Palaeozoic structures at the margin of the Baltic Shield revealed by new and reprocessed marine reflection seismic data from Kattegat, south-west Scandinavia

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This study focuses on the late Palaeozoic tectonic evolution and deformation of the SW border of the Baltic Shield, Scandinavia. New and reprocessed seismic data are used to show a fault controlled structural depression in the Skagerrak–Kattegat Platform (SKP), located between the Baltic Shield and the Sorgenfrei-Tornquist Zone (STZ). The depression is characterised by a material with unusual seismic structures, which are undulating to conical, have a lateral width of about 5 km, and a height of more than 1 km. They are truncated at their top by the Top Pre-Zechstein unconformity, and they occur above Top Lower Palaeozoic. The stratigraphic interval where the undulating structures occur is characterised by unusually high seismic velocities. A plausible tectonic setting for the undulating structures is found in the tectonic and volcanic events during the Late Carboniferous–Early Permian. Correlation of seismic and drilling data suggests that the faults controlling the SW border of the Baltic Shield are of at least two generations. The Børglum Fault and the Sæby Fault are interpreted to be of Silurian age, and the faults of the SKP of Late Carboniferous–Early Permian age. A proposed erosional phase in Devonian or early Carboniferous time removed Lower Palaeozoic rocks from the SKP, before the deposition of Late Carboniferous sediments. Such an erosional phase may explain the well-established Devonian and early Carboniferous hiatus in Kattegat and surrounding areas. The seismic data display key features from Late Carboniferous and Early Permian times, in an area where such structures have survived subsequent erosion and deformation.