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New microfossil and magnetostratigraphical data as well as geochemical and clay mineral weathering indices are documented from the uppermost Jurassic Owadów–Brzezinki palaeontological site in central Poland. The newly discovered chitinoidellid assemblage of the lowermost part of the section and the previously documented assemblage from the middle part of the section are assigned, respectively, to the uppermost Dobeni and Boneti Subzones of the Chitinoidellidae Zone. The same part of the succession is correlated to the magnetosubzone M20n.2n. The new data allow refinement of the Tithonian stratigraphical scheme including an assignment of the upper part of the Boreal Zarajskites Subzone of the Scythicus (Panderi) ammonite Zone to the Upper Tithonian and its correlation with the lowermost part of Tethyan Microcanthum ammonite Zone and the lower portion of the M20n.2n magnetosubzone. The data show that the Fittoni/Albani ammonite zone boundary should likely be placed within the Boneti Subzone. The geochemical data show decreasing chemical weathering intensity during the earliest Late Tithonian in central Poland, which is linked to aridification of the latest Jurassic climate. The same trend is observed in coeval sections of NW and NE Europe. Supplementary material: Additional rock magnetic results, correlation of magnetic proxies with Al. and X-ray diagrams for clay minerals are available at https://doi.org/10.6084/m9.figshare.c.6299266

The Czertezik Succession of the Pieniny Klippen Belt in Poland is assigned herein to its type area of occurrence – the main Pieniny Range, between Zamkowa Góra and Czertezik mounts. The reworked deposits of uppermost Pliensbachian, Toarcian and possibly Aalenian to lowermost Bajocian discovered in crinoidal limestones which indicate redeposition processes, especially during the Bajocian, are considered to be clearly important for reconstructing the depositional history. The redeposited Pliensbachian is represented by clasts of spotty limestones, the Toarcian by ferruginous grains and fragments of crusts/large oncoids of the ammonitico-rosso type (?Adnet Fm.), whereas the Aalenian and lowermost Bajocian is possibly represented by clasts of siliciclastic deposits and phosphatic nodules. This part of the succession resulted from the activity of rifting phases at the end of the Early Jurassic, and in the Bajocian, which caused the development of the special sedimentary environments typical of the Czertezik Succession. The younger Middle to Late Jurassic deposits represented by nodular limestones, radiolarites and micritic well-bedded limestones show a less distinct facies pattern, which is in part similar to that of other successions of the Pieniny Klippen Belt, although some rock-units such as the newly established Zamkowa Góra Bed, revealing the continuation of redeposition processes, remain specific to the Czertezik Succession. The Jurassic structure of the central part of the Pieniny Klippen Belt in Poland is revised due to the introduction of the Czertezik Ridge as a new palaeogeographic unit being the place of deposition of the Czertezik Succession. The revised position of the deposits shifts the structural affinity of the Czertezik Succession from the Subpieniny Nappe to the base of the Pieniny Nappe sensu Uhlig, 1907, and implies its closer palaeogeographic position to the Branisko–Pieniny successions than to the Czorsztyn–Niedzica successions as has been interpreted so far.

Conventionally, foraminifera were divided into two separate planktic and benthic taxonomic groups. However, more recent molecular studies call this paradigm into question, showing that mode of life of foraminifera is not diagnostic of their taxonomic affiliation. Our study shows that some Cretaceous benthic foraminifera might be more ecologically flexible than traditionally believed. World-wide paleogeographic range along with a bimodal distribution of Mg/Ca ratio for Cretaceous benthic foraminifera with serially arranged chambers suggest their propagule dispersal mechanism and a tychopelagic mode of life (i.e. the ability to occupy both planktic and benthic domains). The studied taxa possess a poremound ornamentation and/or delicate pustules that are relatively rare in benthic species and more common in planktics. It is inferred that pore-mounded test texture might have been an exceptional morphological advantage, which evolved in rotaliid foraminifera during the Mesozoic and Cenozoic. This adaptation had likely enhanced the ability to float and became a bridge between a benthic and planktic foraminiferal mode of life.

Oxygen and carbon isotope data of 11 Lower Campanian and 11 Upper Maastrichtian co-existing rotaliid foraminiferal taxa from Eastern Poland are presented. Pristine preservation of the studied material is documented by studies of cathodoluminescence, elemental contents and micro/nano-structures of foraminiferal tests. The variability in δ18O and δ13C values of the foraminifera is taxon-specific and relatively constant within the investigated intervals. It results from the combination of vital and microhabitat effects. A comparison of the measured isotope signatures with the published data of similar Cretaceous or modern taxa have allowed us to find benthic foraminifera which precipitated oxygen and carbon isotopes in near-equilibrium with bottom water. These are Praebulimina sp., Gyroidinoides globosus, Pullenia jarvisi, and Bolivina incrassata for oxygen, and Cibicidoides voltzianus and Cibicides beaumontianus for carbon isotopes. The observed differences between δ13C values of infaunal and epifaunal foraminiferal taxa are related to the presence of δ13CDIC (DIC - dissolved inorganic carbon) gradient in the sediment column, which was much higher in the Chelm section. Although planktic foraminifera studied are characterized by different lifestyles, this feature is not mirrored in their oxygen and carbon isotope compositions. This is probably due to effects of vital isotope fractionation and minor thermal and carbon isotope gradients in a part of the water column inhabited by these organisms. The thermal gradient between near surface and bottom waters is calculated to be ca. 4.0 °C, and ca. 7.5 °C for the Early Campanian and the Late Maastrichtian seas of East European Platform, respectively, based on the comparison of δ18O values of selected planktic and benthic foraminifera.

Oxygen and carbon isotope ratios of calcareous tests of foraminifera can serve as a tool for reconstructing seawater temperatures and bioproductivity. The foraminiferal isotope studies are, however, largely limited to Neogene, Paleogene and Cretaceous strata. In the current study are presented δ18O and δ13C values of well-preserved Jurassic representatives of different groups of benthic foraminifera: low-Mg calcite Lenticulina (Lagenata), high-Mg calcite Paleomiliolina (Miliolida, Tubothalamea) and aragonite Epistomina (Robertinida, Globothalamea) derived from clay deposits of Poland. Moreover, it provides the detailed comparison of isotopic data of Jurassic foraminifera with those of various co-occurring macrofossils (belemnite rostra, ammonite and bivalve shells). Our study and comparative data substantiate the existence of the offset of Lenticulina's δ18O values from isotope equilibrium of ca. 1‰, which seems to be relatively constant over geological time. This value may be used for calculation of ancient water temperatures from oxygen isotope ratios of well-preserved specimens of this very common and widespread Jurassic foraminiferal taxon. δ18O values of Epistomina and δ13C values of all studied foraminifera are significantly biased from isotope equilibrium.

New biostratigraphical, chemical and stable isotope (C, O) data are presented from the Lokut section (Transdanubian Range, Hungary) representing a ca. 13 m thick continuous succession of Lower Tithonian–Lower Berriasian pelagic limestones. The study is conducted to verify timing of nannofossil events and major palaeoenvironmental changes at the Jurassic/Cretaceous transition including lithogenic input, palaeoredox and palaeoproductivity variations. Nannofossil zones from NJT 16b to NKT have been identified in the Lokut section and correlated with magnetostratigraphy, covering an interval from polarity zone M21r to M18r. The nannofossil Zone NJT 16b spans the interval from the upper part of M21r to lowermost part of M19n2n but its lower limit is poorly defined due to large diachronism in first occurrence (FO) of Nannoconus infans in various Tethyan sections. FOs of N. kamptneri minor and N. steinmannii minor are situated in the topmost part of the M19n2n and lowermost part of M19n1r magnetozones, respectively. They are located ca. 2–2.5 m above the J/K boundary defined as Intermedia/Alpina subzonal boundary, which falls within the lower half of magnetozone M19n2n. The position of first occurrences of these taxa is similar to that from the Puerto Escano section (southern Spain) and slightly lower than in Italian sections (Southern Alps). Concentrations of chemical element proxies of terrigenous transport (Al, K, Rb, Th) decrease towards the top of the Lokut section, which suggests a decrease in input of terrigenous material and increasing carbonate productivity during the Early Tithonian and the Berriasian. Slight oxygen depletion at the sea bottom (decrease of Th/U ratio), and large increase in concentrations of productive elements (P, Ba, Ni, Cu) is observed upsection. Nutrients supply via upwelling seems to be the most likely explanation. Increase in phosphorus accumulation rate and a microfacies change from Saccocoma to calpionellid dominated took place in the polarity chron M19r, which apparently coincided with the worldwide Nannofossil Calcification Event, related to a bloom of strongly calcified calcareous nannoplankton taxa. Deposition in the Lokut area was probably affected by long-term climatic trends: aridization and warming. Decreasing δ13C values of bulk carbonates throughout the Tithonian and the Berriasian are interpreted as a result of a global trend of accelerated carbonate productivity supported by local factors such as increased upwelling intensity, and a possible change in the composition of carbonate mud.

A study is conducted to supplement the uppermost Lower Jurassic–lowermost Cretaceous marine strontium isotope dataset and to present new statistical fits of the Middle–Late Jurassic seawater strontium isotope curve based on a numerical time scale and a detailed biostratigraphical zonal scheme. The use of the stratigraphical scheme allows reduction of dating errors related to uncertainty of numerical age determinations. The presented correlation charts enable direct calibration between strontium isotope stratigraphy and regional biostratigraphical frameworks. New strontium isotope data have been obtained from well-preserved Lower Bajocian, uppermost Callovian, Oxfordian, Kimmeridgian, and Upper Volgian belemnite rostra. The presented seawater 87 Sr/ 86 Sr curve is characterized by reliable 95% confidence limits (mean width of ± 0.000007), which take into account precision of dating of particular data points. A decrease of seawater 87 Sr/ 86 Sr ratio, from ca. 0.70730 to ca. 0.70683, is observed throughout the Middle Aalenian–Early Oxfordian (172.1–160.8 Ma ago). The steepest Phanerozoic fall of the ratio, with a rate of change of up to 0.00015 per 1 Ma, is recorded in the Bajocian segment of the strontium isotope curve. The Phanerozoic minimum of the marine 87 Sr/ 86 Sr ratio occurred at the Early–Middle Oxfordian transition. The 87 Sr/ 86 Sr ratio increased starting from the Middle Oxfordian till the end of the Jurassic (160.8–145.7 Ma) reaching a value of ca. 0.70720 at the Jurassic–Cretaceous transition. The Middle–earliest Late Jurassic decrease in seawater 87 Sr/ 86 Sr ratio is interpreted as a result of the increased hydrothermal activity of the seafloor during the breakup of Gondwana, and the formation of new Atlantic–Tethyan oceanic basins. The successive rise of the ratio is probably related to the decelerated hydrothermal venting of the oceanic crust although a partial increase in radiogenic strontium input from continental weathering cannot be excluded.

Oxygen and carbon isotope ratios of well-preserved calcitic bivalves from the Lower–lowermost Upper Kimmeridgian of Central Poland (SW margin of the Holy Cross Mountains) are studied to reconstruct palaeoenvironmental conditions and variations in ancient water chemistry. Low and scattered δ 18 O and δ 13 C values of bivalve shells from shallow carbonate deposits of the Hypselocyclum and the Hypselocyclum–Divisum zone boundary (-3.5 to -1.5, and 2.6 to 4.0‰, respectively) are a result of salinity changes, and local variations in the composition of dissolved inorganic carbon (DIC) under the restricted water circulation. A slight increase in bivalve δ 13 C values and more densely clustering of δ 18 O values is observed after the marine transgression at the Divisum–Mutabilis zone boundary. A global decrease of δ 13 C values of marine carbonates is partly recorded in carbon isotopes of Lower–lowermost Upper Kimmeridgian bulk carbonates from Central Poland (from the Radomsko Elevation and the Wielun Upland). Local negative shifts and the data scatter are, however, observed in very shallow sediments deposited on carbonate platforms during the Platynota and Hypselocyclum chrons. This interval corresponds to the uppermost part of the lowstand systems track of a major regressive trend, which started already in the Late Oxfordian Oxygen and carbon isotope ratios of well-preserved calcitic bivalves from the Lower–lowermost Upper Kimmeridgian of Central Poland (SW margin of the Holy Cross Mountains) have been studied to reconstruct palaeoenvironmental conditions and variations in ancient water chemistry. Low and scattered δ 18 O and δ 13 C values of bivalve shells from shallow carbonate deposits of the Hypselocyclum and the Hypselocyclum–Divisum zone boundary (–3.5 to –1.5, and 2.6 to 4.0‰, respectively) are a result of salinity changes and local variations in the composition of dissolved inorganic carbon (DIC) in conditions of restricted water circulation. A slight increase in bivalve δ 13 C values and more densely clustering of δ 18 O values is observed after the marine transgression at the Divisum–Mutabilis zone boundary. A global decrease of δ 13 C values of marine carbonates is partly recorded in Lower–lowermost Upper Kimmeridgian bulk carbonates from central Poland (from the Radomsko Elevation and the Wielun Upland). Local negative shifts and data scatter are, however, observed in rocks deposited in a very shallow environment of carbonate platforms during the Platynota and Hypselocyclum chrons. This interval corresponds to the uppermost part of the lowstand systems tract of a major regressive trend, which had started in the Oxfordian.

Upper Berriasian chemostratigraphic, clay mineral and calcareous nanofossil data are presented from a precisely dated hemipelagic section of Barlya (Western Balkan, Bulgaria). The section covers an interval from the upper part of the lower Berriasian (Calpionella elliptica Subzone, magnetozone M17r) to the lowermost Valanginian (Calpionellites darderi Subzone, magnetozone M14r). The study aims to reconstruct the major palaeoenvironmental changes (variations in lithogenic input, palaeoredox and palaeoproductivity) and their relation to palaeoclimate and regional tectonic regime, as well as their application to stratigraphic correlations with the Vocontian Basin and Jura Mts. A long-term increase in terrigenous input during the late Berriasian was controlled mostly by the orogenic activity in the NeoTethyan Collision Zone and to a lesser degree by climate humidification, as revealed by variations in kaolinite content and in lithogenic proxies (Ti/K, Th/K, Ti/Al and Zr/Rb ratios). A good correlation is observed between geochemical palaeoproductivity proxies (sedimentation rates of non-detrital (excess or authigenic) portions of P, Zn and Cd) and nannofossil fluxes, determined as the total abundance and species richness. Major calcareous nannofossil peaks, represented by high-diversity and high-abundance nannofossil assemblages, fall within the low-productivity intervals. A smaller peak formed by a low-diversity and high-abundance assemblage, dominated by Watznaueria barnesiae/fossacincta, coincides with the variable, but mostly high-productivity interval, which indicates high plasticity of Watznaueria concerning to environmental conditions. Additionally, trophic changes seem to correspond to bulk rock carbon-isotopic composition, with rising δ13Ccarb values in more oligotrophic intervals. This offers perspectives for long-distance chemostratigraphic correlations between pelagic and platform sections, supplementing traditional schemes based on bio- and sequence stratigraphy. A holostratigraphic correlation is proposed between the Western Balkan (Barlya section), Vocontian Basin (Berrias and Monclus sections) and Jura Mts (La Chambotte section) based on bio-, magnetic and carbon-isotope stratigraphy, as well as climatic and palaeoproductivity proxies.

In the comment on our paper (this issue), Zaton (2020) questions the conclusions reported in Blazejowski et al. (2019). We present further arguments defending our theses. Late Jurassic horseshoe crabs preserved in sediments of the Kcynia Formation, (Owadow-Brzezinki Quarry), lived in a restricted lagoon repeatedly subjected to dysoxia/anoxia, which promoted their excellent state of preservation. The palaeobiological interpretation of the traces visible on horseshoe crab exoskeletons is consistent with the occurrence of temporal oxygen deficiency.

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.

Results of clumped isotope, oxygen isotope and elemental (Mg/Ca, Sr/Ca) analyses of exceptionally well-preserved belemnite rostra and ammonite shells from the uppermost Callovian–Upper Kimmeridgian (Lamberti–Mutabilis zones) of the Russian Platform are presented. Despite a significant decrease in belemnite δ18O values across the Upper Oxfordian–Lower Kimmeridgian, the clumped isotope data show a constant seawater temperature (ca. 16 °C) in the studied interval. The decrease in belemnite δ18O values and lower δ18O values measured from ammonite shells are interpreted as a result of the salinity decline of the Middle Russian Sea of ca. 12‰, and salinity stratification of the water column, respectively. The postulated secular palaeoenvironmental changes are linked to the inflow of subtropical, saline waters from the Tethys Ocean during a sea-level highstand at the Middle–Late Jurassic transition, and progressive isolation and freshening of the Middle Russian Sea during the Late Oxfordian–Kimmeridgian. The obtained clumped isotope data demonstrate relative stability of the Late Jurassic climate and a paramount effect of local palaeoceanographic conditions on carbonate δ18O record of shallow epeiric seas belonging to the Subboreal Province. Variations in Mg/Ca and Sr/Ca ratios of cylindroteuthid belemnite rostra, which are regarded by some authors as temperature proxies, are, in turn, interpreted to be primarily dependent on global changes in seawater chemistry. The paleoenvironmental variations deduced from clumped and oxygen isotope records of the Russian Platform correspond well with changes in local cephalopod and microfossil faunas, which show increasing provincialism during the Late Oxfordian and the Early Kimmeridgian. Based on the review of literature data it is suggested that the observed salinity decrease and restriction of Subboreal basins during the Late Jurassic played a major role in the formation of periodic bottom water anoxia and sedimentation of organic rich facies.

A continuous sedimentary and stratigraphic record of Late Kimmeridgian – Early Berriasian age is presented from the pelagic succession from the eastern part of the Pieniny Klippen Belt (Velykyi Kamianets section, Ukraine). The studied section, 26-m-thick, was calibrated using biostratigraphy (calpionellids, calcareous dinocysts, calcareous nannofossils), magnetostratigraphy, stable isotope stratigraphy (δ13C and δ18O) and gamma ray spectrometry. Magnetic polarity zones from M23r to M18n were identified. The magnetostratigraphic calibration of calcareous dinocysts zonation around the Kimmeridgian/Tithonian boundary has been performed for the first time. The Carpistomiosphaera borzai/Committosphaera pulla calcareous dinocyst zonal boundary is situated at the bottom of magnetozone M22n, slightly lower than first occurrence of calcareous nannofossil Conusphaera mexicana minor and higher than the standard Kimmeridgian/Tithonian boundary (M22Ar/M22An; Hybonoticeras beckeri/Hybonoticeras hybonotum Ammonite Zone boundary). The position of the Tithonian/Berriasian boundary in the magnetosubzone M19n2n (Crassicollaria/Calpionella Calpionellid zonal boundary) has been confirmed. A decrease of terrigenous input and an increase of carbonate productivity correlate with increasing sedimentation rates from 0.7 to 1.1 m/Myr in the Upper Kimmeridgian (M23r to M22r) to 5–7 m/Myr in the uppermost Tithonian and Lower Berriasian (M19n to M18n). Transition between the Saccocoma and calpionellid microfacies occurs in a narrow time interval, mostly within polarity subchron M20n1r. This event is traceable in similar stratigraphic position in several Western Tethyan sections and correlates perfectly with Nannofossil Calcification Event of the early Late Tithonian.

New isotope (δ18O, δ13C) and elemental (Mg/Ca, Sr/Ca) data of well-preserved belemnite rostra, ammonite and gastropod shells from the Middle Oxfordian–Lower Kimmerdgian (Densiplicatum–Kitchini zones) of the Russian Platform are presented. This record is supplemented with published data from the Upper Callovian–Lower Kimmeridgian interval (Athleta–Kitchini zones). Significant differences in average temperatures calculated from δ18O values of particular fossil groups (5–15 °C) show the thermal gradient and the presence of cold bottom waters in the Middle Russian Sea during the Late Callovian–Middle Oxfordian. An Upper Oxfordian–lowermost Kimmeridgian decrease in δ18O values and an increase in Sr/Ca ratios of cylindroteuthid belemnite rostra likely reflect a warming of the bottom waters of ca. 3.5 °C. The gradual Late Oxfordian–earliest Kimmeridgian warming is followed by an abrupt temperature rise of 3–6 °C that occurred at the transition of the Early Kimmeridgian Bauhini and Kitchini chrons. The occurrences of cold bottom waters and of (Sub)Mediterranean ammonites and belemnites in the Middle Russian Sea at the Middle–Late Jurassic transition are regarded as a result of the opening of seaways during a sea level highstand. The bottom waters are considered to have been formed in the cool Boreal Sea. The subsequent retreats of the cold bottom waters and of the (Sub)Mediterranean cephalopods from the Middle Russian Sea in the Late Oxfordian are explained by the restriction of water circulation during a sea-level fall. The Early Kimmeridgian rise of bottom temperatures of the sea is linked to a global climate warming. The data presented do not support a major cooling of the Arctic and a consequent glaciation in this region at the Middle–Late Jurassic transition. Since occurrences of cold water masses are diachronous in different European basins, the observed variations in sea water temperatures are interpreted as a result of changes in marine currents and water circulation. δ13C values of belemnite rostra from the Russian Platform are scattered but show the long-term Upper Callovian–Middle Oxfordian positive excursion consistent with the previously published isotope records of the Boreal Realm and terrestrial organic matter.

Strontium isotope ratios of well-preserved belemnite rostra and ammonite shells are presented from stratigraphically well-dated Upper Bajocian–Callovian sediments of the Polish Jura Chain in central Poland. Nekto-benthic belemnites show a narrow trend of changes of 87 Sr/ 86 Sr ratio that are interpreted to record secular variations in the strontium isotope composition of seawater. A new fit of the seawater strontium isotope curve for the Late Bajocian–Callovian is presented based on current and literature data. The data show a gradual decrease of seawater 87 Sr/ 86 Sr ratio throughout the Late Bajocian–earliest Middle Callovian, lowest 87 Sr/ 86 Sr ratios (0.706850) and the flat minimum of the curve were reached in the latest Middle and the Late Callovian. The Middle Jurassic decrease in seawater 87 Sr/ 86 Sr ratio is interpreted to have been a result of the increased volcanic activity of the seafloor. Studied nektonic ammonites are considered to have lived in surface or shallow near-coastal waters of the Polish Jura Chain basin and been affected by the freshwater influx. A slight enrichment of ammonite shells in 87 Sr isotope is linked to a change in strontium isotope composition of the surface or near-coastal waters due to the riverine strontium input.

Oxygen and carbon isotope data of well-preserved belemnite rostra and ammonite shells are presented from the Callovian–Oxfordian boundary (uppermost Lamberti to lowermost Cordatum zones) of the Dubki section near Saratov in the Russian Platform. Palaeotemperatures calculated for nektobenthic belemnites (averages of 5 °C and 8 °C for cylindroteuthids and belemnopseids, respectively) show the presence of cold bottom waters in the central part of the Middle Russian Sea during the studied interval. Palaeotemperatures calculated for ammonites, which are assumed to have lived in near-surface waters, are considerably higher (average 13 °C). The presented data show a vertical thermal gradient in the Middle Russian Sea. The belemnite oxygen isotope record and the relative abundances of ammonite families in the Dubki section do not correlate with each other probably as a result of different depth habitats of ammonites and belemnites. A review of literature isotope data shows the climatic zonation in European seas at the Middle–Late Jurassic transition. Despite the flux of cold polar waters to the Middle Russian Sea and the area of Scotland there is no evidence for glaciation at the Middle–Late Jurassic transition. Changes in water circulation during a sea-level highstand were likely a source of spreads of cold bottom waters and cardioceratid ammonite fauna in this time period. The belemnite isotope record of the Callovian–Oxfordian boundary in the Russian Platform is characterized by significant scatter of δ13C values. No temporal carbon isotope trend is observed. The δ13C values of Russian belemnite rostra average 2.6‰ VPDB being 1 to 2‰ higher than the values of coeval Lower Oxfordian belemnites from the area of the Submediterranean ammonite province. Higher (than Submediterranean) δ13C values of Russian belemnite rostra are likely related to high biologic productivity and/or high organic matter burial in semi-isolated Boreal–Subboreal marine basins.

Oxygen and carbon isotope data of well-preserved and stratigraphically well-dated belemnite rostra are presented from a Callovian–Lower Oxfordian succession of the Polish Jura Chain (south-central Poland) that was deposited in a deep shelf environment. Palaeotemperatures calculated from belemnite δ 18 O values (9 to 14 °C) indicate relatively constant climatic conditions during studied Callovian and Early Oxfordian intervals. Belemnite δ 13 C temporal trends, which are interpreted to record primary variation in the isotope composition of dissolved inorganic carbon reservoir, display a prominent positive carbon isotope shift (up to around 1.7‰ VPDB) in the Upper Callovian. This excursion is preceded and followed by a drop in average δ 13 C values of belemnite rostra of around 1‰. The Late Callovian carbonate carbon isotope excursion is likely linked to the enhanced storage of organic carbon in shelf sediments during a global sea-level rise. The presented data are not compatible with the theory of prolonged global glaciation at the Middle–Late Jurassic transition.

Stables isotopes and elemental composition of two well-preserved belemnite rostra (Hibolithes beyrichi and H. hastatus) from the Bathonian of central Poland were studied. Average temperatures calculated from the oxygen isotope ratios of Hibolithes beyrichi and H. hastatus are 10°C and 6°C, respectively. The absence of high-amplitude variations in high-resolution temperature profiles suggests these belemnites lived in deeper waters. This interpretation is compatible with a nektobenthic habitat of belemnopsid belemnites. Carbon isotope ratios of the rostra are assumed to be affected by vital fractionation with prominent fluctuations in the δ13C records resulting from changes in the metabolic activity. Observed variations in Mg:Ca ratios of the rostra (from 5 mmol·mol−1 to 28 mmol·mol−1) are predominantly a primary signal. Temperature dependence of the Mg:Ca ratio is inferred for H. beyrichi on the basis of a correlation with δ18O values; however, no such correlation is observed for H. hastatus. No ...

Four occurrences of Jurassic stromatactis mud-mounds were found in the Czorsztyn Unit of the Pieniny Klippen Belt (Western Carpathians) — in western Slovakia (Slavnicke Podhorie, Babina), and in the Transcarpathian Ukraine (Priborzhavskoe and Veliky Kamenets). Their stratigraphic range is from Bajocian to Callovian. The mounds consist of micropeloidal mudstones, wackestones to packstones with a fauna including pelecypods, brachiopods, ammonites and crinoids. Spicules and skeletons of siliceous sponges are abundant in every section. All of the mounds contain networks of stromatactis cavities that are partially filled with radiaxial fibrous calcite (RFC) and locally by internal sediments. At Slavnicke Podhorie, the sparry masses that fill stromatactis cavities are weathered out and show casts of sponges. Parallel study of the weathered casts and their cross-sections in slabs showed that they bear all the signs of stromatactis (relatively flat bottoms and digitate upper parts, RFC initial fillings and eventual blocky calcite later filling). Almost no original sponge structures were preserved. This strongly supports the possible sponge-related origin for stromatactis cavities.

The Owadów-Brzezinki quarry is one of the most important paleontological sites in Poland, 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.

The oxygen and carbon isotope composition of skeletal and inorganic calcites and aragonites was measured with or without pre-treatments (vacuum roasting, NaOCl and H2O2 treatments) used for removing organic matter. In addition, mixtures of pure calcium carbonate and organic matter (simple organic compounds, coal and kerogen) were analyzed with or without the thermal and oxidizing treatments. The studied organic substances have no effect on isotope analyses of untreated samples carried out by using the phosphoric acid method. The experimental results indicate that the roasting treatment may produce carbon isotope exchange between calcium carbonate and organic matter. Changes in original δ18O and δ13C values of calcites and δ13C values of aragonites were observed after the NaOCl treatment of the skeletal and inorganic samples. The H2O2 treatment causes minor deviations in original δ values, although may cause partial dissolution of calcium carbonate. Unnecessary usage of pre-treatment methods may be a source of errors in stable isotope analyses and palaeotemperature determinations based on the oxygen isotope composition of skeletal carbonates.

Oxygen and carbon isotope analyses were carried out on Upper Bajocian – Bathonian calcitic belemnite rostra and oyster shells as well as aragonitic ammonite, nautiloid and trigoniid shells from the “Ore-bearing Czestochowa Clay Formation” in south-central Poland. All samples were studied by means of cathodoluminscence microscopy, trace element, X-ray, and scanning electron microscope (SEM) analysis in order to select best-preserved material. SEM studies allowed classifying some aragonitic ammonite and nautiloid shells (> 99% aragonite) as diagenetically altered. Average δ18O values of oysters, belemnites and trigoniids translate into relatively low palaeotemperatures of 10.1, 9.2 and 7.4 °C, respectively. The comparable δ18O values of bivalves and belemnites indicate that belemnites had a nectobenthic lifestyle and did not record surface water temperatures. The ammonite fauna is interpreted to have been nektonic, however, palaeotemperatures derived from ammonite δ18O (around 18.6 °C) may be overestimated due to a lower, than normal marine, salinity of surface waters. The reduced salinity is inferred as well from sedimentological observations and faunal composition. The obtained δ18O values indicate cool climatic conditions during the Late Bajocian–Bathonian in south-central Poland, which may have been linked with the occurrence of a cold climatic episode. Despite the fact that all studied shells were not precipitated in carbon isotope equilibrium with ambient waters, the δ13C shell values enabled us to roughly estimate isotope composition of dissolved inorganic carbon (DIC) in the Late Bajocian–Bathonian sea of south-central Poland. Water δ13CDIC values calculated from ammonite δ13C are lower in comparison to δ13CDIC values calculated from oyster and belemnite carbon isotope ratios, which in conjunction with ammonite δ18O values indicates lower salinity of surface or shallow near-coastal waters.

Stable isotope analyses have been undertaken on Oxfordian–Early Kimmeridgian belemnite rostra derived from three palaeogeographic provinces of Europe: (1) the Boreal–Subboreal Province (Isle of Skye in Scotland); (2) the Submediterranean Province (central Poland and southern Germany); and (3) the Mediterranean Province (Pieniny Klippen Belt in the Western Carpathians). The samples have been screened for possible diagenetic alteration by using cathodoluminescence and trace element analyses and have been found to be largely well-preserved. Calculated palaeotemperatures (10–15°C) and analyses of belemnite habitats suggest that the Boreal–Subboreal belemnites were living in a relatively shallow sea (not deeper than 100–150 m) while the other belemnites possibly inhabited deeper neritic environments. Despite the influence of a vital effect, the δ13C values of belemnite rostra are interpreted to reflect primary variations in the oceanic carbon isotope signal. The fairly uniform Submediterranean δ13C values indicate a similar isotope composition of dissolved inorganic carbon (DIC) in the area of sedimentation of sponge megafacies in the deep Tethyan shelves. The slightly lowered δ13C values of some Mediterranean belemnites might occur due to upwelling providing 12C enriched bottom waters onto the area of the Czorsztyn Ridge in the Oxfordian. The discernibly more positive (1–2.5‰) δ13C values of Boreal–Subboreal belemnites are related to a high biologic productivity and a high organic matter burial in the partly isolated Boreal Sea. The stated differentiation in carbonate δ13C values distinctly exceeds present-day differences in isotope composition of seawater DIC.

Rostra (bullet-shaped internal shells) of two species of belemnites: Belemnopsis sp. (from Bathonian Stage sediments ∼161–166 Ma ago) and Hibolites sp. (from Middle Oxfordian sediments ∼154–157 Ma) were investigated by the use of 1B2 microfluorescence beamline in Pohang Light Source in Korea. The cross-sections of the rostra showed an ordered structure of concentric growth laminae cut across by radial calcite crystals. The inner and outer parts of the cross-section differ in the size of calcite crystals, building the block. Very fine crystals existing in the inner parts of rostra are replaced by monocrystals in their external parts. Some compounds of metallic elements such as iron and zinc are present in the calcite matrices of belemnites. Their presence is especially pronounced in the zones separating particular growth rings. The concentrations of elements in calcite matrix were calibrated by atomic absorption method and the results for alkaline elements are: for Sr ∼1000 ppm for Oxfordian specimen and ∼3000 ppm for Bathonian; for Na, ∼2000 and ∼1400 ppm; for K, ∼160 and ∼100 ppm, respectively. The synchrotron-based investigations were complemented with the electron microprobe search for low-Z elements; using this method sodium, potassium, aluminum, silicon, chlorine and sulfur were detected in the matrix. The variability of molar Mg/Ca ratio follows the optical variability of the annual growth zones of the samples, suggesting that this ratio could be used as a palaeothermometer. Possibilities of both application of the elemental data for the estimation of palaeotemperatures, and cross-checking with the isotopic data are discussed. The substantial amounts of the excess carbon were detected in the samples. They are concluded to be potentially useful for the analysis of remnants of original biological matter.

A collection of 73 belemnites and brachiopods from detailed stratigraphically documented sections in the Polish Jura Chain of Central Poland representing almost the whole Oxfordian Stage was studied for oxygen and carbon isotopes. The δ18O and δ13C (V-PDB) values range from –3.6 to +0.5‰ and from –1.6 to +2‰ for belemnite rostra, and from –2.5 to +0.4‰ and from +1.6 to +4.3‰ for brachiopod shells, respectively. The δ13C temporal trends of belemnite rostra and brachiopod shells show a constant isotopic difference (ca. 2.5–3‰), which is interpreted as a vital effect of belemnites or as a result of different life environments. δ18O values are similar in both groups of fossils. The δ18O values in the Lower and Middle Oxfordian oscillate around 0‰ and decrease in the Upper Oxfordian. This decrease results mainly from diagenetic overprint as proved by the cathodoluminescence studies. The Lower and Middle Oxfordian δ18O-derived temperatures were constant in consequence of significant ocean depth. For this reason there are no established links with distribution of ammonite faunas. The δ13C temporal trend displays a gentle slope through the Oxfordian and reaches maximum values at the turn of the Plicatilis/Transversarium Zones of the Middle Oxfordian, which is commonly considered as a global event. It can be related to the sea-level highstand and growth crisis of carbonate platforms. The decrease in δ13C values starting in the upper Middle Oxfordian is interpreted to be due to the acceleration of carbonate sedimentation rate during this time period.

Strontium isotope composition of seawater is homogenous in all oceans and marginal seas but has varied through time with changing strontium fluxes. Strontium isotope ratio of ancient seawater may be reconstructed from well-preserved authigenic minerals and used for dating marine sediments. Because of a change in the strontium isotope ratio between sea- and freshwaters it can also be employed for the determination of palaeosalinities or the reconstruction of diagenetic processes of marine limestones. A review of methodology and practical hints concerning the utilization of strontium isotopes in geological studies of both marine and brackish sediments are presented in the current article.