Small pyrite ammonites in Aptian grey marls. The gray marls around Apt were proposed by Alcide d'Orbigny as a reference for the Aptian stage, for their rich paleontological content. Some thirty different species of ammonites have been recorded in the Tuiliere sections, and belemnite rostrums are abundant in certain levels, as are gastropods and lamellibranchs (oysters and plicatula). These marls also yield corals, sea urchins, brachiopods and shark teeth. The Aptian is the penultimate stratigraphic stage of the Lower Cretaceous. It extends from -121.4 to -113.0 Ma, succeeding the Barremian and preceding the Albian (Secondary or Mesozoic Era). France