Pokrywowe utwory pyłowe w Polsce środkowej (najmłodszy less)

Abstract

COVERING SILT FORMATIONS IN CENTRAL POLAND (THE YOUNGEST LOESS)SummaryIn Central Poland are found patches of silt deposits no more than 1 m in thickness. In older literature these deposits have barely been discussed and thought to be only “deluvia”, or ice-marginal lake deposits, or even a product of boulder cay disintegration under conditions of arctic climate. Beginning with the year 1953, an opinion prevailed that this was the youngest aeolian loess (W. Pożaryski, 1953; S. Z. Różycki, 1965, 1967; J. Dylik, 1964, 1969; B. Manikowska, 1969). This, among others, is evidenced by glanurometric composition and colour, like in the case of aeolian loess (K. Konecka-Betley, 1972), as well as by their occurrence on various substratum and at various heights a.o. As a rule, at the bottom of this youngest loess are found pebbles showing aeolian polishing, at places in the form of “pavement”. Locally, this layer discloses large boulders, the surfaces of which are intensely wind-polished. At several sites of the section are found carbonates, washed out in other places. Interesting is here that the patches of tile depostits considered are as a rule elongated from WNW to ESE. This is also a characteristic feature of loess patches.As before, the discussion is focussed mainly on the problem of age of the youngest loesses found to occur in the areas of Central Poland. In his monography, devoted to the Pleistocene deposits found within the Vistula river break through the South Polish Upland, W. Pożaryski (1953) distinguished here the youngest loess, which as a rule occurs in a thin, one metre layer. The emphasized also a fact that the loess appears at places almost on the flood terrace of the Vistula river. This, among others was a basis, for W. Pożaryski to accept that the accumulation of the youngest loess had taken place at the Youngest (Upper) Dryas. Some authors (J. Dylik, 1064, 1969; S. Z. Różycki, 1965. 1067; B. Manikowska, 1069) are inclined to move back the period of sedimentation of this loess to the pleniglacial of Wòrm. However due to a fact that in many places the youngest loess of Central Poland enters the slopes and tops of low dunes, as, among others, it was emphasized by S. Z. Różycki (1965, 1967), the present author inclines to the opinion pronounced by W. Pożaryski in 1953 that the deposits under consideration were accumulated during the last, cool Wòrm phase, i.e. at the Youngest Dryas time. The period of the Youngest Dryas, amounting to about 800-900 years, was sufficiently long to deposit a somewhat less than one metre thick layer of the youngest loess, as it results from the research made by M. Pecsi (1969). In the Pleistocene deposits found in the vicinity of Warsaw there also occur loess-like silts underlying dune sands.It appears that exactly this layer is thought by some authors to be the youngest loess described above, and that this is why the age of the youngest loess is frequently removed. Most probably, the equivalent of the youngest loess is represented rather by the loess-like silts that occur at the top of the young Pleistocene terrace of the Vistula river and its tributaries, and are underlain with the soil produced during the AllerØd linterglacial.The examples presented in this paper are taken entirely from the areas of Central Poland. However, the deposits, discussed here are more widespread and this is why the present author intends to call attention of other scientists to this problem.In addition to this the author emphasizes the economical importance of the youngest loess on which fertile soils have developed. In connection with this it is necessary to protect these soils during the planning of industrial objects and housing estates.