Nubecularia‐coralline algal‐serpulid‐microbial bioherms of the Paratethys Sea—Distribution and paleoecological significance (upper Serravallian, upper Sarmatian, Middle Miocene)

Nubecularia bioherms represent unique bioconstructions that are restricted to the upper Serravallian of the Paratethys and have been reported since the 19th century. They occur in the Central Paratethys in the late Sarmatian and the Eastern Paratethys in the Bessarabian both regional stages of the respective Paratethyan areas. In this study, several locations in the Vienna and Styrian basins of the Central Paratethys were studied out of which four localities were documented in detail (Wolfsthal, Maustrenk, St. Margarethen—Zollhaus, Vienna—Ruzickagasse) to reconstruct their sedimentary setting, their internal composition, and their indications of environmental parameters. The detailed studies included logging of outcrop sections, petrographic, facies and biotic analyses of polished slabs and thin sections and also cathodoluminescence analyses. These concluded that these bioconstructions are not only composed of the foraminifer Nubecularia but represent a complex mixture and interrelationships of Nubecularia, serpulids and microbial carbonate. Four boundstone types can be differentiated: Nubecularia boundstone, Nubecularia‐coralline algal boundstone, stromatolitic/thrombolitic boundstone and serpulid‐nubeculariid‐microbial boundstone. The first 3 types are characteristic of specific localities; the fourth type occurs in all studied locations and represents the terminal association on top of the three other types. The three basal boundstones are predominantly of columnar growth form irrespective of dominance of Nubecularia, coralline algae or microbial carbonate, and the terminal boundstone is widely irregularly organized. The general depositional environment is characterized by cross‐bedded oolitic grainstones with abundant quartz grains, miliolid foraminifers and mollusks. Intercalated are microbial carbonates mostly stromatolites but also thrombolites. This indicates a general high water energy environment interrupted by more calm periods when the microbial carbonate was built. The 3 basal types of bioconstructions are interpreted to reflect decreasing food supply and/or oxygenation from Nubecularia over Nubecularia‐coralline algal to stromatolitic/thrombolitic boundstone. The serpulid‐nubeculariid‐microbial boundstone reflects an internal succession with a decrease of the same parameters. Water depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline. The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic!


| INTRODUC TI ON
The Sarmatian (late Serravallian, Middle Miocene) of the Paratethys is a very peculiar interval because at the Badenian/Sarmatian boundary, a major drop in marine biodiversity occurred called the Badenian-Sarmatian Extinction Event (BSEE) by Harzhauser & Piller (2007).
Not only biodiversity decreased dramatically but also, due to a thirdorder sea level drop at the boundary, several organism groups were not able to re-immigrate into the Paratethys, most importantly corals, echinoderms and sharks.During the Badenian (Langhian-early Serravallian) coral buildups were abundant and widespread in the Paratethys, in the Sarmatian instead microorganisms colonized this ecological niche.The early Sarmatian was, in general, fully marine (Kranner et al., 2021b;Harzhauser & Piller, 2007) and buildups were constructed by bryostromatolites indicating eutrophication but also polyhaline salinities (Piller & Harzhauser, 2023) (Table 1).Around 12 Ma, the environmental conditions in the Paratethys changed again, related to a fourth-order sea-level low stand, and oligotrophic, normal marine to hypersaline conditions prevailed (Kranner et al., 2021b;Latal et al., 2004).Very widespread oolite shoals were established (Piller & Harzhauser, 2005), and the bryostromatolites were replaced by buildups characterized by the sessile, porcelaneous foraminiferal genus Nubecularia (Table 1).These buildups are very widespread extending from the Vienna Basin (Central Paratethys) to the eastern shore of the Caspian Sea (Eastern Paratethys), known since the 19th century and repeatedly reported.In the literature, the focus on these structures was clearly on the foraminifer Nubecularia.After several reports in the literature (see below) and their own studies, Piller & Harzhauser (2005) stated that these structures are not only built by foraminifera but represent "nubeculariid-coralline algal-microbial bioconstructions" (p.453).Nevertheless, detailed studies on these structures are still missing.To document the internal composition of these unique buildups, their possible spatial and temporal internal organization on a small scale, and to interpret the environmental conditions under which they formed, we studied several such structures in the Central Paratethys.Herein, we deal only with the best outcrops in depth is considered very shallow ranging from 0 to a few meters, and salinity was normal marine to hypersaline.The reconstructed paleoenvironment with dominating oolite shoals and seagrass meadows was not restricted to the Central Paratethys but  the Vienna Basin (Figure 1).From this detailed study in the Central Paratethys, we extend our paleoenvironment implications also to the Eastern Paratethys covering a huge area (reaching from the Gulf of Lyon in the west to Lake Aral in the east during its greatest extent).

| Historical background and geographic distribution
Eichwald (1855, p. 322-323) first described the taxon under discussion from a Bessarabian limestone (Table 1) in Kishinev (now Chişinău, capital of the Republic of Moldova) (Figure 2), Eastern Paratethys, however, classified it as serpulid Spirorbis nodulus.In the Central Paratethys, Fuchs (1868, p. 281) first mentioned the taxon from Wolfsthal, Lower Austria (Figure 1), not assigning it to any known taxon.Karrer & Sinzow (1876) assigned the fossils from sands in Chișinău to the porcelaneous foraminiferal genus Nubecularia and described three morphotypes (solitaria, nodula, deformis) of the species N. novorossica.Andrusov (1899, p. 114, 115) clearly showed the wide distribution of nubeculariid limestones in the lower Bessarabian (Table 1) from the Ukraine to the east coast of the Caspian Sea (Figure 2) and reported the oolitic nature of these limestones (Andrusov, 1899, p. 100).
For the Central Paratethys, Steinmann (1903)-receiving material from Fuchs from the locality Wolfsthal (see above)-assigned the biota also to the foraminifer Nubecularia and described a new species, N. caespitosa.Andrusov (1923) described in detail Nubecularia bioconstructions from Mangyshlak (western Kazakhstan) and Crimea peninsulas (Figure 2) reporting and documenting the morphotypes described by Karrer & Sinzow (1876) and Steinmann (1903).He also mentioned possible coralline algae.
Overall, several studies were carried out in the Eastern Paratethys more recently, but we cite here only a selection.Rostovtseva (2009) reported "algal-nubecularian limestones" from the Kerch Peninsula without specifying the algae.Koleva-Rekalova & Darakchieva (2017) described for the first time Nubecularia novorossica from NE Bulgaria (Figure 2), which occur in beds of 5-30 cm thickness in rock forming quantities and comprises two morphotypes (solitaria and nodula).They co-occur with mollusks, bryozoan fragments, algae and ooids (Koleva-Rekalova & Darakchieva, 2017, p. 91) but do not form a framework.Koleva-Rekalova (2019) studied bedded limestones from the same horizon and described dome shaped bodies up to 2.5 m in height and 1-3 m in width, which were termed "nubeculariid bioherms" containing "microbial peloids (consist of cyanobacteria) as well as encrusting red algae and bryozoans" (Koleva-Rekalova, 2019, p. 120).The Nubecularia beds can be traced for more than 20 km along the Black Sea coast between Cape Kaliakra and Cape Shabla.In a more detailed study, Koleva-Rekalova & Darakchieva (2020) reported new localities and summarized knowledge on the Bulgarian occurrences and stated that Nubecularia taxa occur in rock forming quantities and also documented that the 3 morphotypes co-occur together with caespitosa in one single thin section (Koleva-Rekalova & Darakchieva, 2020, Figure 7).In the figure caption, however, these authors assigned them to the genus Sinzowella.Generally, they do not form a framework and the authors classified these stratified Nubecularia beds as biostromes (Koleva-Rekalova & Darakchieva, 2020, p. 30).
The Sarmatian Paratethyan foraminiferal taxon was originally classified with the genus Nubecularia by Karrer and Sinzow (1876) but classified into the genus Sinzowella without explanation by Cushman (1933).Subsequently, both generic names have been used in parallel in the literature also without any further arguments.In the course of our studies, we evaluated the status of the genus and the actual valid genus name is Nubecularia (Piller and Harzhauser, under review).On the species level, it turned out that only one species is represented in the Central Paratethys, which has to be assigned as Nubecularia nodulus (Eichwald, 1855) (Piller & Harzhauser, under review).

| S TUDY LO C ATI ON S
Studied outcrops are located in the Vienna Basin (Austria), including the Eisenstadt-Sopron Basin (Figure 1), and the Styrian Basin (Austria).
2.4 | Vienna-Ruzickagasse, Liesing, 23rd district of Vienna (Vienna, 48°08′53″ N, 16°16′56″ E, ÖK50-UTM 5325 Baden) At this locality, limestones, also named "Atzgersdorfer (Kalk)Stein" in the literature (e.g., Cžižek, 1849), could be observed, which have been widely used as building stones in the city of Vienna (e.g., Rohatsch, 2005).The former quarries were completely exploited and used as waste dump and were finally filled.This limestone belongs to the Wolfsthal Member of the Skalica Formation.The studied material originates from a batter along the Ruzickagasse near the crossing with the Endresstraße and exposed only a few decimeters of rocks.

| ME THODS
The studied sediment successions were logged in detail (cm scale) in the field, documented and several samples were taken out of each bed attempting to cover all microfacies types.Samples of limestone and cemented sandstone beds were thin-sectioned.Beds with buildups were sawed into c.4-5 cm thick slabs, and 6 were polished to inspect internal details macroscopically or in low microscopic magnification.The sediment samples and some of the slabremains were thin-sectioned to study the internal composition.

| Wolfsthal
In two adjacent quarries 2 sections (WA, WB) have been measured and studied also to identify lateral variability.Overall, the outcrops expose about 20 m of predominantly well cemented bedded limestone of meter scale beds.In some parts of the sections, less cemented sandy beds occur (Figure 4a).In the thicker beds, which show cross bedding, putative microbial layers/lenses occur, e.g., in section WB approx.5c).
The oolite beds consist of ooid grainstone, rarely also packstone, with variable contents of quartz grains, crystalline rock fragments, foraminifers (miliolids, elphidiids, peneroplid Spirolina) and mollusks.Ooid nuclei are mostly quartz grains but also miliolids occur (Figure 6a).Ooid beds show frequently cross bedding representing probably wave ripples.In the troughs of the ripples, microbialitic lenses can be observed (Figure 4b).The microbialites are mostly composed of micrite in some parts showing a stromatolitic lamination (Figure 6b).
The caliche horizon (Figure 4c) is a good correlation level between both sections.At the base of the caliche horizon, oolitic structures are still preserved but ooids are nearly completely dissolved and only an outer micritic rim is preserved.
The lower bioherm horizon (WB 1-3) is made up of a framestone of columnar growth forms with oolitic sediment between the columns.
Also, an inverted cone-shaped bioherm is present, which is, however, toppled over.The height of this bioherm reaches about 80 cm, the diameter at the top about 80 cm (Figure 5a,b).The displacement of the bioherm can be clearly seen in the growth direction of the columns but also by geopetally infilled sediments between the columns (Figure 5b).Both features point at a turn of more than 90°.The columns reach several centimeters in height and 2 mm in diameter and may branch or laterally coalesce (Figure 7).The columns can be interrupted by disconformities with a microrelief (Figure 7).

| Maustrenk
The upper Sarmatian sediments start above a disconformity with oolitic grainstones, which are also deposited between the lower Sarmatian bryoherms as described by Piller & Harzhauser (2023, under review, Figures 3 and 4).The oolites between the bryoherms and in the bed

| St. Margarethen-Zollhaus
The Sarmatian part of the succession starts with about 7 m polymictic, cross bedded gravel with rare intercalations of marly sandstone with scattered bioherms between 5 and 5.5 m above the base (Figure 4).biostrome unique serpulid-microbialitic bioherms were discovered (Harzhauser, Guzhov, et al., 2023).The study of these structures and the surrounding sediment also provide information important for the here described Nubecularia biostromal structures (Harzhauser, Guzhov, et al., 2023).Within this study cathodoluminescence analy-

| Vienna-Ruzickagasse
Since the outcrop situation is very poor, no section can be described because only isolated samples could be collected.The sediments below, above, and also in between the bioherms are mostly terrigenous sandstones dominated by subangular to subrounded quartz grains, but also lithic particles occur.They are rich in foraminifers, mostly miliolids and elphidiids but also Spirolina and mollusks.The components are frequently coated but only rare multi layered ooids occur.However, oolites are well reported from an earlier better outcrop situation (e.g., Rohatsch, 2005).(Figure 13a-f).Within serpulid-Nubecularia-microbial boundstone also crustose bryozoan colonies occur (Figure 13b) and the microbial carbonate shows stromatolitic lamination (Figure 13e,f).The succession is terminated by an erosional surface and the boundstone is overlain by sandstone (described above) (Figure 13a).

| Paleoenvironment
Based on foraminiferal associations, mean salinity during the late Sarmatian was 37 psu, ranging from 33 to 41, and the mean bottom water temperature was 21°C ranging from 17 to 22°C (Kranner et al., 2021a(Kranner et al., , 2021b)).Overall, the late Sarmatian is characterized by well oxygenated conditions and seagrass meadows, reflected by dominance of epifaunal herbivore foraminifers.Also, the reports by Silye & Filipescu (2016)

| Sedimentary setting
The reported bioherms are mostly found in an oolitic environment.
The ooids can occur as multi-layered radial allochems of grainstones/packstones with predominantly quartz grains or foraminifers as nuclei (Piller & Harzhauser, 2005, Figure 9e,f).Other rocks are terrigenous sand-/grain-/packstones with a dominance of quartz and rock fragments with oolitic coatings but also conglomerates occur with well-rounded polymictic components.All these sediment types reflect high water energy conditions in very shallow water.In addition, all sediments are cross bedded either reflecting dunes or wave ripples (oolites) or foresets (conglomerates).A special feature is that these sediments are partly cemented with a micrite cement, which surrounds particles or form a meniscus cement type at particle contacts but also form bridges between wider spaced components (Figure 10b).The occurrence and appearance of this cement indicates a microbial origin, which first stabilized the sediments (Hillgärtner et al., 2001).Later, the remaining interparticle space was Pannonian Basin System (Cornée et al., 2009) but also for the Eastern Paratethys (e.g., Andrusov, 1899).High water energy and biological processes inducing the formation of massive oolites and point at high water temperature, high salinity and high alkalinity as reported from modern oolite forming areas such the Great Bahama Bank (e.g., Harris et al., 2019) and the Persian Gulf (e.g., Picha, 1978).The microbial structures occurring as thin layers within the oolites and as microbial cement (Figures 4b and 6b) seem to resemble modern microbial mats as described from the Bahamas by Dupraz et al. (2011) and from Shark Bay (Grey & Awramik, 2020).There, three different mat types are differentiated, which, however, cannot be identified

| Bioconstructions
Bioconstructions are composed of various main elements arranged in complex internal successions and can be classified into four major types.These can be intergrown with each other or may occur in temporal successions: No modern examples are described where foraminifera are able to form widespread bioconstructions such as described from the Paratethys.This does not allow to apply a simple actualistic approach.
Concerning CCA most taxa were obviously not able to re-enter the Paratethys after its sealing off from other seas during the BSEE.This could explain the very low diversity.Due to this reduced diversity, it is difficult to reconstruct environmental parameters based on the 3 taxa because they may have adapted to a broader spectrum of environmental conditions due to missing competition.Most wellknown CCA taxa occur in fully marine environments with a partly broad range of tolerance, but most are euhaline some considered euryhaline (e.g., Qui-Minet et al., 2021).An example for tolerance of broad environmental conditions is known from Shark Bay (Western Australia).There, 10 species of CCA occur, out of which four species were found in salinity levels >50‰, four in metasaline waters (39‰-50‰) and two under normal marine (37‰-38‰) conditions (Barry & Woelkerling, 1995).Lithophyllum pustulatum (=genus Titanoderma herein) occurs in the metasaline category.In addition, Shark Bay is known for one of the best examples of modern big stromatolites co-occurring with oolites (e.g., Grey & Awramik, 2020;Playford et al., 2013;Suosaari et al., 2016) and may act as good analogue to the Sarmatian Paratethys conditions.We consider these similarities a support for interpreting normal marine to hypersaline conditions.to each other (Andres & Reid, 2006, p. 324 f.).Preservation of stromatolites is highly related to sand burial or movement, lack of burial leads to degradation and ultimate demise.
Although not a comparable setting, occurrences of metazoanmicrobial biostalactites in modern submarine caves in, e.g., the Mediterranean Sea show some accordance to the Sarmatian serpulid-Nubecularia-microbial boundstones.In these caves, serpulids and bryozoans are the dominant metazoan groups but besides others also foraminifers are abundant.Serpulids (mostly Protula) are considered to represent pioneer elements forming aggregates as nuclei of the biostalactites, which are composed in the outer part of microbial carbonate.As possible reason for the community changes a reduction in food supply is considered (e.g., Guido et al., 2022;Sanfilippo et al., 2015).The dominant foraminifer is Cornuspiramia adherens, which exhibits a sessile growth form belonging to the family Nubeculariidae.Although the growth form is different because Cornuspiramia forms a network of very thin, tubular chambers some similarities to Nubecularia do exist.
The cyanobacterial genus Rivularia is an interesting biotic element in the herein studied bioconstructions.Kershaw & Guo (2006) reported Rivularia mounds from Pleistocene sediments in Greece, which are associated with only one corallinacean taxon, L. pustulatum (= T. pustulatum herein).The authors discuss two possible environmental settings, marine versus non-marine.In our material we also observed Rivularia, however, of much smaller size but also associated with T. pustulatum.The abundant foraminiferal fauna and the oolites clearly proof a marine environment for these upper Sarmatian sediments.The genus Rivularia is mostly represented in freshwater environments but occur also in marginal marine settings, in particular, in the uppermost limit of the eulittoral (Khoja et al., 1984).The modern species R. atra lives under great fluctuation of temperature, salinity and pH and is able to use organic phosphate (from masses of decaying seaweeds) and shows a marked reduction in the rate of nitrogen fixation during the dark period of the day (Khoja et al., 1984, p. 71 f.).
We interpret this with a decrease in food supply (particulate organic material) and oxygenation possibly also with shallowing (Figure 15).
The upper parts of the three bioconstruction types are made up by serpulid-Nubecularia-microbial boundstone.This represents the terminal cap of the bioconstructions.This succession, serpulids-Nubecularia-microbial carbonate, represents a smaller scale cycle compared to the total bioconstructions and may reflect a decrease of food supply and oxygenation within an internal sequence (Figure 15).The very shallow water setting, both for the sediments and the bioconstructions, is also indicated by repeated emersion horizons, stalactitic cements and caliche horizons.
The described buildups and their intimate occurrence with massive oolite shoals and seagrass meadows is, as already mentioned in earlier chapters, not restricted to the Central Paratethys but also occurs in the Eastern Paratethys (Figure 2).The Central Paratethys is relatively small compared to the Eastern Paratethys, but all the mentioned sedimentary and biotic characters occur from the Vienna Basin in the west to the area east of the Caspian Sea spanning a W-E distance of about 2700 km and c. 1000 km in N-S direction.These environments do not cover the entire Paratethys sea floor but occur at least in very broad coastal areas (Popov et al., 2004;Schneider et al., 2013).Since the overall water depth in the Paratethys was low in the late Sarmatian/Bessarabian the aerial coverage by this paleoenvironment was huge (Popov et al., 2004;Schneider et al., 2013).Compared to modern counterparts only the Great Bahama Bank reaches also a big aerial in this setting, which may be related with fluctuations in oxygenation, food resources and salinity.This only period of leveling in the Paratethys is also expressed in homogenous mollusk faunas (Harzhauser et al., 2023a).

| CON CLUS IONS
The four studied sites in the Vienna Basin, which contain "Nubecularia reefs", show that the sedimentary environment is similar in all localities consisting of cross bedded oolites, foraminiferal grainstones or/ and conglomerates, which are frequently stabilized and cemented by microbial carbonate in various growth forms.These sediments were deposited in very shallow water under high to moderate energy and marine or hypersaline conditions.The presence of seagrass meadows is indicated by specific Nubecularia nodulus growth forms.
The Nubecularia bioconstructions show a complex composition that varies from site to site:

ACK N OWLED G M ENTS
Thanks go to Thomas Hofmann (Geosphere Austria) for literature support.We thank Christine Perrin and two anonymous reviewers for constructive and helpful comments and suggestions.

CO N FLI C T O F I NTER E S T S TATEM ENT
No conflict of interest exists.
extended over the entire Paratethys and represented the largest oolite facies area of the entire Cenozoic!K E Y W O R D S boundstone, coralline algae, Nubecularia, serpulids, stromatolites, thrombolites TA B L E 1 Middle-Upper Miocene stratigraphy with stratigraphic position of the Nubecularia bioherms.
reported Nubecularia limestones from the Zsámbék Basin west of Budapest (Hungary), and Cornée et al. (2009) described boundstones with serpulids, nubeculariids, bryozoan, red algae and microbialites from this location (Figure 2).Bucur et al. (1992) described several facies with nubeculariids and coralline algae and dasyclads from Romania and Bucur et al. (1993) described calcareous algae (Central Paratethys), including Titanoderma ucrainicum (Maslov, 1956) and Lithoporella cf.minus Johnson, 1964 and (b) location of study sites (red circles) in the Vienna Basin and Eisenstadt-Sopron Subbasin (ESS).Boundaries of the Vienna Basin and the ESS are indicated.

upper
Sarmatian follows directly above the bryoherms with an erosional surface and oolites and a nubeculariid bioherm of up to 50 cm F I G U R E 3 Lithology and sample locations of the 3 studied sections.in height.The upper Sarmatian sediments belong to the Wolfsthal Member, which is overlain by badly outcropping Pannonian (Late Miocene) clay (Piller & Harzhauser, 2023, Figure 3).The studied section "Zollhaus" exposed upper Sarmatian and Pannonian sediments.It was exploited as a gravel pit in the communal forest close to the Austrian/Hungarian border (c. 5 km S-SSE of the village St. Margarethen) and represented the largest Sarmatian/ Pannonian outcrop within the Neogene Eisenstadt-Sopron Basin.
7.5 m above the base.At around 12.5 m, a 30-40 cm thick caliche horizon occurs in both sections.Approximately 8.5 m above the base, a horizon with bioconstructions occurs in section WB (1-3) (Figure 5a,b).In the upper part of the section cross bedded, oolitic beds very rich in mollusks (e.g., Polititapes tricuspis, Obsoletiforma vindobonensis, Plicatiforma latesulca, Pithocerithium rubiginosum) continue.Section WB extends higher up compared to WA but at c. 15 m an outcrop gap of 50-60 cm occurs.At around 16 m above, the base of the second horizon with bioconstructions can be observed (Figures 3 and The columns are composed of Nubecularia tests regularly interbedded with coralline algae and microbial carbonate (Figure8a-d).Volumetrically the coralline algae dominate over Nubecularia (Figure8c,d).Three taxa of coralline algae are represented and show crustose growth form.One taxon can be assigned to the genus Lithothamnion sp.(Figure8a-c), which corresponds to Lithothamnion sp. 10 ofHrabovský (2015, p.   47 f.).It is the most abundant constituent in the columns.The second can be classified with Titanoderma pustulatum (Lamouroux) Nägeli, 1858(Figure 8c,d), which is also reported byHrabovský (2015, p.    75 f.) from Wolfsthal.The third taxon shows a thin incrusting thallus with distinct monoporate conceptacles projecting above the thallus surface.FollowingHrabovský (2019, p. 431), we assign this morphotype to Lithoporella minus Johnson, 1964 (Figure8a).The upper bioherm horizon only present in WB (5) starts with columnar growth forms at the base, which grade into irregular structures that are made up of Nubecularia and coralline algae but are incrusted by putative microbial carbonate (Figure8c,d).The microbial carbonate is of light grey color without well-defined internal structures except small peloids and clotted structures (mesoclots).The surface of the microbial carbonate is sharp and overgrown by various cement generations.Higher up, microbial carbonates increase in volume, Nubecularia occurs predominantly as irregular tests (deformis morphotype) and a variable number of serpulid worm tubes.Within the microbial carbonate isolated straight or bent undivided filaments (diameter: 20-37 μm) occur.Besides the unspecific microbial carbonate also filamentous algal/cyanobacterial pillow-like structures occur, which are badly preserved (Figure8e,f) but acted as substrate for Nubecularia colonies.
above are cross-bedded and consist predominantly of multi-layered, radial oolites with quartz-nuclei (Piller & Harzhauser, 2023, Figures 4 F I G U R E 4 Field photographs from Wolfsthal.(a) Overview of the lower part of section WA with predominantly thick (meter size) limestone beds with thinner interlayers (caliche horizon, microbialite).(b) Oolite dunes with microbialite (stromatolite) horizons terminating the dunes (red arrows-strom).(c) Caliche horizon.(d) Oolite limestones alternating with molluskan coquinas.(e) Details of molluskan coquina.and 5b).The grainstone is well cemented by several generations, the first is a micritic meniscus cement.The oolites reach a thickness of 1 m.The section above the oolites is rather poorly outcropping but is made up of fine siliciclastics with abundant cardiid bivalves in life position (Plicatiforma latisulca) intermingled with or grading into a few centimeters of caliche crusts.This sediment is overlain by a quartzand lithoclast-rich oolitic sandstone to molluskan packstone-rudstone with very abundant spirorbid tubes.Nubeculariid bioherms up to 50 cm in height occur approx.4.5 m above the base of the section intercalated with oolites & overlain by a caliche horizon (Piller & Harzhauser, 2023, Figures 1 and 3).At the base of the highly terrigenous oolitic grainstone/packstone polymictic gravel components (up to 5 cm) occur made up either of clasts of the surrounding oolitic sediment but also of crystalline rocks.Above follows a discontinuous thin layer (up to 1 mm) of fine-grained angular sandstone.This layer and/or oolitic grainstone (where the sandstone is laterally missing) is topped by an erosional disconformity surface (Figure 9a,b,e,f) on which Nubecularia in horizontal or/and columnar growth forms occur (Figure 9e,f).In places also crustose bryozoan colonies are present.The bulk of the bioherm is made up of columnar Nubecularia, which show growth interruptions in which also crustose bryozoan colonies may occur (Figure 9a,b).Columnar Nubecularia also started to grow on molluskan shells and gravel.The Nubecularia framework is encrusted by microbial carbonate.No coralline algae were detected.
These gravels are topped by a 3-m-thick peloidal limestone.Its lower part is characterized by marly silt with abundant freshwater-and terrestrial gastropods, fish remains, Potamides fraterculus and scattered pebbles.Towards the top, the marly silt passes into dark-brown clay and silt with a nearly monospecific mass occurrence of Tiaracerithium pictum.This layer is overlain by up to 3 m yellowish marly sand with F I G U R E 5 "Nubecularia bioherms" in the Wolfsthal sections.(a) Nubeculariacoralline algal bioherm in the lower part of section WB.(b) Details of the bioherm in (a) with indicated outline (red dashed line) and growth direction (red arrow) of the columnar structures.(c) Bioherms in the upper part of section WB with indicated outlines (red dashed lines).F I G U R E 6 (a) Oolite of multilayered ooids with abundant miliolid foraminifers and badly rounded terrigenous components (lower part) overlain by a microbialite.Wolfsthal, thin section WB-4-01-1.(b) Details of the microbialite, showing distinct wavy laminations (stromatolite).Wolfsthal, thin section WB-4-01.frequent pebbles.Potamides disjunctus predominates in the basal part, but towards the top a diverse mollusk fauna appears, consisting of Dorsanum duplicatum, Sarmatigibbula podolica, Polititapes tricuspis, Solen subfragilis, Modiolus incrassatus and Musculus sarmaticus.About 3-m-thick cross bedded gravel follows passing into sand and marly silt towards the top.This top layer is rich in mollusks and bears large numbers of Sarmatigibbula podolica and a characteristic bed with in situ Polititapes tricuspis.Towards the top of the unit, 10 cm greyishbrown silty sand with terrestrial and freshwater gastropods appears, and finally a layer with masses of Tiaracerithium pictum forms the top.This is overlain by a 5-m-thick succession of cross bedded gravel, sand and marly silt with scattered potamidids and serpulids.The Sarmatian sequence of the section ends with 2 m marly sand and a 30-cm-thick top bed of calcareous marls bearing a diverse molluskan fauna characterized by the in situ occurrence of Plicatiforma latisulca.The overlying gravels indicate the Pannonian Zone B (Harzhauser & Kowalke, 2002).The Nubecularia boundstone was represented as several 4-5 cm thick sheets within well rounded, moderately sorted gravel with columnar vertical structures in between.The entire bioconstruction reaches about 70 cm in thickness and could be traced along a 12-m-long transect.In the surroundings of the Nubecularia F I G U R E 7 Overview of a predominantly columnar growth form of a Nubecularia-coralline algal boundstone interrupted by a wavy crustose boundstone.In the crustose part coralline algae dominate.The external part of the boundstone is made of widely structureless microbial carbonate (light grey) (mb and red arrow).Between the columns ooids (oo), miliolid foraminifers (mi) and terrigenous components occur.Wolfsthal, thin section WB-3-01.F I G U R E 8 Details of Nubeculariacoralline algal boundstones from Wolfsthal.(a) Cross section of a column of loosely arranged coralline algal thalli (Lithothamnion sp., Lithoporella minus) and Nubecularia tests.Between the layered boundstone pelletoidal sediments (pe) with foraminifers occur.Wolfsthal, thin section WB-3-01.(b) Lithothamnion sp. with hypothallus and conceptacles.Wolfsthal, thin section WB-3-01.(c) Columnar growth form dominated by Lithothamnion sp.(Li) and Titanoderma pustulatum (Ti).Nubecularia is rare in the lower part but dominates on top.Wolfsthal, thin section WB-3-01.(d) Intergrowth of Nubecularia nodulus and T. pustulatum.Wolfsthal, thin section WB-2-01.(e) Cyanobacterial colony with short protrusions overlain by serpulid-Nubecularia-microbial boundstone.Wolfsthal, thin section WB-5-01.(f) Details of (e) with badly preserved filaments (red arrows).
ses and SEM investigations on various facies and biota have been carried out, which clearly have shown that the limestones are strongly diagenetically altered (mostly by meteoric diagenesis) into coarse neomorphic calcite mosaics making further investigations such as fluorescence and geochemical analyses unreliable.Unfortunately, the outcrop and the studied and documented/analyzed structures were destroyed during our investigations by excavation work in the active gravel pit preventing further documentation in the outcrop, but samples and thin sections allow a detailed study.The conglomerate at the base is polymictic, well rounded and the matrix is either a terrigenous sandstone with angular components or a packstone.The components are cemented by putative microbial micrite surrounding them, forming meniscus-like structures or/and bridges between them (Figure10a,b).This conglomerate is topped by an erosional surface cutting individual components (Figure10a).The surface is overgrown by a thin, dark microbial crust or/and bryozoan colonies or/and by columnar Nubecularia (caespitosa growth form) (Figure10a,c), which is surrounded by light grey, widely structureless microsparite (originally microbial carbonate) in which frequently serpulid tubes are embedded.The sediment between the columns is either an oolitic grainstone or a peloidal grainstone/packstone with mesoclots (Figure10c,e,f).Further up the columnar growth form of the nubeculariids disappears and is substituted predominantly by microbial carbonate with embedded serpulid tubes and non-columnar Nubecularia, which frequently grow on serpulid tubes (Figure10d).The Nubecularia growth forms are highly variable ranging from irregularly coiled tests to tests with a flat lower surface or a (semi)circular F I G U R E 9 Nubecularia boundstone from locality Maustrenk.(a) Polished slab with oolite grainstone at the base overgrown by columnar Nubecularia colonies interrupted by encrusting bryozoan layers (rectangle represents figure (c)).(b) Details of columnar Nubecularia with a bryozoan interlayer (red arrow).Polished slab.(c) Details of (a) indicated by the rectangle.Nu-Nubecularia, oo-ooids.Polished slab.(d) Details of a columnar Nubecularia growth form.Polished slab.(e) Oolite grainstone (oo) at the base partly overlain by medium terrigenous sandstone/packstone (p) and settled by a columnar Nubecularia boundstone (N), which is interrupted by a bryozoan layer (b).Thin section MT-14-03.(f) Basal oolite grain-to packstone (oo) with multilayered ooids and terrigenous components overlain by a terrigenous packstone (p).The top of both the oolite and the packstone show erosional surfaces (e) indicating that both the oolite and the packstone were already cemented before Nubecularia growth.The test wall of Nubecularia contains abundant agglutinated particles (N).Thin section MT-14-03.shape.Crustose bryozoan colonies also rarely occur in this microbial carbonate and also one columnar colony was observed.Interbedded with the serpulid/Nubecularia/microbial boundstone are rare coralline algae only represented by Lithoporella minus.The columnar framestone is occasionally interrupted by weakly laminated microbial carbonate (stromatolite).Overall, the microbial carbonate is volumetrically dominant.In addition to the light grey microbial carbonate also a dense microbial micrite can be observed, which may form incrustations with protrusions (thrombolite) into boundstone cavities before sparitic cement is precipitated.The boundstone is overlain by conglomerate and the frame is a weakly laminated microbialite.
point at hypersaline conditions for the foraminiferal fauna and the late Sarmatian Streptochilus event points at stressed conditions(Filipescu & Silye, 2008).Kranner et al. (2021aKranner et al. ( , 2021b) differentiated two principal environmental settings, one with a low diversity foraminiferal fauna (dominated by Porosononion granosum) and a second miliolid-dominated fauna with elphidiids and Ammonia.The miliolid and elphidiid dominated fauna of the herein studied sediments can accordingly be interpreted to represent hypersaline coastal-lagoonal depositional areas.These results are also supported by stable isotope data byLatal et al. (2004) andHarzhauser et al. (2007).

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I G U R E 11 Nubecularia-microbial boundstones from Vienna-Ruzickagasse. (a) Columnar microbialite (stromatolite/thrombolite) overlain by Nubecularia-microbial boundstone and terrigenous sandstone lenses.Thin section RZ-1.(b) Alternating microbialite (m) with coralline algal layers (Lithoporella minus, c) and some Nubecularia tests (N).Thin section RZ-1.(c) Microbialite with layered and bifurcated (red arrow, fb) cyanobacterial filaments (?Rivularia) preserved (red arrows) and few Lithoporella layers (L) in the lower part.Thin section RZ-1.(d) Wavy growth of microbialites (stromatolite/thrombolite) with cyanobacterial filaments and intergrown coralline algae (Lithoporella) (c) grading into columnar growth forms with coralline algal layers (c) and few Nubecularia (N).The columnar microbialite is overlain by a Nubeculariamicrobial boundstone (Nmb).Thin section RZ-2.(e) Well-layered cyanobacteria?Rivularia at the base with thin intergrown coralline algal thalli (c) overlain by a serpulid-Nubecularia-microbial boundstone (sNmb).Thin section RZ-2.(f) Details of (e) with?Rivularia filaments, rarely bifurcated (fb), and growth layers.Thin section RZ-2.In the sediments below, within and above, the bioconstructions isolated Nubecularia tests are abundant.These tests show a flat basal side, which clearly reflects that they were attached to a vanished substrate and similarly occur semicircular to circular test shapes, which surrounded an also disappeared substrate.For both growth forms, seaweed substrates are highly probable indicating that in areas nearby the bioconstructions seagrass or macroalgal meadows have existed.Within the bioconstructions ooids are present indicating that closeby an oolite factory existed indicating high water energy (see below).This coincides well with the toppled large bioherm at the locality Wolfsthal and with large fragments of Nubecularia-dominated columns that are rounded and reworked.
filled by several sparitic cement generations.The micritic meniscus type cement may indicate subaerial exposure and meteoric cementation although a subtidal origin has been clearly demonstrated byHillgärtner et al. (2001) for modern examples.The shallow setting is clearly indicated by erosion horizons cutting components and cement indicating that the sediment was already fully cemented prior to erosion (Figure10a).Other clear indications of subaerial erosion are the occurrence of caliche horizons but also the formation of microkarst with dripstone cements (Figure13c,d).The oolitic setting is not only characteristic for the Central Paratethys occurrences such as the Vienna Basin(Fuchs, 1868), Styrian Basin(Brandl, 1931) andF I G U RE 1 2 Nubecularia-coralline algal boundstones from Vienna-Ruzickagasse. (a) Columnar growth form of Nubeculariacoralline algal boundstone.Thin section RZ-3l.(b) Details of Nubecularia-coralline algal boundstone.Coralline algae are represented by Titanoderma pustulatum and Lithoporella minus (for details see Figures 12d-f).Thin section RZ-3l.(c) Wavy-planar Nubecularia-coralline algal boundstone.Coralline algae are dominated by Lithoporella minus with microbial carbonate in between.Thin section RZ-1.(d) Lithoporella minus with monoporate conceptacle embedded in clotted microbial carbonate (mesoclots).Thin section RZ-1.(e) Columnar Nubecularia-coralline algal boundstone.Coralline algae represented by T. pustulatum.Thin section RZ-3l.(f) Detail of T. pustulatum boundstone with monoporate conceptacles (c).Thin section RZ-3l.
in the studied material.Similar micrite cement is also reported from Hamelin Pool, Shark Bay byJahnert and Collins (2012) andSuosaari   et al. (2016, Figure 7d).

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Serpulid-Nubecularia-microbial boundstones from Vienna-Ruzickagasse. (a) A basal Nubecularia-coralline algal boundstone (Nc) is overlain by serpulid-Nubecularia-microbial boundstone (s-serpulids, N-Nubecularia, mb-microbial carbonate) with large primary cavities.The final microbial carbonate (thrombolite) forms biostalactitic protrusions into the cavities (bs).The boundstone is overlain by an oolitic terrigenous sandstone/packstone.Thin section RZ-1.(b) Peloidal carbonate (mesoclots) at the base is overgrown by a laminar bryozoan layer (b) succeeded by serpulid-Nubecularia-microbial boundstone (s-serpulids, N-Nubecularia).The microbial carbonate shows indistinct stromatolitic laminations (st).The sediment in the boundstone cavities is terrigenous packstone with abundant miliolid foraminifers.Thin section RZ-8.(c) Serpulid-Nubecularia-microbial boundstone with large cavities partially filled by peloidal carbonate (mesoclots) and terrigenous packstone/sandstone.This boundstone is eroded (e) and overlain by bryozoans (b) and serpulids (s) and again followed by serpulid-Nubecularia-microbial boundstone.The cavities in the boundstone show a microstalactitic first cement generation (red arrows).Thin section RZ-7.(d) Details of (c) (red rectangle) of the serpulid-Nubecularia-microbial boundstone with serpulids dominating over Nubecularia.Red arrow indicates microstalactitic cement (red arrow).Thin section RZ-7.(e, f) Details of serpulid-Nubecularia-microbial boundstone with stromatolitic structures (laminations) in the microbial carbonate.Thin section RZ-7.Nubecularia boundstone, Nubecularia-coralline algal boundstone, Nubecularia boundstone: Above an erosional disconformity Nubecularia tests grow predominantly in lateral direction and cover the substrate.Then, they start to produce vertical columns of up to several cm in height and few mm in diameter.These columns can branch or laterally coalesce and may also be interrupted by horizontal layers of Nubecularia followed again by vertical columns.At the base but also in phases of growth interruptions, thin bryozoan crusts can occur.The columns are overgrown by structureless, micro-peloidal (microclots) or/and clotted mesostructured (mesoclots) microbial carbonate.This type is best developed at the locality Maustrenk (Figures7 and 9).•Nubecularia-coralline algal boundstone: This type is constructed by Nubecularia and crustose coralline algae in variable quantities (Figures8a-d and 12a-f).The main part of the frame is built by Lithothamnion thalli, which may alternate with Nubecularia tests or form multiple thallus layers (Figure12c-f).Besides these thicker thalli also thin crusts formed by Titanoderma and Lithoporella are frequently present mostly in the upper part of the respective bioconstruction.They may occur as isolated sheets or occur stacked (Figures8a-d and 12c-f).Within the frame they are volumetrically less important than Lithothamnion but their thalli occur frequently (Figure8c,d).This frame is incrusted by structureless or laminated, micro-peloidal (microclots) or/and clotted mesostructured (mesoclots) microbial carbonate (Figure8a).Incorporated within and also in between the columns ooids occur.This type is best developed at the locality Wolfsthal.•Stromatolitic/thrombolitic boundstone: Well-laminated planar to laterally linked hemispheroids with thin coralline algae intercalated (mostly Lithoporella) grade into columnar structures dominated by coralline algae (Lithoporella, Titanoderma) and stromatolitic/thrombolitic carbonate (Figure11a-e).Rare isolated Nubecularia tests occur within the columns (Figure11d).At the base and in the lower part of the columns colonies of the cyanobacteria?Rivularia occur (Figure11e,f).This type is best developed at the locality Vienna-Ruzickagasse.• Serpulid-Nubecularia-microbial boundstone: Irregular framework constructed by serpulid worm tubes of various taxonomic groups that act as substrate for Nubecularia nodulus and being thickly surrounded by structureless to laminated or micro-peloidal (microclots) microbial carbonate (Figures10d-f and 13a-f).In some places also dark microbial micrite occurs forming small protrusions.This type occurs in all locations studied and marks the top of the three bioconstructions mentioned above (Figure13a).The bioconstructions started growing at a discontinuity surface also representing a hardground or at least partially cemented sediment.In some places Nubecularia are the first settlers, rarely and only spatially restricted thin crustose bryozoans form the base and in other places microbial stromatolites/thrombolites.Growth of the bioconstructions may reflect a range of energy conditions ranging from calm to high.For the latter the toppled bioherm at Wolfsthal and in some locations reworked and rounded branched fragments of Nubecularia boundstone indicate high water energy conditions.Termination of the bioconstructions varies locally and temporarily.In some cases (St.Margarethen) the bioconstructions became eroded or/and covered by conglomerates in other locations the bioconstruction became eroded due to subaerial exposure (Figure 13a,b).
Columnar growth represents surface area enlargement.Since the columnar constructions are made of different organism groups the question arises what the reason for this augmentation is.Sessile foraminifers such as Nubecularia and serpulids are suspension feeders, coralline algae and cyanobacteria are photosynthesizing organisms.This indicates that they need adequate light conditions, which may be provided by columnar growth form.This direct relationship has, however, been questioned for columnar stromatolites byPetryshyn & Corsetti (2011).In the case of foraminifers, the surface enlargement may allow several individuals growing above each other in a single column forming colonies receiving enough suspended food particles.Another explanation could be that columnar growth form may prohibit sediment cover.In respect to this interpretation a comparative example exists in the Bahamas, in particular, at Highborne Cay(Andres & Reid, 2006).There, stromatolites occur in a back reef lagoon in less than 1 m water depth at low tide.Two growth forms are represented-ridges and columns-which nucleate primarily on hard substrate.Stromatolite columns reach up to 40 cm in height and 50 cm in diameter.Their dimensions are highly variable from study site to study site.The controlling factors for stromatolites' growth shape are considered to be accommodation space, hydrodynamics and burial by sand and these parameters are linked from southern Italy.Although both publications use somewhat different terminologies for the microbialitic structures a strong overlap exists with the upper Sarmatian examples.A major difference is the occurrence of corals in the Messinian TCC, which are completely missing in the upper Sarmatian of the Paratethys (see also report on the BSEE above).Many of the facies types reported by Vescogni et al. (2022) are indicative for shallow-water with moderate to high energy conditions and normal marine salinity, but laminated peloidal stromatolites (LPS), which are also present in the herein studied material, may point at fluctuations in salinity and/or oxygenation.Bourillot et al. (2020) differentiate stromatolitic and thrombolitic mesostructures and a variety of macrofabric types.Most of these structures are interpretated to have formed in shallow subtidal to supratidal settings in protected lagoons/salt lakes.These structures both from the Messinian (Late Miocene) of Spain and Italy point at similar environmental conditions as interpreted for the upper Sarmatian (Middle Miocene) bioconstructions.The general setting of the studied upper Sarmatian sediments is a shallow (0-5 m) marine, euhaline to hypersaline paleoenvironment with ooid shoals and dense seagrass beds what has also been clearly shown byKranner et al. (2021a).In parts of this shallow marine setting, bioconstructions occur, which are commonly known as "Nubecularia reefs", but their composition is, in fact, highly variable and their size does not necessarily meet the term reef (Figure14).Overall, three different boundstones are represented in the studied material forming the lower part of the bioconstructions: (1) Nubecularia boundstone; (2) Nubecularia-coralline algal boundstone; F I G U R E 1 4 Schematic paleoenvironmental reconstruction of Nubecularia bioherms (NR) setting within or next to oolite shoals and neighboring seagrass meadows.In the oolite dunes occur stromatolites (St) stabilizing the ooid sand (background picture © Shannon Moran).
coverage of oolite shoals, but this is c. 5 times smaller than the Paratethyan occurrences.These occurrences indicate that the environmental conditions in the Paratethys were relatively uniform for the entire sea, representing a shallow marine, high water energy, well oxygenated setting with normal to hypersaline conditions and high alkalinity of the sea water.Such a uniform facies distribution and environmental condition over such a huge area is not reported from any shallow marine area and did also not occur in the Paratethys prior to the Sarmatian/Bessarabian reflecting the general shallowing of the Paratethys Sea and isolation from other oceanic realms.The complex biotic buildups in this general uniform setting reflect local and short time changes

1.
Nubecularia boundstones are dominated by the sessile foraminiferal tests showing predominantly columnar growth form (caespitosa) and are best developed at the locality Maustrenk.2. Nubecularia-coralline algal boundstones are characterized by interlayering of both biota groups in columnar growth form and are best developed at Wolfsthal.3. Stromatolite/thrombolite boundstone is internally highly variable composed of microbial structures ranging from micritic crusts to various shapes of stromatolites but also frequent filamentous microbial micrite or peloidal mesoclots.Columnar growth form is dominating, and filamentous cyanobacteria are abundant.Best examples occur in the locality Vienna-Ruzickagasse.These boundstone types show vertical changes that can be, at least in part, related to shallowing water depth and even subaerial exposure.The three boundstone types are overlain by (4) serpulid-Nubecularia-microbial boundstone with irregular growth forms but a clear sequence from serpulids to Nubecularia and microbial carbonate.This succession reflects a further decrease in food supply and oxygenation.The Nubecularia bioconstructions formed in agitated coastal settings, where they were associated with ooid shoals.The buildups have no fully matching modern analogue, but based on the co-occurring crustose coralline algae and microbialites great similarities exist to the microbial buildups in the Bahamas, Shark Bay and the Persian Gulf.Based on these similarities we suppose normal F I G U R E 1 5 Schematic representation of boundstone types and environmental parameters.The 3 boundstone types in the lower part of the graphics reflect a decrease in nutrients and oxygenation from left to right.The serpulid-Nubecularia-microbial boundstone in the upper part also shows a decrease in nutrients and oxygenation but this sequence reflects a decrease within the boundstone type.to hypersaline salinities in the late Sarmatian Paratethys Sea.This is in stark contrast to the bryoherms of the early Sarmatian, which dwelled under polyhaline conditions.On a broader perspective these mentioned environmental conditions were distributed all over the (Central and Eastern) Paratethys indicating a vast area of oolite shoals and relatively uniform conditions all over the Paratethys area.The oolite shoals may have been the most widespread occurrences known, at least, during the Cenozoic (including the modern Great Bahama Bank).