Numerical dating of the Eckfeld maar fossil site, Eifel, Germany: a calibration mark for the Eocene time scale

Sediments of the Eckfeld maar (Eifel, Germany) bear a well-preserved Eocene fauna and flora. Biostratigraphically, Eckfeld corresponds to the Middle E ocene mammal reference level MP (Mammals Paleogene) 13 of the ELMA (Europea n Land Mammal Age) Geiseltalian. In the maar crater, basalt fragments were drilled, representing explosion crater eruption products. By Ar-40/Ar-39 da ting of the basalt. for the first time a direct numerical calibration mark for an Eocene European mammal locality has been established. The Eckfeld ba salt inverse isochron date of 44.3+/-0.4 Ma suggests an age for the Geiselt alian/Robiacian boundary at 44 Ma and, together with the 1995 time scale of Berggren et al,, a time span ranging from 49 to 44 Ma for the Geiseltalian and from 44 to 37 Ma for the Robiacian, respectively. Additional Ar-40/Ar- 39 dating on a genetically related basalt occurrence close to the maar conf irms a period of volcanism of ca. 0.6 m.y, in the Eckfeld area, matching th e oldest Eocene volcanic activity of the Hocheifel volcanic field.