Geological Evolution and Resources of the Baltic Sea Area from the Precambrian to the Quaternary - The Baltic Sea Basin - page 16

Fig. 2.2 Main sedimentary basins in the vicinity of the Baltic Sea area (after Bandlowa 1998 ,
Ziegler 1990 , Hoffmannetal. 2001 )
The younger Jotnian quartzites, siltstones and conglomerates are reported from
the Gotska Sandön area and the southern periphery of the Åland rapakivi massif in
the north of the Baltic Sea. These sediments have also accumulated in graben depres-
sions, reaching 900 m of maximum thickness. According to Gorbatchev ( 1962 ) ,
the Gotska Sandön sandstones were accumulated between 1300 and 1400 Ma.
They were deposited in fluvial, tidal or aeolian environments and are generally not
affected by folding or other deformation.
After a long break in sedimentation, the deposition was re-established in Early
Ediacaran time. Corresponding sediments are preserved in local areas of western
Latvia and the adjacent offshore (well P6-1, see Fig. 2.1 for location). The Early
Ediacaran sediments are defined as the Zura formation and composed of 2-30-m-
thick partly tuffitic sandstones and conglomerates, siltstones and shales.
The first wide transgression in the Baltic region took place in Late Ediacaran-
earliest Cambrian time (Figs. 2.2 and 2.3 ) . Sea transgressions occurred from the east
and from the west. Therefore a typical western facies is distributed in the south-
west of the Baltic Sea and in the adjacent onshore area which is attributed to the
Zarnowiec formation (wells A8-1, B16-1) and the Nexø formation (Bornholm area).
Sandstones and conglomerates exceeding 100 m thickness were mainly deposited
in a floodplain environment (Jaworowski and Sikorska 2003 ) .
The Late Ediacaran transgression in the east was of a much wider extent and
related to the gradual widening of the Moscow marine basin in the east. Arkosic
conglomerates and sandstones of up to 200 m thickness are the dominating sedi-
ments there. The succession is bounded by the lowermost Cambrian blue clays of
the Moscow basin (Jankauskas and Lendzion 1994 ) . They are up to 120 m thick and
crop out along the northern coast of Estonia.