2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 3
Presentation Time: 8:30 AM


TÜTKEN, Thomas, Institut de Minéralogie et Géochimie, Université de Lausanne, BFSH 2, Lausanne, 1015, Switzerland, VENNEMANN, Torsten W., Earth science, Univ of Lausanne, BFSH 2, Lausanne, 1015, Switzerland and JANZ, Horst, Institute for Geochemistry, Univ of Tuebingen, Wilhelmstr. 56, Tuebingen, D-72074, Germany, thomas.tutken@img.unil.ch

The Steinheim basin is a 3.5 km wide crater in Upper Jurassic limestone of the Swabian Alp formed by a meteorite impact during the middle Miocene (~14.3 Ma). The crater basin was successively filled by freshwater, forming a long-term-lake with strong lake-level fluctuations during its several 100 kyrs history within a period of large-scale global climate change. The up to 36 m thick, fossil-rich, calcareous lake sediments contain a diverse invertebrate and vertebrate fauna. According to the mammal remains Steinheim is dated to the mammal zone MN 7 (~13.5 to 14 Ma), for which it represents the international reference locality.

δ13CVPDB and δ18OVPDB values of tooth enamel-apatite of different sympatric large herbivorous mammal taxa (Gomphotherium, Anchitherium, suidae, cervidae, rhinocerotidae) were used as proxies for paleoenvironmental conditions in the Steinheim basin and for a paleoecologic reconstruction. Mean δ13C values of –12.4 to –10.2‰ are similar to those of other investigated Central European Miocene localities, indicating a C3 plant diet. Mean δ18OCO3 values vary from –6.3 to –7.7‰ except for the cervids, which have a δ18OCO3 value of –4.1‰. Despite the small overall isotopic variability the taxa display systematic intra-specific differences with rhinoceroses having the lowest and Gomphotherium the highest δ13C values. Several cervids, a Palaeomeryx, and a peccary have δ18OCO3 values between –3.9 to –1.8‰, possibly due to consumption of plant tissues with 18O-enriched water. The δ18OH2O value of the lake water, probably being the only drinking-water source on the Karst plateau, will be calculated from enamel δ18OPO4 values using existing species-specific calibrations for large mammals.

The fossil freshwater snail Gyraulus of the Steinheim basin displays a gradual evolution of the shell morphology triggered by lake-level fluctuations and changes in lake water chemistry. A similar evolution is observed for the sculpture of ostracod carapaces and the changes in abundance of surface and deep-water dwellers. δ18OCO3 values of aragonitic Gyraulus shells and calcitic ostracod carapaces from the seven different planorbid beds will be used to calculate the water temperatures using the δ18OH2O values derived from the mammal teeth and to infer the development of the lake water composition.