The youngest sedimentary rocks unconformable with Carboniferous beds at Idrija

Abstract

The previous interpretation of the Middle Triassic Idrija graben and adjacent structures suspected unconformity between the Carboniferous and Langobardian beds building the Northern Idrija fault ridge. Each successive younger stratum of the Langobardian substage extends more and more toward north. The youngest deposit unconformable to Carboniferous slate appeared to be Langobardian tuff. Recently, however, an upper drill-hole made in the lst level of the Idrija mercury mine penetrated a junction between the Carboniferous and Cordevolian beds. Dark gray and black Cordevolian dolomite intercalated with Skonca shale rests upon Carboniferous slate and passes up into a light gray dolomite variety. Such a structural relationship between rock strata in contact indicates persistence of the marked Middle Triassic tectonic phase from the Langobardian through the Cordevolian substage. The researched section is the northernmost part of the Northern fault ridge of the Middle Triassic Idrija structure.