Climate and tectonic controls on Pleistocene sequence development and river evolution in the Southern Vienna Basin (Austria)

The impact of climate and tectonism on sedimentation and lithofacies development is demonstrated for Austria's largest Pleistocene sedimentary basin situated within the Vienna Basin. The coarse grained, massive facies is associated with high-energetic flood events reflecting a distinct seasonality effect of discharge during glacial times. In contrast, fine grained, well stratified sediments mark periods of rather high discharge to sediment supply ratios during warmer periods. Preservation of depositional sequences was facilitated by subsidence rates of approx. 0.5–1 mm/a. High subsidence rates in the basin preserve a relatively large record of sequences compared to fluvial terraces which reflect mainly sediments deposited during and shortly after glacials. 14C and relative ages demonstrate the strong impact of oscillations in climate on fluvial stratigraphy covering times from the upper period of MIS 3 to MIS 1.
Abundant sediment supply and the associated increase in accumulation space as well as tectonic factors affect not only the sequence development but also the geomorphology of two mountain front alluvial fans which toe out into the Mitterndorf Basin. High discharge to sediment supply ratios leads to fan incision and to abandonment of fan surfaces. During phases of reduced sediment supply the effect of subsidence results in headcut erosion, and, if sufficient time is available, may lead to complete through trenching. Abandoned fan surfaces are exposed to widespread soil formation which mark sequence boundaries to the following coarse grained, massive facies reflecting high sediment supply to discharge ratios.