The stratigraphic position of the Lower Oligocene Yrieu Sands (southwestern France), based on calcareous nannofossils and a new Helicosphaera species
Steurbaut, E. (1983). The stratigraphic position of the Lower Oligocene Yrieu Sands (southwestern France), based on calcareous nannofossils and a new Helicosphaera species. Eclogae Geol. Helv. 76(2): 327-331