An Integrated Stable Isotope Record from the Late Miocene Pannonian Basin System: the Ecology of Horses, the Life Histories of Bivalves, and Mass-balance Modeling

The Pannonian Basin System in Central Europe contains excellent sedimentary and fossil records through the Late Miocene. These records capture the transition from marine to lacustrine environments, and finally the filling of the basin by a large and steadily advancing delta front. The paleontological record of molluscs shows the turnover from marine to brackish-tolerant and freshwater taxa as well as morphological and ecological change within lineages. This dissertation analyzes terrestrial and lacustrine stable isotope data from the Pannonian Basin System as a record of environmental change. The terrestrial record is based on the horse Hippotherium, whereas the lacustrine record is a composite of newly-constructed profiles of mollusc shells and whole-shell data from the literature. These data offer new interpretations of basin environments, and permit a reevaluation of lake hydrology.;The terrestrial carbon and oxygen isotope record from Hippotherium spans nearly the entire duration of the adjacent Lake Pannon, and serves as a proxy of changes in vegetation and surface water. These respectively indicate the opening of the landscape, and the basin-wide integration of rainfall. Profiles of the isotope composition of aragonitic mollusc shells were constructed for eleven species from three lineages of Lymnocardium bivalves. These profiles indicate that bivalves achieved greater body size through greater longevity in similar fashion to melanopsid gastropods, which suggests that Lake Pannon offered stable habitats for its endemic fauna. Seasonal variations in temperature inferred from profiles are dampened in comparison to those in the literature, but this may be a consequence of vital effects or seasonal precipitation. The correlations between carbon and oxygen isotopes in Lake Pannon molluscs indicate a shift in lake hydrology from closed- to open-basin during the Late Miocene. The terrestrial and lacustrine isotope records constrain two mass-balance models of oxygen isotopes in Lake Pannon. One model incorporates the kinetic effects of evaporation on isotope fractionation. The second assumes that fractionation occurs at equilibrium and is defined to balance the isotope composition of mollusc shells. Both suggest similar patterns in water balance, and indicate that Lake Pannon had a substantial outflow that drove the transition to freshwater.