Geoscience Reference
In-Depth Information
Fig. 2.3
Geological subcrop map (Pre-Quaternary level) of the Baltic region and geological cross
section (
dotted line
shows location of the profile)
A drastic rearrangement of the sedimentation pattern took place in the mid-
dle of Early Cambrian time. While sedimentation ceased in the Moscow basin, a
vast marine transgression from the west took place and resulted in the deposition
of quartz sandstones, siltstones and shales. The thickness of the Cambrian section
attains 250 m in the central part of the Baltic Sea and more than 500 m in the area of
central north Poland. Figure
2.4
shows thickness maps of sub-stages of the Middle
Cambrian. The distribution of those sediments is nearly consistent to the recent out-
line of the Baltic Sea. Although later erosion also plays a role in the distribution of
these formations, the outline impressively supports that this time period is defined
as the nucleation stage of the basin.
The Cambrian is overlain by a shaly carbonaceous succession of Ordovician
age, which is between 60 and 160 m thick in the offshore part and reaches up to
250 m thickness onshore. The sediment pattern shows a split between a carbonate-
dominated facies in the east and a deeper marine facies with graptolitic shales in
