Geoscience Reference
In-Depth Information
Fig. 2.1
Depths of the Early Precambrian crystalline basement below the sedimentary section of
the Baltic basin (nearly equivalent to sediment thickness). Wells referred in the text are shown.
Dotted lines
indicate major faults. TTZ indicates Teisseyre-Tornquist zone
Latvia and 2,300 m in western Lithuania. The maximum thickness of sediments is
reached in the western part of the basin (central north Poland) where the depth of
the Early Precambrian crystalline basement exceeds 4,000 m. The basin extended
further to the southeast and the northwest prior to the Caledonian deformation phase
and its extent had been limited to the subsidence and sedimentation area northeast
of the Danish-North German-Polish Caledonides thereafter. Today, the Baltic basin
The western boundary of the basin is formed by the Teisseyre-Tornquist zone.
The oldest non-metamorphosed sediments, infilling local depressions in the
Baltic basin area, are of Mesoproterozoic age. The corresponding Hogland Series is
locally distributed in the Gulf of Finland, on Saaremaa Island and on the Kurzeme
Peninsula. The series is represented by quartz sandstones and conglomerates inter-
calating with mafic and felsic volcanic rocks. The isotopic age of the volcanic rocks
was dated from 1580 to 1670 million years using the K-Ar dating method (Puura
the Gulf of Finland, where the layers are tilted at an angle between 5 and 30
◦
. These
rocks are spatially associated with cratonic granitoids of Middle Proterozoic age
(Vyborg, Riga massif). Contemporaneous Sub-Jotnian sediments are mapped in the
Gotska Sandön Island (north of Gotland). They are composed of quartz sandstones,
which fill local half-graben structures with up to 400-500-m-thick sections. Ages of
these sandstones are dated to a time period between 1490 and 1540 Ma (Gorbatchev
