa se ne pojavljajo. Glede na stopnjo ohranjenosti nanolitov lahko sklepamo, da so diskoastri v profilu A avtohtoni. Pri profilu B se o avtohtonosti diskoastrov pojavlja dvom zaradi precej slab{e ohranjenosti od spremljajo~e zdru‘be. Da so presedimenti-rani lahko zaklju~imo tudi na podlagi vrstne sestave vzorcev iz profila B, ki je precej podobna tisti, ki jo opazimo pri vzorcih iz profila C, kjer se diskoastri ne pojavljajo. Rod Helicosphaera je zna~ilen za hemipe-lagi~na okolja, njegovo pojavljanje praviloma ozna~uje obmo~ja dvigovanja s hranili bogate globinske vode (Perch-Nielsen, 1985). Za razliko od tega so diskoastri zna-~ilni za pelagi~na oligotrofna okolja (Chapman & Chepstow-Lusty, 1997). Ome- (Northeast Slovenia, Central Paratethys) 221 njene ekolo{ke preference se ujemajo z vzorcem pojavljanja v pregledanih vzorcih. V zgornjih vzorcih profila A se pove~a dele‘ diskoastrov, dogodek sovpada z upadom de-le‘a kokolitov vrste Helicosphaera carteri. Upad pogostnosti H. carteri in porast pogostnosti na oligotrofna obmo~ja vezanih diskoastrov je indikator zmanj{ane koli~ine hranil v vodi. Lithostromation je rod brez ve~je strati-grafske vrednosti, znana pa je njegova pa-leoekolo{ka preferenca do hemipelagi~nih morskih okolij (Perch-Nielsen , 1985). V sedimentih, odlo‘enih dale~ od obal ali morskih plitvin ga najdemo le redko. Podobno domnevno velja za celotno dru‘ino Pontosp-haeraceae (Perch-Nielsen, 1985). Rod Pontosphaera je v znatni meri prisoten v vseh obravnavanih profilih, medtem ko se vrsta Lithostromation perdurum pojavlja le v nekateri vzorcih profilov A in C. Izmed rodov, ki se pojavljajo v pregledanem materialu, sta za odprto morje zna~ilna rodova Discoaster in Thoracosphaera. Prvi se pojavlja le v kratkih intervalih, prisotnost drugega pa je bolj stalna, a omejena na zelo nizko pogostnost. V badeniju se je za~el kon~evati 6 milijonov let trajajo~i miocenski klimatski optimum (Jiminez-Moreno, 2005). Koli~ina padavin je v spodnjem badeniju upadla, njihova razporeditev ~ez leto pa postala izrazito sezonska (Böhme , 2003). Povpre~na letna temperatura je do zgornjega badenija ostala precej visoka. Na podlagi pelodnih analiz je povpre~na letna temperatura ocenjena na 16–20 °C (Jiminez-Moreno et al. 2005), na podlagi fosilov ektotermnih vre-ten~arjev, rastlin in boksita pa na 17,4–22 °C (Böhme, 2003). Prag temperaturne tolerance, ki za diskoastre zna{a 14 °C (Chapman & Chepstow-Lusty, 1997), v odbobju ba-denija torej najverjetneje ni bil dose‘en. Izo-topska analiza pektinidnih in brahiopodnih lupin iz [tajerskega bazena Paratetide nakazuje, da so v morju do pred 14,2 (+/- 0,1) mio let vladali subtropski pogoji (Bojar, 2003). Sode~ po tem je ohladitev morja nekoliko, a ne bistveno, zgodnej{a od ohladitve na kopnem v srednji Evropi, ki jo Böhme (2003) postavi med 13,5 in 14 mio let. Nanofosili iz vseh treh profilov ka‘ejo na toplo morje. V profilih B in C na to ka‘e relativna pogostnost sfenolitov (Perch -Nielsen, 1985). Vzorci iz profila A vsebujejo 222 bistveno manj sfenolitov, kljub temu je tudi za te vzorce mo‘no predpostaviti nastanek v toplem morju, saj ka‘ejo visoko vrstno pestrost, zna~ilno za tropska in subtropka okolja. Razen tega so v zgornjem delu profila v opazni meri prisotni diskoastri, ki so prav tako kot sfenoliti indikatorji tople vode (Perch -Nielsen, 1985; Bown, 1999). Odsotnosti diskoastrov torej ne moremo pripisati nizkim temperaturam. Tudi sezonska dinamika ne pojasni opa‘enih sprememb nanoplanktonske zdru‘be, saj najdemo v istih vzorcih tako vrste, ki so po Beaufort u (2001) zna~ilne za zimo in poletje. Razlikam v vrstni pestrosti in sestavi profila A od profilov B in C torej ne botrujejo razlike v temperaturi vode, ampak drugi dejavniki. Razen temperature je prisotnost hranil v vodi dejavnik, ki najodlo~ilneje vpliva na sestavo nanoplanktonskih zdru‘b. Dis-koastri so zna~ilni za oligotrofna pelagi~na okolja. Chapman in Chepstow-Lusty (1997) opazita ~asovno ujemanje med porastom {tevil~nosti populacij diatomej, ki so zna~ilne za okolja z ve~ nutrienti, in obdobji upada pogostnosti diskoastrov. Na trofi~-nost hemipelagi~nih okolij vpliva tudi koli-~ina nutrientov, ki doteka s kontinenta, ta dotok pa je odvisen od koli~ine padavin. Böhme (2003) poro~a o klimatskih spremembah v obdobju badenija v osrednji Evropi. Na podlagi {tudije raz{irjenosti vrst vre-ten~arjev sklepa na sezonsko razporeditev padavin v spodnjem badeniju, in na vse bolj suho podnebje na prehodu iz spodnjega v srednji badenij. Datacija profila A s helikos-ferami postavlja vzorce v prav ta ~as (Ste-ininger et. al., 1976). Tudi palinolo{ke analize sedimentov centralne Paratetide (J i-minez-Moreno et al., 2005) ka‘ejo na upadanje povpre~ne letne koli~ine padavin v badeniju. Upad koli~ine padavin bi lahko povzro~il nastanek oligotrofnih razmer v po-vr{inskih vodah Paratetide in pomagal ustvariti ugodne razmere za pojav diskoastrov. Nasprotno bi pove~anje koli~ine padavin zaradi ve~jega spiranja hranil s kopnega po-vzro~ilo spremembo trofi~nih razmer v prid sfenolitov in helikosfer. Nenaden pojav in izginotje diskoastrov bi lahko pojasnili z nihanjem koli~ine padavin in v povezavi z dostopnostjo hranil, temperaturo in slanostjo vode. Dotok nutrientov lahko povzro~i kompe-titivno ekskluzijo, oziroma lokalno izumrt- Milo{ Bartol & Jernej Pav{i~ je, vrst rodu Discoaster. Ponoven pojav dis-koastrov bi omogo~ila rekolonizacija v ugo-dnej{ih razmerah, za to pa je potrebna povezava z drugimi morji. V obravnavanem ~asovnem intervalu je znana povezava z Mediteranskim morjem med Alpami in Di-naridi, ki pa se postopoma zapira. Glede na izsledke {tudije badenijskih diatomej Hor-v a t (2004) sklepa, da se povezava med Pa-ratetido in Mediteranom ohrani do konca badenija. Povezava Vzhodne Paratetide z Indijskim oceanom v badeniju je vpra{ljiva (B i c c h i et al., 2003). Zaklju~ki Pregledan fosilni material ka‘e na nastanek sedimentov v toplem hemipelagi~nem okolju. Diskoastri, zna~ilni za oligotrofna pelagi~na okolja se pojavijo v dveh kratkih intervalih, od katerih so le v enem zanesljivo avtohtoni. Vzorec pojavljanja diskoastrov ni posledica temperaturnih sprememb, saj so vrste, zna~ilne za toplo morje prisotne v vseh vzorcih. Na podlagi sestave nanoplankton-skih zdru‘b sklepamo, da lahko spremembe najbolje pojasnimo s spremembami koli~ine dostopnih hranil. To potrjuje so~asen upad dele‘a Helicosphaere carteri in porast dele-‘a diskoastrov med pre{tetimi kokoliti v vzorcih. Koli~ina padavin, ki v obravnavanem ~asovnem intervalu niha in postopoma upada, lahko pojasni trofi~ne spremembe v vodnem okolju. Zahvala Avtorja se zahvaljujeva dr. A. Horvatu za pozorno branje rokopisa in koristne pripombe, M. Grmu za izdelavo risb in sestavo tabel in M. Gole‘, da je omogo~ila slikanje nano-fosilov z vrsti~nim mikroskopom na Zavodu za raziskavo materialov in konstrukcij v Ljubljani. References - Literatura Baumann, K.H., Böckel, B. & Frenz, M. 2004: Coccolith contribution to South Atlantic carbonate sedimentation. - Coccolithophores, From molecular processes o global impact. ed. 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