Stratygrafia mezoplejstoceńskich osadów lodowcowych

Abstract

STRATIGRAPHY OF MESO-PLEISTOCENE GLACIAL DEPOSITS

Summary

Both division and age of the lowermost glacial horizons, found to occur within the lowland area, are the most important problem in the Quaternary stratigraphy of Poland. These horizons are referred either to the South-Polish Glaciation, or to the Podlasie Glaciation, older than the former one and separated from it by the Przasnysz Interglacial. Drillings recently made by the Geological Institute in the central part of the eastern regions of Poland yielded new materials necessary to determine the age of the lowermost glacial horizons and of the accompanying deposits. Of particular importance are here Quaternary sections at Ferdynandów, Luszawa and Serniki, within the area of the Middle Wieprz River basin (Fig. 1). Here, Quaternary deposits, older than those of the Mazovian (Holstein, Likhvin) Interglacial, fill in several, more than 100 m deep valleys incised into the sub-Quaternary surface. These deposits are overlain with the lacustrine sediments of Mazovian Interglacial, dated by means of a spore-and-pollen analysis (at Ferdynandów - by Z. Janczyk-Kopikowa, 1963; at Serniki - by M. Sobolewska, 1956). Laboratory examinations of several thousand, samples of these drillings were made on the Geological Institute, under the leadership of J. Rzechowski. The examinations comprised petrographic, mineral and grain size compositions, chemical nature of deposits, physiography of quartz grains and rounding degree, allowing the author to subdivide the deposits examined into horizons, and to determine their genesis and conditions of origin. Pleistocene deposits, older than those of the Mazovian Interglacial, are related to the South-Polish Glaciation. They occur at three horizons. The lower horizon, the so-called Serniki Stage, consists of two phases and of one separating interphase. The lower phase is represented by boulder clays, up to 7.3 m in thickness (Fig. 2, bed 3). The interphase deposits are built up of fluvial sands amounting to 58.4 m in thickness (Fig. 2, bed 4), laid down under cool climate conditions. The upper phase of the Serniki Stage is represented by glacifluvial deposits and by boulder clays, up to 9 m thick (Fig. 2, beds 5 and 6). The deposits of the Serniki Stage are overlain with three series of various facies related to the fluviatile deposits of the Luszawa Interstadial. The sequences of each of these series begin with a channel facies (gravels with sands), ending with predominating silts or even clays of flood and of old channel facies (Fig. 2, beds 7, 8 and 9; Fig. 3, beds 4, 5 and 6). Climatic optimum fell on the decline of the second accumulation and the accumulation of the third interstadial series. The thickness of the interstadial deposits amounts to 58.8 m. To the Luszawa Interstadial belong also silts and peats of an overgrowing basin at Kolonia Bronisławów (Fig. 1), disclosing Pinus, Betula, Picea and pollen grains of more thermophilic trees (B. Grabowska). The upper horizon of the South-Polish Glaciation, called the Kock Stage, is represented by sands with glacifluvial gravels, by boulder clay, frequently weathered at the top, or by periglacial talus covers, up to 24.25 m in thickness (Fig. 2, beds 10 to 14; Fig. 3, beds 7 and 8). In its unweathered part the boulder clayis everywhere characterized by similar boulder indices, this being its characteristic feature that differs it from the boulder clays of the Serniki Stage (Table 1, Fig. 4). On the whole, the section of the deposits related to the South-Polish Glaciation, found to occur in the area of the Middle Wieprz River basin (Fig. 5), is similar to that of the part of Pleistocene, older than the Mazovian Interglacial, in the Lower Bug River area and within the north-eastern region of Mazovia. This is a basis to correlate the respective deposits, as shown in Table 2. Such a correlation with the adjacent areas allows us to draw the following conclusions:

1. The Pleistocene deposits, older than those of the Mazovian Interglacial, may be subdivided into three horizons, the lower and the upper of which being developed in glacial and glacifluvial facies, the middle one (Luszawa Interstadial, Przasnysz Interglacial?) - in both fluvial and lacustrine facies;

2. The thickness of the middle horizon is always greater than that of both remaining horizons;

3. All the deposits fill in the valleys incised row the sub-Quaternary surface. The depths of these valleys range from 100 to 250 m;

4. The Quaternary sequence begins in such valleys mainly with boulder clays underlain, at places, with a thin bed of sands and gravels. Any more distinct traces of fluvial deposits, which could be expected to occur under such geological conditions, are absent. This is an important evidence that permits us to accept a thesis that the valley-type lowerings, like those described above, found to occur in the Quaternary substratum, are the result of a quick and deep erosion stimulated by an intense although short-lived uplifting of the earth crust.