Academic journal article UTMS Journal of Economics

Epigenetic Valleys in the Tikves Basin in the Republic of Macedonia

Academic journal article UTMS Journal of Economics

Epigenetic Valleys in the Tikves Basin in the Republic of Macedonia

Article excerpt

INTRODUCTION

Epigenetic valleys are a part of the inconsistent fluvial relief, and are used in the Balkans as the benchmark for establishing the height limit between the abrasive and fluvial relief (Zeremski 1965). The term 'epigenetic' refers to the secondary nature of the bedrock gorges, which occur after the formation of the original gorge (Kothyari et al. 2013; Ouimet et al. 2008). These are forms created from the lateral displacement of bedrocks during episodes of alluvial sedimentation with partitions of alluvial material that force the river to incise down into solid rocks in the form of a "canyon" rather than exhume its own paleovalley (Ouimet et al. 2008). The epigenetic gorges are also called: bypass valleys, or modern slot canyons. They have narrow, scalped steep-sided valleys. At first sight, the epigenetic gorges are anomalies in the fluvial relief since they are cut into an elevation of resistant rocks in the surroundings of which there is lower ground built of softer rocks. The key question in the geneaology of the epigenetic valleys is why the rivers incised the gorge in more solid rocks rather than into deposited softer sediments in the immediate surroundings, which seemed easier to be eroded and where actually there were lower topographic positions? Accordingly, one of the conceptual models for formation of epigenetic valleys (gorges) is displacement of the riverbed resulting from the burying of the paleovalley with sediments or due to the side pressure of the water and the deposited alluvial flow material from the tributaries (Lazarevic 1975). The second concept of the genesis of epigenetic valleys attributes an active role to the tectonic dynamism that predisposes accelerated and exclusively deep erosion of valley sections located on elevation. Therefore, in literature, the epigenetic narrowings (gorges) refer to composite valleys formed by local tectonic faulting in the longitudinal profile of rivers that predispose sequences of erosive widening and sequences of pronounced deep dissection. The basic conditions for differentiating the epigenetic gorges are: lithological (existence of resistant rocks at the top) and morphological (existence of soft soil position lower in comparison with the upper edges of the gorge, incised in the resistant rocks (Petrovic 1953, 1977). Generally, studying the epigenetic valleys has an enormous scientific meaning. Actually, epigenetic valleys are preferred in geomorphology as the relevant indicator for determining the height of the central- lake plains of neogene lakes all over the Balkans. In fact, they have also been taken into consideration for determining the level of the central-lake plains of the Pliocene lakes in Macedonia through which subsequently, in Quaternary, a new network of rivers was formed (Manakovic 1960, 1968). The whole research process was initiated by several established fluvial landforms in Tikves Basin characterized by physiognomy of the epigenetic gorges that have no geographical nor geomorphological explication published any data yet. So, the main objectives in the study were some sequences from the valleys of the rivers in the Tikves Basin. The main task was to determine which of them according to visual clues, really possess character of epigenetic gorge, ie epigenetic built. The second task was to perform an altitude correlation with the plane of neogene lake in Tikves Basin and see if epigenetic valleys correspond to its height, like in some previous conclusions about the wider territory of the Balkans. The research activities through field survey related with other necessary methods turned out that in the area there are ten, so far undiscovered epigenetic gorges and river incissions. Their genesis is purely epigenetic. This statement was derived from all considered geomorphological, geological and genetic indications in the study. It also turned out that altitude of some epigenetic gorges genetically correspond to the level of neoge lake in the area while some epigenetic incissions lay above that level and are formed independently on the dwindling neogene lake in the Tikves Basin. …

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