AN INTERPRETATION OF UPPER CRETACEOUS SEDIMENTATION AND TECTONICS AND THE NATURE OF PYRENEAN DEFORMATION IN THE NORTHWESTERN BASQUE PYRENEES (SPAIN)

Oblique convergence between Iberia and Europe during the middle to late Eocene resulted in the development of nappe and right-lateral wrench fault systems in the northwestern Basque Pyrenees. Three tectonostratigraphic units were defined. The lowest unit, termed the Allochthon, is exposed in the area between Vera and Zugarramurdi and consists of Paleozoic and Triassic rocks unconformably overlain by mid- to Upper Cretaceous strata. It represents a parautochthonous basin. The intermediate unit, termed the Allochthon, consists of Paleozoic and Triassic rocks of the La Rhune, Cinco Villas, and San Narciso massifs and mid-Cretaceous through Eocene strata exposed north and west of those massifs. It is a sequence of nappes tectonically transported NNW-ward along low-angle thrust faults and gravity glide surfaces from an original "homeland" then south of the present day Cinco Villas massif. The highest unit consists of Jurassic and Cretaceous strata in the San Marcos area and represents a northern klippe of the "Nappe des Marbres".;Three formations were defined for Sequence II: (1) the Zugarramurdi Conglomerate (Albian-Vraconian) consists of conglomerate and sandstone; (2) the Sare Limestone (Aptian-Santonian) consists of fossiliferous and micritic limestone; and (3) the Dancharia Flysch (Campanian) consists of sandstone and limestone interbedded with shale.;Both Sequences record transgressive events from fluvial/paralic to slope/basin plain environments.;Sedimentologically, two forms of metastable standing waves were recognized in turbidites; small-scale hummocky cross-stratification in the Behobie Formation represents "3-D" antidunes whereas asymmetric waveforms in the Socoa Formation represent "2-D" antidunes.;Mid- to Upper Cretaceous strata of the Allochthon and the Autochthon, termed Sequence I and II, respectively, were examined in detail. Five formations were defined for Sequence I: (1) the Oyarzun Formation (Aptian-Vraconian) consists of conglomerate, sandstone, shale, and limestone; (2) the Portoua Formation (Vraconian-Cenomanian) consists of thin-bedded sandstone and limestone, shale, and olistostromes; (3) the Behobie Formation (Cenomanian-Santonian) consists of resedimented conglomerate, calcarenite, shale, and debris flow deposits; (4) the Socoa Formation (Santonian-Campanian) consists of calciclastic "classic" turbidites and debris flow deposits; and (5) the Loya Bay Formation (Campanian-Maastrichtian) consists of pelagic limestone and marl.