ALPINE UPLIFTMENT AND REGIONAL CLIMATE: IS THERE A LINK?

The north Alpine molasse sediments of southern Germany and Austria were deposited during the Early to Late Miocene. This period is characterized by significant global change in oceanography and climate but also by a change in the regional paleogeography because of the ongoing Alpine orogeny. To address the influence of the Alpine orogeny on the regional climate and oceanography, the chemical and isotopic composition of fossil shark teeth and ostracods in molasse sediments are investigated.

Paleoecological evidence, Sr/Ca ratios, Sr-isotope compositions of ostracods and shark teeth, as well as the O-isotope composition of phosphate in shark teeth and mammalian fossils (dolphin teeth and seacow ribs) from the same horizon, support an open marine environment during deposition of the molasse sediments in the northern Paratethys, a marginal sea during the Miocene. The O-isotope compositions of ostracods and shark teeth vary in parallel, albeit with a different magnitude related to their ecological differences. Comparison of the present O-isotope data with that reported for planktonic and benthic foraminifera from the North Atlantic and Mediterranean Tethys, indicates similar trends between 20 to 14 Ma, compatible with a parallel climatic evolution and no influence of the Alpine orogeny on the regional climate at this stage. The Nd-isotope compositions of ostracods and shark teeth do not change markedly either, suggesting no major change in ocean circulation for the northern Paratethys during this time. The Nd-isotope compositions are generally similar to those measured for samples from the North Atlantic. For samples younger than 14 Ma, O- and C-isotope compositions of ostracods vary widely, indicating variable freshwater influence and complicating paleoclimatic interpretations. However, temperature changes deduced by a comparison of O-isotope compositions, Sr/Ca, and Mg/Ca ratios for the period from 12 to 8 Ma do not correspond to changes in global temperature, and may hint at a regional Alpine influence on climate.