HR: 08:00h
AN: T31E-01    [Abstracts]
TI: Changes in the Circum-Alpine Climate as a Function of the Alpine Upliftment: Constraints from Isotopic Compositions of Fossils, Sediments, and Vein Quartz
AU: * Vennemann, T W
EM: Torsten.Vennemann@unil.ch
AF: Institute of Mineralogy and Geochemistry, BFSH-2 University of Lausanne, Lausanne, CH-1015 Switzerland
AU: Tutken, T
EM: Thomas.Tuetken@uni-tuebingen.de
AF: Institute of Mineralogy and Geochemistry, BFSH-2 University of Lausanne, Lausanne, CH-1015 Switzerland
AU: Kocsis, L
EM: Laszlo.Kocsis@unil.ch
AF: Institute of Mineralogy and Geochemistry, BFSH-2 University of Lausanne, Lausanne, CH-1015 Switzerland
AU: Mullis, J
EM: Josef.Mullis@unibas.ch
AF: Mineralogic-Petrographic Institute, Bernoullistr. 30 University of Basel, Basel, CH-4056 Switzerland
AB: The Tertiary circum-Alpine Molasse sediments were deposited during major periods of Alpine tectonism but also at a time of large global climatic change. They are well suited to study the effects of tectonic forcing on climate, because the sediments were deposited in marginal basins, partly to completely isolated from other major oceanic basins. Hence, a comparison of the past climatic and oceanographic evolution indicated by the sediments to those on a global scale, does allow for a qualitative evaluation of the relationship between tectonism and regional climate. Much is known about the geological-geochronological framework of alpine tectonism, including associated erosional rates and sediment volumes. Estimates of changes in paleoelevation and its direct influence on climate have, however, been less well constrained. Three independent lines of evidence indicate significant altitudes of the Alps during the Miocene: 1) H isotope compositions of clay minerals, formed as weathering products and subsequently deposited as part of the Alpine Molasse, have δD reaching values as low as -97‰. 2) O isotope compositions of retrograde metamorphic vein and fissure quartz and H isotope composition of its included fluids have δ¹⁸O values as low as -3.5‰ and δD values of -140‰, respectively. 3) ``Exotic" shark teeth from Swiss Upper Marine Molasse sediments that have δ¹⁸O values (VSMOW) around 11‰ (n=2), values unlike those from other teeth of the same locality (20.7 to 21.8‰; n=6), but for which the REE patterns support the same diagenetic history, hence supporting a freshwater formation of the low δ¹⁸O teeth (also supported by distinct Sr isotope compositions). Using these three approaches as a basis for estimating the isotopic composition of past precipitation and applying the present-day altitude effects on the compositions, it can be concluded that the Miocene Alps had mean altitudes of about 1500 to 2000 m, that is elevations similar to those of today. Paleoclimatic reconstructions from North Alpine Molasse sediments are based on oxygen isotope compositions of fossil mammalian tooth enamel for freshwater molasse deposits, and shark teeth, marine ostracoda, foraminifera, and mammalian phosphatic fossils for the Upper Marine Molasse deposits. The δ¹⁸O values (VPDB) of carbonate in phosphate from Oligocene and Miocene large mammal teeth (n=270), for example, vary over a large range from -11.9‰ to -0.5‰, but these variations parallel the composite O isotope curve of Tertiary benthic foraminifera, thus reflecting major global climatic changes such as the Late Oligocene warming, Mid-Miocene climate optimum, and Middle to Late Miocene cooling trends. The δ¹⁸O values (VSMOW) of phosphate in shark teeth (19.8 to 23.3‰; n=130) from Miocene marine molasse sediments as well as those of ostracods and foraminifera from these sediments all have variations that parallel those of composite curves for global changes. Collectively, the data support a Neogene paleogeography with a high mountain belt adjacent to marginal marine or freshwater depositional basins but with a regional climate, at least for the northern Molasse realm, that was strongly coupled to the global climate. The Alps thus appear not have influenced the local climate and/or atmospheric circulation patterns significantly.
DE: 8177 Tectonics and climatic interactions
SC: Tectonophysics [T]
MN: Fall Meeting 2005