Klasyfikacja form kemowych na tle typów i dynamicznych etapów deglacjacji

Abstract

CLASSIFICATION OF KAME FORMS IN THE LIGHT OF TYPES AND OF DYNAMIC STAGES OF DEGLACIATION

Summary

The article was prepared on the basis of the materials gathered by the geological crew of the Department of Lowland Geological Surveys, Geological Institute. A possibility of classifying kames was analysed, and a classification was presented for discussion. The dependence of kame forms upon the type and stage of deglaciation within the Lowland area and the forelands of the Świętokrzyskie Mountains and the Lublin Upland was considered, too. The examples presented in Fig. 1 come from the area of the maximum extent of the Middle-Polish (Riss) Glaciation, and from the areas covered with the inland ice of the Mazovian-Podlasie and North-Mazovian Stages that belong to this glaciation, as well as from the areas of the North Polish (Würm) Glaciation. Kames are considered here to be one of numerous relief types found to occur within the areas of the continental glaciations. The origin of these forms is related to the deglaciation periods. The following is the author’s definition of the kame forms: positive (convex) forms of relief, formed at the contact with the inactive or dead ice, built up of the material melted out of an inland ice, and laid down in closed basins. The kame forms are subdivided (Table 1), according to their position in relation to the inland ice sheet, into external (group I) and internal (group II) ones. The external forms developed at the contact with the inland ice margin on the one side, and with the slope of the non-glaciated area, on the other, e.g. external kame terraces (Fig. 2). The internal forms, in turn, were produced within the ice sheet under various conditions and to various degree of deglaciation. The internal kame forms are subdivided into the following groups: IIa - crevasse forms, IIb – melted-ice lake forms, IIc - englacial melting forms. Group IIa - developed during the initial periods of the inland ice destruction, in a zone situated close to the inland ice front. Here were produced cracks and crevasses, primarily along the radial lines running on the outside of the individual glacier lobes. The crevasses may have been fined in with kame deposits. During the later stages of the inland ice melting, no conditions existed in that zone to accumulate the kame deposits, since at that time water streams were already active along the lines of the crevasses. The following are forms distinguished within group IIa: channel kame terraces, longitudinal kame bars (Fig. 3), and channel kame hills (Fig. 4). Group IIb was formed during the initial stage of the inland ice destruction, in a zone remote from the glacier front. Here, the formation of melted-ice lakes and of crevasses, related mainly to the rough subglacial surface, initiated the destruction of the inland ice that later broke up into irregular blocks. Both the melted-ice lakes and the crevasses were drained off by subglacial water. To group IIb belong: kame hills and hillocks (Fig. 5), kame bars (Fig. 6) and plateaus, including also digitate kame plateaus (Fig. 7). Group IIc developed during the later stage of the inland ice destruction. The englacial melting kames were formed in the central portions of the glacier tongues. At that time the inland ice substratum was flat, or basin-like. The englacial melting kames were accompanied by melting basins, and within the North-Polish Glaciation area - also by melted-ice lakes. To group IIc are referred: internal kame terraces (Fig. 8), kame bars round about the melting basins (Fig. 9), and complexes of kame hills (Fig. 10). It was also ascertained during the elaboration of this classification, that the researches of kames had contributed to the knowledge of the history of the late stages of deglaciation. A relation was discovered to appear between the occurrence of kames and the relief and composition of deposits of the inland ice substratum. We are able now to indicate – on the basis of the occurrence of kames – certain features of the substratum relief examined. Moreover, in addition to both limnological and glacifluvial types of sedimentation, also deltoglacial type of sedimentation of kame deposits was ascertained. The classification no doubt contributes to a clearance of the geological materials so far gathered within the kame areas. Further works will allow us to explain the situation that accompanies the kames, known from some typical examples.