Facies analysis of Omarčevo Formation (Lower Triassic) in Sveti Ilija Heights (SE Bulgaria)

The Omarčevo Formation (Spathian) belongs to the Sub-Balkanide Triassic formed over the southernmost parts of the Moesian Shelf. In order to restore the initial peculiarities of the rock fabric and composition the diagenetic and metagenetic processes are studied. Recrystallization, silicification, albitization, and dolomitization in carbonate rocks and formation of phyllosilicate porphyroblasts in clay rocks, resulting from a very low-degree regional metamorphism, are established. On the basis of the initial features of the sediments four facial environments are distinguished: supratidal, intertidal and most shallow subtidal, shallow subtidal with a good circulation and shallow subtidal with a periodically weaker circulation. The alternation of supratidal with intertidal and subtidal sediments determines a transgressive order of the facies. They are formed in the process of marine transgression on a piedmont alluvial arkose plain.