Geological Evolution and Resources of the Baltic Sea Area from the Precambrian to the Quaternary - The Baltic Sea Basin - page 19

the west (Laskovas 2000 ) . Deposition occurred nearly continuously throughout the
Ordovician. The sedimentation rate considerably accelerated during the Silurian.
Thickness patterns show an increase to the west and a maximum thickness of
around 3,500 m in the southwestern part of the Baltic Sea (and north Poland).
This maximum thickness was even larger in the past since parts of the section have
been eroded. The Silurian is composed of graptolitic shales with some marlstones
and limestone interlayer in the deeper marine central basin parts, while carbonates
predominate in the shallow periphery of the basin (Lapinskas 2000 ) .
Sedimentation shifted to the central part of the Baltic basin during the Devonian
(Fig. 2.3 ) . Shallow marine and lagoon carbonates and marlstones alternate with
sandstones and shales which were deposited in shallow marine and continental envi-
ronments. The maximum thickness is reached in the Klaipeda area (west Lithuania
and adjacent offshore) with up to 1,050 m. Lowermost Carboniferous sediments
(sandstones and carbonaceous shales with a thickness of up to 110 m) are of limited
extent and so far only known from northwest Lithuania, southwest Latvia and the
adjacent offshore areas. Numerous Carboniferous diabase sills are also identified in
the central part of southern Baltic Sea (Šliaupa et al. 2004 ) .
The Permian, Mesozoic and Cenozoic deposits show a shift of sedimentation
to the southwest (Fig. 2.3 ) . By contrast to the Palaeozoic period, which was mainly
marked by rather continuous sedimentation and persistent subsidence, the Mesozoic
and Cenozoic periods were dominated by non-deposition which was only partly
interrupted by recurrent marine transgressions from the west (Fig. 2.5 ) . The Upper
Permian consists of carbonates and evaporates with a maximum thickness of up to
350 m in the southern part of the Gdansk depression. The Lower Triassic reaches
its maximum thickness in the same area and is composed of red coloured lacus-
trine mudstones with subordinate fine-grained arkosic sandstones (Suveizdis and
Katinas 1990 ) . The Jurassic succession shows a typical development from lacustrine
sediments in the lower part to marine sediments in the upper part. It is composed
predominantly of fine-grained sandstones, siltstones and shales and shows lime-
stone interlayer in the upper part. The thickness attains 200 m in the southern
Baltic Sea area. Two distinct facies can be defined in the Cretaceous section. While
sediments of Albian age are composed of glauconitic sandstones and siltstones,
chalk, marlstones and siltstones are typical for the Upper Cretaceous. The total
thickness of the Cretaceous section reaches 400 m along the southern coast of the
Baltic Sea.
Cenozoic terrigenous sediments are mapped only in the southernmost part of the
Baltic Sea and further south onshore. The thickness of the Palaeogene attains 80 m.
It is composed of shallow marine shales, sandstones and siltstones. A large deltaic
complex with amber deposits developed in the western part of the Kaliningrad dis-
trict. Sediments of Neogene age are distributed south of the Baltic Sea. They were
deposited in lacustrine-alluvial environments and are composed of fine-grained
sandstones, siltstones and shales of grey and dark-grey colours.
Figures 2.3 and 2.5 give a summarizing picture on the geological setting
and the development of sedimentation in the Baltic basin and the surrounding
areas.