Udział peryglacjalnych osadów stokowych w budowie tarasu wysokiego Lubrzanki

Abstract

Dla ustalenia udziału osadów stokowych w budowie tarasu wysokiego w środkowym odcinku Lubrzanki przeanalizowano wykształcenie strukturalne materiału, jego skład granularny, petrograficzny, obtoczenie oraz ułożenie kamieni i żwirów.W spągowej części tarasu stwierdzono materiał typowo rzeczny (piaski i żwiry), w stropowej – przewarstwienia osadami stokowymi (gliniasto-gruzowa brekcja).Wiek tarasu wysokiego wiąże się ze zlodowaceniem środkowopolskim, w tym też czasie zachodziło przemieszczanie materiału stokowego i jego akumulacja. THE SHARE OF PERIGLACIAL SLOPE DEPOSITS IN FORMATION OF HIGH TERRACE OF THE LUBRZANKA RIVERThe high terrace of middle Lubrzanka river (Fig. 1) was studied. In order to estimate the share of slope deposits in formation of this terrace, there were analysed structural development, granulation, petrographic composition, rounding as well as distribution of boulders and gravels in the material.The studies showed a complex, slope-fluvial origin of the high terrace. Its lower parts (Figs. 2–4) are built of typical fluvial material represented by stratified sands and gravels fairly uniform in granulation (Fig. 5) and well rounded (Fig. 6A). Quartz grains with longer axes set normal to the direction of current (Fig. 8) predominate here. In top parts this material is intercalated by one or two layers of slope deposits represented by loamy-rubble breccia with predominance of angular debris of local rocks (Fig. 6B, Table 2), usually with longer axes parallel to the direction of slope (Fig. 7). These slope deposits also form a coherent cover over 1 m thick on the terrace surface.The studies showed that fluvial and slope accumulation led to interfinging of deposits of the fluvial and slope environments after formation of basal and middle – parts of the profile of the terrace by the river. The processes were characterized by intensity changing in space and time and they acted seasonally and independently from one another. This resulted in subsynchroneous contact of fluvial and slope deposits in top parts of the profile (Fig. 9).The Lubrzanka high terrace is dated at the decline of the Mid-Polish Glaciation and, therefore, translocations and accumulation of slope deposits should be also dated at that time.