Calpionellid biostratigraphy and microfacies across the Tithonian/Berriasian boundary interval in the Western Fore-Balkan, Bulgaria

The upper Tithonian and the lower Berriasian in the Western Fore-Balkan in Bulgaria (Gintsi and Glozhene Formations) represent a remarkable, stratigraphically expanded record of pelagic nodular and micritic limestones. More than 50 studied thin sections revealed the succession of the Chitinoidella, Praetintinnopsella, Crassicollaria, and Calpionella zones, further divided into subzones. The stratigraphical ranges of 22 chitinoidellid (the genera Almajella, Borziella, Carpathella, Chitinoidella, Daciella, Dobeniella, Longicollaria, and Praetintinnopsella) and 26 calpionellid species of the genera Tintinnopsella, Crassicollaria, Calpionella, Remaniella, Borzaiella and Lorenziella have been recorded. Eight microfacies, two of which in the Gintsi Formation, and six microfacies in the Glozhene Formation have been distinguished, all being wackestones and mudstones, characteristic of open-marine pelagic deposits and differing from each other in the prevailing bioclasts. The Tithonian/Berriasian boundary was tentatively drawn at the Crassicollaria/Calpionella boundary.