OXYGEN, STRONTIUM, AND NEODYMIUM ISOTOPE COMPOSITION OF FOSSIL SHARK TEETH AS A PROXY FOR THE PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY OF THE MIOCENE NORTHERN ALPINE PARATETHYS

The Upper Marine Molasse sediments of southern Germany were deposited during the Early to Middle Miocene, a period of significant change for the global Miocene palaeoceanography, palaeoclimate, and the regional palaeogeography because of the ongoing Alpine-Himalayan orogeny. To a ddress the influence of the Alpine uplift on climate and oceanography of the northern Alpine molasse basin, a combined O-, Sr-, and Nd-isoto pe study was undertaken on fossil teeth from sharks (Synodontaspis sp. , Galeocerdo cf. aduncus, Chaenogaleus sp.), and button-like teeth fro m the bony fish of the Upper Marine Molasse (Chrysophrys molassica). A verage delta(18)O values for hydroxyapatite of teeth from two sites ar e 20.3 parts per thousand (l sigma = 0.6) and 21.2 parts per thousand (l sigma = 0.5), while their average Sr-87/Sr-86 and Nd-143/Nd-144 rat ios are 0.70850 (+/-0.00001, 2 sigma) and 0.70882 (+/-0.00003, 2 sigma ), and 0.51220, and 0.51223 (both at +/-0.00001, 2 sigma), respectivel y. By comparison to the Sr-evolution curve for the global ocean, the S r-isotope compositions suggest ages of about 22 and 17 Ma for the teet h. These ages are in good agreement with the depositional ages, which suggests open marine conditions. Open marine conditions are also compa tible with (1) lower average delta(18)O values and 87Sr/86Sr ratios fo r the one site compared to higher delta(18)O values and higher Sr-87/S r-86 ratios for the other site, (2) estimates for seawater temperature s which are similar to other estimates from deposits of similar latitu de and age, (3) a comparison of seawater temperatures with average amb ient air temperature estimates deduced from continental palaeoclimate indicators. Nd-isotope compositions are compatible with an influence o f the North Atlantic on the Paratethys. Assuming constant salinity and seawater oxygen isotope composition, a 4 degrees C cooling can be inf erred from average delta(18)O values of the teeth between 22 and 17 Ma . This is similar to trends observed for foraminiferal records from th e Mediterranean Tethys, but different from foraminiferal and molluscan records of the North Atlantic and the North Sea during this period, a nd allows for the possibility that the Alpine orogeny had an influence on the regional, circum-Alpine climate. (C) 1998 Elsevier Science B.V . All rights reserved.