On the ostracod fauna of the Upper Sinemurian and lowermost Pliensbachian in the area of Tuningen (Baden-Wurttemberg)

This paper reports the results of an investigation of the ostracod fauna of the stratigraphic borehole Tuningen. The complete Turneriton (Upper Sinemu rian) was penetrated there, together with parts of the arietenkalk (Lower S inemurian) and Numismalismergel (Lower Pliensbachian). A total of 53 specie s of ostracods were identified belonging to of 28 genera, 4 suborders and 2 orders. In the lowermost obtusum-zone a large number of species are found; this div ersity reflects the Lower Sinemurian transgression, which opened connection s to other parts of the ocean and made possible the immigration of species from the Tethys (e.g. Progonoidea auleata). Higher in the obtusum-zone, the number of species decreases: with the exception of single occurrence of By thoceratina see bergensis and Nanacythere simplex, there are no species fou nd that are not also found in the lowermost obtusum-zone. The beginning of the oxynotum-zone marked the improvement of ecological conditions, and some species are found to reappear there. The transgression at the boundary of the raricostatum and the jamesoni-zones (with the opening of connections to the Burgundy Trough and the Rhone Basin and via the Hessian Strait - to th e North-West German Basin) resulted in no significant rise in the number of species, probably because of the existence of "swells" in the Black Forest and Nordlinger Ries areas (see SCHWEIZER 1968): these "swells" are charact erized by reworking and condensation, and the conditions on and around them could probably be tolerated only by specially adapted species. The present results support those of earlier investigations (see HERRIG 198 8). Thus, in accord with HERRIG's theory of faunal migration, Progonoidea a uleata and Polycope decorata disappear in the middle and upper obtusum-zone . And a faunal exchange occurred via the Hessian Strait during the late Sin emurian, which could only take place from south to north (HERRIG 1988). The log of the borehole Tuningen has been subdivided here into faunal horiz ons on the basis of its ostracod fauna; this has been done because it has p roved impossible to adapt the present results to those of previous investig ations (e. g. NEUWEILER 1954). The results presented here are now being ver ified in other selected sections from the same overall region.