Micropalaeontological dating of the Prémontré mammal fauna (MP10, Prémontré Sands, EECO, early late Ypresian, Paris Basin)

1. IntroductionAs a result of long-term and intensive fossil collecting (see Russell, 1964; Rat, 1965 and Louis, 1996 for overviews) the Paris Basin has become one of the hot spots in the reconstruction of Paleogene continental mammal evolution, and the home of about two thirds of the reference levels of the European Paleogene mammalian biochronological scale (Schmidt-Kittler, 1987). This particular status is also due to its position along the eastern edge of the Atlantic Ocean, allowing marine and continental strata to meet, and its particular tectonic history. Large parts of the Paris Basin were affected by strong subsidence generating relatively complete and rather thick sedimentary successions, marine as well as continental (Gely & Lorenz, 1991; Duprat, 1997a). In spring 1980, an almost 20 m thick succession of essentially sandy sediments has been exposed during works inside the Psychiatric Hospital of Premontre. This hospital was built on the ruins of the medieval Premontre Abbey, about 15 km west of the city of Laon, in the northeast of the Paris Basin (Fig. 1). Since its discovery scientists have been mainly focussing on the lower part of the Premontre section (unit 2 of Degremont et al., 1985, for which these authors introduced the term Premontre Sands), which yielded an intriguing mix of continental, terrestrial as well as aquatic, and marine fossils. A preliminary list of these taxa was given by Degremont et al. (1985), mentioning plant fragments (seeds, wood, leaf