Isotopic, geochemical and bulk mineralogical analyses in the Trabakua
and Ermua sections, Basque Basin, reveal major changes across the
Paleocene-Eocene transition. Expanded sedimentary records exhibit a
gradual decrease of 1.0 parts per thousand in delta(13)C values in the
lower part of Zone P5 followed by a more rapid 3 parts per thousand
negative excursion. The 3 parts per thousand delta(13)C excursion is
associated with an abrupt decrease in carbonate sedimentation, increased
detrital flux and decreased grain size which suggest changes in
marine/atmospheric currents and/or size and structure of the ocean
carbon reservoir. The clays recognized at Trabakua record a deep burial
diagenesis as indicated by two generations of chlorite, the presence of
mixed-layers chlorite-smectite and illite-smectite, the absence of
smectite and the near absence of kaolinite. The very low delta(18)O
values (<-3.5 parts per thousand) throughout the Trabakua and Ermua
sections reflect diagenetic alteration rather than paleotemperatures.
Because of deep burial diagenesis and very poorly preserved
microfossils, the Trabakua Pass and Ermua sections are not optimal
potential stratotypes for the Paleocene-Eocene boundary.