The Lower Tertiary outcrop along the coast of Guipuzcoa, northern Spain, consists exclusively of deep-marine sediments, deposited in a narrow elongated (ESE-WNW) basin. The early Tertiary sedimentary history of this basin can be described in terms of three main phases:<p/>- a phase of predominantly (hemi-)pelagic deposition (almost the entire Paleocene);<br/>- a phase of deposition from axially flowing carbonate-rich turbidity currents (latest Paleocene to earliest Eocene);<br/>- a phase of lateral input of predominantly terrigenous clastics via submarine fans (largest part of the early Eocene).<p/>During the latter two phases (hemi-)pelagic sedimentation became proportionally less important -due to increasing rates of turbidite sedimentation. Late Maastrichtian to early Paleocene diapirism of Upper Triassic evaporites had created swells and depressions In the basin floor and controlled the deposition of turbidites well into the early Eocene. Various facies associations can be distinguished In the Lower Eocene turbidite successions. In the 'middle fan association' thick-bedded proximal turbidites are concentrated in overall non-channelised packages, tens of metres thick, which internally show channelling. In the 'outer fan association' thick-bedded proximal turbidites have planar geometries but are still concentrated in packages. A vertical section through these packages commonly displays a crude coarsening - and thickening - upward trend of beds. In the 'fan fringe association' thick-bedded proximal turbidites no longer occur concentrated in groups but disseminated in a matrix of thin-bedded distal turbidites. The 'basin plain association' is characterised by monotonous successions of thin-bedded turbidites. (Hemi-)Pelagic interbeds may be present in all of these facies associations. Vertical and later 1 arrangements of different facies associations can be interpreted to terms of episodes of progradation and abandonment of submarine fan systems. Long-distance lateral facies relationships could only be established with the aid of biostratigraphic control, for which use was made of calcareous nannoplankton from the interbedded hemipelagic marls. In the Lower Eocene the turbidites derived from the northern basin margin are carbonate-cemented quartz-arenites. Those derived from the southern basin margin have a lithic-arenitic composition. The stratigraphic superposition of submarine fans fed from opposite basin margins directly indicates that the deep-marine basin must have been rather narrow, probably only a few tens of kilometres wide.
|Qualification||Doctor of Philosophy|
|Award date||10 Nov 1982|
|Place of Publication||S.l.|
|Publication status||Published - 1982|
- geological sedimentation
- iberian peninsula