Wetland vegetation types in the Late Miocene Alpine Molasse Basin in Upper Austria

Abstract

84 plant taxa have been identified by seeds, fruits and a few by flower fragments, which have been extracted from the lignite-bearing Late Miocene clayey sediments of Hinterschlagen (Hausruck area, Upper Austria). The fruit and seed assemblages from different samples show two distinct patterns: the dominance of aquatic herbaceous elements and the dominance of woody wetland elements. The combined mass-occurrence of Myriophyllum and Proserpinaca is documented for the first time in fossil seed and fruit assemblages in Europe. The combined numerous occurrences of Taxodium and Swida are also a new and distinct pattern. Eoeuryale irtyshensis and some other genera are reported for the first time from Austrian deposits. A new species of the Euphorbiaceae genus Acalypha is described. The numerous different genera indicate a variety of wetland habitats, like lakes of different sizes, sluggish streams, floodplain forests, hummocks, natural levees, and swamps. Pocosin-like habitats are not indicated by the Hinterschlagen assemblages but from other sites of the Hausruck area. Hinterland elements or elements of drier habitats are rare in specimens. The floristic composition points to a Cfa-climate sensu Köppen with about 16–17 °C mean annual temperature. The early Late Miocene (Early Pannonian = Early Tortonian) position of the sediments is concluded from the regional geology and the mammal assemblage from the Hausruck gravels at the top of the lignite-bearing sediments, which indicate the mammal zone MN 10 for the gravels and MN 9 (Early Vallesian) for the lignite-bearing sediments.