Diversification of Slope Deposits and Forms in Jeseniky (Eastern Sudetes)
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DIVERSIFICATION OF SLOPE DEPOSITS AND FORMS IN JESENIKY (EASTERN SUDETES) Dominika Stan Department of Reconstructing Environmental Change, Faculty of Earth Sciences, University of Silesia ul. Będzińska 60, 41-200 Sosnowiec, Poland Correspondig author: [email protected] Abstract Slope covers are the most widespread Quaternary deposits. They are often the only source of information of local relief evolution and environmental changes in different regions. For over the last thousands of years climatic changes and especially Holocene warming initiated their intensified forming on inclined slopes in mountain areas of Jeseniky. Intensive mechanical weathering turned rock outcrops in the rubble, which together with finer material undergone by gravitational movement. Further they were subjected to soil processes under influence of the contemporary environment. That is way they characterized by distinct properties to form distinctive sequences. Non-uniform solifluction flow caused asymmetry of slope valleys lasting longer on slopes of northern and eastern exposures, resulting in slower thaw of snow. The research of weathered layers included micro- and macroscopic measurements of their structural and textural features. It makes possible to specify reconstruction of climatic conditions in which it most likely proceed. Presence of differentiated slope deposits and forms is spatially variable and mainly related to the variability of lithology, shape and inclination of study area. Key words: slope covers, solifluction, periglacial, Jeseniky, Eastern Sudetes 1 Introduction Over last 50 thousand years recent glaciation (Würm) and late Pleistocene, the Sudetes mountains were lying in periglacial zone with permafrost. During the progress of scientific research and more precisely studies of Quaternary formations increase the number of observations concerning phenomenon conditioned by periglacial climate. In Pleistocene cold climate conditions led up to exposure rock layers, which were subjected to intensive mechanical weathering (Ballantyne, Harris, 1994, French, 1996). Within the slope valleys and mountain ridges there were outcrops composed of more resistant rocks. It caused the beginning of formation of frost-riven cliffs and cryoplanation terraces. When the cliffs were retreated and subjected to separation. In the next stage they transformed into isolated rocks – tors (Davies, 1969). Slope cover formations reflect three types of conditioned processes of displace weathered material usually on variable action intensity in time and space (Kowalkowski, 1999). Beyond climatic conditions, which influenced on nature and weathering rate or transfer down slope, also significant role is played by base features (Allen, 2000; Kukulak, 2001). Lithological factor closely affects on structural and textural features of these deposits, and therefore also on the way and rate of bedrock weathering at the time of its creation and during further development. Geological variability is very relevant, namely is effecting on granulometry and sorting of slope deposits condition the character of disintegration (Rylp, Kadubec, 2007). The nature of the cover is also determined by local topography - shape and slope inclination (Migoń, Traczyk, 1998). Their thickness is inversely correlated with slope gradient and local flattening, which create places of waste mantle accumulation often affecting on fraction bedding of individual rock clasts (fig.1). Identification of the origin of sediment on the basis of its structural features and conditions prevailing during its formation provides paleoenvironmental informations (André, 2003, 268 Cremeens et all, 2005). Type of mountain-side process determines primarily climatic factor which is an amount of water on the slope (Rapp, 1963, Rapp, Strömquist, 1976). The nature of deposits, particulary their structure and texture, provides information about its uprising. In the study area the aim of the research was reconstruction of Pleistocene and Holocene climatic processes responsible for development of residual rocks and also determination of grain composition of bed rock, which creates rock forms as well as structural and textural features of diversified weathered covers. Fig. 1 Parallel oriented rock fragments to the inclination of the slope (Stan, 2011). 2 Localization and Methods The Orlik Massif (1204 m) is extending in NW-SE direction and localized in N-E part of Czech Republic in precincts of mid-mountain range of the Eastern Sudetes (Walczak, 1972). This area belongs to Medvědska Hornatina - part of Hrubý Jesenik (Czudek, 1997) and border with lower mountain ranges. Describing part of the Sudetes is qualify to Silesian-Moravian structure, belongs to Eastern Sudetes Metamorphic unit. The Proterozoic and Lower Devonian rock complex is folded and strongly methamorphised with Proterozoic rocks of Desna Massif where is localize the study area (Cymerman, 2004). On top of Orlik Massif there is quartzite overlay – cap (Fediuková, Aichler, 2004) which lay on metamorphic schists, migmatites and mylonites. Also on this area there are frequently metagranitoids (fig.2) – both fine-grained forms, biottite-plagioclase and laminating with coarse-grained forms local metamorphosed (Geologicka Mapa Čr, 1997). Fig. 2 Coarse-grained ocellar gneiss with shearing effect and microscopic pictures of the metagranitoid grain structure with quartz and micas intrusions. Magnification: x14 (Stan, 2011). 269 In order to determine the petrographic composition, which co-creates deposits and landforms related to the study area, samples were taken from outcrops previously prepared according to requirements (Mycielska-Dowgiałło, 1995). During geological mapping exposures were located at the foot ridge of the Massif (1094 m), on the eastern slope in dissection of the source funnel of Sokoli potok (940 m) and at the foot of the slope (750 m). In each of the points was made macroscopic examination for particular types of rocks. Samples were consisted of 200 randomly selected rock fragments that are 100 percent on each of the graphs. Microscopic analysis were made using Olympus BX-51M. 3 Results and discussion Slope covers appearing on the ridge and eastern slope of Orlik Massif are spatial diversified. Theirs existence is closely connected with lithology of foundation. Prevail weathered deposits having form of sorted heterogeneous block – clayey formations and also blocks rubble or clay with rock waste with solifluction origin. The role of lithology of covers forming is first of all connected with local diversification of its mechanical composition. Petrographic analysis show spatial variability of examined sediments connected with the occurrence of various rock material (fig. 3). They are linked with geological structure and presence of local rock inclusions. At the same time it must be noted that the presented results are related with the randomness of selected stands and with subjectivity of macroscopic tests. Delivery of the covers from the slopes caused, that only in some places was kept the record of climatic fluctuations. Gently slope rise and slope flats are places, where deposits were superstructure in climate periods persisting up till now. At high altitudes is present thick block - clay layered accumulations. A B C Fig. 3 The diagrams show percentage petrographic diversity of study area. Chart A (foot of the ridge of the Massif 1093 m) is the most variable and is related to located above outcrops of shales and orthogneiss. Other material was accumulated most likely due to granular disintegration of larger blocks to a single grains. This indicate a short, but fast transport, during which the rock material has broken down and then grinding. Graphs B (source funnel of Sokoli potok 940 m) and C (foot of the slope 750 m) are less diverse. Predominance of particular rocks types is connected with the occurrence on such altitudes specified outcrops: orthogneiss (B) and phyllites (C). 270 The source of rock material were tors and rock outcrops in the edge zones. The material varies depending on substrate and lithology of the slope. Larger pieces of rock coexists with fine-grained material, which simultaneously break up into large blocks, for example quartzite or single grains (fig.4). In the upper parts of the Massif it can be seen predominance of blocks over fine material. Quartzite and metagranitoid (relatively gneiss) outcrops supply blocks and stone debris, whereas metamorphic schists or phyllits are source of clay and dust. Fig. 4 Block field localised on the eastern slope of the Massif (845 m), with crust vegetation. Straight ahead sharply metagranitoid rocks covered by lichens Rhizocarpon geographicum. Lower:Thick layer of chemical distributed material (950 m) and example of residual quartzite rock on the ridge which was the spring of delivery of fresh material (1116 m) (Stan, 2010) A characteristic feature of described sediment texture is clear, bimodal size distribution of debris. The dominance of metamorphic rocks especially schists, phyllits or mainly gneisses caused intermix and coexistence of clay - dust material with rubble (10 - 35 cm) in places with blocks with diameters exceeded 1m. It can also be observed reverse fractional sorting occurring accumulation of large blocks at the top of upper parts of covers (fig. 5). Fig. 5 Bimodal decomposition of rock material with blocks on the top with rhythmically stratification of studied deposits (Stan, 2011). 271 Described covers contain a lot of chemically decomposed material characterized by weakening