Osady zwietrzelinowe z okolic Michałowic (Karkonosze)

Abstract

 Opisano żwirowo-ilaste osady wczesnoholoceńskie występujące w dolinach potoków w niższych partiach Karkonoszy. Dokonano próby poznania mechanizmu transportu i warunków ich sedymentacji. Osady te reprezentują odmianę potoków gruzowo-błotnych powstałych w wyniku torrencjalnych opadów.Z różnic w sposobie transportu klastów różniących się wielkością wynika ich podział na subpopulacje w obrębie badanych próbek. Analiza składu mineralnego okruchów wykazała istnienie różnic we wzajemnych stosunkach między składnikami mineralnymi w różnych klasach wielkości. Udowodniono genetyczny związek badanych osadów z granitowymi zwietrzelinami zboczowymi. WEATHERING DEPOSITS FROM THE VICINITIES OF MICHAŁOWICE (KARKONOSZE MTS) The paper presents characteristics of weathering deposits from the vicinities of Michałowice (Karkonosze Mts - Fig. 1). The deposits occur in the form of packets over 1 m thick, infilling flat-bottomed stream valleys. They rest on weathering covers of granites and are covered with recent soil layer or, locally, peats. The deposits are characterized by highly nonuniform granulation, the wealth of silt-size grains and relatively large share of clay-size ones (Fig. 2). Rock fragments are angular and there may be found granite, feldspars, quartz and biotite in their composition. Quartz predominates in the silt fraction and illite was identified to be present among clay minerals.In the studied sequence, a few types of deposits have been differentiated with reference to composition of grains. Deposits of the type B – rich in silt-size grains (50–60%) and with clearly marked maximum of fine gravels (Fig. 2b, c) – are most common here. Those of the type A (Fig. 2a) are somewhat less common and those of the type C (Fig. 2d) – the rarest and thinnest. Individual layers vary from a few to 60 cm in thickness. Their boundaries are gradational or, occasionally, sharp. Several layers may be usually traced in the vertical section.The analysis of granulation and mineral composition of rock fragments showed connection between the weathering deposits and slope weathering covers of granites. The former originated in result of washing material from slopes after torrential rains and its subsequent deposition by flows of the debris flow type. The results of granulation analysis, when plotted in the probability scale, made it possible to identify three subpopulations of grains in the studied deposits. The subpopulations differ from one another in the mode of transportation. The wealth of the suspension subpopulation (40–80%) resulted in marked increase in density of transporting medium as well as in importance of cohesion in the course of the transportation.The analysis of mineral composition of rock fragments showed some differences in share of individual components depending on grain-size class (Fig. 4). The results most close to those for the parent rock (i.e. granite) are given by analysis of large grains. The weathering deposits are dated at the Lower Holocene with reference to genetic relation to local slope weathering covers, the presence of solifluction structures and their setting in the studies sections.