Conodont Biostratigraphy and Lithostratigraphy of the Late Givetian–early Frasnian Interval in the Arpi Section (Central Armenia)

The Givetian–Frasnian (G–F) transition marks a time of significant palaeoenvironmental perturbations and biotic turnover, yet its stratigraphic record in the southern Caucasus remains poorly constrained. This study presents the first integrated examination of conodont biostratigraphy and lithofacies across the G–F transitional interval in Armenia, based on material from the Arpi section. The section yielded a relatively diverse and abundant conodont assemblage, with taxonomic assessment allowing to identify eleven species and subspecies assigned to genera Polygnathus, Icriodus, and Ancyrodella. The first occurrences of Ancyrodella rotundiloba s.s., A. pristina, and A. binodosa in the upper part of the section enable correlation with the upper FZ1–FZ2 zones of the Frasnian conodont zonation, constraining this interval to the lowermost Frasnian. The absence of Ancyrodella in the underlying strata, coupled with the presence of species such as Polygnathus dubius, Icriodus cedarensis, and I. excavatus, suggests that the lower to middle part of the section corresponds to the upper Givetian. This interval is further correlated with the Upper hermanni to norrisi zones. Lithostratigraphic observations and microfacies analyses indicate that the sedimentary sequence of the section accumulated in a ramp setting. Moreover, a shallowing trend is observed, from relatively deeper, low-energy black shale facies in the late Givetian to more oxygenated, proximal carbonate facies in the early Frasnian.