Miocene shifts of the drainage divide in the Alps and their foreland basin

The sediment budget of circum-Alpine basins has been quantified in order to compare sediment masses derived from the northern (western) versus the sou thern (eastern) flank of the Alps. The evolution of the major catchment are as since Oligocene times is shown in a series of sketch maps. A fast shift of the drainage divide towards the N at similar to 17 Ma and b ack to the S at similar to 11 Ma is deduced in the Swiss and Western Alps. The shifts affected a catchment area of similar to6,000 and similar to 13,0 00 km(2) in size, respectively. Since no indications of a relevant asymmetr y in climate, especially contrasting precipitation, exist in Miocene times for the two opposite flanks of the orogen, a tectonic explanation for the s hifts of the drainage divide is favoured. Important catchment reorganizatio ns in the Alpine foreland, occurring also at 17 Ma and 11 Ma, were forced b y Alpine collision and uplift in Lower Austria (Amstetten swell, as part of the Bohemian massif), and thrusting and uplift of the Swiss Jura, respecti vely.