Field-guide excursion to the Cretaceous-Tertiary boundary section at Zumaya (northern Spain)

Resumen

The Basco-Cantabrian Domain (Basco-Cantabrian Basin of some authors) represents the eastern part of the southern side of the Bay of Biscay. In Late Cenomanian, as a result of previous environmental and morphological modifications, it was composed of two approximately E-W oriented elements, which are, from north to south: A deep marine area and a marine shelf called the Navarro-Cantabrian Platform.

The deep marine area comprised two major elements that were, from north to south: a) An E-W oriented and westward open depression: the Saint-lean-de-Luz Trough; b) A topographically higher region: the Biscay-Guipúzcoa Shallows. It connected at north, through a northward dipping slope, with the St-J-Luz Trough. At south, it rose up to the Navarro-Cantabrian Platform and its limit might correspond to a great structural element: the Bilbao Fault (Amiot, Floquet, Mathey, 1982; Engeser et al., 1984). The southeastern part of the B-C Shallows was a small, always E-W trending despression: the Plencia Trough. On the contrary, its eastern part was a shoal: the Basque Shoal, whose some sectors are small platforms of inner type, whereas some other are emerged.

The eastern limit of the whole deep marine area could correspond with an alignment of diapirs: the. Line of Navarra Diapirs (Rat, 1983). During the Cretaceous, that line separated an Occidental and Navarro-Cantabrian domain from an Oriental and Pyrenean one.