El Aptiense inferior del Anticlinorio Nor-Vizcaino entre Gernika y Azpeitia (Cuenca Vasco-Cantábrica)

Abstract

The Lower Aptian of the North-Biscay Anticlinorium between Gernika and Azpeitia outcrops in three anticlines: Gernika, Nabarniz (Narea) and Azpeitia. Three representative sections of these outcrops have been dated, correlated and interpreted. Their deposits correspond to a distal mixed siliciclastic-carbonate platform, sedimented below the wave base level. Four main facies and two subfacies have been distinguished: 1) lutites and siltstones; 2) marls and nodular limestones; 3) lutites and sandstones; and 4) grainstones (4a: ooid and orbitoline grainstone; and 4b: orbitoline, miliolid and peloid grainstone). Facies 1 and 2 correspond to a quiet water background sedimentation, facies 3 to tempestites, and facies 4 to subtidal channel-fill deposits. The whole unit shows a predominantly terrigenous lower part and a predominantly carbonate upper part. Sandy deposits (tempestites) appear only in the more proximal eastern section (Azpeitia). Thickness distribution, finally, indicates a synsedimentary activity of the Gernika anticline during the early Aptian