Newly recognized Upper Triassic and Jurassic formations in Southwest Bulgaria: palaeogeographic and palaeogeodynamic implications

Abstract

Four formal lithostratigraphic units are introduced for the first time in the national stratigraphic nomenclature in accordance with the National Stratigraphic Code and the International Stratigraphic Guide. The Upper Triassic Kobile Formation is situated at the top of the Triassic section (over the red beds of the Norian Komshtitsa Formation). It consists of phosphate- and sulphate-bearing yellowish sandstone and siltstone interbedded with grey limestone and dolomitic limestone. Occasionally, they contain echinids, gastropods, crinoid ossicles, algae and foraminifers. The Metohiya Fonnation (basal conglomerate built up of quartz and Iydite pebbles; quartz sandstone; loose yellowish sandstones and occasional limestone interbeds) covers the Upper Triassic with unconfonnable depositional contact. The age is considered as Middle Jurassic (eventually beginning in uppermost Lower Jurassic) on the basis of regional correlations. The other two newly introduced Jurassic formations belong to the Treklyano Group and are of Middle - Late? Jurassic age. The Momchil Formation is built up of shales and siltstones interbedded with limestones. The Sredorek Formation consists of limestones and marls with shaly interbeds and olistostrome built up of Triassic limestones and siltstones. Lateral correlations with the deep marine sequence (shales and radiolarites) of the Dobridol and Rayantsi Formation make possible the reconstruction of a Jurassic narrow and deep submarine canyon within the Peri-Tethyan shallow sea.