Vertebrate microfossils from the Upper Freshwater Molasse in the Swiss Molasse Basin: Implications for the evolution of the North Alpine Foreland Basin during the Miocene Climate Optimum

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 426; pp. 22 - 33
• Main Authors: Jost, Jürg, Kälin, Daniel, Börner, Saskia, Vasilyan, Davit, Lawver, Daniel, Reichenbacher, Bettina
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.05.2015
• Subjects: atmospheric precipitation; basins; Central European region; Channidae; climate; climate change; Cyprinidae; Cyprinodontiformes; egg shell; euryhaline species; evaporation; fauna; Freshwater; freshwater fish; Germany; Gobiiformes; hinterland; humidity; microfossils; Miocene Climate Optimum; Otoliths; paleoclimatology; Reptiles; rivers; sediments; Small mammals; Switzerland; teeth; temperature; Turtle eggshells; turtles; Europe, North Alpine Foreland Basin; Switzerland; Germany; Central European region; Reptiles; Otoliths; Small mammals; Turtle eggshells; Miocene Climate Optimum
• DOI: 10.1016/j.palaeo.2015.02.028
• ISSN: 0031-0182

The older part of the Upper Freshwater Molasse (OSM) in the Swiss and South German Molasse Basin records the extended warm period known as the Miocene Climate Optimum. However, dating and global correlation of fossils and palaeoclimatic data from OSM sediments remains challenging, because sections are often incomplete and biostratigraphic data sometimes ambiguous. Here we present the rare case of a fossiliferous OSM section that can be securely dated to the late Early Miocene and early Middle Miocene (c. 16.1–15.7Ma). Vertebrate microfossils have been recovered from three levels in superposition. Fish teeth document primary freshwater fishes (Cyprinidae, Channidae), but otoliths found in the middle level indicate dominance of euryhaline fishes (Cyprinodontiformes, Gobiiformes). The herpetofaunal assemblages largely consist of taxa that were widely distributed in Central Europe during the Miocene Climate Optimum and fragments of turtle eggshells assignable to the Oofamily Testudoolithidae Hirsch, 1996. The small-mammal fauna is dominated by the cricetid Megacricetodon bavaricus Fahlbusch, 1964. The fossil biota implies that the lowermost level (late Early Miocene, c. 16.1Ma) represents a palaeo-soil that formed under humid conditions, while the levels above it (early Middle Miocene, c. 15.7–15.8Ma) record a warm freshwater pond subject to evaporation (middle level), and mean annual temperature ≥17°C in the vicinity of a river with an open hinterland (upper level). Our results, together with previous data, suggest that the palaeoclimate of the North Alpine Foreland Basin of Switzerland and Southwest Germany was humid during the late Early Miocene and earliest Middle Miocene, and that the Middle Miocene onset of seasonality and low mean annual precipitation occurred by c. 15.7–15.8Ma. We conclude that global climate change and the 100-kyr orbital eccentricity minimum at 15.75Ma may have triggered the decrease in humidity in the North Alpine Foreland Basin. •Microvertebrates are reported from c. 16.1 to 15.7Ma old continental sediments.•Palaeoenvironmental reconstructions for the Upper Freshwater Molasse are presented.•Palaeoclimate of the Molasse Basin was humid during the late Early Miocene.•Middle Miocene onset of seasonality most probably occurred by c. 15.7–15.8Ma.•Decrease in humidity may be related to 100-kyr eccentricity minimum at 15.75Ma.