Lithostratigraphy and correlation of the Dogger sediments in the boreholes of Weiach, Riniken and Schafisheim

Middle Jurassic sediments (the 'Dogger Group' of Switzerland) in three Nagra boreholes (Weiach, Riniken and Schafisheim) are correlated on the basis of facies relationships with the equivalent sediments at outcrop in the Jura mountains of canton Aargau (Switzerland) and southern Germany. In Weiach, the Dogger Group is dominated by mudrocks and forms a typical basinal sequence known locally as the 'Schwaebische facies'. By contrast, in Schafisheim the sequence is very similar to the outcrop in the Aargau Jura mountains and is represented by carbonate sediments forming a typical platform facies. The Dogger Group sediments at Riniken lie in an intermediate position and comprise an interfingering of platform and basinal facies. In all three boreholes a series of shallowing-upward regressive cycles can be recognized in the Dogger Group sediments. These cycles are correlated with world-wide sea level changes. The culmination of the shallowing-upward sequences is usually marked by the occurrence of iron-rich oolites formed during periods of low sedimentation rate either at the end of a regressive phase or during rapid sea level rise at the beginning of the subsequent transgression. (author) 34 refs., 5 figs., 1 tab