Ten mammalian taxa have been recovered from four localities in the upper part of the Tremp Formation (south-central Pyrenees). Its stratigraphic position allows the localities to be correlated with the Sphaerochara edda charophyte zone, the lower part of the NP9 nannoplancton zone and magnetochron C24r, below the marine Paleocene/Eocene boundary. Seven of these taxa are described, among them: Afrodon ivani Pelaez-Campomanes nov. sp., related to other congeneric species from the MP 5-6 mammal units; Nosella europaea Pelaez-Campomanes nov. gen. nov. sp. also found in the MP 6 Cernay locality, and Microhyus cf. musculus Teilhard de Chardin, similar to the MP 7 Dormaal sample. The mixed composition between Cernaysian and Neustrian faunas of the Tremp sites make necessary the definition of a new reference level MP 6b with Claret 4 as a reference locality. The new reference level MP 6b is correlated with the lower Clarkforkian Cf 1-2 units, both showing a low species richness and low diversity index comparing with earlier and younger assemblages. This diversity change is related to the late Paleocene Thermal Maximum event, detected in a similar chronological situation (base of C24r chron) in the marine and continental realms. The beginning of the Neustrian reference level MP 7 with highly diversified faunas is correlated with upper Clarkforkian Zone Cf 3, based on faunal composition and the delta 13 C excursion.