Callovian to Lower Cretaceous pelagic carbonates in the West Balkan Mountains (Komshtitsa and Barlya sections): integrated biostratigraphy and microfacies

Abstract

The Jurassic System in the West Balkan Mountains attracted the attention of the first scholars of geology and stratigraphy in Bulgaria F. Toula and V. Zlatarski more than 100 years ago. The intense field, palaeontological and stratigraphical studies of the Upper Jurassic and Lower Cretaceous pelagic carbonates in the Izdremets Syncline led to the lithostratigraphic subdivision and establishment of all stages from the Callovian to the Hauterivian as a relust of publications of I. Sapunov, I. Nachev, T. Nikolon and G. Mandov in the 60s and 70s of the last century. An integrated micropalaeontological zonation of the Tithonian, Berriasian and Valanginian was elaborated by I. Lakova, K. Stoykova and D. Ivanova. Recently, P. Tchoumatchenco divided the sections at Komshtitsa and Barlya into second- and third-order sequences. The subject of this paper is a synthesis of the existing stratigraphic knowledge of the Callovian to Valanginian pelagic carbonate succession at the sections of Komshtitsa and Barlya in the West Balkan tectonic unit, as well as a correlation with new micropalaeontological and microfacial results. A zonation on calcareous dinocysts for the Upper Jurassic is here presented and correlated to the ammonite zones in the Yavorets, Gintsi and Glozhene Formations. The used biostratigraphical criteria of determination of the stage boundaries (Callovian to Valanginian) are discussed. Six successive microfacies are determined and described: filamentous, Globuligerina-radiolarian, Saccocoma, Globochaete, calpionellid and spicule.