Geological Structure of the Quaternary Sedimentary Sequence in the Klaipeda Strait, Southeastern Baltic - The Baltic Sea Basin - page 143

tills or other lithological components, are also very changeable and not suitable for
the above-mentioned purposes. Thus, indirect methods are to be used to solve the
problems of stratigraphic correlation of tills.
The results of IR-OSL studies show that the inter-till sediments investigated in
the Klaipeda Strait were formed during the ice-free interval MIS 5d-5a. The sam-
pled inter-till sediments are occurring not in situ but as blocks (rafts) in the till bed
(Fig. 6.2 ) . This opinion is confirmed by an abundance of micro-glaciodislocations
observed in borehole cores (Figs. 6.4 and 6.5 ) . Based on the geotechnical proper-
ties of sediments, some additional conclusions about till age could also be drawn.
It was established that the geotechnical properties of the lowermost complex of tills
both in the Klaipeda Strait area and in the whole Klaipeda City region at altitudes
close to zero or below sea level significantly differ from those of the relief-forming
tills situated at higher altitudes (Gadeikis 1998 ) . There are some differences in the
density of tills (1.96-2.20 g/cm 3 for the younger and 2.21-2.24 g/cm 3 for the older
ones, respectively), but the biggest distinction is the module of deformation, which
varies from 16 to 74 MPa for the beds of relief-forming tills and reaches up to
100-110 MPa for older till beds. A big difference is observed in the values of
cone resistance, which are 1.1-5.0 and 5.0-14.0 MPa, respectively. According to
the presented geotechnical properties, the above-mentioned separate group of tills
was in different conditions of consolidation - the older one was additionally influ-
enced by compression from the glaciers and long-lasting lithification processes,
i.e. this till was formed significantly earlier than the relief-forming till beds that
belong to the late Weichselian (late Nemunas). This difference is very obvious in
the above-mentioned Olando Kepure section (Molodkov et al. 2010 ) .
Hence, we may conclude that the till containing these incorporated inter-till sed-
iments could be formed only during the Weichselian (Nemunas) glaciation. Some
other indications corroborating this hypothesis are also reported (ibid.).
The limnic sediments - sand alternating with silty-clayey or organogenic sedi-
ments - are widespread in the Klaipeda Strait area where they have been established
in tens of boreholes. Thus, it is possible to presume that during the MIS 5d-5a time
span a quite big freshwater sedimentary basin (or basins) existed within our study
area - very likely in the depression of the Baltic Sea; lately it served as a source of
terrigenic material for till formation during the Weichselian glacial advances.
According to the interpretation of results of pollen analysis, the pattern of
the vegetation development including the immigration of particular tree species
is different from those typical for Holsteinian (Butenai) and Eemian (Merkine)
interglacials, but is in good agreement with the biostratigraphical records of
the Drenthe-Warthe (Snaigupele, Lubavian, Schöningen) interglacial, late middle
Pleistocene that suggest the similar age of the investigated inter-till sediments
(Kondratiene and Damušyte 2009 ) . However, such interpretation is in disagreement
with our IR-OSL data.
Taking into account all the above-mentioned factual data, it is possible to main-
tain that the till bed beneath the bottom of the Klaipeda Strait was most probably
formed by a glacier advance during MIS 4, i.e. during the Weichselian early
pleniglacial. This till bed can be correlated with the lowermost till complex in the