Stratigraphic arquitecture of a storm-dominated shallow marine platform (Valmaseda Fm., Up. Albian - Lw. Cenomanian, Basque Cantabrian Basin)

The Valmaseda Fm. comprises a thick siliciclastic shallow marine depositions! system, developed in the southern margin of the Basque Cantabrian basin. Its western sector, located ¡between the Tornos Pass (Cantabria-Burgos) and Llodio (Alava) displays a thickness ranging from 1000 to 3500 m. Detailed facies analysis have allowed to establish five facies assemblages which build up the basic facies tract. It consists on a prograding / shallowing upward sequence developed on a storm-dominated siliciclastic platform. The stacking pattern of these basic sequences yields composite higher rank sedimentary cycles which represent overall shallowing upward / prograding units of regional extent, capped by transgresive deposits. These sedimentary cycles can be further grouped into four regionally extensive stratigraphic units which outline four depositional stages controlled by sedimentary tectonics. These comprise: encroachment of shallow marine siliciclastic fades within a tectonicilly induced trough, spreading of shallow marine facies across the studied area, phase of strong differential subsidence, and sharp replacement of siliciclastic facies by outer shelf carbonate fade