Kształtowanie rzeźby terenu między górną Rawką a Pilicą w czasie zaniku lądolodu warciańskiego
SUMMARY The research was carried out in the north-eastern part of Łódź Upland and in the neighbouring fragment of Mazovian Lowland, about 20-80 km to the E and SE of Łódź. The area, of about 1,400 km2, is located in the marginal zone of the Warta ice-sheet. The upper Rawka valley and its accompanying interfluves were thoroughly analysed, whereas the remaining areas were subject to a more surveying type of research. The northern part of the study area is more diverse than its southern part - consisting mostly of plains. Its main form is the upper Rawka valley, which in its central and eastern part reaches 5-6 km of width and 25-45 m. of depth. The widening was called the Upper Rawka Basin. The significant diversity of landscape is caused mainly by the rich inventory of glacial forms, constituting what may be generally called the slope zones of the depression and appearing island-like within the reach of fluvial terraces. One of the biggest kame complexes in Central Poland is found here. The fluvial elements of the Rawka valley are: Vistulian low terrace, elevated 3-6 m. over the bottom of the valley, and Holocene floodplain. Tomaszów Plain, situated in the southern part of the study area, is a flat moraine interfluve, slightly inclined from NW towards SE. Small river valleys (of Piasecznica, Gać, Struga, and Luboczanka) also run accordingly to that direction. The area of Rawa Interfluve within the study area is situated a little lower than the described interfluves on the western side. The relief is diversified by kame hills and ridges of different size, usually in groups of N-S or NW-SE orientation. The analysed area, in comparison with other parts of Łódź Upland, was characterised by very modest geomorphologic recognition until the nineteen-sixties. Only then the thesis about terminoglacial origin of most ¬¬of the local convex forms, formed, according to that theory, in the process of multi-stage frontal recession of the Warta ice-sheet (Balińska-Wuttke 1960; S. Z. Różycki 1961) was formulated. During the following years different views concerning the way of deglaciation in the area of Łódź Upland were presented (Klajnert 1966, 1978; Klatkowa 1972; Krzemiński 1974 among others), but upper Rawka valley and its vicinities hardly ever underwent this kind of geomorphologic research, taking into consideration modern structural, textural, and facial analyses. Another important fact for the decision of starting the research was that of little recognition of the post-Wartian relief transformations in this area. To fulfil the goals of this work it was necessary to apply various methods of research. During the field works morphologic research, covering typical range of morphometric measurements and morphographic analyses, as well as detailed sedimentological testing was done. Over 350 excavations and outcrops, including 30 especially for the study purpose, were analysed; 1100 borings up to 4 m. deep and 10 borings 6 to 9 m. deep were dug. Laboratory works included: – grain-size analyses (340 samples), – analyses of grain abrasion by B. Krygowski’s method (1964), – roundness of quartz grains degree by W. C. Krumbein’s method (1941), – morphoscopic marking by a modified method of A. Cailleaux (Cailleaux, Tricart 1959), – feldspar content analyses, – radiocarbon absolute dating, – pollen analyses - 60 samples made by Z. Balwierz. Maps, geologic sections, and other graphic materials based on author’s own ground works, borings and archival materials. Archival documentation of over 1200 borings, of which 170 punctured Quaternary formations was examined. QUATERNARY BEDROCK AND SEDIMENTS It was observed that structures and dynamics of the sub-Cainozoic bedrock had a considerable influence on the course of the last glaciation and, as a consequence, on the present relief. It is proved by the fact that main features of the Mesozoic bedrock relief of the study area are reflected in the present relief. In the case of particular forms of the Wartian age, both convex and concave, the prevailing direction of their morphologic axes is NW-SE. Transverse direction is also accentuated in the relief. Long segments of Rawka, Pilica, or Krzemionka valleys correspond to that direction. The facts indicate the influence of the elements of the anticlinorium block tectonic on the spatial layout of Wartian age forms. In connection with that the author is inclined to support the earlier conclusions (Baraniecka 1971; Klajnert 1978), that the layout of kame ridges (NW to SE orientation) was influenced by tectonic movements, active in the anticlinorium during the final Warta stage. General style of the Quaternary structure origination is characterised by a calm, undisturbed arrangement of the principal sedimentation series. The series are characterised by prevalence of sandy and sandy-gravelly formations over tills, silts and clays. In the Quaternary profiles the predominant deposits are those of the Middle-Polish Glaciation, the last one in this area, and among them - the Wartian ones. Older Pleistocene sediments are preserved mainly in the depressions of Mesozoic bedrock. Analysis of Wartian sediments leads to a statement that the Warta ice-sheet was comparatively thin, and at its maximum extent it reached Pilica river. Thus, the author tends to acknowledge the newer research results, among others those of M. D. Baraniecka (1984) and B. Trzmiel (1986). The ice-sheet waned in vast areas in a way typical of areal deglaciation. It is indicated among others by low proportion of tills to the meltwater sediments in an average Wartian profile. Such proportion is typical for the areas of areal deglaciation (Krzemiński 1974). Among deglaciation sediments the author distinguishes two main facies: meltwater and ablation sediments. Among the meltwater sediments one can distinguish glaciofluvial, glaciolimnic, and paraglaciolimnic sediments (term according to K. Brodzikowski, 1993). It has to be noted that in the study area these formations are specifically distributed, with glaciofluvial formations domination on the interfluves and paraglaciolimnic ones in the Upper Rawka Basin. An important feature of the spatial distribution of the deglaciation sediments is also a general increase of their thickness towards the depressions - towards the centres of the depressions in the immediate ice-sheet bedrock (Klajnert 1978; Klajnert, Rdzany 1989). That was where the meltwaters of the ice-sheet run, carrying the mineral material with them. The elevated areas under the ice-sheet, which still are elevations, are characterised by a reduction in deglaciation sediments. Merely till is often found there (fig. 20). MORPHOLOGY, INTERNAL STRUCTURE, AND GENESIS OF GLACIAL RELIEF FORMS Upper Rawka Basin was analysed most thoroughly. This form is a significant widening (up to 5-6 km) of the parallel fragment of Rawka valley between Jankowice and Boguszyce (ca 11 km). The depression reaches depth of 24-45 m. Its relief is clearly distinct from the less diverse flat interfluves, mostly those on the southern side. Among the presented landforms from the basin area are: – a kame ridge of the kame tongue type of paraglaciolimnic structure, and glaciofluvial-ablation ”kame cones” in the vicinity of Kochanów; – a group of kames between Głuchów and Naropna (among them: kame plateau, kame ridges of kame claw type e.g. Dębowa Góra, kame hills, outmelted depressions and erosion-outmelted depressions i.e. outmelted depressions widened by glaciofluvial erosion); there is a prevalence of paraglaciolimnic sediments in these kames; – a kame ridge of complex glaciolimnic-glaciofluvial structure at Zarzecze. Forms of similar structure have also been observed in the narrower segments of upper Rawka, both on the western and the eastern side of Upper Rawka Basin, among them: – paraglaciolimnic kame terraces in Popień and Wola Łokotowa; – a kame ridge of kame tongue type of deltoglacial structure in Rawa Mazowiecka - Tatar. Within of the moraine interfluves, adjacent to upper Rawka valley, the following features were analysed among others: Miłochniewice ridge, Złota esker, kames in the vicinity of Żelechlinek, and kames on the watershed of Rawka and Pilica, mainly in the neighbourhood of Koluszki and Czerniewice. It was noticed that the features existing here displayed a little greater differentiation in their structure than those in the Upper Rawka Basin. There were to be found the kames of perforation type, consisting mostly of paraglaciolimnic sands, and glaciofluvial kames in which series of coarse gravels several metre thick are visible. It was also observed that on the moraine plateau outside kames the glaciofluvial sediments lie as patches and the dips of diagonally layered deposits are from the side of watershed elevations towards valley depressions. Relief forms analysis in the area of Rawa Interfluve has also supplied evidence for the kame genesis of local convex forms - from great ridges, mainly glaciofluvial, to small hummocks and ”kame claw” type ridges. Among the forms of this area one may distinguish the 8 km long ridge between Julianów and Ossowice displaying diapire-like disturbances. Tomaszów Plain is different from the previously discussed areas in its much more levelled relief of little diversity. The area is mainly covered with till and glaciofluvial sediments with the prevalence of S and SE dips. Lack of kames is caused here by lack of water blocking during deglaciation, caused by strong fissuring of the ice body and the surface inclination towards SE. Large number of closed depressions, clearly visible in the landscape in spite of the long-lasting lake sedimentation, peat-land processes, and periglacial morphogenesis (eolian and slope processes) is characteristic for this area. An assumption has been made that the area also underwent the process of areal deglaciation. SPATIAL AND DYNAMIC DIVERSITY OF DEGLACIATION PROCESSES It was observed that the Warta ice-sheet encountered a landscape generally similar to the present one, which is evidenced by the fact that the youngest till pads the valley depressions, and on the interfluves it often lies on the land surface. The ice-sheet spread over the study area as a thin cover and soon became stagnant and then completely dead. Four main stages of deglaciation have been distinguished: 1. ice-sheet dying, 2. perforation deglaciation (Pilica-Rawka watershed, along which perforation kames developed), 3. formation of moraine interfluves (dead ice cover waning run then separately on the Tomaszów Plain - water flow southward, towards Pilica depression - and on the interfluves around the Upper Rawka depression), 4. formation of kame relief in the sub-ice depressions (mainly in the Upper Rawka Basin). The first, not numerous yet kames originated during the second deglaciation stage on the Rawka-Pilica watershed - where there was the thinnest ice-sheet and the most elevated ice-sheet floor. It was observed that those hills are built mainly of meltwater deposits, mostly paraglaciolimnic sands, which indicates that they are not front moraines, as it has been believed so far. During the third stage larger and larger areas of sub-ice elevations were uncovered from underneath the ice. The Rawka-Pilica watershed was at that time the watershed of ablation waters, flowing down South, towards Pilica depression on one side, and on the other flowing down North, towards the Upper Rawka Basin. It is confirmed by the measurements of diagonal stratification in glaciofluvial deposits. Dead ice remained for the longest time in the Upper Rawka Basin, where in the glacial lakes, between ice patches, various kames originated: multi-level terraces, plateaus, hills and ridges. It was the last, fourth stage of deglaciation. All forms that originated here are so to speak ”hidden” in the basin. It is significant that in the study area the relief of the immediate ice-sheet bedrock played fundamental role during all areal deglaciation stages. It controlled the location and the order of origination of thawing holes, the flow directions of ablation waters and the distribution of individual forms of glaciogenic relief (of kames). Three phases were distinguished in the development of kames in the study area: the limnic phase, the glaciofluvial phase, and the ablation phase. The phases correspond to, respectively (beginning from the floor): the glaciolimnic and paraglaciolimnic sediments, sands and gravels, and - in the peripheral area of kames - diamictone (ablation) covers with zones of gravitational disturbances (falls, landslides, subsidences). The phases were distinguished on the basis of recurring elements of the structure of kames. Meltwater sediments of the limnic stage, beginning from the floor, sometimes start with silts, typically glaciolimnic. Nevertheless, prevailing parts of them are of paraglaciolimnic origin. In most cases they are very fine-grained sands, sedimented in vast basins, under conditions of slow flow. As for this fraction they are well sorted. It is true that according to Folk-Ward indicators, it is most often medium sorting, but we have to bear in mind that these authors’ classification is too ”harsh” for glaciogenic sediments. Standard deviation (1) close to 0,6 - typical of these sediments - is very difficult to find in samples from different facies of Wartian sediments in the study area. During this phase the sediments were deposited, which form the essential part of the levels of accumulation terraces (kame terraces) and of accumulation-erosion terraces, ”stuck” to the slopes of the basin at different heights. Most of the morphologically diverse kame hills and ridges in the Upper Rawka Basin are also built of these sediments. Glaciofluvial phase started at the time, when water basins, due to the advancing disintegration of dead ice, began to diminish - they began to be even more flowable. During this phase paraglaciolimnic accumulation began to be replaced with accumulation of ablation waters of high-energy flow in the braided channels. At first, these waters cut the erosion-susceptible, formerly accumulated fine-grained sands, creating secondary erosional flattenings, vast ”gravel furrows” etc. in them. The sediments accumulated during this phase consist of series of various-grained diagonally stratified sands, and imbricated gravels. It is worth noticing that the flows and the accumulation and erosional activity of meltwaters during this phase of kame accumulation proceeded in temperatures near 0° C, which caused thermo-erosional processes to occur. These processes are documented with lumps of paraglaciolimnic sands. Often they are buried in glaciofluvial deposits and still preserve their original layering. In places of coarser material accumulation (e.g. gravel cones at the walls of dead ice), meltwaters operation was selective, leaving the coarse material in convex forms. So it was then - in the deglaciation conditions - when the first accommodation of relief to lithology took place, continued constantly in post-Wartian conditions, and also in the present conditions (concave forms come into being in fine sands and silts, whereas convex forms in coarse, gravelly material). The ablation stage may be characterised as the phase of forming of the peripheral parts of kames in the conditions, when the forms gradually raised above the surrounding dead ice. During this phase intensive mass movements, mainly falls and landslides, took place on kame slopes. They were accompanied by the development of faults and gravitational cracks. Simultaneously, lithologically diverse ablation material flowed and slid down from the ice walls and even from the considerably flattened ice-mineral surfaces. They interbedded gravitational structures and partially coated them. Further melting of dead ice blocks outside the kame hills - in the interkame (thawed) depressions, is recorded in numerous examples of strongly diverse lithologically ablation or intermediate between ablation and glaciofluvial material. Some dead ice blocks after the kame creation stage were still vast, which is indicated by the size of the melt depression of over 1 km in diameter. Formation of water flow systems between kames during the ablation stage, was the event that initiated the development of the post-Wartian river network. One can assume that as long as there were still dead ice blocks, releasing high amounts of water, buried in depressions, and the erosion bases were being lowered as a result of deglaciation, there were favourable conditions for river erosion, continued later in the interglacial conditions of the Eemian period. POST-WARTIAN TRANSFORMATIONS OF GLACIAL RELIEF It is a well known fact that the relief of the Łódź region is characterised by a considerable diversity in the degree of post-Wartian transformations. On the one hand, examples of forms or whole complexes of them, which have their glacial features well preserved are enumerated, and on the other, symptoms of intensive activity of destructive post-Wartian processes, visible particularly in the peripheral zone of the Łódź Upland, are exhibited. The author has observed a great diversity of post-Wartian relief transformations, in both the spatial and the chronological aspect, also in the area between Rawka and Pilica. It has been observed that the effects of post-Wartian erosional-denudational processes on the interfluves are inconspicuous. A little stronger relief transformations took place in the valley areas. In spite of this, the major part of kames preserved their morphological and structural distinctness also here. It is proved, among others, by the presence of ice-contact sediments and structures in edge parts of most of the forms. The facts are another confirmation for the thesis about the relative freshness of Wartian glacial relief, particularly in the interfluves in the Łódź region (Krzemiński 1974). Contemporary denudation processes, particularly the rill wash, especially active since the deforestation, cause road cuttings and ravines to develop in areas of diverse relief. Coarse-grained material is much more resistant to the denudation than fine-grained one and this is why mounds are usually built of gravels and pebbles, whereas depressions develop in fine-grained sands, silts, clays, muds, etc. (paraglaciolimnic sediments).