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Stages of the formation of the Łeba
Barrier-Lagoon system on the basis of the geological cross-section near Rąbka
(southern Baltic coast, Poland)
Karol Rotnicki1, Stefan W. Alexandrowicz2, Anna Pazdur3,
Tomasz Goslar4, 5, Ryszard K. Borówka6
1Institute of Palaeogeography and Geoecology, Adam Mickiewicz University,
Dzięgielowa27, 61-680 Poznań, Poland; e-mail: rotnicki@amu.edu.pl
2Polish Academy of Sciences and Arts, Sławkowska 17,
31-016 Kraków, Poland
3Institute of Physics, Silesian University of Technology, Krzywoustego 2,
44-100 Gliwice, Poland; e-mail: anna.pazdur@polsl.pl
4Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614
Poznań, Poland
5Poznań Radiocarbon Laboratory, Rubież 46, 61-612
Poznań, Poland; e-mail: goslar@radiocarbon.pl
6Institute of Marine Sciences,
Szczecin University, Mickiewicza 18, 70-383 Szczecin, Poland; e-mail:
ryszard@univ.szczecin.pl
Abstract
The article presents the
results of a detailed study of the geological structure of the Łeba
Barrier in the Rąbka cross-section (Southern Baltic, Poland). The barrier
separates Lake Łebsko from the Baltic. Five sedimentary complexes were
distinguished there (M2-M6). The spatial variability of the grain-size
distribution was examined and succession stages of the mollusc fauna occurring
in the individual sedimentary complexes were distinguished. Radiocarbon dating
was used to establish the age of the most important events during the process
of formation of the barrier, which took place in the course of several relative
sea-level changes. The first sedimentary complex (M2) at Rąbka is connected
with the second ingression (i2) of the Baltic Sea (ca. 6,700-6,000 14C
years BP), sea-level stabilization (6,000-5,500 14C years BP), and
at last sea-level lowering (5,500-5,000 14C years BP) in the region
of the Gardno-Łeba Coastal Plain. The sedimentary complex M3 developed in a
lagoonal environment when the barrier was situated north of its present
position (5,000-3,000 14C BP). The next lowering of the sea-level
made the lagoon shallower and caused the emergence of small but already
subaerial stretches of barrier land with a freshwater fauna in the north
(4,880±40 14C BP). With the next ingression stage (i3), which took
place between 4,500 and 3,000 BP, the barrier shifted to its present-day
position and the lagoon changed into a freshwater lake. From 3,000 to 1,700 14C
BP fossil soil and peats developed on the barrier surface as a result of
another sea-level lowering. The last ingression stages (i4 and i5), younger
than 1,700 BP, built up the barrier, practically in its today's location
(sedimentary complexes M4 and M5). The youngest sedimentary complex (M-6) is
represented by present-day beach sands.
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