The role of the microencruster-microbial reef-building consortium in organic reefs evolution (Late Jurassic, northern Tethys shelf, southern Poland)

The carbonate sediments of the Polish part of Tethys shelf contain Crescentiella-microbial-cement facies. The facies is associated with Middle Oxfordian-Lower Kimmeridgian microbial-grain dominated reefs, microbial-sponge dual hybride reefs, and less frequently sponge/coral-microbial-abiotic triple hybride reefs. The Crescentiella (incertae sedis) and microbialites form numerous cluster bioconstructions with stromatactis-like cavities in which rapid lithification was supported by early marine cementation. However, the factors controlling the development of such bioconstructions and the role of Crescentiella in the development of reef frameworks remain enigmatic. The sediments from five localities were investigated using thin-sections analyses supported by cathodoluminescence observations, stable oxygen and carbon isotope analyses and dispersive X-ray spectrometry. The development of Crescentiella-microbial-cement facies took place in three intervals spanning the Transversarium, Upper Bifurcatus, and Planula zones and coinciding with the period of maximum development of the Late Jurassic reefs in Poland. The reefs contain microencruster Crescentiella which was an important rigid framework constructor among the microbialites while the skeletal metazoans were rare. The inferred palaeosetting of the facies ranges from the seaward steep-fronted outer margin to the upper slope broad reef complex/microplatform where the development of skeletal metazoans was limited and mainly formed stratiform microbialites binding coated grain-bioclastic dominated sediments. The occurrence of Crescentiella-microbial-cement boundstone facies is useful for palaeogeographic, palaeobathymetric, and palaeotectonic investigations.

The Crescentiella morronensis (former Tubiphytes morronensis ;Crescenti 1969;Senowbari-Daryan et al. 2008; 1 3 4 Page 2 of 22 Fig. 2) ranges from the Oxfordian to the Aptian with an acme in the Kimmeridgian-Tithonian (e.g., Senowbari-Daryan et al. 2008;Pleş et al. 2013). The significant contribution of Crescentiella in the reef facies was also noted from the northern Tethys shelf in southern Germany and southern Poland (e.g., Pomoni-Papaioannou et al. 1989;Schmid 1995;Leinfelder et al. 1996;Matyszkiewicz 1997;Senowbari-Daryan et al. 2008;Krajewski et al. 2016. However, these works did not include detailed research on the spreading, palaeosetting and the role of the microencruster Crescentiella in developing the reef framework. In southern Germany, Pomoni-Papaioannou et al. (1989) noted that Crescentiella formed an organic framework that developed within a shallow subtidal environment. Also, Matyszkiewicz and Felisiak (1992) and Matyszkiewicz (1997, 37 p) emphasized the significant role of Crescentiella in the development of a rigid framework in large carbonate buildups on the Polish Jura.
This study aims to present factors controlling the development of bioconstructions formed by the microencrustermicrobial-cement reef-building consortium dominated by the Crescentiella morronensis microencruster from the Polish Jura (PJ abbreviation;Figs. 1,2). The timing, regional distribution and the palaeosetting of the Crescentiella-microbial-cement boundstone facies (Cmc abbreviation) within the PJ, and its position among the Phanerozoic organic reef types are also discussed.

Geological background
The investigated area includes the SE parts of Wieluń and Kraków-Częstochowa Uplands located in central and southern Poland (Fig. 1). During the Late Jurassic, the investigated area formed the eastern part of an epicontinental ramptype carbonate platform (sensu Burchette and Wright 1992) on northern Tethys shelf (e.g., Gutowski et al. 2005;Krajewski et al. 2017;Olchowy et al. 2019;Olchowy and Krajewski 2020). In this area, the microbial-sponge-reef limestone facies were composed of different types of microbialites, calcified siliceous sponges and carbonate sand-dominated sediments stabilized by microbialites (e.g., Trammer 1989;Matyszkiewicz et al. 2006Matyszkiewicz et al. , 2012. One of the most important factors affecting sedimentation on PJ was the synsedimentary tectonics and reactivation of the transcontinental Kraków-Lubliniec Fault Zone. The fault separated Upper Silesian and the Małopolska terranes ( Fig. 1) periodically modified the sea-bottom morphology (e.g., Matyszkiewicz et al. 2012Matyszkiewicz et al. , 2016Brachaniec et al. 2016;Krajewski et al. 2016Krajewski et al. , 2017Kowal-Kasprzyk et al. 2020). As a consequence, numerous intra-platform ridges (up to tens of kilometres long) formed along the boundary of these terranes. In particular, intensive development of the reef complexes took place on tectonic ridges that constituted shelf palaeohighs (e.g., Matyszkiewicz et al. 2006Matyszkiewicz et al. , 2012).

Materials, methods, terminology
In this study, new data along with previously published data from outcrops from the PJ (Fig. 1) and field observations are analyzed (Table 1). The facies and microfacies observations were carried out on 260 thin sections and polished slabs from the studied sample exposures. The microfacies observations were carried out using an optical microscope and supported by cold-stage cathodoluminescence microscope observations with an accelerating voltage of 13-17 kV and electron-beam intensity of 400-500 mA. Such a combination of analytical methods allowed the observations of microstructure of microencrusters and enabled the identification of the various generations of the carbonate cements. Additionally, the sedimentological studies were supplemented with geochemical analyses of stable carbon and oxygen isotopes. The samples were analyzed at GeoZentrum Nordbayern in Nürnberg, Germany. The Wavelength Dispersive X-ray spectrometry (WDS) was used for quantitative analysis. The samples were investigated in terms of the content of major elements (wt.%) from the Rębielska Mt., Wielkanoc and Zabierzów quarries ( Table 2). The WDS was applied using the JXA-8230 electron microprobe.
In the case of Jurassic microbialites, classifications of Leinfelder et al. (1996) were used. The organic reef types are based on the classification of Riding (2002). In this paper, the authors apply the term stromatactis-like cavities (sensu Matyszkiewicz 1997). The systematic position and interpretation of Crescentiella morronensis (Crescenti 1969) is after Senowbari-Daryan et al. (2008;Fig. 2). The Crescentiella is interpreted as an encrustation or symbiosis between nubecularid foraminifera or as tube-like structures (see Schlagintweit and Gawlick 2009) and cyanobacteria (see Fig. 2 for the internal structure of Crescentiella).

Examples of the exposures with Crescentiella-microbial-cement boundstone facies
Crescentiella, microbialites, and early marine cements dominate locally within the sedimentary succession of the PJ, and also form the main reef constituents. In such sedimentary intervals, the skeletal metazoans are either rare or completely lacking (e.g., Matyszkiewicz and Felisiak 1992;Matyszkiewicz 1997;. Thus, in some reef limestones, the term Crescentiella-microbialcement boundstone facies (Cmc facies) or more general microencruster-microbial boundstone facies is preferred rather than the microbial-sponge or microbial facies, that were commonly used for reef limestones descriptions. Therefore, the Cmc facies is separated from the microbialsponge or microbial facies types as a distinct facies type and is the subject of this paper.   Fig. 3).
The sedimentary succession at the quarry with the Cmc boundstone facies begins with sponge-pelitic facies that grades into coral-fine-grained facies (Fig. 5). Above the coral-fine-grained facies, a 2 m thick bed of Cmc boundstone facies with numerous stromatactis-like cavities occurs (Figs. 4a,b,5a,b). The boundary between these facies is sharp (Fig. 5a). The dominant components of the Cmc facies include Crescentiella, microbialites, non-skeletal grains, and numerous bryozoans, serpulids, crabs (Dromioidea), echinoids, and brachiopods. Crescentiella is very abundant both as individual specimens and in colonial forms (Fig. 5b, d).   The Będkowska Valley is located in the southern part of the Kraków-Częstochowa Upland (Fig. 1). In this region in Poland the largest Oxfordian reef complex (Sokolica Reef Complex) is available for direct observation (Fig. 3). This reef complex is developed on the horst of an intra-platform palaeohigh that was tectonically active during the Late Jurassic . The Cmc facies from the reef complex represents the ammonite Bifurcatus Zone Fig. 4c).
The Cmc facies together with the microbial-Crescentiella-ooid facies are observed between the microbial-sponge facies and the microbial-cemented ooid-intraclast-bioclastic facies (Fig. 4c). The Cmc facies consists of Crescentiella, stromatactis-like cavities and various types of microbialites (mainly agglutinating or peloidal stromatolites and layered thrombolites) that bound coated grains and bioclasts (Fig. 4d). The Crescentiella and microbialites form clusters up to several tens of centimetres in diameter within the grain-dominated sediments (Fig. 6e). The skeletal metazoans in Cmc facies are rare and represented by calcareous sponges and calcified siliceous sponges.
The Kromołowiec Hill is situated in the central part of the Kraków-Częstochowa Upland (Fig. 1) and represents active in the Late Jurassic western part of the Smoleń-Niegowonice Range (Matyszkiewicz et al. 2006). The sedimentary succession represents medium-bedded pelitic-bioclastic limestones with sponges and Upper Oxfordian massive reef limestone facies (Upper Bifurcatus Zone; Matyja and Wierzbowski 1992). The Kromołowiec Hill represents a transitional zone extending between an elevated reef complex and a deeper basin situated further to the north (Fig. 11a). The upper part of a sedimentary succession of the reef complex contains microbial-sponge facies and occurs as the marginal part of the reef complex, while the Cmc and the microbial-Crescentiella-ooid facies, form its internal part (Figs. 6a, 11g).
The Cmc facies consists of coated grains, peloids, coprolites and bioclasts, commonly bound by various types of microbialites mainly agglutinating or peloidal stromatolites (Figs. 6a, 11d-e). The Crescentiella and microbialites form clusters up to several tens of centimetres across embedded within the grain-dominated sediments (Fig. 11d). The skeletal metazoans in the Cmc facies are rare. These are calcified siliceous sponges and calcareous sclerosponges.
The Zabierzów Quarry is situated in the southern part of the Kraków-Częstochowa Upland (Fig. 1), on the escarpment of the Tęczynek Horst that was tectonically active during the Late Jurassic Woźniak et al. 2018). The Lower Kimmeridgian bioconstructions in the nearby area represents an open-frame microbial-sponge reef and thick biostromal bedded facies of the ammonite Planula Zone (Fig. 3).
The Cmc facies is observed in the upper SW part of the Zabierzów Quarry, where Crescentiella is very abundant and together with microbialites dominate and form a rigid framework of carbonate reef with growth cavities and stromatactis-like cavities (Matyszkiewicz et al. 2012, p. 124). The microbialites are developed as agglutinating stromatolites, micropeloidal stromatolites, or pure and layered leiolites. They form massive, irregular clusters of tens of centimetres across that bind the abundant benthic fauna of the reef framework. The reef framework fauna includes Crescentiella and serpulids, brachiopods, bryozoans, bivalves, and relatively rare siliceous and calcareous sponges. The sediments from the Zabierzów Quarry grade toward the tectonic graben located north of the quarry into gravity flow deposits, tectonic breccia and thick-bedded pelitic-bioclastic and spongemicrobial limestones ).
The Wielkanoc Quarry is located in the eastern part of the Kraków-Częstochowa Upland (Fig. 1). The quarry is located in the marginal zone of the Wielkanoc tectonic horst that is situated on the marginal part of the fault zone active in the Mesozoic. The lithology of the ~ 10 m Upper Jurassic sequence is dominated by the reef and thick-bedded In the Wielkanoc quarry, the Cmc facies contains numerous stromatactis-like cavities (Fig. 4f). The dominant components include Crescentiella and microbialites (mainly laminated thrombolites and stromatolites; Fig. 5f). The rock contain also fragments of siliceous sponges, echinoderms, bivalves and serpulids. Locally, hermatypic corals (Cladophyllidae, Microsolena) and elongated and oval biomolds after cladophyllid corals are present (e.g., Fig. 4 in Olchowy 2011).

Description of the Crescentiella-microbial-cement boundstone facies
The most important macroscopic features of the Cmc boundstone facies that distinguish it from other Oxfordian-Kimmeridgian reefs/biostrome facies types from PJ, are: (i) very strong lithification, (ii) microencruster Crescentiella commonly forming cluster-like structures together with microbialites, (iii) the lack or minor occurrence of skeletal metazoans, and (iv) numerous stromatactis-like cavities. The thicknesses of individual Cmc facies vary from ~ 1 m up to several metres (Figs. 3, 4a, c, e). In vertical succession, the boundary between the Cmc facies and the coralfine-grained limestone facies is either sharp and irregular ( Fig. 5a; cf. Krajewski and Schlagintweit 2018, p. 8) or diffused and gradual in a distance of several to tens of centimetres (Fig. 4d). Observations made at exposures suggests that the lateral extent of the Cmc facies is wider than horizontal dimensions of exposures which attains hundreds of metres.
In the largest Crescentiella-microbial clusters of the MT1, three stages of development are noted: (i) initial, (ii) aggradational, and progradational with massive Crescentiella development, and (iii) final microbial-dominated (Fig. 7). The initial stage of development of clusters are characterized by the presence of single specimen of Crescentiella, enveloped by micropeloidal-micrite crusts (Fig. 7aI, bI), embedded within primary soft grain-dominated sediments (MT2). These single pioneering specimens formed the basis for the development of clusters, which in this stage, form finger-like forms up to 2.5 cm high and 1 cm wide (Figs. 6b, 7aI, bI). At the aggradational stage, numerous specimens of Crescentiella are often in life position (for Crescentiella strategy of growing see Schmid 1995;Senowbari-Daryan et al. 2008;Figs. 2, 5d, e, 6b, 7aII, bII, 8c-f). Crescentiella is elongated in different directions and can be observed in longitudinal, transverse, and oblique sections along their longer axes (Figs. 7, 8). Often, successive generations of Crescentiella are built one after another to form a microrenticulate framework (Figs. 4e, 5d, 6b, 7aII, bII). In the final stage of the cluster development, the amount of Crescentiella decreases, and the sediment is formed by agglutinating or peloidal flat or domal stromatolites (Figs. 6b, 7aIII, bIII). The few Crescentiella specimens developed on the upper surface of the cluster formed by stromatolite, are often erosive cut (Fig. 8a). The individual neighboring clusters are often joined together to form the larger Crescentiellamicrobial clusters up to several ten of centimetres in size (Figs. 5b, c, 6c).
One of the characteristic features of the Cmc facies is the stromatactis-like cavities (Fig. 4b, d, f). These isolated cavities are up to 4 cm wide and 2 cm high. The side walls  and thin shells. e Spaces between Crescentiella specimens are occupied by early diagenetic cements (back arrows) and microbial laminae (white arrows). f Clotted micropeloidal fabric, microbial laminae, and early diagenetic cements (black arrows) between Crescentiella specimens. Serpulids encrustation (S) is developed on Crescentiella. The white arrows show a direction change in Crescentiella accretion of the cavities are covered by the isopachous cement, that passes towards the central parts of the cavities into radiaxial and blocky cements.

Geochemical results
The investigated sediments are characterized by the values of δ 13 C varying from 0.15‰ to 3.17‰ and δ 18 O varying from -3.81‰ to − 2.26‰. In the δ 13 C and δ 18 O plot, three sets of points are distinguished (Fig. 10), showing the differentiation between investigated Middle Oxfordian and Lower Kimmeridgian examples. In the first set, representing the Wielkanoc Quarry, the values of δ 13 C range from 2.85‰ to 3.17‰ (average 3.02‰), and δ 18 O values range from -2.85‰ to − 2.26‰ (average − 2.56‰). The second, characterizing the sediments from the Rębielska Mt. Quarry, covers the values of δ 13 C in the range from 1.63 ‰ to 2.28 ‰ (average 2.05‰), and δ 18 O from -3.81‰ to -3.29 ‰ (average -3.62‰). The third set of results from the Zabierzów Quarry includes the values of δ 13 C from 0.15 The investigated Cmc facies do not show significant differences in the content of major elements between Wielkanoc, Rębielska Mt. and Zabierzów quarries (Table 2) and are comparable with the data from similar facies types from other PJ outcrops (e.g., Kochman and Matyszkiewicz 2012;Matyszkiewicz et al. 2012;Krajewski and Olchowy 2021). There are slight differences in the content of MgO. The MgO content is highest in the Cmc facies from the Wielkanoc Quarry (average 0.335 wt.%) and the lowest in samples from the Rębielska Mt. Quarry (average 0.189 wt.%).

Interpretation of Cmc boundstone facies
Cmc boundstone facies from the PJ is formed by a large number of decimetre-scale clusters (MT1) forming lowrelief cluster bioconstructions on the sea bottom. The Cmc facies developed in an environment with grain-dominated sediments (MT2) bound by microbial crusts. In the environment where the Cmc boundstone facies developed, skeletal metazoans did not constitute important reef-building organisms. Crescentiella-microbial clusters can be classified as microencruster-microbial-cement reef builder consortiums that caught and bound peloids, bioclasts, and other grains, which was an important process of cluster accretion (Suarez-Gonzalez et al. 2019).
Rapid lithification is supported by the early marine cementation leading to the formation of different types of carbonate cements between Crescentiella specimens. The fibrous cement developed on the microencrusters indicates the synsedimentary origin of the cement (Kendall and Tucker 1973;Koch and Schorr 1986;Flügel 2004;Richter et al. 2011;Krajewski and Schlagintweit 2018). Moreover, the succession of microbial laminae alternated with radiaxial-fibrous cement (Fig. 8e, f), also supports a synsedimentary origin of the cement (e.g., Flügel 2004, p. 306;Popa et al. 2014;Krajewski and Schlagintweit 2018).
The development of Crescentiella clusters with microbialites played an important role in stabilizing the soft grain-dominated sediments. The Crescentiella-microbial clusters probably also took an important role as a habitat for microbial mats feeding fauna e.g., echinoderms and gastropods, settling the clusters and the surrounding seafloor.
The presence of rather fine-grained sediments and allochthonous internal sediments within the cluster indicates moderate water energy. However, the water energy had to be high enough to enable early cementation.

Timing of Crescentiella-microbial-cement facies in the upper jurassic sedimentary succession of the Polish Jura
In the Oxfordian-Lower Kimmeridgian sedimentary succession from the PJ (Fig. 3), three intervals are distinguished during which Cmc boundstone facies developed. These are Interval I (Middle Oxfordian, Transversarium Zone), Interval II (Upper Oxfordian, Upper Bifurcatus Zone), and Interval III (Lower Kimmeridgian, Planula Zone) ( Fig. 3; Table 1). The above sedimentary intervals are separated by pelitic-bioclastic bedded limestone facies and marly limestone and marl facies (Fig. 3). In addition the intervals I-III are emphasized by the horizons in which gravity flow deposits (e.g., olistolites, debris-flow deposits) originated from the erosion of microbial-sponge, Cmc, and microbial-graindominated reef facies were deposited. Their genesis, like the development of the neptunian dykes, in the study area, is associated with periodic synsedimentary tectonic activity along the marginal parts of the Małopolska and Upper Silesian terranes ( Fig. 1; e.g., Matyszkiewicz et al. 2012Matyszkiewicz et al. , 2016Woźniak et al. 2018). The mentioned facies changes and intervals in the sedimentary succession can be correlated with the Late Jurassic sequences and variations in the sea level (e.g., JOx5, JOx6; Haq 2018).

Regional distribution and palaeosetting of the Crescentiella-microbial-cement boundstone facies
The wide regional distribution of Crescentiella-microbialcement boundstone facies within the PJ ( Fig. 1; Table 1) suggests that during some periods (Intervals I-III; Fig. 3) of the main reef complex development, these facies were relatively common. Data from the Mid Oxfordian-Lower Kimmeridgian PJ reefs allows for the distinction of two basic types of depositional systems. The first type represents a low-relief depositional system where sponge-microbial cluster or segment reefs or siliceous sponge-microbialite mud mounds or sponge biostromes developed (Leinfelder et al. 1996;Matyszkiewicz 1997;Schmid et al. 2001). No Cmc boundstone facies were found in these sediments. The second, depositional system type is related to the development of large reef complexes/microplatforms on sea bottom palaeohighs ( Fig. 11; Matyszkiewicz et al. 2006Matyszkiewicz et al. , 2012. During the aggradational phase of the reef complex development, the microbial-sponge frame reefs prevailed. During the progradation stage, in the conditions of shallow water (close to wave base) sedimentation on the marginal and inner flat part of the reef complexes, microbial and grain-dominated deposition with Cmc boundstone facies, dominated (Fig. 11). In such paleosettings on the PJ, the microbialites intensively developed, especially stratiform, agglutinating, peloidal stromatolites and layered thrombolites, along with the development of facies with graindominated coated grains, intraclasts, bioclasts including coprolites, calcareous green algae (Matyszkiewicz et al. 2006Kochman and Matyszkiewicz 2012;. The microbial-dominated reef facies from the PJ including the Cmc boundstone facies were studied in detail by Matyszkiewicz et al. (2012) who concentrated particularly on the microbialite structures related to the environmental setting. According to Matyszkiewicz et al. (2012), the diversification of microbialites is an effect of local sedimentary conditions. The changes in the seawater chemistry changes did not play a role in microbial diversification. Such statements are confirmed by the geochemical data from major and minor elements ; Table 2).
In the Polish Jura (PJ), it can be observed that microbialsponge facies overlap with Cmc facies and microbial-grain dominated facies ( Fig. 11; Matyszkiewicz et al. 2006Matyszkiewicz et al. , 2012Kochman and Matyszkiewicz 2012;. The microbial mats provided effective traps and bounded grain-dominated sediments that were quickly cemented. The microbial-grain-dominated facies, in which coated grains and bioclasts predominate, are typical of the internal parts of flat-topped microplatforms during their progradational phase (Fig. 11). In marginal and upper slope parts of the reef complexes, where grain-dominated sediments prevailed, and intensive synsedimentary cementation took place, the Cmc boundstone facies, occurred. On the reef complex slope grain-flow, detrital facies with numerous bioclasts and Crescentiella dominate while in more distal parts of the slope, microbial-sponge facies predominate. The more distal and deeper parts of slopes and areas between the reef complexes are filled with mud-dominated pelitic-bioclastic facies. In these areas, among bioconstruction, small sponge cluster reefs or biostromes forming bedded limestones, dominate (Fig. 11).
The δ 13 C and δ 18 O values indicate that calcite precipitation in the investigated localities took place in marine waters for which δ 13 C values vary from 0‰ to ± 4 ‰ and δ 18 O from -4 ‰ to 0‰ (Hudson 1977;Tucker and Wright 1990;Hoefs 2004). The oxygen isotope values for primary carbonates in normal marine conditions are approximately close to 0‰ PDB (Milliman 1974;Faure 1998;Moore 2001). The rock samples from the studied localities do not differ significantly geochemically in terms of major elements, indicating that carbonate sedimentation occurred under similar geochemical conditions. However, variations of δ 18 O values between the limestones from localities suggest slight changes in water composition within the sedimentary environment from normal seawater to slightly diluted seawater. The calcite precipitation in limestones from the Rębielska Mt. Quarry took place in slightly different environmental conditions compared to the limestones from the Wielkanoc and Zabierzów quarries. Calcite precipitation took place generally in marine waters with a small share of meteoric waters, as evidenced by the values of δ 18 O up to -3.81 ‰ (Matthews and Allan 1978;Allan and Matthews 1982;Hoefs 2004).
In the case of the Polish-German part of the northern Tethys shelf, so far, similar analogues regarding facies relationship with microencruster-microbial boundstones have not been described in detail. In the area of the PJ, the examples from the Sokolica Reef Complex, Wielkanoc and Czajowice quarries, and Zegarowe Rocks (Table 1) are similar to those observed in the presented model (Fig. 11). Similar Upper Jurassic example is the microbial cemented grain-dominated facies described from the reef complex as platform sands from the Franconian Jura (Germany; e.g., Koch et al. 1994 Porta et al. (2013, p. 249), the microbial microencruster boundstone probably expanded to the outer platform facies belt when environmental conditions excluded most of the metazoans (e.g., corals) and microbial precipitation was favoured. The composition of the biota is similar to the Upper Jurassic deposits from the PJ. Therefore, it can be assumed that in both cases, microencruster-microbial boundstone palaeosetting can be classified as steep-fronted, moderate energy, outer margin to upper slope settings, that were tectonically active in Late Jurassic, as structural palaeohighs. The examples discussed in this paper, similarly to the Lower Jurassic example, indicate that the occurrence of microencruster-microbial-cement bioconstructions may be useful for palaeogeographic, palaeobathimetric, and palaeotectonic investigations (see also Hoffmann et al. 2021;Kołodziej and Ivanova 2021).

Position of the Crescentiella-microbial-cement boundstone facies among organic reef types
In the Phanerozoic, various types of bioconstruction are formed by corals, sponges, stromatoporoids, microbialites, microencrusters, and synsedimentary cements that were classified by Riding and Virgone (2020) as the so-called hybrid carbonates forming various types of organic reefs (e.g., Wood 1999; Kiessling 2002;Leinfelder et al. 2002;Flügel 2004;Riding and Virgone 2020). Hybrid carbonates are understood as in situ associations of two (dual hybrid) or three (triple hybrid) of abiotic (or quasi-abiotic), bioinduced (mainly microbialites) and biocontrolled (skeletal e.g., corals or sponges) carbonates. Examples from the northern Tethys shelf were most often formed by dual hybrids of microbial-sponge open frame reefs or microbial agglutinated reefs (pure microbial reefs (> 10% metazoans) or microbial dominated metazoan reefs (sensu Leinfelder et al. 1996). In the Late Jurassic sediments of the northern Tethys shelf, the triple hybrids are rare. The Crescentiella included in the microencruster-microbial-cement consortium is an important reef-builder in the dual hybride microbialgrain dominated reefs, and the microbial-sponge reefs and occur less frequently in the triple hybride carbonate skeleton-microbial-abiotic components on the Late Jurassic northern Tethys shelf. In the case of the PJ, some fragments of the presented Sokolica Reef Complex and Wielkanoc Quarry examples (Table 1) can be included in the microencruster-sponge-cement triple hybrids. A similar Upper Jurassic example of triple hybride carbonates has been reported from the Oxfordian and Tithonian Crimea reef (Krajewski and Olszewska 2006;Krajewski and Schlagintweit 2018). In the case of the PJ, abiotic carbonates are often associated with microbial carbonates which indicates that conditions that were favourable for abiotic carbonate precipitation also favoured microbialites development. The Cmc boundstone facies most closely resembles agglutinated microbial reefs or the sponge and coral microbial-dominated open frame reefs. Some studies (e.g., Schlaginweit and Gawlick 2008; Krajewski and Schlagintweit 2018) emphasize that the Late Jurassic bioconstructions formed by microencruster-microbial-cement microframework with numerous Crescentiella resembles the Permian reefs (e.g., Flügel 1994;Wood 1999;Weidlich 2002;Kershaw et al. 2007;Peryt et al. 2016) and the Triasic Tubiphytes and cement crust-dominated reefs (e.g., Senowbari-Daryan et al. 1993;Flügel 2002;Marangon et al. 2011;Popa et al. 2014). As in the examples studied, radiaxial-fibrous cements reported in boundstones from the Middle-Upper Triassic carbonate platforms represent mainly the margin and upper slope settings with synsedimentary marine cementation (e.g., Keim and Schlager 2001;Seeling et al. 2005).

Conclusions
The Upper Jurassic succession from the Polish Jura displays a distinct variability of reef facies with the locally dominant Crescentiella-microbial-cement boundstone facies. These facies are dominated by Crescentiella-microbial-cement consortium forming decimetre-scale bioconstructions with stromatactis-like cavities.
The intensive development of Crescentiella-microbialcement boundstone facies took place during three sedimentary intervals, encompassing the ammonite Transversarium Zone of the Middle Oxfordian, Upper Bifurcatus Zone of the Upper Oxfordian, and the Planula Zone of the Lower Kimmeridgian.
The sedimentary environment of Crescentiella-microbialcement boundstone facies is characterized by a relatively small amount of metazoans, together with the intensive development of microbialites and the intensive deposition of non-skeletal grains that were stabilized by microbial mats. The trapping and bounding of such grains were an important process of bioconstruction accretion.
The Crescentiella-microbial-cement boundstone with stromatactis-like cavities is best explained by their development in the marginal and upper parts of the slope of broad reef complexes/microplatforms developed on structural palaeohighs. The palaeosetting of such facies can be associated with the transition zone between deeper microbial-sponge and generally shallow water microbial-bioclastic-coated grain dominated and/or coral-fine-grained facies representing the internal part of the reef complexes/microplatforms.
Microencruster-microbial-cement boundstones can be classified as microbial-sponge or microbial-grain dominated dual hybrids, less often microencruster / microbial-skeletal metazoan-cement triple hybrids. Described microencrustermicrobial-cement boundstone resembles and coexists with agglutinated microbial reefs formed by microbial trapping and binding of grains and microbial-sponge skeleton-supported open frame reefs with significant contribution from microencrusters and early cements.