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1997 | 1 |
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Zagłębienia bezodpływowe w Polsce środkowej i przydatność analizy ich wypełnień do interpretacji paleogeograficznych

Title variants
Closed depressions in central Poland and a significance of their fillings to the palaeogeographical interpretation
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Closed depressions in Central Poland are different origin. Two main groups are anthropogenic
and natural forms. Many genetic types of the latter can be indentified, e.g.: l. blow-outs
accompanying dunes and their complexes; 2. fluvial depressions, e.g. cut-off oxbow lakes at
a various stage of decay; 3. karst collapse depressions, both young and largely buried by
younger sediments; 4. suffosion steep-walled kettles and gentle hollows; 5. a significant and
extensive group of Pleistocene forms in origin of which ice-sheet and permafrost are involved,
thus depressions conditioned by: a. irregular glacial accumulation, b. uneven postglaciotectonic
surface, c. dead ice melting out, and also from d. degradation of ground ice, e. progressive
melting of intrusive ice.
The Pleistocene in age depressions commonly occur on till plains and also in the upper
sections of dry valleys (Fig. l). Their significance consists, fust of all, in the usefulness of
their fillings to palaeogeographical reconstructions. It is the reason for which they were
a subject of detailed analyses. Also, an attempt to correlate the results with the existing
climatic curves of the Vistulian for Europe and Poland has been made. The interpretation
has been based on the studied profiles from closed depressions, supported by palinologic
documentation and radiocarbon dates. They are shown in Fig. 2, while the conclusions are
presented below.
During the Warta ice-sheet recession (150-140 ka BP) the relief of newly deposited tills and of
fresh postglaciotectonic surfaces created local base levels in which deposits of wash and solifluction
and afterwards mineral-organic sediments accumulated. There processes were retarded somewhat
by very poor communities of treeless tundra that changed gradually to a park tundra and a boreal
forest corresponding already to the interglacial succession. The Eemian landscape in Central
Poland was aboundant in closed depressions. The primary lakes (gyttja, mineral-organic silts) were
in the middle and upper Eem transformed into the raised bogs (peats, peat shales).
At some places the process of organic sedimentation went 9.n during the Vistulian (Fig. 2
- Rudunki, Krzepczów). The type of sediments as well as the type of plant cover of the fust
stadial of Vistulian (VS1) confum the opinion on an increase of humidity and a fall in
temperature. The AmersfoortjBrmup warming, about 10000 years, with the mean temperature
of July 15-l7°C and pine forest with larch, birch and spruce ~as followed by the second
Vistulian stadial (VS2) with the mean values for July slighthy above 5°C. The succeeding
interstadial, which in the vicinity of Łódź is called "Rudunki Interstadial" and is correlated
with the Odderade, is the final forest episode of the early glacial that lasted for about 60 000
years. Simultanously, the organic accumulation in Rudunki and Krzepczów fmished (Fig. 2).For the Plenivistulian, until the Denekamp, no correlative deposits (naither organic nor
mineral) have been found. Only the Krzepczów profile displays the probable fluvial sedimentation.
In the other promes the hiatus comprises all Plenivistulian warmings.
Form the Denekamp on, a lot of data on deposits and numerous 14C and TL dates are
available. The climatic deterioration enabled silts and fine-grained sediments with numerous
syngenetic frost deformations to form on slopes and in depressions. The maximum of cold
and aridity, with continuous permafrost, occurring in the Leszno and Poznań Phases corresponds
with the gravel-stone horizon. It is correlated with the "Beuningen Steinsohle" and dated at
20000-18 000 years BP. During the ice-sheet recession up to the line of Pomeranian moraines
thinly-laminated sands and their oversnow facies deposited. With the ice-sheet withdrawal up
to the Gardno Phase, there was renewal of aeolian activity, which has an equivalent at the
top of 'deposits of some depressions. The succession observed at the Rudunki site (Fig. 3) is
a case in point. However, other facies, e.g. on interlluves or in river valleys, can exist.
Omówiono genetyczne typy zagłębień bezodpływowych najczęściej występujących w środkowej
Polsce. Podkreślono dużą, ale zróżnicowaną rolę rodzaju ich wypełnień dla rekonstrukcji
paleogeograficznych. za najważniejsze uznano kopalne dziś zagłębienia wieku plejstoceńskiego.
Wybrane spośród nich przykłady pochodzące z własnych badań, z dobrze udokumentowanymi
osadami wypełniającymi, poddano dokładnej analizie, zwracając szczególną uwagę na sedymentologiczne
cechy osadów mineralnych, paleobotaniczną charakterystykę serii organicznych oraz
korelacje z wynikami pomiaru wieku bezwzględnego, uzyskanymi metodami 14C i TL. Na
podstawie tych danych podjęto próbę rekonstrukcji paleogeograficznej zmieniających się
warunków przyrodniczych w środkowej Polsce. Interpretację przedstawiono w porządku
stratygraficznym, poczynając od schyłku zlodowacenia warciańskiego, poprzez interglacjał
eemski, wczesny vistulian, plenivistulian i późny vistulian, do czasów współczesnych.
Wyniki, jako oparte na danych z denudacyjnych systemów zamkniętych, z natury swej
nie uwzględniają udziału procesów erozyjnych, a eksponują jedynie tendencje agradacyjne lub
fazy stabilizacji.
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