Stratigraphical distribution of Givetian ostracods in the type-area of the Fromelennes Formation (Fromelennes, Ardennes, France) and their relationship to global events

Abstract

Bed-by-bed sampling of three sections (Flohimont, Cul d'Houille and Nichet) exposing almost the entire Fromelennes Formation (Devonian, Middle and Late Givetian) in the historical type-area of the Givetian (Givet, Ardennes Department, France) provided more than 12,000 benthic ostracods. A high ostracod biodiversity is reported in these sections; 113 taxa are recognized of which 2 species are new: Acratia lucea sp. nov. and Orthocypris? cristae sp. nov. The stratigraphical distribution of the ostracods shows the installation of a Givetian fauna close to the base of the Fromelennes Formation with many endemic taxa and its disappearance as well as its subsequent replacement with more cosmopolitan taxa at the top of the formation with Frasnian affinities. This distribution is closely related to the major events of the Middle and Late Givetian in the Ardennes: the transgression pulse at the top of the Mont d'Haurs Formation, the global Taghanic Biocrisis and the global Givetian/Frasnian sea level rise. Climate change at the end of the Givetian possibly amplifies the effects of the sea level rise. The pattern of disappearance of many ostracod taxa in the Middle Givetian and their replacement by a new fauna as early as the Late Givetian is at least a supraregional phenomenon. Orthocypris? cristae sp. nov., Kielciella arduennensis Adamczak & Coen, 1992, Jefina kaisini Coen, 1985 and Cavellina rhenana Krommelbein, 1954 are considered as regional to supraregional stratigraphic markers. We establish the presence of a Middle Givetian ostracod province on the Givetian carbonate platform.