Osady czwartorzędowe w rejonie Piecek na Pojezierzu Mazurskim

Abstract

Przedstawiono budowę geologiczną osadów czwartorzędowych i ich podłoża w okolicach Piecek na Pojezierzu Mazurskim na tle ogólnego rozwoju obszaru. Stratygrafię oparto na analizie wykształcenia i zalegania utworów, uwzględniając wyniki ekspertyz palinologicznych wykonanych przez Z. Borowko-Dłużakową i I. Grabowską. Poza poziomami glacjalnymi wyodrębniono trzy różnowiekowe serie jeziorne, które zaliczono do interstadiału rozdzielającego stadiały zlodowacenia południowopolskiego (interglacjału małopolskiego według S.Z. Różyckiego, 1978), interglacjału mazowieckiego oraz eemskiego. QUATERNARY SEDIMENTS IN THE PIECKI AREA, MAZURY LAKELANDIn 1981, four drillings Babięta, Goleń, Jakubowo, and Baranowo were made in the vicinities of Piecki, Mazury Lakeland (Figs. 1,2). The drillings penetrated the Quaternary to be stopped in the Tertiary. Eocene marine clays and muds from the borehole Baranowo are the oldest strata recorded. The remaining three drillings were stopped in noncalcareous clays and muds, possible Miocene in age (Fig. 3). The recorded depth of occurrence of top surface of the Tertiary in the drillings Babięta, Goleń, and Jakubowo gives further support to the assumed high position of this surface in the Piecki area. In turn, the drilling Baranowo showed the presence of a new element of the sub-Pleistocene relief - a deep depression with the base situated at depth over 100 m below sea level. Similar deep sublongitudinal valleys formed during the Cromerian Interglacial were previously reported from the neighbouring areas.Palynological analyses of core material from the drillings Goleń and Baranowo showed the presence of sediments of the Eemian and Masovian interglacials in the former (Fig. 3), and those of an interglacial separating lower and upper stadials of the South-Polish Glaciation (Małopolska Interglacjal of S.Z. Różycki, 1978) in the latter. There were identified seven till horizons separated by series of fluvial, lacustrine, fluvioglacial, and ice-dammed lake sediments.The Cromerian Interglacial is represented by well washed fluvial sands from Babięta (Fig. 3).The complex of South - Polish Glaciation sediments comprises two till horizons underlain and separated by fluvial, lacustrine, fluvioglacial, and ice-dammed lake sediments. Ice-dammed lake muds from Baranowo are the oldest member identified here (Fig. 3). Tills of the lower and upper stadials of the South Polish Glaciation were found in all the boreholes (Fig. 3). They are separated by lacustrine and fluvioglacial or, locally, possibly fluvial sediments. At Baranowo, the lacustrine sediments are represented by a layer of clays with plant detritus, one meter thick (Fig. 3). Palynological analyses showed interglacial character of these sediments. The Author assigned the clays to the interstadial separating stadials of the South-Polish Glaciation (Małopolska Interstadial of S.Z. Różycki, 1978 - Table 1). The clays are overlain by deluvial loam full of plant detritus, covered in turn by fluvioglacial sands. The South-Polish Glaciation till horizons are separated by fluvial sands coeval with the clays in the remaining boreholes.The Masovian Interglacial is mainly represented by lacustrine sediments. Sediments from the borehole Baranowo are similar in development to the interglacial from the borehole Węgorzewo III (W. Słowański, 1975 - Figs. 3 and 4), comprising red-brown strongly clayey deluvial loams overlain by lacustrine sands with intercalations of silts and clays and an admixture of humus matter. In the borehole Jakubowo, red-brown strongly clayey deluvial loam is overlain by lacustrine muds with thin layers of plant detritus. The muds are separated by a horizon of fluvial sands (Figs. 3). The interglacial horizon is represented by a peat layer and overlaying finely detrital gyttja with gravels and silty sands in the borehole Goleń (Fig. 3).Till of the Pre - Maximum Stadial of the Mid - Polish Glaciation was found in the borehole Baranowo only, and that of the Maximum Stadial - throughout the whole area (Fig. 3). The latter is overlain by fluvioglacial sands with gravels in the boreholes Jakubowo and Goleń. The fluvioglacial sands are in turn covered by till of the Masovian Stadial (Fig. 3). Thick packets of ice-damme lake muds and silty sands with intercalations of varved clays are referable to the end part of this stadial.Eemian Interglacia lacustrine muds with small gastropods were found in the borehole Goleń (Fig. 3). Muds with single lumps of humus matter, found in the borehole Baranowo (Fig. 3), may be of the same age.Two till horizons (of the Leszno and Pomeranian phase) were assigned to the North – Polish Glaciation. The tills are accompanied by fluvioglacial and, locally, ice-dammed lake sediments.In the Piaski area, Quaternary sediments are the thickets (over 250 m thick) and most completely developed in the vicinities of Baranów (Fig. 3). This became possible because of origin of a very deep valley (possibly along previously existing glacial furrow) in the Cromerian Interglacial times. Quaternary sediments are markedly thinner throughout the remaining part of the area and even the succession appears incomplete in several places. This suggests that the area was a highland throughout the major parts of the Pleistocene.The present-day relief of the Piaski area was shaped in connection with deglaciation of the North- Polish Glaciation ice sheet, as well as due to the subsequent denudation processes.