Osady stadiału Warty i młodsze osady plejstoceńskie w odsłonięciu kopalni węgla brunatnego Bełchatów

Abstract

W odsłonięciu kopalni węgla brunatnego zbadano jeden z profili na zachodniej ścianie wyrobiska, gdzie w 1977 r. ukazały się osady zbiornika jeziornego (Kwart. Geol., t. 22, nr 1), nie znane poprzednio z przekrojów geologicznych opartych na wierceniach.Pod osadami jeziornymi (obocznie) leży glina zwałowa stadiału Warty, a niżej utwory wodnolodowcowe i zastoiskowe. Możliwe jest też występowanie osadów interstadiału Pilicy. W stropie osadów jeziornych występują piaski rzeczne tarasów akumulacyjnych Widawki i utwory holoceńskie.Zbiornik wypełniony jest osadami jeziorno-bagniskowymi. Są to mułki, torfy i gytie akumulowane, jak wynika z analizy palinologicznej, w okresie chłodnym. Spąg osadów zbiornika datowany jest na 43700 lat, co wraz z sytuacją osadów i charakterem roślinności określa przynależność do środkowegovistulianu. Przypuszcza się kilkakrotne wahania klimatyczne.  WARTA STADIAL AND YOUNGER PLEISTOCENE DEPOSITS EXPOSED AT BEŁCHATÓW BROWN COAL OPEN-CUT MINEThe paper presents the results of studies and some conclusions concerning the deposits discussed in an earlier preliminary note (Kwart. Geol., vol. 22, no. I).In the studied exposure of brown coal open-cut mine (Fig. I), there was found till belonging to almost continuous Warta glacial horizon. The till occurs in the form of layer (Fig. 2), relatively thin but traceable at the distance of at least 0.5 km in southern part of the exposure. The following parts may be traced in the section: lower – stratified and pressed out, middle – uniform, with random arrangement of components, and upper with sandstone intercalations and partly weathered (Fig. 3). The layer is gently rising south of Tertiary tectonic trough (in which the mine is located), forming a coherent till plain near Kleszczów. The till is exposed in claypit at Kleszczów and at margins of esker at Antoniówka. Petrographic indices of the till from the open-cut mine (section A) and comparative material from Antoniówka are the same as those previously obtained for core material from the Widawka drainage basin (M.D. Baraniecka, Z. Sarnacka, 1971; J. Rzechowski, 1971).In northern part of the exposure, close to the axis of the tectonic trough, the till layer of the Warta Stadial is cut into patches. This is the case of the area of occurrence of deposits of cold climate lacustrine reservoir. Till patch stretching north of the reservoir (Figs. 2, 3) is characterized by local increase in thickness, variability in degree of reduction of carbonates, and change in colour from red to green-blue and gray, depending on reduction of iron oxides. Petrographic indices are debatable, somewhat differing of those typical of deposits of the Widawka drainage basin.In top part of Warta Stadial till, there was found a depression in which sedimentation has been taking place. Detailed profilling and palynological studies and 14C analysis made it possible to date the deposits and to reconstruct their origin and individual stages of their sedimentation.Deposits of the above mentioned reservoir are wedging out southwards and northwards, being underlain by fluvioglacial sands or tills of the Warta Stadial (Fig. 4).Sedimentation in the reservoir, monotonous at the first sight, is shown to be highly complex (Figs. 5, 6). The series deposited here comprises organic swampy and lacustrine deposits as well as minerallacustrine and sandy and silty ones. There were found three organic (humus) horizons: lower (lower peats and gyttja) , middle (gyttja and gyttja muds) and upper (upper peats), and some others.Lower peats are dated at 43,700 ± 3.700/2.400 y B.P., and upper peats – at 21 970±810 y BP.Qualitative palynological analysis showed the presence of Quaternary tundra vegetation in lower part of the section, and Quaternary elements with admixture of Tertiary pollens in the upper part. In the part of the section with palynological record, there were identified two very cold intervals with numerous representatives of Salaginella salaginoides at the base (samples no. 4 and 3), the maximum cold interval (samples no. 44–41–40) as well as two intervals characterized by relatively less severe climate and, possibly, the presence of tundra-forest vegetation (presence of spruce and lycopodium) at the boundary of the lower peats and gyttja (samples no. 1, la, 47) and layer no. 14, middle humus horizon (sample no. 26), respectively.Taking into account the types of deposits, changes in granulometric composition, the inferred breaks in sedimentation, content of humus or the complete lack of plant remains in some zones, and the results of palynological analyses, several climatic changes may be traced in the section (Fig. 6). Despite of small thickness, the section presumably represents a fairly long time interval: the 14C datings of the lower peats indicate that its accumulation began about 45,000 y ago. The lacustrine series is overlain by allochtoneous pavement, regarded as the boundary of the maximum and regressive phases in the development of the Vistulian icesheet in the regional scale. It follows that the lacustrine deposits may be assigned to middle part of the Vistulian.The pavement is overlain by Upper Pleistocene fluvial deposits of the Widawka River terraces and Holocene floodplain deposits (Fig. 5).In the studied sections, there were found a few horizons of disturbances of stratified deposits (Figs. 2, 5). Involution (? frost) structures are displayed by ice-dammed lake muds below tills of the Warta Stadial in the proximity of the section B. Traces of flow and, possibly, involution (frost) structures were also noted in upper peat layer close to the section F. Involution structures are also marked in more silty sands of the fluvial series near the section A.The studies on deposits displayed in the brown coal open-cut mine, reported here as well as in the earlier preliminary report (Kwart. Geol., vol. 22, no. 1) made it possible to date and trace distribution of Warta Stadial tills and to define composition and age of Vistulian lacustrine deposits unknown, in this area untill the open-cut mine has been constructed.