Paleotectonic evolution of the Zurcher Weinland (northern Switzerland), based on 2D and 3D seismic data

A new interpretation of the Permo-Carboniferous (PC) troughs in the Zurcher Weinland region in northern Switzerland is proposed on the basis of 2D and 3D reflection seismic surveys. The presence of two WSW-ENE oriented grabens separated by a crystalline basement horst block, confirmed by the Benken borehole, is well established, though the presence of PC deposits in its surroundings remains uncertain. The interpretation of the 3D seismic data shows a transtensive tectonic regime for this period confirming the results of earlier interpretations of 2D-lines. There is no evidence for a compressive Saalian phase (around 265 Ma) as postulated for the PC trough west of Weiach. Several observed faults show signs of reactivation during a late Triassic inversion phase. Detailed mapping of the Mesozoic sequence reveals that further and minor reactivations along the border of the PC trough south of Benken may have influenced deposition of the younger sediments and the local structuration of the base-Tertiary unconformity. The findings of the local investigations are interpreted in the context of large-scale paleotectonic models.