Nassariid assemblages from the Korytnica Clays – a useful tool for local stratigraphic correlation

Abstract

Analysis of the distribution of species of the family Nassariidae (Gastropoda, Prosobranchia) in the Middle Miocene Korytnica Clays (Holy Cross Mountains, central Poland) enabled five nassariid assemblages to be distinguished, viz. the (1) Nassarius restitutianus, (2) N. restitutianus-korytnicensis, (3) N. korytnicensis, (4) N. korytnicensis-limatus and (5) Nassarius schoenni assemblages. The schoenni and korytnicensis-limatus assemblages occupied the littoral zone of the Korytnica Basin. The remaining nassariid assemblages inhabited different offshore environments. Nassariid assemblages appear to be a useful tool for local stratigraphic correlation as their succession is identical within almost the entire study area, excluding the littoral zone. The lower limit of one of the most widespread nassariid assemblages (korytnicensis assemblage) is proved to be an isochronous surface. The isochronous nature of other boundaries between the nassariid assemblages recognised in the succession is also postulated. The entire nassariid sequence is interpreted as a record of temporal changes in the relative size of two large gastropod populations: the population of Nassarius restitutianus and the population of Nassarius korytnicensis. Environmental requirements of the most abundant nassariids are described in detail.