The Paleocene to lowermost Eocene Zumaia series, situated along the
Basque Coast (northern Spain), consists of pelagic limestones and
marlstones with interbedded, mixed calcarenite turbidites. We have
compared the composition and frequency of turbidite beds in time, as
well as the clay-mineral and bulk-rock carbon isotope composition of the
pelagic beds, to discern the factors controlling turbidite deposition.
The pelagic beds are coccolithic mudstones with mainly planktic
foraminifera, The sources of detrital material to turbidites were the
carbonate-producing shelves (bearing Foramol associations) around the
evolving Bay of Biscay, and to a minor extent the incipient Pyrenean
chain for siliciclastic components, We have found close relationships
between variations of turbidite facies and depositional rates with
day-mineral assemblages and carbon isotopes in the pelagic beds. The
latter are in line with global trends. It appears that in the early Bay
of Biscay, climate and nutrient availability controlled turbidite
sedimentation. The bulk-rock late Paleocene (NP 5-NP 9) positive
carbon-isotope excursion coincides with a period of relatively cool and
dry climate characterized by the highest frequency of turbidity flow. We
propose that during this period globally enhanced latitudinal
temperature gradients and strong thermohaline ocean circulation
increased bioproductivity in surface waters by upwelling and/or by wind
driven Ekman pumping, In contrast, warm, perennially wet periods such as
the early Paleocene (NP 1-NP 4) and the Paleocene/Eocene transition
(upper NP 9-NP 10) are characterized by low frequency of turbidity flow
in the basin. This may have been caused by sluggish thermohaline
circulation and low carbonate productivity during this time period.