New data on the stratigraphy of the Middle Jurassic siliciclastic rocks from the West Balkan Mountains (West Bulgaria)

The present study is a contribution to the lithostratigraphy of Middle Jurassic strata in area Zimevitsa Plateau (West Balkan Mts, West Bulgaria). Based on its lithological and regional properties, Dobravitsa Member distinguished from surrounding rocks Etropole Formation. new member consists alternating shales, siltstones fine-grained sandstones. It also contains abundant siderite calcite concretions, which are distributed discrete stratigraphic horizons both mudrocks coarser lithologies. Fossils extremely rare. Poorly preserved ammonites belemnites found only. several ammonite finds, Formation assigned narrow interval lower Bajocian (unlimited, probably part Witchellia laeviuscula Zone). Although it has restricted lateral distribution, exclusively confined type-area, proper place formal Bulgarian lithostratigraphic scheme, as represents discernible atypical development Mts region. Another emphasis this laid concretions Besides few examples iron oxyhydroxide localities outside area, described. latter an component Formation, deserves further special systematization, implies unknown history lithofacies, depositional diagenetic terms.