Faunal dynamics of juvenile gastropods and associated organisms across the Valanginian transgression-regression cycle in central Poland

Abstract

The Valanginian fossil assemblages at Wawał in central Poland are dominated by juvenile gastropods with planktotrophic, mostly pelagic larvae, their occurrence thus being largely independent of local bottom environment in their distribution. The gastropod-dominated associations show a pattern of species turnover that is surprisingly consistent with a eustatic cycle and changes in biogeographic provincialism, both also strongly expressed in the distribution of ammonites. The Valanginian sea expanded into central Poland from the north, bringing cold waters with boreal faunas, and on the deepening sea-bottom the diversity of benthonic macro-organisms decreased. During the early Late Valanginian highstand, the seaway connecting the North European sea with the Carpathian ocean expanded enough to allow migration of Tethyan organisms into central Poland. In the late Late Valanginian this eustatic trend reversed and Boreal faunas again replaced those from the Tethys. The isotope record in benthonic foraminiferal tests suggests that, despite the sea-level changes, the bottom-water temperatures remained relatively stable.