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The last interglacial-glacial cycle recorded in Polish loess - selected problems.

Zdzisław Jary1
1 Department of Physical Geography, University of Wrocław

V 2.13 in Löss und terrestrische Archive (Fortsetzung)

18.09.2012, 17:00-17:20, H8

Loess sequences are commonly considered as one of the most valuable terrestrial sources of palaeoclimate information. This is because of the assumed way of loess deposition: continuous through all the Quaternary period as at the Chinese Loess Plateau or almost continuous deposition during the cold Pleistocene phases in Europe.

The most important factor that effects the spatial differentiation of loess covers is climate. Loess covers are researched in vertical sections - loess-soil sequences. Such sequences consist of the litho- and pedostratigraphic units, successions that are characterized by the specified properties. They are formed as a result of depositional, deformational and pedogenic processes which can be reconstructed. These processes have changed in particular place and time as consequences of the impact of environmental factors, which refer to the regional and global succession of climate events.

Polish loess areas are situated in the southern part of the country as part of the European northern loess belt. The Late Pleistocene succession, which is the most common one, has been investigated by many researchers. However, the most widespread Late Pleistocene stratigraphic schemes were elaborated by Jersak (1973) and Maruszczak (1976, 1991).

Jersak’s scheme consists of four units: pedocomplex Nietulisko I and two calcareous loess units (younger loess IIa and IIb) separated by the fossil tundra-gley soil complex of Komorniki type. Jersak (1973) mainly relied on the palaeopedologic criteria and detailed observation of periglacial structures. He was a strong opponent of stratigraphy based on the results of TL ages. He has never made correlation between loess-soil units and a continuous record of oxygen isotopes in deep sea sediments (Jersak et al., 1992).

There are four loess units above the Eemian – Early Weichselian pedocomplex Gi+GJ1 according to Maruszczak’s (1976, 1991) scheme: lowest younger loess (LMn), lower younger loess (LMd), middle younger loess (LMs) and upper younger loess (LMg). These loess units are separated by three interstadial soils: Gi/LMn, Gi/LMd and Gi/LMs. The stratigraphic correlation of particular litho-pedostratigraphic units defined by Jersak and Maruszczak is not obvious. Additionally it is complicated by the fact that Maruszczak subsequently changed his original interpretation and characteristics of some lithostratigraphic units.

Maruszczak correlated the litho- and pedostratigraphic units of Polish loess with marine oxygen isotope stages on the basis of many TL dates made by Butrym (1985). The Lublin TL chronology of loess was almost entirely consistent with the chronology proposed by Martinson et al (1987). Excessive confidence in the results of Lublin TL dating caused in many cases the abandonment of basic research of lithological properties of lithostratigraphic units. The result of TL dating was the most important and sometimes the only one characteristic feature of loess-soil units.

The development of a more reliable chronology for Last Glacial loess is one of the most important tasks for ongoing research. This can be partly verified using parallel OSL and 14C dating methods (Jary 2007).

There are more controversial topics concerning of Late Pleistocene loess research and interpretation in Poland, which should be taken into account in future investigations:

·          The time span and ecological condition for the formation of the last interglacial-early glacial pedocomplex (S1) in various geographical and topographical settings. This question is connected with a number and chronostratigraphic position of cryogenic wedges with primary mineral infilling, which are common features within this pedocomplex. It is also difficult to determine the number of stages with forest type pedogenesis. There is some evidence that in loess areas of western Poland forest soils developed in all 3 warm substages of MOIS 5.

·          Chronostratigraphic position and correlation of the interstadial soil complex L1S1 developed in the upper part of the lower younger loess unit L1L2. The L1S1 soil is the most important fossil soil complex within the Weichselian loess succession. It separates two main stages of loess accumulation during the Last Glacial. It is the only carbonate free soil in the Last Glacial loess sequence. The substrate of this soil is characterized by high indices of chemical weathering indicating a considerable role of soil processes. However, morphological characteristic and presence of periglacial phenomena suggest a tundra-gley type of pedogenesis. 14C dating of macro-remnants or humus substances is usually much younger in comparison with TL and OSL dating.

·          Genetic interpretation of tundra-gley horizons within L1L1 loess unit, their number, chronostratigraphic position and correlation. There are several weak tundra-gley horizons within Upper Pleniweichselian loess sequences L1L1, which are evidence of short climate variations in the time of loess accumulation. Nevertheless, their recognition and correlation is not unambiguous. There are usually 3-8 tundra-gley horizons the L1L1 unit.

·          The number and environmental interpretation of ice wedge cast generations within the Last Glacial loess-palaeosol sequence. The ice wedge casts indicate the occurrence of permafrost. In stratigraphic schemes developed by some researchers 2, 3 or 4 horizons of such structures are shown, while within the field exposures only 2 horizons of ice wedge casts are noted in superposition.

 

References

Butrym, J. (1985): Application of the thermoluminescence method to dating of loesses and loesslike formations. - In: Maruszczak, H. (ed.): Problems of the Stratigraphy and Paleogeography of Loesses. Guide-book of the International Symposium, UMCS, Lublin: 81-90.

Jary, Z. (2007): Zapis zmian klimatu w górnoplejstoceńskich sekwencjach lessowo-glebowych w Polsce i w zachodniej części Ukrainy (Record of Climate Changes in Upper Pleistocene loess-soil sequences in Poland and western part of Ukraine). Rozprawy Naukowe Instytutu Geografii i Rozwoju Regionalnego Uniwersytetu Wrocławskiego 1, Wrocław: 136 pp.

Jersak, J. (1973): Litologia i stratygrafia lessu wyżyn południowej Polski (Lithology and stratigraphy of the loess on the Southern Polish Uplands). Acta Geographica Lodziensia 32: 139 pp.

Jersak, J., Sendobry, K. & Śnieszko, Z. (1992): Postwarciańska ewolucja wyżyn lessowych w Polsce (Evolutions of Loess covers in Poland During the post-Warta period). Prace Naukowe Uniwersytetu Śląskiego w Katowicach 1227: 198 pp.

Maruszczak, H. (1976): Stratygrafia lessów Polski południowo-wschodniej (Stratigraphy of South-Eastern Poland Loesses). Biuletyn Instytutu Geologicznego, 297: 135-175.

Maruszczak, H. (1991): Zróżnicowanie stratygraficzne lessów polskich (Stratigraphical differentiation of Polish loesses). - In: Maruszczak, H. (ed.): Podstawowe profile lessów w Polsce (Main section of loesses in Poland), Wyd. UMCS, Lublin, A: 13-35.

Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C.Jr. & Shackleton, N.J. (1987): Age Dating and the Orbital Theory of the Ice Ages: Development of a High-Resolution 0 to 300,000-Year Chronostratigraphy. Quaternary Research 27: 1-29.

 



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Letzte Änderung 07.08.2012