Geology and sedimentary history of Lake Traunsee (Salzkammergut, Austria)

Traunsee was formed by glacial overdeepening of a pre-existing fault system. Present-day morphology is characterized by a deep (189 m) narrow trough with steep slopes (>50°) in the southern part surrounded by the Northern Calcareous Alps. The northern part of the lake is bordered by flysch and glacial deposits with gentle slopes (<30°) and exhibits several ridges, basins and troughs. During the late and postglacial period, more than 45 m of sediment has accumulated in the central basin. Sedimentation in the southern part of Traunsee is mainly controlled by the river Traun forming a prograding delta in the south and — within the past 50 years — by industrial tailings consisting mainly of calcite. Sediments are distributed by undercurrents and by turbidites. Cores from the central basin thus show an intercalation of Traun-derived dolomite-rich sediments with anthropogenic muds from the tailings deposited up to more than 6 km from its source. Within the northern basin, land slides from the flysch region played an important role leading to drastic changes in the morphology of slopes and adjacent basins. These slumps have persisted until historic times. Sedimentation in the shallow sublittoral regions is dominated by benthic biogenic decalcification. The frequency of turbidite sedimentation within the profundal basin decreased during the last 200 years probably due to man's activities in the drainage area such as regulation of rivers and torrents. Sedimentation rates during the past decades range from 2–3 cm/a in the southern basin to 0.4 cm/a in the northern part as shown by 137Cs-dating.