Facies, development and interpretation of sedimentary environment of the uranium-bearing Brebovnica Member of the Val Gardena Formation in the Žirovski vrh area, W Slovenia

Abstract

The Brebovnica Member, bearing considerable grades of uranium ore, is the most important member of the Val Gardena Formation. Rocks were subdivided according to grain size, sedimentary structures and composition to conglomerate, sandstone, mudstone and carbonate facies, and the conditions of their formation were interpreted. From detailed partial profiles that illustrate the successions of facies a generalized profile of lithostratigraphic development of the entire Brebovnica Member of a total thickness of almost 400 m was constructed. Two macrocycles were distinguished in it. The first macrocycle comprises the lower half of the Brebovnica Member, and the second macrocycle its upper half and approximately the lower half of the Hobovbše Member. The macrocycles are a product of fluvial depositional environment with its subenvironments, and they are of allocyclic character. The allocyclicity was most probably controlled by tectonic events in drainage and depositional basin. The macrocycles represent the development of fluvial system from its proximal parts with predominant bed-load braided channels and alluvial fans towards more distal parts with mixed-load meandering channels.