Angular tectonic-erosional unconformity in the deposit’s part of the Idrija Middle Triassic tectonic structure

Abstract

The finding of the characteristic Anisian Foraminifera with Meandrospira dinarica proves the Anisian age of the dolomite beds within the ore deposit’s part of the Middle Triassic Idrija tectonic structure, which overlies the eroded Paleozoic and various Lower- and Middle Triassic rocks. The dolomite beds with Meandrospira dinarica exhibits also on its upper side a characteristic erosional surface, upon which characteristic and lithologically variegated rocks of the Ladinian stage and the Cordevolian dolomite came to rest. This structural and sedimentary evidence attest to two erosion episodes in the framework of the Idria tectonic event. During the first period encompassing the Middle Anisian time, the Anisian, Scythian, Permian and part of the Permo-Carboniferous beds of the Middle Triassic Idria tectonic structure were removed. A short-lived transgression with sedimentation of the Meandrospira dinarica dolomite followed. The next erosion period took place during the Upper Anisian or the Lower Ladinian times. The Anisian dolomite which sedimented upon the erosional surface of the first erosion cycle was removed, with part of the underlying older beds included. These findings rendered possible a detailed morphological analysis of the deposit’s part of the tectonic structure and the assessment of displacements along faults.