Geoscience Reference
In-Depth Information
Fig. 2.10 Total and tectonic
subsidence curves for the
time period of Middle
Cambrian to Lower
Carboniferous - example of
the central basin part (well
D1-1, Baltic Sea)
break apart of continental landmasses and opening of the Tornquist Sea in the west
(Poprawa et al. 1999 ) . With progressing continental separation, the marine basin
expanded to the east, first within the area of what is known now as the Baltic Sea and
later into the present-day onshore regions. Lithosphere extension and sedimentary
and thermal loads of adjacent rift system, presumably situated west of the Tornquist-
Teisseyre zone, are accounted for the subsidence of the Baltic basin during that time
(Šliaupa 2002 ) .
The passive continental margin subsidence of the Baltic basin gradually deceler-
ated during the Ordovician causing further but slower basin subsidence. By contrast
to the Cambrian, subsidence in the western part of the basin was not compensated
by conformable sedimentation rates which imply cessation of the terrigenous source
in the west due to widening of the Tornquist Sea. The Ordovician is characterized
by a nearly continuous sedimentation in a basinal facies and in a shallow marine
environment. Minor thickness variations hint of considerable decreasing tectonic
activities.
2.3.3 Foreland Stage
Subsidence intensity started to accelerate in the Late Ordovician again and increased
drastically during the Silurian (Figs. 2.8 and 2.9 ) . This change in subsidence was
due to the flexural bending of the western margin of the Baltica plate because of
the docking of the East Avalonian plate in the west (Poprawa et al. 1999 ) . The pro-
gressing advancement of the North German-Polish orogenic build-up in the west is
reflected by the compensation of the subsidence by the sedimentary load during Late
Silurian time. The basin was finally completely filled by Early Devonian Old Red
deposits. By contrast to the hard coupling of Laurentia and Baltica, which caused
 
Search WWH ::




Custom Search