Ostracods across the Frasnian/Famennian boundary (Devonian) in the Hony railway section (southern border of the Dinant Synclinorium, Belgium)—geochemical consequences

Abstract

Ostracods are extremely rare in the upper part of the Frasnian but sometimes very abundant in the base of the Famennian exposed in the Hony railway section. The associations of ostracods in the base of the Famennian belong to the Eifelian Mega-Assemblage and are indicative of shallow and sometimes semi-restricted marine environments, but this fauna has been mobilised periodically most likely by seismic activity. The abnormally high abundance of particularly well-preserved dissociated valves of adults and instars indicates a depositional environment very close to the shore at Hony, as is the case in some other localities in the southern border of the Dinant Synclinorium. In the fine dark shales straddling the Frasnian/Famennian boundary, ostracods are silicified and are evidence of an intense circulation of ground water during diagenesis. That may explain the increase of chalcophile elements and the absence of a significant iridium anomaly reported in this bed. A new zone based on metacopid ostracods, the Ovatoquassilites avesnellensis Zone, is established in the base of the Famennian.