depositional environment of the owadów-brzezinki conservation … · 2016-11-14 · microfacies...

Depositional environment of the Owadów-Brzezinki conservation Lagerstätte (uppermost Jurassic, central Poland): evidence from microfacies analysis, microfossils and geochemical proxies

Hubert Wierzbowski, Zofia Dubicka, Tomasz Rychliński, Ewa Durska, Ewa Olempska, and Błażej Błażejowski

With 15 figures and 2 tables

Abstract: The Owadów-Brzezinki quarry is one of the most important paleontological sites in Po-land, known for its exceptionally well-preserved Upper Jurassic (Middle Volgian = uppermost Lower Tithonian) fossils. Carbonate deposits of the section record a transition from an offshore to coastal and lagoonal settings and have been studied based on microfacies, micropalaeontological, isotope and chemical proxies. The obtained data point to normal marine conditions during the deposition of the older part of the quarry section in an offshore setting and a gradual transition into lagoonal environment characterized by high-amplitude variations in seawater salinity and oxygenation level of bottom waters, both of which resulted in considerable changes in benthic fauna assemblages or in the total lack of the fauna at some intervals. Above-mentioned conditions during the deposition of the middle part of the quarry section have probably allowed the preservation of diversified fauna with soft tissues. The microfacies and chemical data indicate that dysoxic/anoxic episodes may have occurred not only during the deposition of known fauna-rich beds but also during the deposition of poorly studied, so far, younger part of the section. The uppermost part of the carbonates exposed in the Owadów-Brzezinki quarry originated during the re-appearance of normal marine chemistry mostly in the intertidal-subtidal settings. The depositional conditions of the Owadów-Brzezinki site are non-typical, among famous conservation Lagerstätten, owing to the rapid fluctuations in the oxygenation and salinity of bottom waters.

Key words: Lower Tithonian, fossil Lagerstätte, central Poland, microfossils, oxygen and carbon isotopes, elemental concentrations, depositional environment.

1. Introduction

Middle Volgian deposits of central Poland have been studied for lithology, stratigraphy and palaeontology by Lewiński (1923), witkowski (1969), Dembowska (1973, 1979), kutek (1994), kutek & Zeiss (1997), ZieLińska (2003), saLamon et al. (2006), kin et al. (2013), błażejowski et al. (2014), matyja et al. (2016), and matyja & wierZbowski (2016). These deposits are exposed nowadays in a sole place in the Tomaszów

Syncline, in the Owadów-Brzezinki quarry, located about 19 km southeast of Tomaszów Mazowiecki (Fig. 1). The section comprises the uppermost part (ca. 1.6 m) of the clay-marly-mudstone Pałuki Formation and a lower limestone part (ca. 26.2 m) of the limestone-evaporite Kcynia Formation (cf. Dembowska 1979).

The Owadów-Brzezinki site is of high palaeonto-logical importance because of recent findings of excep-tionally well-preserved fossils of fragile marine and ter-restrial creatures. The findings include rich horseshoe

©2016 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de

DOI: 10.1127/njgpa/2016/0606 0077-7749/2016/0606 $ 7.00

N. Jb. Geol. Paläont. Abh. 282/1 (2016), 81–108 ArticleStuttgart, October 2016E

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82 Hubert Wierzbowski et al.

crab fauna, crustaceans, terrestrial insects and parts of skeletons of sea and terrestrial vertebrates (kin & błażejowski 2012; kin et al. 2012, 2013; błażejowski et al. 2014; błażejowski 2015; FeLDmann et al. 2015). The state of preservation of this fossil assemblage is unusual and may be compared to those from the fa-mous Jurassic conservation Lagerstätten i.e. Solnhofen and Nusplingen in southern Germany, both of which document, in fact, a bit older ecological communities of the earliest Tithonian, and the latest Kimmeridgian age, respectively. The Polish locality also shows a more northern palaeogeographical position and fauna affin-ity to the eastern and western parts of the Subboreal Province.

The aim of the present study is to provide detailed information on the palaeonvironment during the for-mation of the Owadów-Brzezinki carbonates as based

on newly studied microfaunistic, microfacies and geo-chemical (oxygen and carbon isotope and elemental concentration) proxies. The palaeoenvironmental data are used for the inference of the habitat of the well-pre-served ancient marine faunas, history of the sedimenta-ry basin, and the parameters of early diagenesis, which have allowed the fossilization of fragile skeletons of marine and terrestrial organisms. The presented inter-pretation is compared with published information about the studied section (cf. kin et al. 2013; błażejowski et al. 2014). The palaeoenvironment and depositional history of the Owadów-Brzezinki carbonates are also discussed in comparison with palaeoenvironments of other famous Jurassic palaeontological sites, which may be helpful in deciphering factors controlling the pres-ervation of fossils in ancient proximal marine basins.

Fig. 1. Location map of the Owadów-Brzezinki quarry (lat. 51.374238, long. 20.136343) in Poland.

Fig. 2. Lithology, stratigraphy, and the distribution of macro-, microfossils, and pseudomorphs after evaporates in the Ow-adów-Brzezinki section. The stratigraphy is given after matyja & wierZbowski (2016) and matyja et al. (2016). Microfossil data of ZieLińska (2013) are marked with a letter Z.

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Depositional environment of Owadów-Brzezinki conservation Lagerstätte 83

Fig. 2.

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2. Geological setting

The uppermost part of the Pałuki Formation (so called “Brzostówka marls”), which is exposed the Owadów-Brzezinki quarry (ca. 1.6 m thick), consists of black, blue-greyish and yellow-bluish marls with the interca-lation of thin oyster layers and marly limestone beds (Fig. 2; cf. błażejowski et al. 2014). The marls yield abundant ammonites and bivalves.

The overlying lower part of the Kcynia Formation (so called “Sławno limestones”) has been subdivided in 4 distinct lithological units visible in the quarry sec-tion (Fig. 2; cf. ZieLińska 2003; saLamon et al. 2006; błażejowski et al. 2014). Unit I (ca. 9.1 m thick) con-sists of massive, chalky limestone characterized by a general absence of sedimentary structures except for parallel lamination of single beds. Deep-burrowing bi-valves (Pleuromya sp.) accompanied by oysters (Del-toideum delta) and unidentified trigoniid bivalves, rhynchonellid and terebratulid brachiopods, small gas-tropods and ammonites are common, especially in the lower part of this unit (Fig. 2). The unit yields a rich crinoid assemblage (saLamon et al. 2006) and echi-noderms (ZieLińska 2003). Moreover, quite common and well-preserved marine reptile bones (ichthyosaurs, turtles and crocodylomorphs) also occur in this unit (tyborowski et al. 2016). Unit II (ca. 2.2 m thick) is rep-resented by thin-bedded micritic limestones, which are underlain and overlain by very thin (2-4 cm in thick-ness) marly beds. Ammonites, bivalves, brachiopods, lobsters, shrimps, polychaete tubes and rare echino-derms are found in these deposits (cf. ZieLińska 2003; saLamon et al. 2006; kin et al. 2013; raDwańska 2003; FeLDmann et al. 2015). Overlying well-bedded micritic limestones (also called Corbulomima limestones; cf. Kin et al. 2012) belong to the unit III (ca. 12.8 m thick). Its lowest part (bed D14, 1 m thick) consists of thick-bedded, hard, yellow limestones. Younger D13 and D12 beds (0.5 m thick) are paler and highly fossiliferous. They contain mass-accumulations of small, unidenti-fied bivalves (either protobranchs or corbuloids; Fig. 2), and yield exceptionally well-preserved horseshoe crabs, decapod crustaceans, remnants of fishes as well as marine and flying reptiles, terrestrial insects (drag-onflies, beetles, grasshoppers), and rare ammonites (Fig. 3; kin & błażejowski 2012; kin et al. 2012, 2013; błażejowski et al. 2014, 2015; błażejowski 2015).

The middle-upper part of the unit III mainly con-sists of thin-bedded micritic limestones with thinner marly limestone intercalations and does not yield well-preserved fragile fossils. A few thicker limestone beds

(D10, C2, C1b, A18, A2) are also encountered in this part of the section. U-shaped burrows with polygonal patches at upper surfaces of the beds are sometimes ob-served in the limestones from this interval (cf. kin et al. 2013). Worth noting is the occurrence of a hard ground in the upper part of this unit III (between beds C1a and A18) and the common low-angle, fine cross-lamination of the younger limestone beds. kin et al. (2013) re-port the occurrence of an intraformational breccia in the middle part of the unit III, which was interpreted as a tsunami or storm surge deposits. The breccia has not been visible any more in the moving quarry sec-tion since year 2012, therefore, may have represented a small lens in the bedded sediments. Mass-accumula-tions of small, unidentified bivalves (protobranchs or corbuloids) occur in the younger deposits of the unit III, but they are less frequent than in the fossiliferous beds (Fig. 2); the same applies to the ammonite fauna. Only a few small oyster shells were derived from the unit III and these rocks are devoid of echinoderms and brachiopods (cf. ZieLińska 2003; saLamon et al. 2006; kin et al. 2013). The preliminary study of kin et al. (2013) shows a rather monotonous ostracod assemblage in the unit III deposits.

The uppermost part of the Owadów–Brzezinki is represented by the unit IV (ca. 2.2 m thick), which is developed as organodetritical limestones rich in small oyster-like bivalves (Nanogyra sp.), bryozoans and ser-pulids (Fig. 2). The fossils form small bioherms. The rocks of this unit belong to the lower part of the so called “serpulite” beds described in the Polish geologi-cal literature (cf. Lewiński 1923; bieLecka & sZtejn 1966). A deeply burrowed omission surface occurs in the lower part of this unit. The rocks of the unit IV from the quarry are highly weathered and karstified, especially at the contact with Quaternary sand cover. It is worth noting that two karst sinkholes filled with sands and clays, which cut limestones of IV and III units, are observed in the Northern and Western sec-tions of the Owadów-Brzezinki quarry.

The sedimentary succession of the units I and II is interpreted as a record of the shallowing of the depo-sitional environment, from an offshore to a nearshore, perhaps lagoonal or coastal one (ZieLińska 2003; kin et al. 2013). Fossiliferous D12 and D13 beds are thought to be formed in shallow, stagnant water during small bivalves (protobranchs or corbuloids) blooms. Fossils of these beds are interpreted to have been rapidly buried (kin et al. 2013). The unit IV (the “serpulite”) may rep-resent short-term opening of the basin although it prob-ably passed into anhydrite-gypsum regressive series of

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the Wieniec Evaporite Member, which is known from a central part of the mid-Polish basin (cf. bieLecka & sZtejn 1966; Dembowska 1973, 1979). The younger Ju-

rassic deposits have been removed from the Tomaszów Syncline by the Early Cretaceous erosion, and are not present in the study area (witkowski 1969).

Fig. 3. A – Panoramic view of the highest level of exploitation in the Owadów-Brzezinki quarry comprising the unit III of the Kcynia Formation (most fossiliferous horizon with microbivalves is arrowed). B – Limestone slab (bed D12) with mass-accumulation of microbivalves with well-preserved limuline horseshoe crab. C – Abundant representatives of microbivalves.

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According to the stratigraphical study of kutek (1994) based on ammonite fauna from the nearby Br-zostówka section, the upper part of the Pałuki Forma-tion and the lower part of the Kcynia Formation belong to the Regularis and Zarajskensis horizons, respective-ly, of the Zarajskites Subzone of the Scythicus Zone of the Middle Volgian. New data indicate, however, that the upper part of the Owadów-Brzezinki section (units III and IV of the Kcynia Formation) belongs to the Gerassimovi Subzone of the younger Virgatus Zone of the Middle Volgian (Fig. 2; Matyja et al. 2016; Matyja & wierZbowski 2016). The entire stratigraphic interval of the Owadów-Brzezinki section should be correlated with the uppermost Lower Tithonian (cf. rogov 2013).

3. MethodsThe Owadów-Brzezinki section has been studied in detail, in the years 2012-2015. Thin-sections made from studied rocks have been investigated using a polarizing light microscope for microfacies and microfauna. Twenty-four rock samples from the Owadów-Brzezinki section (shown on Fig. 4), derived from all lithological units, were collected for micropalaeontological study. The rock samples were mechanically disintegrated using liquid nitrogene method (remin et al. 2012), cleaned in an ultrasonic bath and subsequently sieved to get the 63-600 μm fraction. Foraminiferal tests were manually picked from the obtained residues and analysed for the taxonomy and abundance of particular taxa using light and scanning electron microscopes. Quantitative microfauna analyses were performed on the first 150- 200 specimens. The relative abundance of particular species is presented in Fig. 4. Five samples (8, 10, 12, 19, 21) have been macerated according to the standard palynological procedure: they were washed, crushed, treated with 10% HCl to dissolve carbonates and with 15% HF to dissolve silicates, sieved through a 15 µm sieve, then ZnCl2 heavy liquid was used to separate remaining mineral particles. The obtained residuum was examined under light microscope using glycerine jelly medium. More than 100 specimens of ostracod shells have been recovered from ten rock samples collected.

Bulk carbonates from the whole Owadów-Brzezinki section were sampled for oxygen and carbon isotopes. The bulk carbonate samples were drilled from fresh micritic and marly rocks fragments.

Thin sections made from oyster shells (Deltoideum del-ta) collected from the lower part and the middle part of the section (Pałuki Formation, unit I and unit III limestones of the Kcynia Formation) were analysed using a cold-cathode cathodoluminescence microscope. The shells were cleaned of adherent sediment using a micro-drill. Fragments of the non-luminescent or dully luminescent oyster shells were powdered and homogenized to get average isotope values (the sample size was usually ca. 200 mg). Aliquots of the carbonate powders were used for element and isotope analy-ses. Element (Ca, Mg, Mn, Fe, Na, Sr) contents of the oyster

shells were determined by the ICP-OES (Inductively Cou-pled Plasma Optical Emission Spectrometry) method using Thermo iCAP 6500 Duo system in the Polish Geological Institute–National Research Institute after dissolving the carbonate powders in 5% (v/v) hydrochloric acid. Limits of quantification of trace elements using the ICP-OES method were 20 ppm for Fe, and 1 ppm for Sr. The laboratory refer-ence material (Ca 38.5%, Mg 2066 ppm, Mn 21 ppm, Na 1530 ppm, Sr 1088 ppm, Fe 238 ppm) was used for the qual-ity control analysis. The reproducibility (2 SD) was: 2.4% for Ca, 2.6% for Mg, 5.2% for Mn, 3.0 % for Na, 3.7% for Sr, and 3.8% for Fe. The accuracy for all elements was better than 3%.

Bulk carbonate samples were crushed and pulverized to 75 μm grain fraction. Chemical analyses of bulk carbonate samples were conducted in the AcmeLabs, Bureau Veritas Commodities Canada, according to 4 Acid digestion ul-tratrace ICP-MS method (MA250 procedure; for details see – http://acmelab.com). Quality control of the method was conducted by replicate analyses of laboratory references and three studied samples (SHW15, SHW17, SHW72).

Powdered oyster and bulk-carbonate samples were re-acted with 100% H3PO4 at 70 °C in an online, automated carbonate reaction device (Kiel IV) connected to a Finnigan Mat Delta Plus mass spectrometer at the Institute of Geo-logical Sciences, Polish Academy of Sciences in Warsaw. Isotopic values are reported in per mille relative to the VPDB scale and referenced to the values of NBS19 standard (δ13C = 1.95‰, δ18O = -2.20‰). Reproducibility and accuracy of the measurements were monitored, over the course of analyses, by replicate analysis of NBS19 standard (n = 235). The re-producibility for δ13C and δ18O values was 0.03‰ and 0.09‰ (±1σ), respectively.

Estimated δ18O values of basin water, assuming modelled sea surface temperatures for the Late Jurassic, were calcu-lated from the δ18O values of oyster shells using the Eq. (1) of o’neiL et al. (1969) modified by FrieDman & o’neiL (1977) and SMOW to PDB scales conversion given of FrieDman & o’neiL (1977).

103 lnαcalcite–water = 2.78*106/T2 - 2.89 (1)

where αcalcite–water is equilibrium fractionation factor between calcite and water, T is the temperature in Kelvin.

4. Results

4.1. Microfacies analysis

Small to moderate microfacies diversity is observed in all lithological units of the Owadów-Brzezinki section (Figs. 5, 6). Two microfacies – mudstones with rare bioclasts and bioclastic wackestones are observed in the marls of the Pałuki Formation. Bioclasts of the marls are represented mostly by oysters and benthic foraminifera, which are usually well preserved, with recognizable internal structure of the shells.

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Fig. 4. Abundance fluctuations of benthic foraminifera species in the Owadów-Brzezinki section.

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The overlying chalky limestone of the unit I of the Kcynia Formation is dominated by mudstones with bioclasts while bioclastic wackestones are subor-dinate. Microfacies of this unit are characterized by significant bioclast diversity. The most common bio-clasts are bivalves shells, strongly crushed in some in-tervals, serpulid worm tubes, echinoderms, ostracods, foraminifera, brachiopods and bone fragments (Figs. 2, 5A). Moreover, rare quartz grains were found in one sample. The microfacies locally reveal poorly visible planar lamination.

Limestones from the unit II of the Kcynia Forma-tion show small diversity of microfacies, which are rep-resented by mudstones and peloidal wackestones with

rare bioclasts (mostly crushed ostracods and bivalves; Figs. 2, 5B).

Microfacies of limestones of the unit III of the Kc-ynia Formation, which include the fossiliferous beds D12 and D13, are bipartite. In their lower and middle parts dominate mudstones built of fine micrite, being rarely recrystallized to microsparite, locally laminated or burrowed, as well as mudstones with bioclasts. The bioclasts consist mostly of ostracods (Fig. 2).

Starting from the bed C1, in the unit III occur mudstones with rare peloids. They are partly replaced upward by peloidal bioclastic wackestones/packstones with preserved fine lamination. The lamination is em-phasized by the peloid accumulation, and also locally

Fig. 5. Microfacies of limestones of the Kcynia Formation. A – Bioclastic wackestone from the unit I. Note well-preserved punctate brachiopod shell and benthic foraminifera test with recognizable multilayered wall structure. B – Peloidal mudstones from the unit II. Note crushed ostracod shells and foraminifera. C – Laminated wackestone from the upper part of the unit III with disarticulated and crushed ostracods carapaces arranged parallel to the lamination. D – Peloidal grainstones from the upper part of the unit III with faecal pellets (arrows) infilling the bioturbation structures. Scale bars are 1 mm.

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by crushed ostracods shells (Fig. 5C). Bioclasts are represented mostly by ostracodes preserved similarly to those from the lower part of the unit III. Microfa-cies of some beds of the upper part of the unit III also comprise peloidal packstone/grainstones with biotur-bation structures. The burrows are filled with peloidal grainstones with preserved faecal pellets (Fig. 5D). The uppermost bed A2 consists of mudstones with bioclast-rich lamina.

Ostracods are present in most beds of the unit III except for beds D1, C5, the majority of the bed C2, and beds A10, A7, A6, A4, A3,. They are preserved as disarticulated valves or whole carapaces. When the whole ostracod carapaces are preserved, their interiors

are filled with micrite or blocky calcite spar. Foramin-ifera are subordinate in the unit III, and echinoderms totally absent (Fig. 2). Besides the proximity of the fossiliferous beds, individual foraminifera tests are observed in thin sections made from beds D8 to C1a. Some individual beds (D3, D5), located 2 meters above the fossiliferous beds, comprise rare, small (up to 1 mm) pseudomorphs after evaporative crystals (prob-ably gypsum, Fig. 6A). The pseudomorphs are filled with microsparite. The ostracod mudstones from the bed C7 comprise crustacean faecal pellets of Favreina type (Fig. 6B).

Microfacies of the unit IV of the Kcynia Forma-tion slightly differ from those of the underlying units

Fig. 6. Microfacies of limestones of the Kcynia Formation. A – Mudstone from the unit III with pseudomorphs after evapo-ratives (gypsum ?; arrowed) filled with microsparite. B – Crustacean faecal pellets of Favreina type from the unit III. C – Peloidal packstone/grainstone microfacies from the base of the unit IV. D – Bioclastic wackestones from the unit IV. Note well preserved internal structure of a bivalve shell and serpulid worm tubes. Scale bars are 1 mm.

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Fig. 7.

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and show a considerable diversity. At the base of the unit they consist of laminated peloidal packstones with small (up to 500 µm) well-rounded intraclasts and pel-oidal grainstones with unrecognizable, highly disartic-ulated bioclasts (Fig. 6C). Peloids are very well-sorted and range from 20 to 40 μm in diameter. Upwards in this unit a bioclastic wackestone/mudstone appears. It comprises bivalve shells, serpulide worm tubes (with preserved laminated wall structure), crushed ostracods and echinoderm fragments (Figs 2, 6D).

Primary rock textures of the studied rocks are well preserved. Diagenetic alteration is restricted to indi-vidual horizontal stylolites, locally present dissolution seams, recrystallization of micrite to neomorphic mi-crospar and recrystallization of bivalve shells. Blocky calcite spar in the interior of ostracod carapaces is lo-cally micritized, while the micritization of bioclasts is generally absent.

4.2. Foraminifera

Benthic foraminifera have been separated from marls of the Pałuki Formation (samples 1, 2), as well as the Unit I (samples 3-7) and a short interval of the Unit III (samples 12, 14, 15) of the Kcynia Formation, includ-ing bed D12 (sample 12) with horseshoe crab fauna. Planktonic foraminifera are absent in the studied ma-terial. Recorded foraminiferal species, in total 23, are figured on Figs. 7 and 8. The foraminiferal assemblages are dominated by the order Lagenida represented by 22 species. The order Miliolida is represented by the only one genus Paleomiliolina.

The Pałuki Formation yielded highly diverse as-semblages, represented by over a dozen species; the most abundant forms belong to the genera: Lenticulina, Dentalina, Planularia, Saracenaria, Tristix and Paleo-miliolina. Similar foraminiferal assemblage occurs in the unit I of the Kcynia Formation, however, in contrast

to the Pałuki Formation assemblage, it is character-ized by the lack of almost all representatives of genera Vaginulopsis, Triplasia and Tristix and the appearance of Belorusiella and Geinitzina. Foraminiferal assem-blages of both intervals show clear domination of a single genus Lenticulina. This genus encompasses 60-80% of the total assemblages and is represented by the species: L. apiculata neocomiana, L. muensteri and L. ponderosa. The number of benthic foraminifera species in marls of the Pałuki Formation, and the unit I of the Kcynia Formation varies between 7 and 15.

The foraminiferal assemblage from the middle part of unit III of the Kcynia Formation (samples 12, 13, 15) differs significantly from the older assemblages because of its significantly lower diversity. This as-semblage is characterized by the occurrence of only three species: Guttulina multistriata, Pseudonodosaria tenuis and Geinitzina wolinensis, however, two first species are predominant, and each of them comprises about 50% of the total foraminiferal assemblage.

4.3. Ostracoda

The Owadów-Brzezinki succession yielded relatively low diversity ostracod faunas, which are derived from the unit I (samples 1, 2, 4, 5, 6, 8), a lower part of the unit II (sample 9), and a lower part of the unit III of the Kcynia Formation (samples 12, 14, 19), including bed D12 (sample 12) and bed D10 (sample 14). No ostracod fauna was found in micropalaeontological samples 20-24 derived from the upper part of the unit III, and the unit IV.

Collected specimens are preserved as carapaces and rarely as isolated valves. Twelve species (2 species in open nomenclature), belonging to eight genera, were identified: Galliaecytheridea compressa (christiensen & kiLenyi, 1970); Galliacytheridea postrotunda (oert-Li, 1957); Hechticythere serpentina (anDerson, 1941);

Fig. 7. Benthic foraminifera of the Owadów-Brzezinki section. 1 – Paleomiliolina egmontensis (LLoyD), sample 1; 2 – Pale-omiliolina egmontensis (LLoyD), sample 1; 3 – Guttulina multistriata bieLecka, sample 12; 4 – Guttulina multistriata Bi-eLecka, sample 9/10; 5 – Paleomiliolina sp., sample 1; 6 – Paleomiliolina sp., sample 1; 7 – Geinitzinita wolinensis bieLecka, sample 1; 8 – Geinitzinita wolinensis bieLecka, sample 1; 9 – Pseudonodosaria tenuis (bornemann), sample 12; 10 – Pseu-donodosaria tenuis (bornemann), sample 12; 12 – Pseudonodosaria tenuis (bornemann), sample 9/10; 11 – Vaginulinopsis incisiformis bieLecka, sample 4; 13 – Vaginulinopsis embaensis (Furssenko & PoLenova), sample 2; 14 – Vaginulinopsis embaensis (Furssenko & PoLenova), sample 1; 15 – Vaginulinopsis embaensis (Furssenko & PoLenova), sample 2; 16 – Nodosaria striatojurensis kLähn, sample 2; 17 – Tristix quadrangularis Furssenko & PoLenova, sample 1; 18 – Tristix quadrangularis Furssenko & PoLenova, sample 1; 23 – Tristix quadrangularis Furssenko & PoLenova, sample 2; 19 – Tristix temirica (Dain), sample 1, sample 1; 20 – Planularia poljenovae kusnetZova, sample 1; 21 – Triplasia althoffi jurassica (mjatLiuk), sample 2; 22 – Tristix sp., sample 1; 24 – Lenticulina muensteri (roemer), sample 1; 25 – Lenticulina muensteri (roemer), sample 1; 26 – Lenticulina muensteri (roemer), sample 2; 27 – Lenticulina ponderosa mjatLiuk, sample 2.

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Macrodentina (Macrodentina) transiens (jones, 1885); Macrodentina (Polydentina) rudis (maLZ, 1958); Monoceratina sp.; Paracypris sp.; Paranotacythere (U.) cf. gramanni (schuDack, 1993); Paranotacythere (U.) cf. rimosa (martin, 1940); Rectocythere (R.) sp.; Schuleridea piechcinensis (kubiatowicZ, 1983); Schuleridea triebeli (steghaus, 1951).

The assemblage is dominated by Cytheroidea, es-pecially by the species Macrodentina (M.) transiens and more rarely M. (P.) rudis. It also includes species of Rectocythere, Parantacythere, Galliaecytheridea, Hechticythere and Schuleridea. The Cypridoidea is represented by rare specimens of Paracypris.

Fig. 8. Benthic foraminifera of the Owadów-Brzezinki section. 1 – Planularia multicostata kusnetZova, sample 2; 2 – Planularia multicostata kusnetZova, sample 2; 3 – Planularia multicostata kusnetZova, sample 2; 4 – Pseudonodosaria tenuis (bornemann), sample 1; 5 – Pseudonodosaria tenuis (bornemann, sample 9/10; 6 – Dentalina sp., sample 2; 7 – Dentalina sp., sample 1; 8 – Lenticulina ponderosa mjatLiuk, sample 1; 9 – Lenticulina ponderosa mjatLiuk, sample 2; 10 – Marginulopsis robusta (reuss), sample1; 11 – Marginulopsis robusta (reuss), sample 1; 12 – Planularia multicostata kusnetZova, sample 2; 13 – Belorussiella wolinensis bieLecka, sample 4; 14 – Belorussiella wolinensis bieLecka, sample 5; 15 – Citharina sp., sample 5; 16 – Citharina sp., sample 6; 17 – Guttulina multistriata bieLecka, sample 9/10; 18 – Nodosaria cf. osynkiensis mjatLiuk, sample 1.

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4.4. Palynology

Amorphous organic matter is present in all samples examined. However, only one sample (sample 12 from the bed D12) yielded black, rectangular organic pa-lynoclasts, abundant acritarch Leiosphaeridia sp. and prasinophycean alga – Pterospermella sp. (Fig. 9). No dinocysts, pollen or spores have been found.

4.5. Bulk carbonate oxygen and carbon isotope data

δ18O and δ13C values of micritic and marly bulk car-bonate samples from the Owadów-Brzezinki section vary between -6.9 and 1.3‰, as well as -6.7 and 1.4‰, respectively (Figs 10, 11). δ18O and δ13C values of most bulk carbonate samples oscillate, however, between -3.3

Fig. 9. Palynomorphs of the Owadów-Brzezinki section. 1a, b – Leiosphaeridia sp. (Acritarcha), sample 12; 2, 3 – Ptero-spermella sp. (Prasinophyta), sample 12.

Fig. 10. δ18O versus δ13C values of bulk carbonates from the Owadów-Brzezinki section. Correlation (r2 = 0.52) between δ18O and δ13C values is statistically significant.

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Fig. 11. Lithology, δ13C and δ18O values of bulk carbonates and oyster shells from the Owadów-Brzezinki section.

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and 0.7‰, and between -0.6 and 1.3‰, respectively. Statistically significant correlation between bulk car-bonate δ18O and δ13C values is observed (Fig. 10). It results mostly from large and simultaneous depletion in 18O and 13C isotopes of twelve bulk carbonate samples.

δ18O and δ13C values of bulk carbonates are rela-tively constant within marls of the Pałuki Formation (with one outlier) and the unit I of the Kcynia Forma-tion, averaging -1.2 and 0.3‰, respectively (Fig. 11). Isotope values decrease in the unit II. Strongest de-creases in δ18O and δ13C values (up to -6.7 and -6.9‰, respectively) are noted in the uppermost part of the limestones from the unit II, beds D14, D13, D12, D9

of the unit III, and in the hard ground at the bound-ary of the beds C1a and A18 in the unit III (Fig. 11). δ18O values of bulk carbonates from the rest of the unit III are characterized by a significant scatter of up to 1.5‰ and oscillate around -2‰. δ13C values of unit III limestones are generally higher (around 1‰) but show considerable decreases in a few beds (beds D11, D10, uppermost part of the bed D9, D8 and A17). Another significant decreases in δ18O and δ13C values (up to -3 and -4‰, respectively) are observed at the boundary of units III and IV, and in the organodetritic limestones of the unit IV.

Fig. 12. Cathodoluminescence images of oyster shells. A – Well-preserved oyster shells, (sample SHW124). Intrinsic bluish luminescence of oyster calcite is predominant, narrow increments reveal dull orange luminescence. B – Poorly preserved oyster shells. Most of the oyster calcite displays bright orange-red luminescence similar to those of surrounding sediment and blocky calcite cement.

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4.6. Diagenetic alteration of oyster shells

The stable isotope composition of marine carbonate sediments and calcareous fossils is prone to the altera-tion in post-depositional processes. The preservation state of skeletal calcite can be screened using minor and trace element concentration analyses and cathodo-luminescence studies. Diagenetic alteration of calcite is often concomitant with an increase in Fe and Mn and a decrease in Sr contents owing to significant differences in concentrations of these elements between seawater and diagenetic fluids in reduced or freshwater envi-ronments (branD & veiZer 1980; veiZer 1983; mar-shaLL 1992; uLLmann & korte 2015). Mn2+ ions are also an activator of orange-red cathodoluminescence observed in diagenetically altered calcites (marshaLL 1992; savarD et al. 1995), although pristine carbonate shells may also reveal dull luminescence or brighter luminescence bands (barbin 2000; 2013).

Studied oyster shells from the Owadów-Brzezinki section show different intensities of luminescence from dull to bright (Fig. 12). As dull to medium lumines-cence of modern oyster shells is observed (cf. barbin

2000; 2013) only the bright, orange-red luminescence is interpreted to be a result of diagenetic alteration. All shells showing bright luminescent have been excluded from the isotope dataset. Oysters shells used for oxy-gen and carbon isotope analyses are characterized by low Mn/Ca (< 0.18 mmol/mol) and Fe/Ca ratios (< 0.45 mmol/mol), and high Sr/Ca ratios (> 0.56 mmol/mol; see Table 1), which are equivalents of concentrations of Mn < 100 ppm, Fe < 250 ppm, and Sr > 490 ppm in pure calcite. Similar threshold levels of element con-centrations are accepted as indicative of a good state of preservation of Jurassic oyster shells (cf. wierZbowski & joachimski 2007; Price & teece 2010).

4.7. Oyster oxygen and carbon isotope data

δ18O and δ13C values of well-preserved Deltoideum delta shells vary between -0.5 and 0.5‰, as well as 0.6 and 2.3‰, respectively (Table 1, Fig. 11). Oxygen isotope values of oyster shells from the Pałuki For-mation, except for one sample from the oyster layer, are slightly higher (δ18O values between 0.3 and 0.5‰)

Fig. 13. Lithology, Ca, Al, Zr concentrations, and P/Al, U/Th, V/Cr ratios of bulk carbonates from the Owadów-Brzezinki section.

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than the values of oyster from the unit I and the unit III (single specimen) of the Kcynia Formation (δ18O values between -0.2 and 0.1‰). Carbon isotope values of oyster shells from the Pałuki Formation, except for one sample from the oyster layer, are lower (δ13C values between 0.6 and 0.9‰) than the oyster values from the Kcynia Formation (δ13C values between 1.9 and 2.3‰).

4.8. Inorganic geochemistry

Inorganic geochemistry has been studied in almost the whole Owadów-Brzezinki section except for short in-tervals in its uppermost part.

The data show very strong correlations (r ≥ 0.8) be-tween the majority of the litho-detrital elements (Sr, Ba, P, Li, Na, K, Rb, Cr, Al, Ti, Zr, V, Nb, Sc, Y, Ni, La, Ce, Th), and strong correlations of this group of elements with Mo, Pb, Fe, Cu and U concentrations of bulk car-bonates (Table 2). Ca concentrations are negatively cor-related with the detrital element group. δ13C values of bulk carbonates, Mg, Mn and Zn do not show strong correlation with other chemical elements studied. δ18O

values are, in turn, positively and strongly correlated with Sr contents and negatively with Ca. Less important but statistically significant correlations are, however, observed between δ18O and, in a few cases, δ13C values of bulk carbonates and many of elements from the de-trital group (Table 2).

The diagrams of concentrations of chemical ele-ments in the Owadów-Brzezinki section show nega-tively correlated and significant oscillations in calcium and detrital element contents of bulk rocks (Fig. 13). The content of detrital elements is particularly high in the lowest part of the section (up to 2% of aluminium in marls of the Pałuki Formation and the lowest part of the unit I as well as at the boundary of units I and II of the Kcynia Formation). The elemental profiles display a gradual long-term decrease in the amount of detrital material throughout the section. P/Al, U/Th and Ni/Co trends are scattered. The highest values of P/Al*1000 (above 140), U/Th (above 5), and Ni/Co ratios (above 8) are observed in the proximity of fossiliferous beds D13 and D12, in the higher part of the unit III, and at the lowest part of the unit IV of the Kcynia Formation

Fig. 14. Lithology, Ni/Co, Mo/Al, Mn/Al, Na/Al, Sr/Al, and Li/Al ratios of bulk carbonates from the Owadów-Brzezinki section.

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(Figs. 13, 14). High Ni/Co ratios are additionally ob-served within the unit II.

V/Cr ratio trend is characterized by a gradual, long-term decrease from ca. 1.7 at the base of the section, followed by a significant increase (to ca. 2.2) in its up-permost part, at the boundary of the units III and IV of the Kcynia Formation (Fig. 13). Mo/Al, Mn/Al, Na/Al, Sr/Al and Li/Al ratio trends of bulk rocks display sig-nificant long-term increases starting from the boundary of the units II and III (Fig. 14). The highest values of the Mo/Al, Mn/Al, Na/Al, and Sr/Al ratios (above 0.4, 180, 100, and 180, respectively) occur at the fossilifere-ous beds D13 and D12, in the middle part of the unit III, and at the boundary of the units III and IV. Highest Li/Al ratios are in turn observed in the whole middle-upper part of the unit III and in the unit IV.

5. Discussion

5.1. Microfacies analysis

As revealed by thin section analyses, marls of the Pałuki Formation and older parts of the Kcynia For-mation (units I, II and a lower part of the unit III) are dominated by mudstone-wackestone microfacies, which were deposited in a low energy sedimentary environ-ment, in part below the storm wave base. This confirms previous palaeoenviromental interpretation of the lower part of Kcynia limestones from the Owadów-Brzezinki quarry as formed in relatively deep, mostly subtidal set-tings (cf. ZieLińska 2003; kin et al. 2013). Laminated mudstones with ostracoda debris represent tempestite layers. The obliteration of primary sedimentary struc-tures in the units I and II resulted from intense sedi-ment bioturbation (cf. kin et al. 2013). The presence of the abundant echinoderm fragments in limestones of the unit I points to the normal marine salinity.

The retread of echinoids at the boundary of the units II and III of the Kcynia Formation is linked to a decrease in water salinity. The presence of small pseu-domorphs after evaporatives in the bed D3 and D5 from the middle part of the unit III indicates periods of water hypersalinity. The relatively high fauna diversity and the absence of evaporative pseudomorphs in other sam-ples derived from the unit III does not point, however, to prolonged periods of hypersalinity of the water. The scarcity of burrows and some microfossils in the unit III indicates poor oxygenation of the pore water below the water-sediment interface.

A minor increase in the water energy is observed

in the uppermost part of unit III and in the unit IV of the Kcynia Formation, where laminated peloidal pack-stones and grainstones with intraclasts appear. Burrows present in this part of the section are filled with peloi-dal intraclastic grainstones, and point to, at least tem-poral, good oxygenation of the bottom water. Detailed thin section analyses confirm the existence of peloidal facies, described by kin et al. (2013) from the same in-terval of the Owadów-Brzezinki section. The presence of coarse-grained microfacies is probably connected with the basin shallowing and the deposition in a shal-low subtidal or intertidal zone. However, occurrences of mudstone/wackestone microfacies in some studied rocks of the unit IV, document short-term resumptions of the low energy environment. The re-appearance of echinoids in the unit IV is associated with an increase in water salinity.

5.2. Foraminifera

In general, calcareous foraminifera are distinctive of marine or brackish environments (sen guPta 2002). The foraminiferal diversity increases from the margin-al-marine to open shelf environment, and the normal marine environment shows much more diverse fo-raminiferal community than hypersaline or hyposaline (brackish) lagoons or estuaries. Hyposaline lagoons display consistently lower foraminiferal variability than hypersaline lagoons (Fisher et al. 1943). In marginal environments, the species richness decreases with de-creasing salinity (haywarD & hoLLis 1994; cuLver et al. 2012). The lowest number of species is observed in lagoonal or deltic areas where salinity is reduced to 2‰ or less (sen guPta 2002). Miliolids are also conspicu-ously rare in brackish lagoons, however, commonly oc-cur in hypersaline environments (murray 1968, 2006). For example, under warm temperate climate (France, Spain) the water of restricted basins may become hy-persaline during summers, which leads to the growth of miliolids (Le camPion 1970; cearreta 1988, 1989).

Based on the diversity of foraminiferal assemblages, marls of the Paluki Formation and almost the entire unit I of the Kcynia Formation may be classified as normal marine environments. Extremely low-diversity foraminiferal assemblages of the lower-middle part of the unit III of the Kcynia Formation (including fossil-bearing beds) point to a marginal hyposaline (brackish) environment, possibly lagoon.

No foraminifera are separated from the uppermost part of the unit I, the unit II, the major part of the unit III and the unit IV of the Kcynia Formation. The disap-

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pearance or scarcity of foraminifera in those parts of the section is, highly probable, related to the presence of non-marine environments with low or elevated sa-linities or characterized be a significant oxygen deple-tion of bottom waters.

5.3. Ostracoda

All ostracod species derived from the lower part of the Owadów-Brzezinki section (unit I and a lower part of unit II of the Kcynia Formation) are marine shallow-water taxa (Galliaecytheridea compressa, Gal-liacytheridea postrotunda, Hechticythere serpentina, Macrodentina (M.) transiens, Macrodentina (P.) rudis, Monoceratina sp., Paracypris sp., Paranotacythere (U.) cf. rimosa, Rectocythere (R.) sp.; Schuleridea piech-cinensis, Schuleridea triebeli; cf. wiLkinson 2008; wiLkinson & whatLey 2009). Non-marine Ostracoda of “Purbeckian Facies”, known from Central Poland (bieLecka & sZtejn 1966; sZtejn 1991), and from west-ern Europe (see horne 2009, and references therein) are absent in the unit I and a lower part of the unit II. At the base of unit III, the ostracod assemblage is still similar to that from units I and II, however, only six species are common (G. compressa, H. serpentina, M. (M.) transiens, Paracypris sp., S. piechcinensis, S. triebeli).

In the Owadów-Brzezinki section, the stenohaline brackish forms known from the Upper Jurassic of Eu-rope e.g., Fabanella boloniensis, Wolbergia visceralis, Procytheropteron bicosta, have not been found. The ostracod assemblage of the sample 19 from the middle part of the unit III is very poorly preserved, which has not allowed its taxonomical determination. The lack of Ostracoda in younger micropalaeontological samples (20-24) and in thin-section derived from beds D1, C5, C2, A10, A7, A6, A4 and A3 of the unit III is probably associated with bottom water anoxia and/or the poor preservation of the fauna. The presence of ostracod shells in older beds, especially isolated valves, which may have been transported after death and deposited at the basin bottom, is, however, not an unambiguous evi-dence for the good oxygenation level of bottom waters.

5.4. Palynology

Prasinophycean algae (Pterospermella), which com-monly occur in a micropalaeontological sample 12, derived from the fossiliferous bed D12, prefer specific environmental conditions and become more abundant when other phytoplankton taxa are absent (taPPan

1980). Low-diversity assemblages dominated by Pter-ospermella (Prasinophyta) and Leiosphaeridia (Acri-tarcha) are known from low-salinity lagoons (Dreyer et al. 2004). They are generally interpreted as indica-tive of near-shore/marginal marine environments (king 2016, and references therein).

5.5. Oxygen and carbon isotope composition of bulk carbonates

Relatively constant δ18O and δ13C values of ca. -1.2 and 0.3‰, respectively, measured from marls of the Pałuki Formation and unit I limestones of the Kcynia Forma-tion (Fig. 11) are similar to the values of uppermost Jurassic bulk carbonates from open oceanic settings (cf. grabowski et al. 2010; jach et al. 2014). The rocks of this interval may, therefore, be interpreted as formed in a sea of salinity close to normal marine and to be not significantly altered by diagenetic processes.

Slight decreases in δ18O and δ13C values of bulk carbonates observed in the lower part of the unit II may result from a decline in the water salinity (cf. keith & weber 1964; huDson et al. 1995; yin et al. 1995; neL-son & smith 1996). Strong decreases in δ18O and δ13C values of bulk carbonates observed at the boundary of the units II and III, around the hard ground in the upper part of the unit III, and at the boundary of units III and IV of the Kcynia Formation (Fig. 11) may point to the precipitation of calcium carbonate from fresh- or low salinity brackish waters (cf. keith & weber 1964; huD-son et al. 1995; yin et al. 1995; neLson & smith 1996). The decreases may also be a result of the post-deposi-tional equilibration of the rocks with meteoric or pore waters (cf. banner & hanson 1990; marshaLL 1992). As horizons with low δ values in units II and III are located within rocks having higher δ values the modern diagenetic alteration is less probable. Carbonates of the units II and III, which have δ13C values lower than -2‰, and very negative δ18O values may, thus, be interpreted as precipitated from freshwater or brackish waters of low salinity, or as being altered soon after their forma-tion by such waters. The other rocks from the discussed intervals, having intermediate δ values, may have been formed in brackish environment (cf. keith & weber 1964; neLson & smith 1996). Carbonates from the middle and the upper part of the unit III are difficult to interpret. They are characterized by relatively high δ13C values (ca. 1‰), and lower (ca. -2‰) and scattered δ18O values. The rocks may be derived from a restricted lagoon, where δ18O values varied because of changing freshwater input and evaporation processes. δ13C values

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of these limestones may be slightly increased, com-pared to seawater values, because of the excess burial of organic matter and the evaporation effect (cf. berger & vincent 1986; horton et al. 2016). Modern diage-netic processes likely caused decreases in δ values of the youngest rocks, which are highly weathered and exposed at the top of the Owadów-Brzezinki section, i.e. in the uppermost part of the unit III and in the unit IV (Fig. 11).

The isotope data derived from ostracod shells from fossiliferous beds D12 and D13, and bulk carbonates from the middle part of the unit III reported by kin et al. (2013) are in good agreement with δ values of bulk carbonates presented in this study. The palaeosalinity reconstruction based on the isotope composition of bulk carbonates should, however, be treated with cau-tion because of many factors that may potentially affect the isotope composition of carbonate mud and rocks during their formation and diagenesis.

5.6. Oxygen and carbon isotope composition of oyster shells

Modern oysters precipitate calcite of their shells in oxygen isotope equilibrium with ambient seawater or close to it (hong et al. 1995; kirby et al. 1998; surge et al. 2001, 2003; titschack et al. 2010; uLLmann et al. 2010). The equilibrium precipitation of oxygen isotopes within Jurassic oyster shells is additionally proved by the similarity of their δ18O values with the values of co-occurring benthic and necto-benthic fossils (anDerson et al. 1994; wierZbowski & joachimski 2007; Price & Teece 2010).

δ18O values of calcite precipitated in the isotope equilibrium with seawater is dependent both on the temperature of its crystallization and the oxygen iso-tope composition of ambient water. The Middle Volgian epicontinental sea of central Poland was shallow and may have been characterized by significant evaporation rate, alternatively freshwater inflow may have resulted in a local decrease in water δ18O value. The possible range of ancient seawater δ18O values of the basin, and its salinities, have been modelled as based on the meas-ured range of δ18O values of well-preserved D. delta oysters (-0.5 to 0.5‰; Table 1), accepted range of Earth surface temperatures for central Europe during the Late Jurassic (see seLLwooD & vaLDes 2008) and the oxy-gen isotope–salinity relation for ancient seas given by raiLsback et al. (1989).

The palaeoclimate model of seLLwooD & vaLDes

(2008) suggests mean December-January-February temperature of ca. 11 °C and mean June-July-August temperature of ca. 21 °C at sea-level in the area of pre-sent Poland. This translates into a annual mean of 16 ± 2 °C. Sea-bottom temperatures may have been, how-ever, lower due to a considerable depth of an offshore or nearshore environment existing during the formation of the older part of Owadów-Brzezinki section, when most of studied oysters lived. Ancient temperature gra-dient in the restricted basin may be similar to that ob-served in the modern Mediterranean Sea in an offshore or nearshore settings at a depth of 50-100 m, where a decrease in mean temperature of ~1 to 3 °C, compared to the sea-surface, is observed (cf. manca et al. 2004). All the data suggest, thus, that mean temperatures dur-ing growth of studied oysters may have varied between 11 and 17 °C.

δ18O values of ancient seawater have be calculated from the equation of FrieDman & o’neiL (1977). For the measured range of oyster δ18Ocalcite values (-0.5 to 0.5‰), and the assumed range of mean temperatures of ambient waters (11 to 17 °C), the calculated seawater δ18O values vary between -1.6 and 0.8‰ VSMOW. Ac-cording to the salinity–δ18O relation model given by raiLsback et al. (1989), which takes into account effects of evaporation and freshwater runoff, the calculated seawater δ18O values translates into the salinity range 31.5 to 39.1ppt (Fig. 15).

Similar palaeosalinities (between 30.7 and 31.9‰) have been calculated from the CNa/(CMg+CSr+CMn) ratios of well-preserved oysters (samples SHW110, 124, 108, 132, 119) derived from limestones of the Kcynia For-mation and an oyster limestone layer within the Pałuki Formation by application of the salinity-element con-centration dependence established for modern Cras-sostrea (cf. rucker & vaLentine 1961; Zakharov & raDostev 1975). The palaeosalinity data derived from oysters from marls of the Pałuki Formation (samples SHW 118, 126, 125) are, however, biased due to elevat-ed magnesium concentrations (see Table 1), probably because of the contamination of the shells by magne-sium derived from surrounding clay minerals.

All the data imply that the oysters studied lived in a sea characterized by a salinity close to the normal marine, which is fully consistent with information on distribution of foraminifera, echinoids and bulk car-bonate isotope data from the Pałuki Formation and the unit I of the Kcynia Formation (Fig. 2). Single oyster specimen derived from the lower part of the unit III may have grown during a short period of the return of normal salinity water, which is supported by the

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re-appearance of foraminifera in the proximity of the fossiliferous beds.

Modern oysters exert disequilibrium fractionation of carbon isotopes, which is probably controlled by res-piration processes (titschack et al. 2010). Therefore, δ13C values of modern Crassostrea virginica is about 1‰ lower than the assumed equilibrium values being similar to the δ13C values of dissolved inorganic carbon (DIC) of ambient water, except for some portions of the shell precipitated during cold seasons, which are enriched in 13C by 0.8-1.0‰ (surge et al. 2001, 2003). Measured range of oyster δ13C values (0.6 to 2.2‰; Ta-ble 1) from the Owadów-Brzezinki quarry is compati-ble with normal marine chemistry of the ambient water. Slightly lower δ13C values of oysters shells derived from the Pałuki Formation may have resulted from the lower bioproductivity of sea surface waters during deposition of the marls and better water mixing, which prohibited the formation of a distinct carbon isotope gradient in the water column (cf. berger & vincent 1986).

5.7. Inorganic geochemistry

Correlation coefficient matrix (Table 2) indicates that the majority of chemical elements (excluding Ca, Mg, Zn and partly Mn) are bound to the detrital fraction of sediments. Variations in non-detrital portions of the elements, which occur at different sites in calcium car-bonate, may be, therefore, retrieved by the normaliza-

tion of their content to the aluminium concentrations of bulk rocks (cf. aLgeo & maynarD 2004).

The amount of detrital elements (like aluminium and zirconium) decreases towards the top of the Ow-adów-Brzezinki section (Fig. 13). This may show a gradual increase in the carbonate sedimentation rate or a decrease in detrital material input to the study basin. Worth noting are sharp maxima of aluminium and zir-conium concentrations at the boundary of Pałuki For-mation and the unit I of the Kcynia Formation, as well as at the boundary of the units I and II of the Kcynia Formation (Fig. 13). They may be linked to condensed intervals.

High U/Th and Ni/Co ratios of the majority of sedi-ments (above 1.25, and 7.0, respectively) point to the prevailing dysoxic/anoxic conditions during the deposi-tion of marls of the Pałuki Formation, and limestones of the Kcynia Formation from the Owadów-Brzezinki section (cf. jones & manning 1994; triboviLLarD et al. 2006; maDhavaraju et al. 2015). Lower V/Cr ratios (be-low 2) are not consistent with the oxygen deficiency (cf. jones & manning 1994). V/Cr ratios of the sediments studied may, however, be biased by the detrital origin of vanadium in studied rocks as its concentrations are perfectly correlated with typical elements of the detrital group (Table 2). The oxygen deficiency was probably more stable during the deposition of the fossiliferous beds and the younger part of the Owadów-Brzezinki section (upper part of the unit III, and boundary of the units III and IV) as these sediments are characterized by the highest U/Th and Ni/Co ratios, as well as el-evated Mo/Al, and Mn/Al ratios, which results from the mobilization of the transition elements under dys-oxia/anoxia (cf. veiZer 1983; marshaLL 1992; jones & manning 1994; aLgeo & maynarD 2004; triboviL-LarD et al. 2006; maDhavaraju et al. 2015). Intervals with high U/Th, Ni/Co, Mo/Al and Mn/Al ratios in the units I, III, and IV are also characterized by high P/Al ratios, which points to the enhanced burial and preser-vation of organic matter (cf. triboviLLarD et al. 2006).

Elevations in Na/Al, Sr/Al ratios and Li/Al ratios of bulk rocks in the upper part of the Owadów-Brzezinki section are more difficult to explain (Fig. 14). Sodium, strontium and lithium concentrations are much higher in seawater than in fresh- or brackish waters but in-crease during evaporation of the latter (veiZer 1983; witherow & Lyons 2011; giLLanDers & munro 2012). Excess of sodium, strontium and lithium in the upper part of the Owadów-Brzezinki section can, thus, be di-rectly related to the episodes of the enhanced evapora-tion and an increase in salinity of the restricted brack-

Fig. 15. Salinity-δ18O value model for ancient oceans (after raiLsback et al. 1989) and calculated range of palaeosalini-ties for studied oyster shells. Estimated range of seawater δ18O values (shaded), which is calculated from δ18O values of oysters and palaeoclimatic data of seLLwooD & vaLDes (2008), translates into palaeosalinities 31.5 to 39.1 ppt

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ish basin (cf. veiZer et al. 1977; chagué-goFF 2010). Such episodes may also have co-occurred with bottom water anoxia due to the formation of a stable halocline. It is also possible that concentrations of sodium, stron-tium, and lithium may have increased in a lagoonal or near-shore environment because of the input of fresh, slightly weathered terrestrial material, as these ele-ments have low ionic potential being easily soluble and removable during weathering processes and prolonged grain transport (buggLe et al. 2011). This may, in turn, indicate the shore progradation and the regression of the basin during the deposition of the youngest part of the Owadów-Brzezinki section.

Chemical proxies are a strong evidence for, at least temporal, oxygen deficiency at the sediment-water interface, which may have been an important factor allowing the preservation of delicate skeletons of ma-rine and terrestrial creatures in the Owadów-Brzezinki quarry. It is important to note that the environmental conditions of a restricted lagoon during the deposition of the younger part of Owadów-Brzezinki limestones belonging to the Kcynia Formation may have varied in month or annual scales as a result of consecutive cycles of freshwater input and evaporation, life blooms and extinctions, which are not distinguishable nowadays in the geological record due to the moderate deposition rate and the effect of time averaging. Extreme changes in the bottom environment are supported by findings of some microfossils, bivalves and burrows in limestones of the units III and IV, whereas other parts of this in-terval are devoid of any fossils and characterized by millimetre scale lamination pointing to the absence of any activity of burrowing organisms. Quantitative in-terpretations of the variations in the oxygen level, water salinities and weathering processes based on elemental proxies are problematic because of possible diagenetic effects i.e. leaching loosely-bound elements or post-depositional migrations of many ions. The geochemi-cal data are, however, compatible with other proxies, showing a general evolution of the basin towards an isolated, and often poorly oxygenated lagoon.

5.8. Depositional settings of the Owadów-Brzezinki limestones versus palaeoenvironments of other famous conservation Lagerstätten

Marls of the Pałuki Formation and the lower part of limestones (unit I) of the Kcynia Formation, which outcrop in the Owadów-Brzezinki quarry, were de-posited in normal marine conditions in an offshore or

nearshore environments. The evolution of the deposi-tional settings to less saline ones is recorded within the uppermost part of the unit I and the unit II of the Kcyn-ia Formation by a gradual retreat of stenohaline faunas and by decreases in δ18O and δ13C values of the rocks. Very low isotope signatures of the youngest rocks of the unit II may be, however, early diagenetic as a result of the percolation of low-salinity waters during the depo-sition of the overlying limestones of the unit III.

Limestones from the middle part of the Owadów-Brzezinki quarry (lower part of the unit III of the Kcynia Formation) were deposited in a shallow and relatively calm lagoonal environment characterized by variations in salinity and the temporal existence of bottom water dysoxia/anoxia, which have enabled preservation of fragile and soft tissues of marine and terrestrial creatures at certain intervals. Significant variability in the level of bottom water oxidation and palaeosalinities have probably enabled short-term life blooms, the preservation of thanatocoenses, and the presence of diversified marine-brackish-terrestrial fossil assemblages in some beds. This is confirmed by the occurrence of low diversified populations of opportunists, such as small bivalves (protobranchs or corbuloids), whose mass-accumulations may appear during brief oxygenation events, as it is observed in Kimmeridgian clays of England (wignaLL 1990).

The environmental variability noted in the mid-dle part of the Owadów-Brzezinki quarry seems to be exceptional compared to the other Jurassic and Cre-taceous conservation Lagerstätten, which were gener-ally characterized by more stable depositional settings. Most of the Jurassic and Cretaceous conservation La-gerstätten contain relatively thick platy and laminated, fossiliferous limestones being a result of a calm and prolonged calcareous sedimentation in restricted, mar-ginal marine basins under water stratification and bot-tom anoxia, which were only occasionally interrupted by the activity of sea-currents (DieTl & schweigert 1999; buatois et al. 2000; schweigert et al. 2005; Für-sich et al. 2007; jurkovšek & koLar-jurkovšek 2007; viohL & ZaPP 2007; stevens et al. 2014). It is worth noting that laminated limestones from Solnhofen area are interpreted in a bit different way as deposited in lagoons possessing a deep saline layers (bartheL et al. 1990; schwark et al. 1998; kemP & trueman 2003; keuPP et al. 2007). Albeit bottom waters of Solnhofen basins may have been temporarily dysoxic the elevated salinities likely prevented any biological activity at the sea bottom.

The upper part of the unit III of the Kcynia Forma-

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tion of the Owadów-Brzezinki section seems to repre-sent, at least at some intervals, more prolonged dysoxic/anoxic conditions as determined on the basis of micro-facies analysis, palaeofaunistic data, chemical proxies, and demonstrated by the occurrence of millimetre-scale lamination and the general lack of macrofauna. This part of the Owadów-Brzezinki section may have been deposited in the more stable anaerobic environ-ment similar to those known from other conservation Lagerstätten. Unfortunately, this interval is poorly ex-posed nowadays, and has not yield many fossils.

The youngest part of the section (unit IV of the Kcynia Formation) with abundant fossils was probably deposited in a shallow coastal zone characterized by the re-appearance of oxic conditions and water of the salinity similar to normal marine.

6. Conclusions

Depositional environments of the Owadów-Brzezinki section varied from offshore and nearshore of normal-marine chemistry (marls of the Pałuki Formation, and unit I limestones of the Kcynia Formation) to coastal and lagoonal one (units II, III, IV of the Kcynia For-mation). The latter were characterized by high-ampli-tude variations in seawater salinities (from brackish to hypersaline) and oxygenation level of benthic waters, which resulted in the variations of benthic fauna as-semblage (from brackish to poor marine faunas) or the total lack of benthic fauna at some intervals.

High variability of the water salinities during the deposition of the unit III limestones in a restricted la-goon, and sudden appearances of dysoxic/anoxic con-ditions have probably allowed the preservation of the diversified fauna and soft tissues of organisms in some intervals. The microfacies and chemical data indicate that dysoxic/anoxic episodes may have occurred dur-ing the deposition of fauna-rich beds (D12, D13) and the younger rocks of the unit III; the latter part of the quarry is poorly studied nowadays but may yield new, exceptionally preserved fossils in the near future. The youngest rocks of the Owadów-Brzezinki limestones (unit IV) show the re-appearance of waters of normal marine chemistry in the intertidal-subtidal and deeper coastal zones.

The depositional settings of the Owadów-Brzeiznki site are non-typical, compared to other famous con-servation Lagerstätten, owing to the short-term fluc-tuations in the oxygenation level of bottom waters and their salinities.

Acknowledgements

The study was supported by the Polish National Science Centre (grant no. 2012/07/B/ST10/04175). Comments and suggestions made by A. munnecke and J. sZuLc has allowed us to improve greatly this manuscript.

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Manuscript received: March 2nd, 2016.Revised version accepted by the Stuttgart editor: August 25th, 2016.

Addresses of the authors:

hubert wierZbowski, Polish Geological Institute – National Research Institute, Rakowiecka 4, PL 00-975 Warsaw, Po-land;e-mail: [email protected] Dubicka, ewa Durska, University of Warsaw, Faculty of Geology, Al. Żwirki i Wigury 93, PL 02-089 Warsaw, Poland;tomasZ rychLiński, Jagiellonian University, Institute of Geo-logical Sciences, Oleandry 2a, PL 30-063 Cracow, Poland;ewa oLemPska, błażej błażejowski, Institute of Palaeobiol-ogy, Polish Academy of Sciences, Twarda 51/55, PL 00-818 Warsaw, Poland.

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Table 1. Stratigraphy, chemical and isotope data of oyster (Deltoideum delta) shells from the Owadów-Brzezinki section.Sa

mpl

eU

nit/

bed

Posit

ion

Ca

Fe

Fe/C

aM

nM

n/C

aSr

Sr/C

a M

gM

g/C

a N

aN

a/C

aδ13

C

δ18O

[m]

[%]

[ppm

]*1

000

[ppm

]*1

000

[ppm

]*1

000

[ppm

]*1

000

[ppm

]*1

000

[‰]

[‰]

SHW

119

Uni

t II /

bed

s D4-

D10

15.3

9 ±

0.9

37.1

100

0.19

140.

0355

60.

6833

61.

512

595.

911.

850.

47

SHW

132

Uni

t I /

ca. 2

.0 m

ab

ove

the

base

3.6

± 0.

538

.210

00.

1915

0.03

511

0.61

594

2.6

1255

5.72

2.33

-0.16

SHW

108

Uni

t I /

ca. 1

.0 m

ab

ove

the

base

2.6

± 0.

537

.810

00.

1916

0.03

469

0.57

731

3.2

1557

7.18

1.80

-0.0

5

SHW

124

Uni

t I /

ca. 1

.0 m

ab

ove

the

base

2.6

± 0.

537

.510

00.

1912

0.02

464

0.57

554

2.4

1748

8.13

2.24

0.07

SHW

128*

Uni

t I /0

.15

m

abov

e th

e ba

se1.7

537

.590

61.7

4*15

30.

30*

179

0.22

*11

094.

958

52.

72-0

.35

-5.8

5

SHW

125

Pału

ki F

orm

atio

n /

ca. 0

.25

m b

elow

the

top

1.35

± 0

.25

36.1

215

0.43

130.

0365

60.

8353

3224

.426

6212

.86

0.94

0.49

SHW

126

Pału

ki F

orm

atio

n /

ca. 0

.25

m b

elow

the

top

1.35

± 0

.25

36.8

100

0.20

290.

0660

90.

7650

5322

.723

7411

.25

0.68

0.32

SHW

137*

Pału

ki F

orm

atio

n /

ca. 0

.25m

bel

ow th

e to

p1.

35 ±

0.2

536

.437

50.

74*

270.

0564

80.

8149

9222

.627

7213

.27

0.77

0.29

SHW

118

Pału

ki F

orm

atio

n /

ca.

0.5

m b

elow

the

top

1.1 ±

0.2

536

.313

70.

2728

0.06

612

0.77

3318

15.1

2365

11.3

60.

610.

46

SHW

110

Pału

ki F

orm

atio

n /

oyst

er la

yer

0.8

37.8

112

0.21

260.

0549

90.

6046

42.

018

008.

312.

05-0

.45

* di

agen

etic

ally

alte

red

sam

ples

eschweizerbart_xxx


Table 2. Pearson correlation coefficient matrix for selected element concentrations measured in the Owadów-Brzezinki section��

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depositional environment of the owadów-brzezinki conservation … · 2016-11-14 · microfacies...

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