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This study malyscs the physical nratigraphy and the microfossil biostr. uigraphy of the Paleocene-Eocene boundary at Trabak. ua Pass and Ermua sections of the Basque Basin, western Pyrences. The T rabakua Pass section is continuously exposed and comprises a Paleoccne-culy Eocene succession of hcmipelagic muls and nurlnones. lmportan [microfossil groups such as planktic and deep-water bcnthic fo= inifera, and calcareous nannofossils are well represented and have been scudied in detail. A prominent 3.5 m thick clayey intercalation largdy devoid of carbonate microfossils occurs within dus section and could probably be related to a large flooding of C01 caused by volcanism which accompmicd the early Tertiary opening of the North Atlantic. The geom~ eti<. a. nd isotopic records of this section uc rC: 1. Sonably well prCliel" Ved, and have been recons! J'Ucted. The Trabakua Pass section can be confidendy correlated with the Ermua section situated about IO km to the south. The Paleocene/Eocene boundary is well exposed also at the Ermu. section, which consists of an alternation of hem. ipclagic limestones, carbonate turbidites, and breccias. The turbiditcs contain abundant shallow-water foraminifcra (including nummulitids, discocyclinids, and a. lvcolinids) a luge proportion of which were derived from coeval carbonate pla. tforms that existed further to the south. ln addition, both marine and terrestrial p: alynomorphs arc present, the former being fairly abundant. oon-n49/96/0201-0179 s t6. 00