Fresh- and brackish water fish faunas (otoliths) from the Oligocene of the western Paratethys – proxies for continental climate, palaeogeography and biostratigraphy

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Reichenbacher, Bettina
Holding Date 08 October 2008

Fish otoliths can be used to identify teleost species. Thus, fossil otoliths contribute largely to the knowledge of fossil teleost faunas. This is especially true for the Cenozoic because marine, brackish and lacustrine Cenozoic sediments often bear fish otoliths in large numbers, whereas determinable fish skeletons are rare. In the western Paratethys area of Switzerland and Southern Germany, otolith-based brackish and freshwater fish faunas appear abundantly from the late Early Oligocene ( 29 Ma) until the late Early Miocene ( 16 Ma). Cyprinodontids or toothcarps (with 50%) and ambassids or glassfishes (with 25%) are the dominating fishes until the late Oligocene, other taxa (e.g. umbrids, atherinids, eleotrids) appear in varying numbers. The fish communities indicate shallow, warm, fresh inland waters in a subtropical climate. However, during the latest Oligocene, a major shift in the fish faunas is apparent. The number of euryhaline species, i.e. atherinids and eleotrids, increased severely, whereas the pure freshwater taxa, i.e. umbrids, vanished. The changes can be related to a prominent break in the environmental conditions. Previously widespread freshwater settings disappeared or were replaced by brackish and hypersaline water bodies. The environmental shift, however, indicates a climate change in the continental realm of the western Paratethys from warm and wet to hot and dry conditions, perhaps similar to the present climate of the Arabian Gulf area. Furthermore, the sudden appearance of marine-euryhaline taxa in the non-marine habitats, i.e. mugilids and moronids, indicate influences from the Mediterranean Sea that can be interpreted as the precursors of the so-called Aquitanian transgression. The continental Paratethys fish fauna of the earliest Miocene (early Aquitanian) is principally rather similar to that of the latest Chattian. Despite of this, it can be easily distinguished from Chattian fish faunas because of strong changes among the taxonomic composition of the cyprinodontids (e.g. replacement of Palaeolebias by Prolebias). The endemic evolution of the cyprinodontid species throughout the Oligocene and early Miocene has allowed for to establish an otolith zonation for the continental deposits of the western Paratethys.