Forschungsstelle Radiometrie

Heidelberg, Germany

Forschungsstelle Radiometrie

Heidelberg, Germany
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Polag D.,Forschungsstelle Radiometrie | Scholz D.,University of Mainz | Muhlinghaus C.,Forschungsstelle Radiometrie | Spotl C.,University of Innsbruck | And 3 more authors.
Chemical Geology | Year: 2010

In recent years, stalagmites have become important archives for paleoclimate. Several studies applying carbon and oxygen isotopes of stalagmites show a simultaneous increase of δ13C and δ18O along individual growth layers, which is interpreted as being indicative of isotope fractionation under disequilibrium conditions. In order to obtain robust paleoclimatic information from calcite precipitated under these non-equilibrium conditions it is important to improve the quantitative understanding of the corresponding isotope fractionation processes. Here we present laboratory experiments simulating calcite precipitation under cave-analogue conditions. The major focus was the investigation of the temporal evolution of the δ13C and δ18O values of the precipitated calcite for varying temperature, drip interval and initial SICaCO3.All experiments show an isotopic enrichment of both δ13C and δ18O with increasing distance from the point of drip water impinge. Longer drip intervals and higher temperatures result in a larger enrichment. In addition, the slope between δ18O and δ13C is lower for higher temperatures indicating faster oxygen isotope exchange between the water reservoir and the bicarbonate in the solution.In case of δ13C, the fractionation factor between the precipitated calcite and the bicarbonate in the solution, 13αCaCO3-HCO3-, shows a larger increase with higher temperatures in comparison to previous studies. This possibly indicates an increasing contribution of disequilibrium isotope fractionation processes for increasing temperatures, which are not accounted for by the equilibrium isotope fractionation factors. Furthermore, a quantitative determination of the calcite precipitation time, Τp, and the oxygen isotope exchange time between the bicarbonate and the water, Τb, yields faster reaction rates in comparison to previously published time constants, particularly at higher temperature (23°C). © 2010 Elsevier B.V.

Meyer M.C.,University of Innsbruck | Spotl C.,University of Innsbruck | Mangini A.,Forschungsstelle Radiometrie | Tessadri R.,University of Innsbruck
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2012

Proxy records from high-altitude locations predating the Last Glacial Maximum are rare but could provide invaluable insights into the response of alpine catchments to the rapid climate fluctuations which characterized the last glacial period. Here we present a detrital-rich flowstone record from Entrische Kirche Cave, an inneralpine cave situated close to the accumulation area of the Pleistocene ice-stream network of the European Alps that expanded repeatedly into the lowlands during glacial maxima. U-Th dating of this calcite is challenging due to high detrital Th. However, petrographic and stable isotope analyses in conjunction with associated clastic cave sediments provide useful insights into the climatic boundary conditions during speleothem formation and into the paleoenvironmental processes which operated in the ~. 2000. m-high catchment above the cave.Our data show that millennial-scale temperature fluctuations had a first-order control on the periglacial activity and vegetation in the catchment which strongly influenced the formation and infiltration of detritus into the karst aquifer. The brown laminated and brown dendritic fabrics that compose much of the detrital-rich flowstone succession reflect these environmental processes. The temperature-dependence of periglacial and permafrost processes allows to constrain the amount of cooling relative to the present-day mean annual air temperature that is required to initiate detrital-rich calcite formation in Entrische Kirche Cave, i.e. - 2.5. °C (minimum) to - 6 °C (maximum), respectively. White inclusion-poor calcite that is intercalated with the detrital-rich calcite indicates warm (interstadial) conditions and geomorphological stability in the catchment area. One such phase has been U-Th dated to 88.3 ± 6.9. ka (i.e. Greenland Interstadial 21 or 22). © 2011 Elsevier B.V.

Cliff R.A.,University of Leeds | Spotl C.,University of Innsbruck | Mangini A.,Forschungsstelle Radiometrie
Quaternary Geochronology | Year: 2010

U-Pb dating is increasingly used to date speleothems that are too old for precise U-Th disequilibrium dating; however there is little data that can independently validate its application to such material. This study presents U-Pb ages for speleothems from the Spannagel Cave in the Austrian Alps including a detailed comparison with U-Th ages from an unusually U-rich sample that yields precise ages by both methods. Sample SPA4 is a flowstone with three growth phases separated by distinct hiatuses. For the youngest growth phase the U-Pb and U-Th ages are 267 ± 1. ka and 267 ± 5. ka respectively; the middle growth phase is 291 ± 1 versus 295 ± 11. ka while for the oldest growth phase a single sub-sample, assuming the same initial Pb composition as for the younger phases, yields an age of 340 ± 2. ka compared to 353 ± 9. ka by U-Th. Correlation of these ages with the marine isotope stages confirms that these speleothems grew during glacial stages as suggested by previous work on the same sample. Sample SPA 15 has U-Th isotopic compositions indistinguishable from secular equilibrium; the U-Pb data on the main growth phase of this sample give an age of 551 ± 10. ka, whereas a single analysis from the oldest phase suggests it may be on the order of 40. ka older. This detailed comparison of U-Pb and U-Th ages provides important support for the potential validity of the U-Pb method in older samples beyond the range of U-Th. © 2009 Elsevier B.V.

Richter D.K.,Ruhr University Bochum | Schulte U.,Ruhr University Bochum | Mangini A.,Forschungsstelle Radiometrie | Erlemeyer A.,Trift 6 | Erlemeyer M.,Trift 6
Geologie und Palaeontologie in Westfalen | Year: 2010

Subject of the study are white, calcific speleoparticles of up to 4 cm that have been found within the loamy sediments of the Apostelhöhle, (SE Brilon, Germany). Because of their typical structure (braid sinter, spherulite sinter, rhombohedral crystal sinter, skeletal crystal sinter) and negative 18O-values (-6 to -17 %o VPDB), a cryogenic formation of the calcite particles can be assumed. TIMS U/Th-dating revealed a middle to upper Pleistocene age. Probably the calcites precipitated slowly "aufeis" in small water basins. After melting of the ice, the calcite particles were mixed with the cave sediments.

Richter D.K.,Ruhr University Bochum | Immenhauser A.,Ruhr University Bochum | Neuser R.D.,Ruhr University Bochum | Mangini A.,Forschungsstelle Radiometrie
International Journal of Speleology | Year: 2015

Electron backscattered diffraction (EBSD) applied to crystal fabric research in speleothems aids in our understanding of the origin of those fabrics. A significant advantage of this approach is the three dimensional data set of crystal c-axes. Here, we show a rare case of both convergent (radiaxial-fibrous) and divergent (fascicular-optic) orientations of the c-axes in pool calcites. The seemingly defective structure of the calcite lattice resulting in radiaxial-fibrous crystal orientations is probably caused by differential incorporation of Mg during crystal growth. The observation that radiaxial-fibrous and fascicular-optic fabrics co-exist in the same pool environment is remarkable and documents the complexity of the system. © 2015, Societa Speleologica Italiana. All rights reserved.

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