Late Quaternary Climate Variations Reflected in Baltic Sea Sediments - The Baltic Sea Basin - page 114

(density and magnetic susceptibility, Table 5.1 ) from core to core. The following
sequence of core comparisons has been used along the profile:

303610-12 → 303620-3 → 303640-6 → 303650-2 → 303590-3 →

303580-5 → 303660-5 → 303670-2 → 303690-2 → 303680-4 →

303720-3 → 303700-9 → 303710-2.

In Fig. 5.8 the results of core-to-core correlation are displayed with regard to
the lithostratigraphic correlation. The zones are colour coded whereby correla-
tion with a strength >0.4 are graphically shown only. It is clearly visible that the
freshwater sediments of the A zones (brown, blue and purple coloured) are well
developed within the basins whereas on the ridge between Gotland and Gdansk
Basin these sequences are represented by thinner sediment successions. This fact
can be explained by the higher proportion of detritus within the sediments and the
closer distance of the basin centres to the terrestrial sediment sources. The brack-
ish sequences of the B zones (green to yellow colours) display a different pattern.
An overall thickness of 1 m within the Gdansk Basin is to be compared with 4 m
thickness within the Gotland Basin and 7 m on the down basin part of the ridge.
This can be explained by the opening of the Öresund Strait about 8,000 cal. year
BP (Björck 2008 ) . As the Littorina transgression began the local coast-to-basin
transport is replaced by a lateral basin-to-basin transport. Driven by west to east
atmospheric energy transfer dense marine water enters the Baltic Basin and follows
the counterclockwise transport path including basin-to-basin flow (paragraph 2). At
the same time a halocline starts to develop inducing the typical estuarine (verti-
cal) current system. Suspended matter including particles from bottom (and coastal)
erosion and from biologic production in the uppermost part of the water column is
transported with the water masses from the west to the east and is being deposited
when transport energy slows down. This is the case in front of submarine chan-
nels and in the deeper basins explaining the sediment accumulation of the Stolpe
Foredelta and of the Eastern Gotland Basin.

5.5.3 Thickness Analysis

In order to extend the first results in thickness analysis of the main Late Quaternary
stratigraphic units within the Baltic Proper achieved by sediment core correla-
tion, the study has been extended to a spatial 2D analysis. The main focus was
directed to a comparison of thickness evolution of the early Holocene (pre-Littorina)
sediments of the A zones with the brackish Littorina sediments of the B zones
within acoustic cross-sections marked in Fig. 5.5 . The base of the early Holocene
(psammitic) Ancylus sediments (A zones) and the brackish muds (B zones) are
clearly defined by reflectors within the seismoacoustic signals. For the identification
of these two lithostratigraphic boundaries within the SES profiles the correlation
results of sediment cores located on the profiles have been used. In Fig. 5.9 the
procedure is explained by using the central basin profile Pr-0.