期刊名称：Annales Universitatis Mariae Curie-Skodowska. Sectio B, Geographia, Geologia, Mineralogia et Petrographia
印刷版ISSN：0137-2025
出版年度：2007
卷号：LXII
出版社：Maria Curie-Sklodowska University, Lublin
摘要：Grain size is the most important loess lithologic property. Grain size composition depends mainly on factors connected with depositional processes (i.e. variety of source areas, distance from source areas, frequency and intensity of dust transporting winds).
The influence of postdepositional processes on changes in grain size composition seems to be of less importance with the exceptions for warm and long periods of intensive pedogenesis, which are favourable for formation of clay minerals. Therefore it can be assumed that grain size differentiation within thick loess sections may be used as a proxy record of climate changes during loess cover development.
As a result of field investigations, four Upper Pleistocene loess-soil sequences were chosen from western part of Ukraine: Korshov, Rivne, Novyj Mylatyn and Zbarazh. The thickness of loess deposits ranges between 6 (Zbarazh) and 11.5 m (Korshov). All these profiles were sampled in vertical sections at close intervals (5-10 cm) and documented in respect of their stratigraphy, sedimentology and palaeopedology. The following analyses were conducted: grain-size distribution (laser diffraction method), magnetic susceptibility and CaCO3 contents.
There are two horizons within the last glacial loess-soil sequences strongly deformed by solifluction and other slope processes: lower part of LMd (lower younger loess), directly above eemian-early glacial pedocomplex Gi+GJ1 (Horohiv) and lower part of LMs (middle younger loess) just above tundra-gley soil complex Gi/:Md (Dubno). Within these layers the most spectacular grain size changes have been found. Therefore we can assume that during the sedimentation of these layers the most considerable, rapid climatic-environmental changes occurred.
The results of grain size analyses indicate the occurrence of short depositional cycles within the thick upper plenivistulian loess sequences of LMg and LMs. Relatively coarse loess is alternated with fine-grained loess. Times of high dust influx coincided with severe climate conditions inferred from grain-size variations. Periods of decreased, fine-grain loess accumulation and development of weak pedogenic gley horizons, marked by relatively low values of magnetic susceptibility, probably represent warmer episodes. However, the number of weak tundra-gley horizons within particular thick loess successions (Korshov, Rivne, Novyj Mylatyn) varies from 5 to 8.
Currently, it is not possible to state univocally, whether depositional cycles and weak tundra-gley horizons within loess successions are connected with local climatic oscillations or they should be linked with global Dansgaard-Oeschger events recorded in ice-cores.
Further investigations of thick Upper Pleistocene loess-soil sequences are necessary to solve the problem of genesis, extent, time and correlations of this feature within Polish and Ukrainian loess areas.
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