Hubert Wierzbowski

Carbon and oxygen isotope composition of Oxfordian–Early Kimmeridgian belemnite rostra: palaeoenvironmental implications for Late Jurassic seas

Abstract 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.

Stable isotopes, elemental distribution, and growth rings of belemnopsid belemnite rostra: Proxies for belemnite life habitat

Abstract 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 significant correlation is observed between Sr:Ca ratios and δ18O values in either taxon. Sulphur contents in the rostra vary from 630 ppm to 4400 ppm and are interpreted to be largely coprecipitated with belemnite calcite. Extreme compositions of sulphur are interpreted to result from the incorporation of diagenetic sulphur during early marine diagenesis, which is also characterized in these rostra by high Mg:Ca and Sr:Ca ratios and low δ13C values. A total number of growth rings in the rostrum of H. beyrichi is calculated at around 600, thus, an expected life span of H. beyrichi is considered to be ∼1.5 years assuming daily precipitation of growth bands.

δ18O(PO43−) and δ18O(CO32−) from belemnite guards from Eastern Europe: implications for palaeoceanographic reconstructions and for the preservation of pristine isotopic values

Abstract The oxygen isotopic composition of coexisting carbonate and phosphate from belemnite rostra was measured according to well established techniques in 42 samples of Early and Middle Jurassic age and in five samples of oyster shells. Most of the samples come from various locations in the Western Carpathians of Slovakia and Ukraine, and from central Poland. Three samples come from the Isle of Skye. The phosphate content of belemnite rostra, though variable, is systematically very low: consistently lower than about 0.3%. However, this phosphate concentration is close to that found in shells of modern marine organisms including pelecypods, gastropods and Sepia cuttlebones which, in some way, could be considered the modern belemnite counterpart. The measured oxygen isotopic composition of carbonate is within the normal range of values obtained from these fossils ranging from about −1.3 to about +0.6‰ (PDB-1) with the exception of three samples; the δ 13 C values range from about −0.8 to about +2.8‰ (PDB-1). With the single exception of one sample from the Isle of Skye, the oxygen isotopic composition of phosphate from belemnite rostra ranges from +19.8 to +24.9‰ (V-SMOW), 22 of the samples measured showing δ 18 O values equal to or heavier than +23.0‰. In contrast, the oyster values are considerably lighter, in the case of both carbonate and phosphate. 18 O-enriched values can hardly be related to diagenetic processes that normally cause an oxygen isotope shift towards light values. If deposition temperatures are calculated from the heavily enriched values by means of the equation of Longinelli and Nuti [Earth Planet. Sci. Lett. 19 (1973) 373–376] and assuming the δ 18 O of Jurassic ocean water to be equal to −1‰ taking into account the lack of ice caps during the Jurassic, the obtained temperatures range from about 8°C to about zero. These temperatures are obviously unreliable when Mesozoic palaeoceanographic conditions and palaeoclimate are taken into account. Two different hypotheses are suggested to explain these results, other hypotheses being rejected as unreliable. (1) Phosphate derived from the decaying organic matter of belemnites might have been introduced into belemnite rostra by early diagenetic fluids. If the phosphate of belemnite organic matter was isotopically heavy as happens nowadays in the flesh of molluscs, the inflow of this phosphate into the rostra could be responsible for the very positive δ 18 O values shown by many belemnite rostra (this hypothesis is suggested by H.W.); (2) previous oxygen isotope measurements on Upper Cretaceous belemnites yielded δ 18 O values very close to the most positive values obtained from Lower Tertiary pelecypods and fish teeth which are known to precipitate their phosphate under isotopic equilibrium conditions with seawater. These data suggest the possibility that the phosphate in belemnite rostra is primary phosphate so that the very positive data reported here can be considered the result of good preservation of the pristine isotopic composition of primary phosphate. Consequently, the only way to explain the very positive δ 18 O values is to consider the oxygen isotopic composition of Jurassic ocean water to be more positive than nowadays by at least 3‰. This hypothesis is suggested by A.L. and A.D.M.

Investigation of chemical composition of belemnite rostra by synchrotron-based X-ray microfluorescence and diffraction and electron microprobe

Abstract 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.

Glendonites track methane seepage in Mesozoic polar seas

During the Phanerozoic, Earth has experienced a number of transient global warming events associated with major carbon cycle perturbations. Paradoxically, many of these extreme greenhouse episodes are preceded or followed by cold climate, perhaps even glacial conditions, as inferred from the occurrence of glendonites in high latitudes. Glendonites are pseudomorphs of ikaite (CaCO3 center dot 6H(2)O), a hydrated carbonate mineral increasingly stable at low temperatures. Here, we show that methane seepage and oxidation provide an overriding control on Mesozoic glendonite formation (i. e., ikaite fossilization). Geochemical and petrological analyses of 33 Early Jurassic to Early Cretaceous glendonites from five sections in Siberia (Russia) reveal that most of their infilling carbonate phases are reminiscent of methane- derived authigenic carbonates. Bulk glendonites and surrounding sediments exhibit exceptionally high and low carbon isotope values (+20% to -45% VPDB [Vienna Peedee belemnite]), typical for carbon sources linked to methane generation and oxidation. Gas inclusion data confirm the presence of methane and longer-chain hydrocarbon gases, suggesting a thermogenic source for the methane. Glendonitebearing layers can be traced for hundreds of kilometers, suggesting widespread trapping of methane in the sub-seafloor during the Jurassic. As such, glendonites constitute an unexplored archive for detecting past episodes of methane release and oxidation in polar settings.

Towards a consistent Oxfordian/Kimmeridgian global boundary : current state of knowledge

New data are presented in relation to the worldwide definition of the Oxfordian/Kimmeridgian boundary, i.e. the base of the Kimmeridgian Stage. This data, mostly acquired in the past decade, supports the 2006 proposal to make the uniform boundary of the stages in the Flodigarry section at Staffin Bay on the Isle of Skye, northern Scotland. This boundary is based on the Subboreal-Boreal ammonite successions, and it is distinguished by the Pictonia flodigarriensis horizon at the base of the Subboreal Baylei Zone, and which corresponds precisely to the base of the Boreal Bauhini Zone. The boundary lies in the 0.16 m interval (1.24–1.08 m) below bed 36 in sections F6 at Flodigarry and it is thus proposed as the GSSP for the Oxfordian/Kimmeridgian boundary. This boundary is recognized also by other stratigraphical data – palaeontological, geochemical and palaeomagnetic (including its well documented position close to the boundary between magnetozones F3n, and F3r which is placed in the 0.20 m interval – 1.28 m to 1.48 m below bed 36 – the latter corresponding to marine magnetic anomaly M26r).The boundary is clearly recognizable also in other sections of the Subboreal and Boreal areas discussed in the study, including southern England, Pomerania and the Peri-Baltic Syneclise, Russian Platform, Northern Central Siberia, Franz-Josef Land, Barents Sea and Norwegian Sea. It can be recognized also in the Submediterranean-Mediterranean areas of Europe and Asia where it correlates with the boundary between the Hypselum and the Bimmamatum ammonite zones. The changes in ammonite faunas at the boundary of these ammonite zones – mostly of ammonites of the families Aspidoceratidae and Oppeliidae – also enables the recognition of the boundary in the Tethyan and Indo-Pacific areas – such as the central part of the Americas (Cuba, Mexico), southern America, and southern parts of Asia. The climatic and environmental changes near to the Oxfordian/Kimmeridgian boundary discussed in the study relate mostly to the European areas. They show that very unstable environments at the end of the Oxfordian were subsequently replaced by more stable conditions representing a generally warming trend during the earliest Kimmeridgian. The definition of the boundary between the Oxfordian and Kimmeridgian as given in this study results in its wide correlation potential and means that it can be recognized in the different marine successions of the World.