Geological Evolution and Resources of the Baltic Sea Area from the Precambrian to the Quaternary - The Baltic Sea Basin - page 34

2.4.4 Late Cretaceous Inversion Phase
Tectonic processes ceased during the Middle Permian and were of minor activity
throughout the main part of the Mesozoic. In the southwesternmost part of the Baltic
basin, tectonic activity strongly increased during Late Cretaceous. Strike-slip and
reverse faults were established within the Bornholm-Darlowo fault zone (Krzywiec
et al. 2003 ) that is a part of a larger Fennoscandian border zone. The island of
Bornholm is a composite fault block. The island and associating Palaeozoic fault
blocks are bounded by WNW-ESE and NNW-SSE trending faults. The faults of
the Mesozoic blocks follow the same trends in part, but the fault orientations have a
wider scatter and an additional NW-SE trending segment. This wrench-dominated
Mesozoic faulting was related to the reactivation of the Pre-Permian fault system.
The Sorgenfrei-Tornquist zone continued to experience tectonic activity in Triassic
and Middle Jurassic times. The zone has experienced an uplift of up to 1,700-2,000
m during the Late Cretaceous to Early Tertiary inversion tectonic phase and the Late
Tertiary regional uplift of Fennoscandia.
An intense Late Cretaceous inversion tectonics is also documented from south-
ern Lithuania and the Kaliningrad district. Amplitudes of inverted structures reach
200 m there (Šliaupa 2004 ) .
2.5 Tectonic Evolution of the Southwestern Basin Rim During
the Early Palaeozoic
The Baltic basin extended further to the west and the southwest during its pas-
sive continental margin stage. The situation changed with the build-up of the
Danish-North German-Polish Caledonides during the foreland stage of the main
basin. An Early Palaeozoic thrust and fold belt formed the southwestern basin rim
since that time (Meissner et al. 1994 , Hoffmann and Franke 1997 , McCann 1998 ,
Katzung 2001 ) . Detailed biostratigraphical analysis of Lower Palaeozoic sediments
from Maletz ( 1997 ) gave evidence for a Llanvirnian age of the first Caledonian
deformation phase. Frost et al. ( 1981 ) dated the low-grade metamorphism of the
Ringkobing-Fyn High to 440 Ma. This metamorphic age seems to mark the peak
of the orogenic processes within the area. Isotope studies from Lower Palaeozoic
sediments of the boreholes from Rügen Island point to a major deformation in the
Early Silurian (Giese et al. 1995 ) . Beier and Katzung ( 2001 ) reconstructed three to
five Caledonian deformation phases and interpreted those as deformation signs in
an accretionary wedge in the forefield of Avalonia that was subsequently thrusted
over the passive margin of Baltica.
Provenance studies of sediments from the Rügen and the Danish area indicate a
sediment transport from a Gondwana-type western provenance and a mixing with
a Baltica source during Late Ordovician to Silurian times (Vecoli and Samuelsson
2001a , b ) , thus reflecting the docking of Eastern Avalonia to the margin of Baltica.
Furthermore, in Bornholm Silurian tuffaceous sandstones deposited in front of the