Seawater temperatures and carbon isotope variations in central European basins at the Middle–Late Jurassic transition (Late Callovian–Early Kimmeridgian)

Palaeogeography, Palaeoclimatology, Palaeoecology 440 (2015) 506–523

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Seawater temperatures and carbon isotope variations in central European basins at the Middle–Late Jurassic transition (Late Callovian–Early Kimmeridgian) Hubert Wierzbowski ⁎ Polish Geological Institute – National Research Institute, Rakowiecka 4, PL 00-975 Warszawa, Poland

a r t i c l e

i n f o

Article history: Received 23 April 2015 Received in revised form 5 September 2015 Accepted 12 September 2015 Available online 28 September 2015 Keywords: Tethys Isotope- and elemental ratios Paleoclimate Belemnites Brachiopods Bulk-carbonates

a b s t r a c t Oxygen and carbon isotope values and elemental ratios of well-preserved belemnite rostra, brachiopod shells and bulk-carbonates from the Upper Callovian–Lower Kimmeridgian of the Polish Jura Chain, Kujawy (Poland) and Swabian Alb (Germany) are investigated to reconstruct environmental conditions and perturbations in the marine carbon cycle. Belemnite δ18O values show relatively constant temperatures (ca. 12 °C) of bottom waters in the Polish Jura Chain basin during a major part of the Late Callovian–Middle Oxfordian, except for a short-term cooling (to ca. 9 °C) at the Callovian–Oxfordian transition. Belemnite and brachiopod δ18O values show a gradual increase in temperature during the Submediterranean Late Oxfordian; the highest temperatures (ca. 16 °C) are calculated for the Submediterranean Oxfordian–Kimmeridgian transition. Belemnite and brachiopod Mg/Ca and Sr/Ca ratios are disregarded as a paleotemperature proxy because of their weak correlation with δ18O values. The belemnite and brachiopod isotope data confirm that the carbon isotope composition of belemnite rostra is affected by a metabolic effect, which results in a depletion of belemnite calcite in the 13C isotope. Belemnite rostra are considered, nevertheless, as a valuable tracer of temporal variations in the carbon isotope composition of marine carbonates. Belemnite δ13C data show the presence of two positive excursions (in the Upper Callovian and the Middle Oxfordian) in the carbon isotope record of peri-Tethyan carbonates. The excursions are divided by a Lower Oxfordian interval characterized by decreased δ13C values. This is most likely a regional feature caused by upwelling. Lowest belemnite and brachiopod δ13C values are observed in the lower part of the Submediterranean Upper Oxfordian and are linked to a well-mixed state of the seawater in the basins studied. The carbon isotope record of bulk carbonates differs from those of belemnites and brachiopods probably because of strong variations in carbonate production in the Polish Jura Chain basin. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Isotope, faunistic and sedimentologic data show, depending on the study area, a short term or a long term cooling at the Callovian– Oxfordian transition, no change or a warming (Kaplan et al., 1979; Abbink et al., 2001; Dromart et al. 2003a, 2003b; Tremolada et al. 2006; Brigaud et al., 2008; Nunn et al., 2009; Wierzbowski et al., 2009, 2013; Rogov and Zakharov, 2010; Wierzbowski and Rogov, 2011; Alberti et al., 2012a, 2012b; Jenkyns et al., 2012; Chumakov et al., 2014; Pellenard et al., 2014a, 2014b). A subsequent Late Oxfordian– Early Kimmeridgian warming is noted in the oxygen isotope record of various paleogeographical areas (Abbink et al., 2001; Brigaud et al., 2008; Nunn et al., 2009; Žak et al., 2011; Alberti et al., 2012a, 2012b; Jenkyns et al., 2012; Wierzbowski et al., 2013). The carbonate and organic matter δ 13 C values show a longlasting positive excursion comprising the Upper Callovian–Middle ⁎ Fax: +48 22 45 92 001. E-mail address: [email protected].

http://dx.doi.org/10.1016/j.palaeo.2015.09.020 0031-0182/© 2015 Elsevier B.V. All rights reserved.

Oxfordian (Nunn et al., 2009; Wierzbowski et al., 2013) or the presence of two positive excursions in δ13C values of marine carbonates in this interval (Wierzbowski, 2002, 2004; Wierzbowski et al., 2009). Because of the discrepancy of the data published, there is a need to study more high resolution and reliable paleoclimatic proxies from various regions. Central European basins had wide connections with the Tethys at the Middle–Late Jurassic transition and their sediments may be a proxy for environmental changes in open marine waters. Upper Callovian–Oxfordian oxygen and carbon isotope records of belemnite rostra and brachiopod shells from central Europe were presented by Wierzbowski (2002, 2004) and Wierzbowski et al. (2009). The data show relatively constant temperatures of bottom waters in the periTethyan basins of these areas during the Late Callovian–Middle Oxfordian, and two positive excursions in δ13C values of marine carbonates (Wierzbowski, 2002, 2004; Wierzbowski et al., 2009). An offset between coeval belemnite and brachiopod δ13C values points to the uptake of respiratory carbon during precipitation of belemnite skeletons (Wierzbowski 2002).

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The Oxfordian samples from the Polish Jura Chain (Kraków–Częstochowa–Wieluń Upland) in central Poland, whose data were published by Wierzbowski (2002), were screened for the state of preservation using cathodoluminescence analysis only. The samples were not analyzed for Mn, Fe and Sr content, which makes the data not fully reliable (cf. Wierzbowski, 2002; Wierzbowski et al., 2009). The time-span of the Polish Jura Chain dataset is limited because of a stratigraphic gap in the uppermost Callovian and diagenetic alteration observed in youngest samples from this area (Wierzbowski, 2002; Wierzbowski et al. 2009). In addition, the stratigraphy of the Zawodzie II section comprising the Bifurcatus Zone of the Upper Oxfordian has been amended by Głowniak (2006a), which results in the necessity of re-dating of the data presented previously (cf. Wierzbowski, 2002). The continuous carbon isotope record of Upper Callovian–Lower Kimmeridgian bulk carbonates of central European basins has also never been presented. Because of the limitations of the central European datasets studied so far, additional investigations of marine carbonates from this area have been undertaken. Chemical analyses of previously studied and stored belemnite and brachiopod materials from the Oxfordian in the Polish Jura Chain have been conducted. The isotope dataset has been supplemented with analyses of new, well-preserved and stratigraphically well-dated belemnite and brachiopod samples from the Callovian– Oxfordian boundary and the Upper Oxfordian–lowermost Kimmeridgian from the Polish Jura Chain and Kujawy (Poland). Some samples have also been re-positioned in the stratigraphic chart according to new stratigraphic data of Głowniak (2006a). In addition, the carbon isotope composition of Upper Callovian–lowermost Kimmeridgian bulk carbonates from the Polish Jura Chain has been studied. The aim of the current paper is a discussion of amended and supplemented oxygen and carbon isotope datasets from the Upper Callovian– Lower Kimmeridgian of central Europe. The data document temporal variations in temperature of bottom waters in the peri-Tethyan basins during the Late Callovian–Early Kimmeridgian, changes in the carbonate carbon isotope composition, and corroborate the presence of a metabolic vital effect in belemnites. Local and global paleoclimatic changes may be deciphered based on the comparison of the presented data with

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the isotope records of other areas. The data may also be used to show the evolution of the temperature of the bottom waters of the Polish Jura Chain basin on a longer time-span i.e. Middle–Late Jurassic (Late Bajocian–Early Kimmeridgian) and to reconstruct long-term fluctuations of the Jurassic climate (cf. Wierzbowski and Joachimski, 2007; Wierzbowski et al., 2009). 2. Geological setting 2.1. Lithology and depositional environment Peri-Tethyan basins of the Polish Jura Chain, Kujawy and the Swabian Alb were incorporated into the northern shelves of the Tethys Ocean during the Middle Callovian as a result of a global sea-level rise (cf. Feldman-Olszewska, 1998; Thierry et al. 2000; Wierzbowski et al. 2009; see also Fig. 1). The Upper Callovian sediments of these areas consist of nodular limestones and deep-water stromatolites with abundant hiatuses and condensations (Geyer and Gwinner, 1984; Norris and Hallam, 1995; Kopik, 1997; Dembicz and Praszkier, 2003b; Wierzbowski et al., 2009). The absence of sedimentation or erosion resulted in the general paucity of lowermost Lower Oxfordian (Mariae Zone) deposits in the Polish Jura Chain and the Swabian Alb, and the Lower Oxfordian stratigraphic gap in Kujawy (Różycki, 1953; Geyer and Gwinner, 1984; Matyja and Wierzbowski, 1985; Matyja et al., 1985; Matyja, 1992; Wierzbowski et al., 2009). Deep-neritic, siliceous sponge and microbial deposits, which formed the so called sponge megafacies, dominate in the Oxfordian in the areas studied (Matyja and Wierzbowski, 1985, 1996). Thin-bedded marly-limestone and mudstone beds, rich in sponges and sponge spicules, were deposited during the late Early Oxfordian (Cordatum Chron) and the earliest Middle Oxfordian (the early Plicatilis Chron) in the Polish Jura Chain, during the Middle Oxfordian in Kujawy, and during the late Early to the Submediterranean Late Oxfordian (Cordatum–Bimammatum chrones) in the Swabian Alb (Różycki, 1953; Geyer and Gwinner, 1984; Matyja et al. 1985; Głowniak, 1997, 2000, 2002, 2006b; Matyja and Głowniak 2003; Wierzbowski et al., 2009).

Fig. 1. Paleogeography and distribution of the main facies types during the Middle Oxfordian in Europe (after Matyja and Wierzbowski, 1995; Wierzbowski, 2004; modified). Areas of stable isotope studies: K — Kujawy; PJC — Polish Jura Chain; SA — Swabian Alb.

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Younger Middle and Submediterranean Upper Oxfordian deposits in the Polish Jura Chain, Submediterranean Upper Oxfordian deposits in Kujawy, and uppermost Submediterranean Upper Oxfordian (Planula Zone) deposits of the Swabian Alb have significant thicknesses and show diversified facies pattern owing to the presence of massive limestones formed in elevated microbial-sponge bioherms and bedded limestones and marls formed in interbiohermal basins (Geyer and Gwinner, 1984; Matyja et al., 1985; Matyja and Wierzbowski, 1996, 2004). The microbial-sponge bioherms were colonized by hermatypic coral colonies at the Submediterranean Oxfordian–Kimmeridgian transition in Kujawy and during the earliest Submediterranean Kimmeridgian in the Polish Jura Chain (Matyja and Wierzbowski, 1985, 1996; Matyja et al., 1985; Wierzbowski et al., 1992). The coral colonization resulted from the shallowing of the basins. The interbiohermal basins of the Polish Jura Chain and Kujawy were filled at that time with foreslope deposits (micritic limestones and marls) of carbonate platforms (Wierzbowski, 1964, 1966; Matyja and Wierzbowski, 1985, 1994b, 1996; Matyja et al., 1985). No distinct signs of the shallowing are observed in the Kimmeridgian of the Swabian Alb. The deposition of deep-neritic marly-limestone sediments of the sponge megafacies continued in this area in the course of the Kimmeridgian and the Early Tithonian (Geyer and Gwinner, 1984). Normal salinity of the Late Callovian sea in the Polish Jura Chain area is indicated by the presence of sea urchins, brachiopods, bryozoans, solitary corals, planktonic foraminifera and an abundant cephalopod fauna (Geyer and Gwinner, 1984; Dembicz and Praszkier, 2003a). A similar faunistic assemblage is found in the Oxfordian strata of all areas studied, which are rich in ammonites, belemnites, brachiopods, echinoderms and bryozoans (Geyer and Gwinner, 1984; Matyja et al., 1985; Głowniak, 2006a; Matyja and Wierzbowski 2006). Hermatypic coral colonies found in the youngest sediments studied in the Polish Jura Chain are also an indicator of normal salinity (Wierzbowski et al. 1992). A local or temporal freshwater input may be excluded due to the paleogeographic position of the investigated areas (Fig. 1) and because of the few-hundred-meter water depth, which is postulated for the siliceous sponge megafacies (Matyja and Wierzbowski, 1996; Pisera, 1997). 2.2. Stratigraphy The Polish Jura Chain, Kujawy and Swabian Alb basins were settled predominantly by Submediterranean ammonites during the Late Callovian to the earliest Submediterranean Kimmeridgian although ammonites distinctive of other bioprovinces were also present in these areas (Geyer and Gwinner, 1984; Matyja and Giżejewska, 1979; Matyja and Wierzbowski, 1995; Fig. 1). The stratigraphy of the outcrops studied is based on the Boreal (Upper Callovian–Lower Oxfordian) and Submediterreanean (Middle Oxfordian–Early Kimmeridgian) ammonite faunas. Recent studies have allowed the elaboration of detailed correlation schemes between the Boreal and the Submediterranean ammonite zonations of Europe (Matyja and Wierzbowski, 1997; Głowniak et al., 2010; Wierzbowski et al., 2013; Wierzbowski and Matyja, 2014). The correlation scheme of Wierzbowski et al. (2013) is used in the present study. It is based on the data of Głowniak et al. (2010) and Wierzbowski and Matyja (2014). Because of differences in the (Sub)Boreal and Submediterranean zonal schemes the boundary of the Oxfordian and the Kimmeridgian stages is placed in different chronostratigraphic equivalents in both biogeographical provinces (Matyja and Wierzbowski, 1997). Although a new proposal of Wierzbowski and Matyja (2014) is to use the (Sub)Boreal definition of the Oxfordian–Kimmeridgian boundary in the Submediterranean ammonite province it is not used in the current paper as it is not traditionally applied in the study area and not yet formally accepted. Precise correlation of Boreal and Submediterranean ammonite zonations is given instead on diagrams with isotope data, and substages which are differently defined are referred to Submediterranean or Boreal zonations.

The stratigraphy of sections studied at Stare Gliny, Ogrodzieniec, Wrzosowa, Wysoka, Niegowonice, Zawodzie, Syborowa Góra, Katarowa Góra, Julianka, Kuchary, Czepurka and small sections at Działoszyn (Pj 110, Pj113, Pj114, Pj139-140, Pj145, Bobrowniki Pj92) in the Polish Jura Chain is studied by Wierzbowski (1964), Matyja (1992), Wierzbowski et al. (1992, 2010), Atrops and Wierzbowski (1994), Matyja and Wierzbowski (1994a, 1997), Głowniak (1997, 2000, 2002, 2006a), Matyja and Głowniak (2003), Barski et al. (2004), and Wierzbowski and Matyja (2014). The stratigraphy of the Plettenberg section in the Swabian Alb is studied by Schweigert and Callomon (1997), and the stratigraphy of the Bielawy section in Kujawy is studied by Matyja et al. (1985), Matyja and Wierzbowski (2002). 3. Material and methods 3.1. Samples The belemnite rostra collected consist of two similar and widespread genera — Hibolithes and Pachybelemnopsis (older name Belemnopsis), which belong to the family Mesohibolitidae Nerodenko, 1983 (a former name of the family was “Belemnopseidae Naef, 1922”). The taxonomical distinction between both genera was often not possible because of the fragmentation of the collected material. The studied brachiopod shells from the Polish Jura Chain belonged to two orders — Terebratulida and Rhynchonellida (Lacunosella sp.). Only the latter have been found to be well-preserved (see Table S2). Bulk micritic and chalky limestones as well as marly limestones and marls from the Polish Jura Chain were additionally collected and analyzed for oxygen and carbon isotopes. Belemnite, brachiopod and bulk-carbonate samples were collected previously from stratigraphically well-dated sections in the Polish Jura Chain, Swabian Alb and Kujawy and studied for stable isotopes (cf. Wierzbowski, 2002, 2004; Wierzbowski et al. 2009). New samples were collected, in the years 2013–2014, from four stratigraphically well-dated outcrops of the Submediterranean Upper Oxfordian (Bobrowniki Pj92, Katarowa Góra, Pj110 and Pj139/140; Fig. 2) in the Polish Jura Chain. Their stratigraphic range comprises the Hypselum Zone, the Bimammatum Subzone of the Bimammatum Zone and the Planula Subzone of the Planula Zone (cf. Matyja and Wierzbowski 1997, Wierzbowski et al. 2010, Wierzbowski and Matyja 2014; Figs. 3 and 4). New samples from the Polish Jura Chain are also derived from well-dated archival materials of K. Dembicz and M. Giżejewska collected from the Callovian–Oxfordian boundary (the paucicostatum horizon of the Lamberti Subzone of the Lamberti Zone and the Scarburgense Subzone of the Mariae Zone) in the Stare Gliny and Rudno-autostrada sections (Dembicz and Giżejewska, unpublished data) as well as archival materials of A. Wierzbowski from the uppermost Submediterranean Oxfordian and lowermost Submediterranean Kimmeridgian (the Planula Subzone of the Planula Zone and the Polygyratus and the Desmoides subzones of the Platynota Zone) in the Kuchary and Czepurka sections in the Polish Jura Chain (cf. Wierzbowski, 1964; Atrops and Wierzbowski, 1994; Fig. 2). Four new belemnite samples are derived from the Bielawy section in Kujawy, whose stratigraphy was studied by Matyja et al. (1985) and Matyja and Wierzbowski (2002). All the data have been correlated with both the Submediterranean and the Boreal ammonite zonations to allow comparison with isotope data from other areas (Figs. 9 and 10). The vertical scale of the presented diagrams is based on assumed equal duration of Submediterranean ammonite subchrons (cf. Wierzbowski et al. 2013). The only change relates to the Hypselum Chron which has been recently upgraded from a subchron level (cf. Wierzbowski and Matyja, 2014). 3.2. Analytical methods Thin sections made from newly collected belemnite rostra and brachiopod shells were analyzed using a cold-cathode cathodoluminescence

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were monitored, over the course of analyses, by replicate analysis of laboratory standards Sol 2 (n = 32) and Erl 5 (n = 21) calibrated to NBS19 and LSVEC. Reproducibility for δ13C and δ18O values was 0.04‰ and 0.06‰ (± 1σ) for Sol 2, and 0.05‰ and 0.04‰ (± 1σ) for Erl 5, respectively. Paleotemperatures were calculated from the δ18O values of belemnite rostra and brachiopod shells rostra using Eq. (1) of O'Neil et al. (1969) modified by Friedman and O'Neil (1977) and SMOW to PDB scales conversion given by Friedman and O'Neil (1977). 103 lnαcalcite–water ¼ 2:78  106 =T2 –2:89

ð1Þ

where αcalcite−water is the equilibrium fractionation factor between calcite and water and T is the temperature in Kelvin. Temperatures calculated using the equation of O'Neil et al. (1969) modified by Friedman and O'Neil (1977) are 0.1 °C higher for the lower range of the measured δ18O values (− 2.5‰) and 0.7 °C lower for the upper range of the δ18O values (+0.9‰) than the temperatures calculated using Eq. (2) of Epstein et al. (1953) corrected by Craig (1965) and modified by Anderson and Arthur (1983). T ð¨CÞ ¼ 16:0 – 4:14  ðδc –δw Þ þ 0:13  ðδc –δw Þ2

ð2Þ

where δc is the oxygen isotope composition of carbonate in the PDB scale and δw is the oxygen isotope composition of water in the SMOW scale. Eq. (2) of Anderson and Arthur (1983), albeit frequently used for skeletal calcite, is based on aragonite-calcitic mollusk shells (see Epstein et al., 1953). Paleotemperatures calculated using Eq. (2) of Anderson and Arthur (1983) are shown on figures for comparison. Fig. 2. Location of the outcrops studied in the Polish Jura Chain (south-central Poland).

microscope. Using a micro-drill non-luminescent belemnite rostra and brachiopod shells were cleaned of adherent sediment, apical line infillings, borings, silicified rim areas, rests of primary brachiopod shell layer, brachidium and muscle scar areas and, if necessary, small luminescent portions of the shells (Fig. 5). Fragments of new 32 belemnite rostra comprising most growth rings and large fragments of new 21 brachiopod shells were powdered and homogenized to get average isotope values (the sample size was usually 100–300 mg). Aliquots of the carbonate powders were used for trace element and the isotope analysis. Trace element contents (Ca, Mg, Mn, Fe, Na, Sr) were determined by the ICP-OES (Inductively Coupled 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. Previously collected and stored 68 samples from the Polish Jura Chain area, whose isotope data were presented by Wierzbowski (2002), have been analyzed for trace element contents using the ICP-OES method in the Polish Geological Institute–National Research Institute or the AAS (Atomic Absorption Spectroscopy) method in the Institute of Geological Sciences, Polish Academy of Sciences. Limits of quantification of trace elements using ICP-OES method were 20 ppm for Fe, and 1 ppm for Sr. The laboratory reference material (Ca 38.5%, Mg 2066 ppm, Mn 21 ppm, Na 1530 ppm, Sr 1088 ppm, Fe 238 ppm) was used for quality control analyses. 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%. Freshly broken surfaces of non-weathered 64 bulk carbonate rocks from the Polish Jura Chain were sampled using a micro-drill. New skeletal and bulk-carbonate samples were reacted with 100% H3PO4 at 70 °C using a Gasbench II connected to a ThermoFischer Delta V Plus mass spectrometer in GeoZentrum Nordbayern and analyzed for oxygen and carbon isotope composition. All values are reported in per mille relative to VPDB scale by assigning a δ13C and δ18O values of +1.95‰ and −2.20‰ to NBS19 and −46.6‰ and −26.7‰ to LSVEC, respectively. The reproducibility and accuracy of the measurements

4. Diagenetic alteration The stable isotope composition of carbonate rocks and fossils may be altered by post-depositional processes. The diagenetic alteration of calcite can be screened using the measurements of minor and trace element concentrations and cathodoluminescence studies. Diagenetic alteration often results in an increase in Fe and Mn contents in calcite and a decrease in its Sr and Na contents as concentrations of these elements differ considerably between seawater and diagenetic fluids in reduced or freshwater environments (Veizer, 1974, 1983; Brand and Veizer, 1980; Marshall, 1992; Ullmann and Korte, 2015). In addition, distribution coefficients of some elements like Sr are higher in many skeletal calcites than those of inorganic calcite, which makes skeletal calcites prone to diagenetic alteration (Ullmann et al., 2013; Ullmann and Korte, 2015). Mn2+ ions are also an activator of orange-red cathodoluminescence which is distinctive of diagenetically altered calcites (Marshall, 1992; Savard et al., 1995). Strict criteria were used for the selection of the best preserved skeletal material. Belemnite rostra and brachiopod shells used for oxygen and carbon isotope analyses were non-luminescent (small luminescent shell fragments were removed using a micro-drill, Fig. 5). Most belemnite rostra are characterized by low Mn/Ca (b0.18 mmol/mol) and Fe/Ca ratios (b 0.36 mmol/mol), and high Sr/Ca ratios (N1.03 mmol/mol; see Table S1), which are equivalents of concentrations of Mn b 100 ppm, Fe b 200 ppm, and Sr N 900 ppm in pure calcite. Similar threshold levels of element concentrations in well-preserved Middle–Upper Jurassic belemnite rostra have been reported from other areas (cf. Nunn et al., 2009; Wierzbowski and Rogov, 2011; Alberti et al. 2012a; Wierzbowski et al., 2013). Although Na concentrations in marine calcites decrease during freshwater diagenesis (Brand and Veizer, 1980; Veizer, 1983) the sodium content is rarely used for the evaluation of chemical alteration of low-Mg calcites (cf. Grossman et al., 1996). The co-variance of Na/Ca and Sr/Ca ratios in belemnite rostra studied suggests, however, that the depletion in sodium, which is observed in some samples, results from diagenetic alteration (Fig. 6A, Table S2). Because of a clear diagenetic trend cut-off

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Fig. 3. Lithology and stratigraphy of the sections studied at Bobrowniki (Pj92) and Katarowa Góra in the Polish Jura Chain (after Wierzbowski et al. 2010; Wierzbowski and Matyja, 2014).

limit of sodium concentrations may be taken from the intersection point of the strontium limit and the trend line. Na/Ca ratio of 4.79 mmol/mol (an equivalent of Na concentration of 1100 ppm in pure calcite) has been accepted for the selection of well-preserved belemnite

samples. Isotope values and elemental ratios of belemnite samples characterized by high Mn/Ca (N 0.18 mmol/mol), and Fe/Ca ratios (N 0.36 mmol/mol), as well as low Sr/Ca ratios (b1.03 mmol/mol), and Na/Ca ratios (b4.79 mmol/mol) have been removed from the studied

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Fig. 4. Lithology and stratigraphy of the sections studied (Pj110 and Pj139/140) at Działoszyn in the Polish Jura Chain (after Matyja and Wierzbowski, 1997).

dataset (Table S1). This applies to δ values and elemental ratios of 13 belemnite samples previously reported by Wierzbowski (2002, 2004) and to 10 new belemnite samples. Because of dull cathodoluminescence and light colors, Submediterranean Upper Oxfordian belemnite rostra collected previously from sections at Działoszyn, are found to be diagenetically altered (Wierzbowski, 2002). Despite the alteration of oxygen isotope ratios the diagenesis had probably not affected δ13C values of these samples, as they show a compact carbon isotope temporal trend consistent with brachiopod data (Wierzbowski, 2002). Most of the Submediterranean Upper Oxfordian belemnite samples studied by Wierzbowski (2002) show decreased Sr and Na concentrations

(samples 14, 6, 15, 45, 52) and have been eliminated from the currently studied dataset. Three Submediterranean Upper Oxfordian belemnite samples (10, 54, and 77) studied by Wierzbowski (2002) have element concentrations distinctive of well-preserved fossils; their δ18O values have been, however, removed from the studied dataset to be in line with the previous interpretation of Wierzbowski (2002). Many brachiopod shells studied show selective silicification (Fig. 7). Silicification resulted in partial replacement of shell carbonate by authigenic silica during early marine diagenesis; non-silicified shell portions, even at the contact with silicified areas, still preserve the original shell microstructure (cf. Świerczewska, 1990; Daley and Boyd, 1996). As

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A

B

Fig. 5. Cathodoluminescence photomicrographs. A. Non-luminescent belemnite rostrum with luminescent apical line area and partial luminescent of outer rim. Sample 389, Hypselum Zone, Submediterranean Upper Oxfordian, Katarowa Góra section (Polish Jura Chain). B. Non-luminescent brachiopod shell. Sample 374, boundary of Desmoides and Polygyratus subzones, Platynota Zone, Submediterranean Lower Kimmeridgian, Czepurka section (Polish Jura Chain).

small silicified areas within brachiopod shells were difficult to remove in many cases, the entire shells were analyzed. Different cut-off limits of element concentrations in well-preserved brachiopod shells are accepted by various authors. Well-preserved brachiopod samples are defined, in the present study, by low Mn/Ca (b 0.18) and Fe/Ca ratios (b0.54) and higher Sr/Ca ratios (N 0.39), which are equivalents of concentrations of Mn b 100 ppm, Fe b 300 ppm, and Sr N 340 ppm in pure calcite (cf. Morrison and Brand, 1986; Popp et al., 1986; Joachimski et al., 2004; van Geldern et al., 2006; Armendáriz et al., 2008; see Table S2). Relatively low limit of the Sr/Ca ratio accepted for wellpreserved brachiopod shells is linked to a low seawater Sr/Ca ratio at the Middle–Late Jurassic transition, which is postulated to have been 40–50% lower than the present one (cf. Holmden and Hudson, 2003; Ullmann et al., 2013; Ullmann and Korte, 2015). Contrary to the trends observed in the belemnite samples, the correlation between Na/Ca and Sr/Ca ratios of brachiopod shells is weak (Fig. 6B). Sodium is, therefore, disregarded as a diagenetic tracer of brachiopod shells studied. Isotope values and elemental ratios of brachiopod samples characterized by higher, than accepted, Fe/Ca and Mn/Ca ratios and lower Sr/Ca ratios, including all terebratulids, have been removed from the studied dataset (Table S2). This applies to δ values and elemental ratios of 8 brachiopod

Fig. 6. Na/Ca versus Sr/Ca ratios of studied fossils. A. The ratios in belemnite rostra studied. Strong positive correlation (R2 = 0.38) between Na/Ca and Sr/Ca ratios most likely results from diagenetic alteration. Cut-off limits of Na/Ca and Sr/Ca ratios accepted for the selection of well-preserved belemnite samples are shown. B. The ratios in brachiopod shells studied. Correlation (R2 = 0.22) between brachiopod Na/Ca and Sr/Ca ratios is statistically significant but results from high Na/Ca and Sr/Ca ratios of two samples.

samples previously reported by Wierzbowski (2002, 2004) and to 2 new brachiopod samples. δ18O values of carbonate rocks are affected by equilibration with meteoric or pore waters at much lower water/rock ratios than their δ13C values (Banner and Hanson, 1990). Significant positive correlation

Fig. 7. Partial silicification and borings in a rhynchonellid brachiopod shell. Polarized light. Sample 372, Hypselum Zone, Submediterranean Upper Oxfordian, Katarowa Góra section (Polish Jura Chain).

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between δ18O and δ13C values of carbonate rock points, therefore, to the open system alteration in the presence of fluids different from seawater (Jenkyns and Clayton, 1986; Marshall, 1992; Huck et al., 2013; Jach et al., 2014). δ18O and δ13C values of bulk carbonates from the Polish Jura Chain are not correlated (Fig. 8). This suggests that the rocks preserve their original or early diagenetic carbon isotope composition. 5. Results 5.1. Oxygen isotope composition of belemnite rostra and brachiopod shells δ18O values of coeval belemnite rostra and brachiopod shells (current data supplemented with data of Wierzbowski 2002, 2004 and Wierzbowski et al., 2009) are similar to each other (Fig. 9, Tables S1 and S2). Coeval samples collected from different areas have comparable δ18O values except for the Hauffianum Subzone of the Bimammatum Zone and the Planula Subzone of the Planula Zone of the Submediterranean Upper Oxfordian, where an offset of ca. 0.4‰ between mean δ18O values of fossils from the Swabian Alb and both the Polish Jura Chain and Kujawy is observed. Contemporary data from the Upper Callovian–Middle Oxfordian (Athleta–mid-Transversarium zones) are characterized by a scatter of up to 1‰, with a few outliers, and oscillate around 0‰ except for lower values noted in the Henrici Subzone of the Lamberti Zone (mean of 0.3‰) and the upper part (= paucicostatum Horizon) of the Lamberti Subzone of the Lamberti Zone (mean of 0.7‰). Submediterranean Upper Oxfordian δ18O values are significantly scattered (up to 2‰, with two outliers) and show a gradual decrease (Fig. 9). Mean δ18O values decrease to ca. − 0.4‰ in the Bifurcatus Zone and ca. − 0.6‰ in the Hypselum Zone and the Bimammatum Subzone of the Bimammatum Zone. In the Hauffianum Subzone of the Bimmamatum Zone and the Planula Subzone of the Planula Zone a mean δ18O value of fossils from the Polish Jura Chain and Kujawy decreases further to ca. −0.9‰, whereas belemnite rostra from Swabian Alb show a higher mean δ18O value of ca. −0.5‰. Three lowermost Submediterranean Kimmeridgian brachiopod data from the Polish Jura Chain, which are derived from the boundary of the Polygyratus and Desmoides subzones of the Platynota Zone, have a mean δ18O value of −1.2‰. 5.2. Carbon isotope composition of belemnite rostra and brachiopod shells δ13C values of coeval belemnite rostra from the Polish Jura Chain, Kujawy and the Swabian Alb are similar to each other (Fig. 10, Table S1). Coeval belemnite δ13C values (current data supplemented

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with data of Wierzbowski 2002, 2004 and Wierzbowski et al., 2009) are characterized by a scatter of up to 1.5‰, with a few outliers, and show a well-defined trend of temporal variations (Fig. 10). Highest belemnite δ13C values (between 0.9 and 2.6‰, with three outliers) are observed in the Upper Callovian (in the Athleta and Lamberti zones) and in the Middle Oxfordian (in the upper part of the Plicatilis Zone and the lower part of the Transversarium Zone). Lower belemnite δ13C values (between − 0.1 and 1.2‰, with one outlier) are measured from the Lower Oxfordian (Cordatum Zone) and the lowermost Middle Oxfordian (the lower part of the Plicatilis Zone) between the Upper Callovian and the Middle Oxfordian carbon isotope maxima. Belemnite δ13C values also decrease after the Middle Oxfordian maximum, starting from the upper part of the Transversarium Zone. Lowest belemnite δ13C values (between −0.9 and 0.1‰, with two outliers) are measured from the lower part of the Submediterranean Upper Oxfordian (the upper part of the Bifurcatus Zone and the Hypselum Zone). A slight increase in belemnite δ13C values (coeval values between −0.2 and 0.7‰, with one outlier) is observed in the upper part of the Submediterranean Upper Oxfordian (in the Bimammatum Zone and lower part of the Planula Zone). Only one δ13C value (of 4.3‰) of a well-preserved brachiopod was measured from the Lower Oxfordian (Cordatum Zone) and two (δ13C values of 3.6 and 4.0‰) from the upper part of the Middle Oxfordian (the upper part of the Transversarium Zone, Fig. 10, Table S2). Numerous brachiopod δ13C values from the Submediterranean Upper Oxfordian (the Hypselum, Bimammatum and Planula zones) range from 2.6 to 3.5‰, with one outlier. Three lowermost Submediterranean Kimmeridgian (Platynota Zone) brachiopod δ13C values range from 3.3 to 3.6‰. A constant offset of 2.5–3.5‰ is observed between belemnite and brachiopod δ13C values (Fig. 10, Tables S1 and S2). 5.3. Mg/Ca and Sr/Ca ratios of belemnite rostra and brachiopod shells Mg/Ca ratios of well-preserved belemnite rostra studied (current data supplemented with data of Wierzbowski 2004, and Wierzbowski et al., 2009) vary between 6.7 and 20.4 mmol/mol (Fig. 11A, Table S1). Sr/Ca ratios of the belemnite rostra vary between 1.0 and 2.2 mmol/mol (Fig. 12A, Table S1). Although Mg/Ca ratios of belemnite rostra are correlated with δ18O values, the correlation is weak and the data are scattered (Fig. 11A). No correlation between Sr/Ca ratios of belemnite rostra and δ18O values is observed (Fig. 12A). Mg/Ca ratios of well-preserved brachiopod shells studied vary between 1.2 and 3.7 mmol/mol (Fig. 11B, Table S2). Statistically significant correlation between brachiopod Mg/Ca ratios and δ18O values is observed; however, it results mostly from the high Mg/Ca ratios of one sample (57) characterized by low δ18O value (Fig. 11B). Sr/Ca ratios of the brachiopod shells vary between 0.40 and 0.52 mmol/mol (Fig. 12B, Table S2). Sr/Ca ratios and δ18O values of brachiopods studied do not correlate with each other. 5.4. Carbon isotope composition of bulk carbonates

Fig. 8. δ18O versus δ13C values of bulk carbonates studied from the Polish Jura Chain. Correlation (R2 = 0.01) between δ18O and δ13C values is statistically insignificant.

δ13C values of coeval micritic and marly limestone from the Polish Jura Chain are characterized by a significant scatter of 0.5 to 1.5‰ but show a clear trend of temporal variations (Fig. 10). Positive carbon isotope excursions are observed at the Callovian–Oxfordian boundary in the uppermost part of the Lamberti Subzone of the Lamberti Zone and the Scarburgense Subzone of the Mariae Zone (δ13C values between 2.0 and 3.2‰), as well as in the Middle Oxfordian — in the Arkelli Subzone of the Plicatilis Zone, the Transversarium Zone, and the lower part of the Bifurcatus Zone (δ13C values between 2.4 and 3.2‰). The Callovian–Oxfordian boundary maximum is preceded by lower and scattered δ13C values (− 0.1 to 2.1‰) in the Upper Callovian (the Athleta Zone and the lower part of the Lamberti Zone) and is followed by an interval with lower bulk-carbonate δ13C values in the Cordatum Zone of the Lower Oxfordian (δ13C values between 0.5 and 2.2‰) before

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Fig. 9. Stratigraphy, δ18O values and paleotemperatures calculated from δ18O values of well-preserved belemnite rostra and brachiopod shells from central European basins. Black diamond — newly collected belemnite rostra, open diamonds — belemnite data presented by Wierzbowski et al. (2009), gray diamond — belemnite data presented by Wierzbowski (2002). Crosses — newly collected brachiopod shells, shaded crosses — brachiopod data presented by Wierzbowski (2002). Area of origin: no signs — Polish Jura Chain; K — Kujawy, S — Swabian Alb. Trend lines (solid and dashed) represent the 5-point running averages for belemnite and brachiopod data, respectively.

the mid-Oxfordian maximum. Bulk-carbonate δ13C values decrease slightly after the Middle Oxfordian but remain relatively high (between 1.6 and 2.8‰ with one outlier) in the rest of the Submediterranean

Upper Oxfordian and the lowest Submediterranean Kimmeridgian (starting from the uppermost part of the Bifurcatus Zone till the lower part of the Platynota Zone).

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Fig. 10. Stratigraphy and δ13C values of well-preserved belemnite rostra and brachiopod shells as well as bulk carbonates from central European basins. Symbols for belemnite and brachiopod data as in Fig. 9. Red circles — bulk carbonates from the Polish Jura Chain. Trend lines (solid, dashed and dotted red) represent the 5-point running averages for belemnite, brachiopod and bulk carbonate data, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

6. Discussion 6.1. Oxygen isotope composition of fossils and paleotemperatures Modern brachiopods, including rhynchonellids, precipitate oxygen isotopes in the secondary shell layer in general isotopic equilibrium with ambient seawater (Carpenter and Lohmann, 1995; James et al. 1997; Brand et al. 2003; Parkinson et al. 2005). Belemnites are considered, similarly to other mollusks, to have secreted calcium carbonate in their skeletons in oxygen isotope equilibrium with seawater (e.g. Wierzbowski, 2002; Rosales et al., 2004; Wierzbowski and

Joachimski, 2007; Price and Page, 2008; Nunn et al., 2009; Price and Rogov, 2009; Wierzbowski and Rogov, 2011; Alberti et al., 2012a). Comparable δ18O values of coeval brachiopod shells and belemnite rostra from the Polish Jura Chain may be used as an evidence for a necto-benthic habitat of mesohibolitid belemnites studied (Fig. 9). This is consistent with the interpretations of Anderson et al. (1994), Wierzbowski (2002), Wierzbowski and Joachimski (2007), Price and Teece (2010), Wierzbowski and Rogov (2011), Wierzbowski et al. (2013). One can assume, owing to the open marine settings (see Fig. 1) and a few hundred meter water depth, that δ18O values of bottom waters of

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A

A

B

B

Fig. 11. δ18O values versus Mg/Ca ratios of studied fossils. A. The data for belemnite rostra studied. Correlation (R2 = 0.14) between belemnite δ18O values and Mg/Ca ratios is statistically significant. B. The data for brachiopod shells studied. Negative correlation (R2 = 0.32) between brachiopod δ18O values and Mg/Ca ratios is statistically significant but results mostly from high Mg/Ca ratios of one sample characterized by low δ18O value.

the Polish Jura Chain, Kujawy and Swabian Alb basins did not change noticeably in the course of the Late Callovian–Early Kimmeridgian. The δ18O values of shells of benthic brachiopods and of rostra of nectobenthic belemnites are, therefore, regarded as a valuable proxy for temporal variations in seawater temperature (see also Wierzbowski, 2002, 2004, Wierzbowski and Joachimski, 2007, Wierzbowski and Rogov, 2011). Paleotemperatures were calculated from δ18O values of wellpreserved fossils assuming normal marine salinity and the commonly accepted δ18O value of Jurassic seawater of −1‰ SMOW as distinctive of an ice-free world (Shackleton and Kennett, 1975). Relatively constant temperatures (ca. 12 °C) are calculated for the Late Callovian–Middle Oxfordian period in the Polish Jura Chain and Kujawy basins. Temperatures decrease, however, in the Henrici Subchron of the Lamberti Chron and the youngest part (the paucicostatum horizon) of the Lamberti Subchron of the Lamberti Chron, and increase in the Elizabethae Subchron of the Transversarium Chron (Fig. 9). The data point to the presence of fairly constant and cool paleoenvironmental conditions during a major part of the Late Callovian–Middle Oxfordian in these basins. A decrease in temperature to ca. 9 °C at the Callovian– Oxfordian transition (the paucicostatum horizon) in the Polish Jura Chain is, however, noticeable, and was not reported earlier from this area (cf. Wierzbowski, 2002, 2004; Wierzbowski et al. 2009). The decrease may be correlated with short-term cooling episodes reported from the Scarburgense Subchron of the Mariae Chron in the Isle of Skye in Scotland (Nunn et al. 2009; Fig. 13) and from the Mariae and/ or Cordatum Chrons in the North Sea and the Paris Basin basins (Abbink et al. 2001; Tremolada et al., 2006; Brigaud et al., 2008; Pellenard et al., 2014a, 2014b). Cooler sea surface temperatures at the Middle–Late

Fig. 12. δ18O values versus Sr/Ca ratios of studied fossils. A. The data for belemnite rostra studied. Correlation (R2 = 0.01) between belemnite δ18O values and Sr/Ca ratios is statistically insignificant. B. The data for brachiopod shells studied. Correlation (R2 = 0.05) between δ18O values and Sr/Ca ratios is statistically insignificant.

Jurassic transition are also reported from high latitudes of the Southern Ocean (Jenkyns et al., 2012). No cooling is recorded at the same time in Dorset (England), in the Russian Platform, North Siberia, and in the Kachchh Basin of India (Kaplan et al., 1979; Price and Page, 2008; Page et al., 2009; Wierzbowski and Rogov, 2011; Alberti et al., 2012a,b; Wierzbowski et al., 2013; Fig. 13). Although a “cold snap”, including glaciation, is sometimes postulated to have occurred at the Callovian– Oxfordian transition (Dromart et al., 2003a, 2003b; Donnadieu et al., 2011), it seems probable that the short-term cooling from the Polish Jura Chain, Isle of Skye, North Sea and the Paris Basin were regional and caused by the incursion of cold bottom waters as a result of a major sea-level rise and the opening of seaways (cf. Wierzbowski et al., 2009, 2013; Chumakov et al., 2014). The acceleration of current activity is observed in European basins at the Callovian–Oxfordian transition (Dembicz and Praszkier, 2003a; Rais et al., 2007) and the warming is observed at the same time in the Kachchh Basin of India and the North Siberia (Kaplan et al., 1979; Alberti et al., 2012a, 2012b; Chumakov et al., 2014). The latest Callovian warming of the Boreal Sea is well-documented based on the disappearance of glendonites, icerafted debris, the occurrences of organodetritic and oolite limestones there, and on the diversification of the Arctic bivalve and macrofloral assemblages (cf. Kaplan, 1978; Kaplan et al., 1979; Vakhrameev, 1991; Rogov and Zakharov, 2010; Wierzbowski and Rogov, 2011; Chumakov et al., 2014). It is worth noting that no glacial deposits, or indicators of near-freezing temperatures are reported from both the Arctic and the Antarctic at the Middle–Late Jurassic boundary (Jenkyns et al., 2012; Chumakov et al., 2014) and that most of the European isotope datasets show rather the existence of a prolonged cooler period during the whole Late Callovian–Middle Oxfordian (cf. Dromart et al., 2003a;

H. Wierzbowski / Palaeogeography, Palaeoclimatology, Palaeoecology 440 (2015) 506–523 Fig. 13. Comparison of the uppermost Callovian–lowermost Kimmeridgian δ18O records obtained from marine calcareous shells and phosphate teeth of various European basins. Data from Wierzbowski (2002, 2004), Lécuyer et al. (2003), Wierzbowski et al. (2006, 2009, 2013), Nunn et al. (2009), Wierzbowski and Rogov (2011), and this study. 517

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Lécuyer et al., 2003; Wierzbowski et al., 2009; 2013; Nunn et al., 2009 and the present data; see also Fig. 13). This phenomenon may, however, be linked only partly to a colder climate and partly to the presence of cold bottom waters during the deepening phase of marine basins (cf. Wierzbowski et al. 2013). An increase in seawater temperature is observed in the basins studied starting from the Elizabethae Subchron of the Transversarium Chron of the uppermost Middle Oxfordian and it continues through the Submediterranean Late Oxfordian (in the Bifurcatus, Hypselum, Bimammatum and Planula chrones; Fig. 9). The calculated temperatures become increasingly more scattered in the Submediterranean Late Oxfordian. Temperatures calculated from brachiopod and belemnite δ18O values from the Polish Jura Chain and Kujawy average 13.5 °C in the Bifurcatus Chron and 14 °C in the Hypselum Chron and Bimammatum Subchron of the Bimammatum Chron. Temperatures of ca. 15.5 and ca. 13.5°C are calculated for the period comprising Hauffianum Subchron of the Bimmamatum Chron and the Planula Subchron of the Planula Chron in both the Polish Jura Chain and Kujawy basins as well as in the Swabian Alb, respectively (Fig. 9). Temperature of ca. 16.5°C is calculated from brachiopod δ18O values for the Platynota Chron of the earliest Submediterranean Kimmeridgian in the Polish Jura Chain. The temperature rise and the more scattered pattern of the results may be caused by the shallowing of the Polish Jura Chain and Kujawy basins during the Submediterranean Late Oxfordian–earliest Kimmeridgian. Submediterranean Late Oxfordian temperatures (13.5 °C) calculated for the Swabian Alb basin, which shows no signs of shallowing, are, however, higher than Middle Oxfordian ones calculated for other basins. This may show the occurrence of the Late Oxfordian warming, in the Submediterranean stage scheme, in all the basins studied. The Submediterranean Late Oxfordian warming is an equivalent of the Late Oxfordian–Early Kimmeridgian warming in the Boreal basins (cf. Fig. 9). A coeval Late Oxfordian(–Early Kimmeridgian) warming is reported from Scotland (Nunn et al., 2009; Fig. 13), Western Europe (Dromart et al., 2003a; Lécuyer et al., 2003; Fig. 13), the Russian Platform (Wierzbowski et al., 2013; Fig. 13), the North Siberia (Žak et al., 2011) and India (Alberti et al., 2012a, 2012b). The warming is also observed in the Paris Basin, albeit it is preceded by a cooling in the Bifurcatus Chron and the time-equivalent of the Hypselum Chron (Brigaud et al., 2008). A stepwise Boreal latest Oxfordian–Early Kimmeridgian warming is likewise postulated, based on sporomorph data from the North Sea (Abbink et al., 2001). The Late Oxfordian(–Early Kimmeridgian) warming is thus regarded as a global phenomenon, although its magnitude may be overestimated in some basins due to their shallowing and increasing freshwater runoff (cf. Wierzbowski et al., 2013).

6.2. Carbon isotope composition of fossils The secondary shell layer of modern brachiopods is reported to be precipitated close to carbon isotope equilibrium with ambient seawater or to be slightly depleted in 13C relative to the equilibrium (cf. Carpenter and Lohmann, 1995; Parkinson et al. 2005, Yamamoto et al., 2010). A constant offset between belemnites and brachiopod δ13C values with belemnite rostra being depleted in 13C is interpreted by Wierzbowski (2002) to be the result of a vital effect exerted by mesohibolitid belemnites. The current data derived from fossils, which were carefully screened for the state of preservation, substantiate the presence of the offset of 2.5–3.5‰ (Fig. 10). Offsets between δ13C values of coeval Jurassic belemnites and brachiopods or oysters are reported from other areas (cf. Wierzbowski and Joachimski, 2007; Korte and Hesselbo, 2008; Price and Teece, 2010; Alberti et al., 2012a; Price and Harwood, 2012). This confirms that the carbon isotope composition of belemnite calcite is not in equilibrium with the seawater carbon isotope pool. The vital effect likely results from the utilization of light metabolic carbon during precipitation of the belemnite skeleton (cf. McConnaughey, 1989; McConnaughey et al., 1997; Wierzbowski, 2002).

Because of the presence of the constant δ13C offset between belemnites and brachiopods or bivalves, homogenized mesohibolitid belemnite rostra are thought to be a reliable indicator of temporal changes in the isotope composition of marine carbonate carbon and the secular evolution of the composition of dissolved inorganic carbon (DIC) in seawater (Wierzbowski, 2002, 2004; Wierzbowski and Joachimski 2007, Wierzbowski et al., 2009; Wierzbowski and Rogov, 2011). Presented belemnite and brachiopod temporal δ13C trends have a similar shape although the latter is well-defined in the Submediterranean Upper Oxfordian only (Fig. 10). Coeval belemnite data from the Polish Jura Chain, Kujawy and the Swabian Alb are similar to each other, which indicate that the isotope composition of DIC was comparable in all studied basins (Fig. 10). The belemnite δ13C record of the peri-Tethyan basins studied is characterized by the presence of two positive carbon excursions. They occur in the Upper Callovian — in the Athleta and Lamberti zones (mean δ13C values up to 2‰) and in the Middle Oxfordian — in the upper part of the Plicatilis Zone and the lower part of the Transversarium Zone (mean δ13C values up to 1.5‰; Fig. 10). The excursions are divided by a decrease in belemnite δ13C values (to ca. 0.5‰) in the Cordatum Zone of the Lower Oxfordian and the lower part of the Plicatilis Zone of the Middle Oxfordian. The belemnite carbon isotope record is consistent with previously published belemnite δ13C data derived from the Polish Jura Chain (cf. Wierzbowski, 2002, 2004; Wierzbowski et al., 2009). The Upper Callovian–Lower Oxfordian belemnite record of the periTethyan basins differs, however, from records of Boreal basins (the Isle of Skye in Scotland and the Russian Platform) and terrestrial organic matter, all of which show a pronounced and long-lasting positive carbon isotope excursion comprising the entire Upper Callovian–Middle Oxfordian interval (Fig. 14; Nunn et al., 2009; Wierzbowski et al., 2013). This is interpreted to be the result of differentiation of the marine carbonate carbon isotope pool due to the local factors that affected both the absolute δ13C values and the patterns of secular trends (Wierzbowski et al., 2013). The carbon isotope record of Western peri-Tethyan basins is suggested to be influenced by the upwelling, which may have carried waters enriched in the 12C isotope during the Early Oxfordian and the earliest Middle Oxfordian (Wierzbowski, 2002; Wierzbowski et al. 2013). The appearance of a mixed cold- and warm-water radiolarian assemblage in the Polish Jura Chain as well as the presence of a diversified (Sub)mediterranean–Boreal ammonite fauna in central European basins at that time confirms intensified seawater circulation (Matyja and Wierzbowski, 1995; Smoleń, 1998, 2002). The positive carbon isotope excursion(s) in the Upper Callovian–Middle Oxfordian are linked to the global sea-level rise that resulted in the enhanced organic matter burial and diminished weathering carbon flux from land areas (Wierzbowski et al., 2009, 2013). Current data corroborate the timing of belemnite δ13C trends after the Middle Oxfordian and the presence of low δ13C values in the Submediterranean Upper Oxfordian (Bifurcatus–Planula zones) in the peri-Tethyan basins (cf. Wierzbowski, 2002, 2004; Fig. 10). The negative shift may be correlated with belemnite δ13C trends from Scotland and the Russian Platform (Fig. 14; cf. Nunn et al., 2009; Wierzbowski et al., 2013). The decrease in belemnite δ13C values after the Middle Oxfordian excursion may result from the well-mixed state of bottom and surface water masses or the occurrence of another upwelling. Lowest δ13C values (below 0‰) are measured from the uppermost part of Bifurcatus Zone and the Hypselum Zone (Fig. 10). The data may show the high level of nutrients and increased productivity of seawater in the basins studied at that time. This interval is characterized by a short-term migration event of Boreal Amoeboceras ammonites into the Submediterranean ammonite province and mass-occurrences of small necto-pelagic haploceratid ammonites and radiolarians, which might have thrived in eutrophic waters (cf. Matyja and Wierzbowski, 2000; Smoleń et al., 2014; Wierzbowski and Matyja, 2014). A slight increase in belemnite δ13C values (mean values of 0 to 0.5‰) in the upper part

H. Wierzbowski / Palaeogeography, Palaeoclimatology, Palaeoecology 440 (2015) 506–523 Fig. 14. Comparison of the uppermost Callovian–lowermost Kimmeridgian δ13C records obtained from marine calcareous shells and terrestrial organic matter from deposits of various European basins. Data from Wierzbowski (2002, 2004), Pearce et al. (2005), Nunn et al. (2009), Wierzbowski et al. (2006, 2009, 2013), Wierzbowski and Rogov (2011), and this study. 519

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of the Submediterranean Upper Oxfordian (Bimammatum–Planula zones) can be correlated with similar increases observed in carbon isotope records of Scotland and the Russian Platform (Fig. 14; cf. Nunn et al., 2009; Wierzbowski et al., 2013).

6.3. Mg/Ca and Sr/Ca ratios of fossils Mg/Ca ratios of belemnite rostra are weakly correlated with δ18O values and Sr/Ca ratios are not correlated with the values at all (Figs. 11A and 12A), therefore, both elemental ratios are disregarded as reliable paleotemperature proxies. In addition, Mg/Ca and Sr/Ca ratios of mesohibolitid belemnites are found, by other authors, not to be temperature dependent, or they, sometimes, show a weak temperature dependence only (McArthur et al., 2004, 2007, Bodin et al., 2009; Wierzbowski and Joachimski, 2009; Wierzbowski and Rogov, 2011). The mesohibolitid rostra have higher Mg contents than the rostra of other co-occurring belemnites, which points to increased partitioning of magnesium to mesohibolitid calcite (McArthur et al., 2004, 2007; Wierzbowski and Rogov, 2011). Weak correlation between Mg/Ca ratios of the brachiopod shells studied and their δ18O values as well as the lack of the correlation between brachiopod Sr/Ca ratios and δ18O values (Figs. 11B and 12B) do not allow the use of these parameters as reliable paleotemperature proxies. Relatively low Mg/Ca ratios of brachiopod shells studied and low Sr/Ca ratios of all studied fossils may, however, point to low Mg/Ca and Sr/Ca ratios of seawater at the Middle–Late Jurassic transition (cf. Stanley, 2006; Ullmann et al., 2013).

6.4. Carbon isotope composition of bulk carbonates δ13C values of bulk carbonates are broadly similar to δ13C values of belemnite rostra in the Upper Callovian. Bulk carbonate δ13C values become increasingly more positive, compared to the values of belemnite rostra, during the Oxfordian (Figs. 10 and 15). This results in a different shape of the temporal trends of bulk carbonates and belemnite δ13C values. The former is characterized by the existence of a short-term positive maximum at the Callovian–Oxfordian boundary, and a long-term maximum, which starts in the upper part of the Plicatilis Zone of the Middle Oxfordian, similar to the belemnite δ13C maximum, but continuing further

Fig. 15. Diagram showing chronostratigraphic zonal scale of the Oxfordian versus a difference between bulk carbonate and belemnite δ13C values. The positive correlation between decreasing zonal age of the Submediterranean Oxfordian and the Δδ13Cbulk carbonate–belem2 nite is statistically significant (R = 0.86). Variations in thickness of inter-biohermal limestones in the Oxfordian of the Polish Jura Chain are given on the right side of the diagram (after Matyja and Wierzbowski, 1994b).

through the rest of the Middle Oxfordian and the Submediterranean Upper Oxfordian (Transversarium–Planula zones). Since the belemnite δ13C trend is considered to reflect temporal changes in the isotope composition of DIC in seawater one can assume that the bulk carbonate δ13C values are affected by some factors such as early submarine cementation of rocks by pore waters enriched in carbonate ions derived from the decay of organic matter or a temporal change in the composition of carbonate mud delivered to the Polish Jura Chain basin (cf. Wierzbowski, 2003). Calcareous nanoplankton is shown to be an important component of Lower Oxfordian sediments in the Polish Jura Chain (Kędzierski 2001). Submediterranean Upper Oxfordian open marine micritic and peloidal limestones in southcentral Poland are, however, interpreted to be a product of in-situ calcification by cyanobacterial mats (Kaźmierczak et al., 1996). Cyanobacteria played a leading role in the calcification of Oxfordian bioherms, being a source of carbonate detritus and mud, which were delivered to interbiohermal basins (cf. Matyszkeiwicz and Felisiak, 1992; Matyja and Wierzbowski, 1994b). A strong stepwise increase in the carbonate sedimentation rate is observed in the Polish Jura Chain basin in the course of the Oxfordian (Fig. 15; Matyja and Wierzbowski, 1994b). During the latest Submediterranean Oxfordian interbiohermal basins of the Polish Jura Chain have been filled by a large amount of foreslope deposits of the approaching carbonate platform (Matyja and Wierzbowski, 1994b) but such material may have been delivered earlier to the basin. Isotope fractionation of carbon in calcite during precipitation by cyanobacteria in open marine settings is not known. However, an increase in the carbonate production rate and shallowing of the Polish Jura Chain basin may suggest the increasing rate of original aragonite grains in Middle Oxfordian–Submediterranean Upper Oxfordian sediments of this area. As shallow water aragonites are enriched in the 13C isotope due to the effect of subsurface biological pumping and a higher carbon isotope enrichment factor than calcite (cf. Berger and Vincent, 1986; Romanek et al., 1992; Swart and Eberli, 2005; Föllmi et al., 2006), Middle Oxfordian–Submediterranean Upper Oxfordian carbonates may be characterized by more and more elevated δ13C values compared to the isotope composition of DIC. The same effect may be related to the progressive dilution of organic matter by calcium carbonate, with increasing rate of carbonate production, as the amount of carbonate ions derived from the decay of organic matter and having low δ13C values might have decreased in pore waters during the Oxfordian. Early marine diagenesis of the carbonate sediments might, therefore, have had a gradually lesser effect on bulk carbonates resulting in higher δ13C values of Middle–Submediterranean Upper Oxfordian deposits. As the Middle–Submediterranean Late Oxfordian acceleration of carbonate accumulation was a common phenomenon observed in various Tethyan and peri-Tethyan basins (cf. Bartolini et al., 1996; Morettini et al., 2002; Dromart et al., 2003a; Cecca et al., 2005) one can consider the general effect of increasing carbonate production on the carbon isotope record of bulk carbonates. If an increasing rate of aragonite precipitation and dilution of organic matter by carbonate mud had occurred simultaneously in many basins, the same isotope changes may be recorded regionally by the elevation of Submediterranean Upper Oxfordian and even Submediterranean Early Kimmeridgian bulk-carbonate δ13C values. In fact, some published bulk carbonate δ13C curves from the Western Tethys show the existence of a prolonged positive carbon isotope excursion encompassing the whole Middle Oxfordian– Submediterranean Early Kimmeridgian interval (cf. Padden et al., 2002; Jach et al., 2014). This may be a regional feature of the Tethyan bulk carbonate isotope record, which is caused by a change in the carbonate production rate and not by original variations in the isotope composition of seawater DIC. The bulk carbonate data from the Polish Jura Chain confirm, however, the presence of a negative carbon isotope shift before the Middle Oxfordian δ13C excursion. This is consistent with the published bulk carbonate isotope records obtained for the Tethyan domain (cf.

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Bartolini et al., 1996; Dromart et al., 2003a; Louise-Schmid et al., 2007; Rais et al., 2007). 7. Conclusions The study allowed the verification and the refinement of previously published Upper-Callovian–Oxfordian belemnite and brachiopod oxygen isotope records from the peri-Tethyan basins of central Europe. Belemnite isotope data from the Polish Jura Chain basin show relatively constant and low temperatures (ca. 12 °C) of bottom waters during the major part of the Late Callovian–Middle Oxfordian, except for a short-term cooling (to ca. 9 °C) at the Callovian–Oxfordian transition. The cooling is linked to the incursion of a cold bottom current during a sea-level rise. A significant increase in temperature of bottom water (by ca. 4 °C), is noted in all the basins studied during the Submediterranean Late Oxfordian (i.e. an equivalent of the Boreal Late Oxfordian–Early Kimmeridgian). It is linked to both the shallowing of the basins and global climate warming. Belemnite and brachiopod Mg/Ca and Sr/Ca ratios are disregarded as paleotemperature proxies because of the weak correlation with δ18O values. The occurrence of a metabolic effect in mesohibolitid belemnite calcite is indicated by the offset of 2.5–3.5‰ between the δ13C values of coeval belemnite rostra and brachiopod shells. Belemnite carbon isotope record is, nevertheless, considered to be a reliable proxy for isotope variations in the marine carbon pool. The data show the presence of two positive carbon isotope excursions in the Upper Callovian and the Middle Oxfordian (belemnite δ13C values increase during these excursions to ca. 2‰ and ca. 1.5‰, respectively). Lower belemnite δ13C values are observed in the Lower Oxfordian and in the lower part of the Submediterranean Upper Oxfordian (belemnite δ13C values decrease in these intervals to ca. 0.5‰ and ca. 0‰, respectively). The bulk carbonate carbon isotope record from the Polish Jura Chain differs partially from the record of coeval carbonate fossils. Bulk carbonate carbon isotope data show the presence of a short-term positive excursion at the Callovian–Oxfordian boundary and the prolonged positive excursion in the Middle–Submediterranean Upper Oxfordian. The long time-span of the latter excursion is suggested to be a consequence of a significant increase in the carbonate production rate and a change in the origin of carbonate mud in the Polish Jura Chain basin. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.palaeo.2015.09.020. Acknowledgments The study was supported by the Polish National Science Centre (grant no. 2012/05/B/ST10/02121). I am indebted to K. Dembicz, M. Giżejewska and A. Wierzbowski for supplying archival samples from their collections from the Polish Jura Chain. C. Ullmann and an anonymous reviewer are thanked for insightful reviews and suggested improvements. References Abbink, O., Targarona, J., Brinkhuis, H., Visscher, H., 2001. Late Jurassic to earliest Cretaceous palaeoclimatic evolution of southern North Sea. Glob. Planet. Chang. 30, 231–256. Alberti, M., Fürsich, F.T., Pandey, D.K., 2012a. The Oxfordian stable isotope record (δ18O, δ13C) of belemnites, brachiopods, and oysters from the Kachchh Basin (western India) and its potential for palaeoecologic, palaeoclimatic, and palaeogeographic reconstructions. Palaeogeogr. Palaeoclimatol. Palaeoecol. 344–345, 49–68. http://dx. doi.org/10.1016/j.palaeo.2012.05.018. Alberti, M., Fürsich, F.T., Pandey, D.K., Ramkumar, M., 2012b. Stable isotope analyses of belemnites from the Kachchh Basin, western India: paleoclimatic implications for the Middle to Late Jurassic transition. Facies 58, 261–278. http://dx.doi.org/10.1007/ s10347-011-0278-9. Anderson, T.F., Arthur, M.A., 1983. Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems. In: Arthur, M.A., Anderson, T.F., Kaplan, I.R., Veizer, J., Land, L.S. (Eds.), Stable Isotopes in Sedimentary Geology: SEPM Short Course No. 10, pp. 1-1–1-151.

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