Abstract

Upper Cretaceous-Eocene deep-water deposits of the Guipúzcoa Basin are well exposed along the Basque coastline. Lower Eocene deposits provide an opportunity to analyze the facies distribution and architecture of a thick-bedded, sand-rich turbidite system, a commonly identified seismic facies.

The Guipúzcoa Basin is a narrow, east-southeast- to west-northwest-trending foreland basin that formed during the Cretaceous and Eocene. Sediment was supplied to deep water via the Aquitanian basin to the northeast and the south Pyrenean foreland basin to the southeast. In the late Cretaceous and Paleocene, the shelf area was largely covered with carbonate platforms, and turbidity currents transported carbonate sediment into the deeper parts of the basin. The deep-water sediment supply changed through early Eocene times to a siliciclasticrich system, and the stratigraphy comprises a series of prograding submarine-fan systems.

Three sedimentary cycles have been identified. These successively increase in their proportion of siliciclastic material, average grain size, and bed thickness. Seven higher order cycles have been correlated more than 10 km (6 mi) downdip within the youngest cycle, the Higuer-Getaria Formation. In the Higuer-Getaria Formation, 20–80-m (49–131-ft)-thick intervals of thick-bedded, immature, coarse-grained sheet sandstones with widespread amalgamated and dewatered contacts are separated by 15–40-m (66–266-ft)-thick intervals of thin-bedded turbidites that preserve a wide diversity of ichnofauna. Updip, bottom currents are interpreted to have reworked the thin-bedded turbidite bed-tops into well-sorted megaripples that suggest bathymetric differences and/or paleocirculation changes within the Guipúzcoa Basin during the early Eocene.