Vegetation, climate and palaeoaltitude reconstructions of the Eastern Alps during the Miocene based on pollen records from Austria, Central Europe

摘要

To reconstruct the flora, vegetation, climate and palaeoaltitude during the Miocene (23.03-5.33 Ma) in Central Europe. Six outcrop sections located in different basins of the Central Paratethys in Austria. Pollen analysis was used for the reconstruction of the vegetation and climate. The altitude of the Eastern Alps that are adjacent to the Alpine Foreland and Vienna basins has been estimated using a new quantification method based on pollen data. This method uses biogeographical and climatological criteria such as the composition of the modern vegetation belts in the European mountains and Miocene annual temperature estimates obtained from fossil pollen data. Pollen changes from Early to Late Miocene have been observed. The vegetation during the Burdigalian and Langhian (20.43-13.65 Ma) was dominated by thermophilous elements such as evergreen trees, typical of a present-day evergreen rain forest at low altitudes (i.e. south-eastern China). During the Serravallian and Tortonian (13.65-7.25 Ma) several thermophilous elements strongly decreased, and some disappeared from the Central European region. This kind of vegetation was progressively substituted by one enriched in deciduous and mesothermic plants. Middle-altitude (Cathaya, Cedrus and Tsuga) and high-altitude (Abies and Picea) conifers increased considerably during the Langhian and later on during the Serravallian and Tortonian. Pollen changes are related to climatic changes and to the uplift of the Alpine massifs. The vegetation during the Burdigalian and Langhian reflects the Miocene climatic optimum. The decrease in thermophilous plants during the Serravallian and Tortonian can be interpreted as a climatic cooling and can be correlated with global and regional climatic changes. This study shows that the palaeoaltitude of the eastern part of the Eastern Alps during the Burdigalian was not high enough for Abies and Picea to form a forest. Therefore, we inferred that the summits of most of the mountains would have been less than 1800 m. The substantial increase of middle- and high-altitude conifers in the pollen spectra suggests that the uplift rate increased during the Langhian in this region. Based on higher palaeoaltitude estimations for the pollen floras from the studied sections of Austria, we infer that the uplift of the easternmost part of the Alpine chain continued during the Serravallian and Tortonian.