Stable isotopic investigation of late Neogene terrestrial paleoecology and paleoclimate of the circum-Mediterranean region

The late Neogene was an interval of important global change, in which gradual cooling and aridification resulted in terrestrial ecosystems over much of the world that became essentially modern. In order to better undstand the late Neogene transition both regionally and globally, the research presented here focuses on reconstruction of terrestrial paleoclimate and paleoecology in Spain and Italy through the development of a stable isotopic record from biogenic and and authigenic minerals preserved in fossil mammals and continental sediments.A reconstruction of Late Miocene to Pleistocene paleoclimate and paleoecology in Spain was developed through analysis of the oxygen isotopic composition (delta18O) of biogenic phosphate in tooth enamel and dentine from fossil mammals. Comparisons of delta18O between clades are consistent with morphological interpretations of habitat and physiology, and suggest a semi-aquatic habitat for anthracotheres, hippopotamids, and castorids, and open or mixed habitats for most gracile taxa such as equids and cervids. Comparisons of enamel and dentine delta18O indicate slight diagenetic alteration of dentine, but also suggest that such comparisons can be used to reconstruct reasonable values of diagenetic water delta 18O. Since the delta18O of modern horses has been demonstrated to be a reasonable proxy for the delta18O of local meteoric water, which is in turn strongly dependent on mean annual temperature (MAT) for modern mid- to high-latitudes, the delta18O of fossil horses from Spain was used to reconstruct terrestrial paleotemperature. These reconstructions are consistent with global cooling during the late Cenozoic, with MAT for the late Miocene that is warmer than today by &sim1.2°C in NE Spain and by &sim4-5°C in SE Spain. The difference of &sim8.9°C between NE and SE Spain for the Late Miocene is &sim60% greater than the MAT difference between these same areas today.To examine the ways in which a desiccated Mediterranean Basin affected surrounding terrestrial environments during the Messinian Salinity Crisis (MSC), a paleoclimatic record of this event was developed through integrated analyses of sedimentology, delta18O, and the stable carbon isotopic composition (delta13C) of latest Miocene authigenic carbonates from the Baza Basin in southern Spain. A transition from dolomite- and calcite-rich palustrine and distal alluvial fan sediments to lacustrine diatomites and calcite-rich limestones is accompanied by a decrease in both delta 13C and delta18O, reflecting increased lake level under a wetter climate. The mean delta18O of latest Miocene lacustrine calcite is significantly lower than that of modern closed-basin lakes in the Iberian Peninsula, and likely represents overflow or through-flow conditions with inflow waters derived from the surrounding Betic mountains. This result is consistent with some aspects of climate model reconstructions of the MSC, which suggest strengthened storm tracks from the Atlantic Ocean over southern Europe. Orographic uplift of these air masses along the Betic Cordillera may have resulted in enhanced precipitation and runoff in southern Spain.To examine the interplay between tectonics, environmental change, and biological evolution, a paleoecological record was developed from the delta 13C of Late Miocene paleosols from the Baccinello Basin in northern Italy. These paleosols span the extinction of Oreopithecus bambolii, which was the only European hominoid to survive an important extinction event ca. 9.6 Ma. Oreopithecus is important for understanding the evolutionary history of Late Miocene hominoids, since its peculiar morphology precludes a simple interpretation of its phylogenetic position. The paleosol delta 13C values show very low temporal and spatial variability (indicating plant ecosystem stability through time) and provide no evidence for ecologically significant changes in floral composition spanning the Oreopithecus extinction event. These results validate assumptions about the importance of tectonics and species interaction as an underlying cause for the extinction of Oreopithecus and its associated fauna. The paleosol delta 13C values fall entirely within the range of isotopic variability for modern plants following the C3 photosynthetic pathway, indicating that C4 vegetation was not an important component of biomass. (Abstract shortened by UMI.)...