Геоморфологічна будова Передкарпатської ділянки долини Бистриці-Підбузької

Abstract

The geomorphological structure of one of the least explored river valleys of the north-west part of the Fore-Carpathians was discovered. Morphological, morphometric characteristics of the BystrytsiaPidbuzka terraces, the structure features of their deposits’ sections were described. The progress of the glacial morpholithogenetic processes in the north-west part of the Fore-Carpathians was detailed. It was found that the river valley has been actively developing during the Early Pleistocene epoch, when the Galician (the fifth over-floodplain) terrace and four different-age terraces, which have formed the Loyeva level (the sixth over-floodplain terrace) till now, and starosilska terrace, which is hypsographically above the Loyeva level and below the Krasna level, were formed. The benches between the bases of the multiple altitude horizons of alluvium of the identified terraces were mainly disguised by the loess cover that is why actually they were not evident in the terrain. During the Early Pleistocene epoch (the Oka stage), at the time of the deglaciation of the adjacent to the Carpathian Mountains interfluve areas of Stryvihor–Dnister and Dnister–Bystrytsia-Pidbuzka, the glacial meltwater flowed along the river valley to the south. This was illustrated by the fact of the covering of the “warm” alluvium of the channel and flood plain facies by the periglacial alluvium in the section of the Galician terrace of the Bystrytsia-Pidbuzka River. During the deglaciation process of the north-west part of the Dnister valley, the Chukva-Vilshanyk palaeovalley was also invoked. The history of its formation and the structure requires further appraisal up to now. Younger Middle-Upper Pleistocene terraces that were obviously “hidden” in the broad bottom of the river valley morphologically were not clearly demonstrated. According to the morphometric, morphological characteristics they corresponded to the first over-floodplain terrace and BystrytsiaPidbuzka floodplain. However, it has been reliably determined that only its upper 6 meters of the total 24–26-meter of the soft sediments of the mass, which was discovered in the bottom of the BystrytsiaPidbuzka River valley, have accumulated during the Holocene. The formation time of the middle and lower parts was not accurately determined so far. It is possible that it has begun to accumulate during the period of the glacial meltwater discharge, which flowed to the river valley, through both the ChukvaVilshanyk palaeovalley and the Upper-Dnister depression. The surface of the fluvioglacial deposits was covered with the Middle-Upper Pleistocene alluvium, and the section of the mentioned mass was finished by the Holocene alluvium. From the beginning of the Holocene the river valley was surrounded by the ascending tectonic movements, which were especially active on the area that is adjacent to the Carpathians, where their base was outcropped in sections the first over-floodplain terrace and the floodplain. Key words: terrace, Loyeva level, alluvium, loess, glacial meltwater, Upper-Dnister depression, Chukva-Vilshanyk palaeovalley.