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Spötl, Christoph
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- PublicationOpen AccessAn integrated multi-proxy study of cyclic pelagic deposits from the north-western Tethys: The Campanian of the Postalm section (Gosau Group, Austria)(2021)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The Upper Cretaceous Postalm section in the Northern Calcareous Alps (Austria) exposes pelagic depositsof the northwestern Tethys whose cyclostratigraphy and palaeoenvironments were examined in thisstudy.The section displays rhythmic deposits of Santonian to late Campanian age (Gosau Group). The San-tonian/Campanian transition is characterised by condensed greyish carbonates, while the younger de-posits are composed of reddish foraminiferal packstones displaying distinct limestone-marl alternations.A biostratigraphic framework based on planktonic foraminifera and calcareous nannofossils is supportedby carbon and strontium isotope stratigraphy as well as magnetostratigraphy. The carbon isotope dataallow to correlate the Postalm section to other Tethyan reference sites and to identifyd13C events, such asthe Late Campanian Event. Spectral analyses of three independently assessed proxies (d13C, Fe contentand the thickness of limestone/marl couplets) in the upper, continuously exposed section part identified17 to 18 405 ka cycles spanning the mid to upper Campanian (Contusotruncana plummeraetoGansserinagansseriZones or CC21/UC15c to CC23a/UC16 nannofossil zones).154 17 - PublicationRestrictedThe Santonian–Campanian boundary and the end of the Long Cretaceous Normal Polarity-Chron: Isotope and plankton stratigraphy of a pelagic reference section in the NW Tethys (Austria)The base of the Campanian still lacks a designated primary marker and a defined GSSP (Global Boundary Stratotype Section and Point). We present a Santonian–Campanian boundary section from the Postalm in the Northern Calcareous Alps of Austria as a possible reference section for the northwestern Tethys. Including nearby complementary Gosau Group sections, the stratigraphy for this time interval is based on palaeomagnetic and stable isotope data, planktonic foraminifera and calcareous nannoplankton bio - stratigraphy, and strontium isotope stratigraphy, together with published ammonite, crinoid and inoceramid data. The Postalm section shows a deepening trend from upper Santonian conglomerates and grey shelf marls to pelagic bathyal red marly limestones of mainly Campanian age. Palaeomagnetic data allow identifying the top of the Long Cretaceous Normal Polarity-Chron C34n and the following reversal in the lower part of the red marly limestones. A 1 m-thick interval of high magnetic susceptibility is present at the end of C34n. Two of the main suggested biomarkers to pinpoint the Santonian–Campanian boundary, i. e. the last occurrence of the planktonic foraminifer Dicarinella asymetrica and the first occurrence of the nannofossil Broinsonia parca parca, occur in close proximity above the reversal, which is suggested herein as the main marker event for the base of the Campanian. Strontium isotope stratigraphy indicates a value of 0.707534 (mean of four measurements at the boundary interval) for the base of the Campanian in the Postalm section. Both carbon and oxygen isotope values show a negative excursion just below the boundary. The positive Santonian–Campanian carbon isotope event starts probably just below the reversal but seems to be diagenetically distorted. This interval is considered to correspond to a short sea-level high in the late Santonian followed by a distinct lowstand at the Santonian–Campanian boundary.
135 1 - PublicationOpen AccessPartitioning of Mg, Sr, Ba and U into a subaqueous calcite speleothem(2019)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The trace-element geochemistry of speleothems is becoming increasingly used for reconstructing palaeoclimate, with a particular emphasis on elements whose concentrations vary according to hydrological conditions at the cave site (e.g. Mg, Sr, Ba and U). An important step in interpreting trace-element abundances is understanding the underlying processes of their incorporation. This includes quantifying the fractionation between the solution and speleothem carbonate via partition coefficients (where the partitioning (D) of element X (DX) is the molar ratio [X/Ca] in the calcite divided by the molar ratio [X/Ca] in the parent water) and evaluating the degree of spatial variability across time-constant speleothem layers. Previous studies of how these elements are incorporated into speleothems have focused primarily on stalagmites and their source waters in natural cave settings, or have used synthetic solutions under cave-analogue laboratory conditions to produce similar dripstones. However, dripstones are not the only speleothem types capable of yielding useful palaeoclimate information. In this study, we investigate the incorporation of Mg, Sr, Ba and U into a subaqueous calcite speleothem (CD3) growing in a natural cave pool in Italy. Pool-water measurements extending back 15 years reveal a remarkably stable geochemical environment owing to the deep cave setting, enabling the calculation of precise solution [X/Ca]. We determine the trace element variability of ‘modern’ subaqueous calcite from a drill core taken through CD3 to derive DMg, DSr, DBa and DU then compare these with published cave, cave-analogue and seawater-analogue studies. The DMg for CD3 is anomalously high (0.042 ± 0.002) compared to previous estimates at similar temperatures ( 8 C). The DSr (0.100 ± 0.007) is similar to previously reported values, but data from this study as well as those from Tremaine and Froelich (2013) and Day and Henderson (2013) suggest that [Na/Sr] might play an important role in Sr incorporation through the potential for Na to outcompete Sr for calcite non-lattice sites. DBa in CD3 (0.086 ± 0.008) is similar to values derived by Day and Henderson (2013) under cave-analogue conditions, whilst DU (0.013 ± 0.002) is almost an order of magnitude lower, possibly due to the unusually slow speleothem growth rates (<1 lm a 1), which could expose the crystal surfaces to leaching of uranyl carbonate. Finally, laser-ablation ICP-MS analysis of the upper 7 lm of CD3, regarded as ‘modern’ for the purposes of this study, reveals considerable heterogeneity, particularly for Sr, Ba and U, which is potentially indicative of compositional zoning. This reinforces the need to conduct 2D mapping and/or multiple laser passes to capture the range of time-equivalent elemental variations prior to palaeoclimate interpretation.183 70