The submarine volcanic system of the Errigoiti Formation (Albian-Santonianof the Basque-Cantabrian basin, northern Spain): Stratigraphic framework, facies, and sequences

The Errigoiti Formation, located in the central domain of the Basque-Cantab rian basin, is an Albian to Santonian bathyal submarine volcanic system of alkali basaltic character. These volcanics occurred in an extensional geody namic context generated by the drifting of the Iberian plate with respect t o the European plate. Stratigraphic analyses reveal the facies distribution and depositional arch itecture of a longitudinal cross section of the Errigoiti volcanic system. Four facies groups were distinguished: sheet lavas (SL), derived from low-v iscosity lava flows at high magma discharge rate; pillow lavas (PL), derive d from intermediate-viscosity lava flows at moderate discharge rate; pillow breccias (PB), derived either from in situ fragmentation of lavas (PBI) or rock-falling from pillow-lava slopes (PB2); and stratified volcaniclastite s (VC), derived from volcaniclast resedimentation through gravity flows, ei ther by early remobilization (VC1) or post-volcanic reworking (VC2), The fa cies groups occur in a predictable repetitive succession, essentially from base to top, an SL PL-PB-VC stacking pattern. This is interpreted to reflec t an upward waning in the magma discharge rate, Five major volcanic sequences make up the Errigoiti Formation. Each compris es packages tens to hundreds of meters thick, deposited during short time s pans of volcanic activity separated by long time intervals of volcanic inac tivity. Consequently, boundaries between sequences are associated with mark ed hiatuses, reworked volcaniclasts, and/or turbidite-pelagic sedimentation . Analysis of lateral and vertical facies evolution enabled us to propose a d epositional model consisting of three depositional environments. From proxi mal to distal settings, these are: amalgamated pillow volcanoes, scattered pillow volcanoes, and volcanic fringe, basically responding to a proximal t o distal PL/PB, PL/VC, and SL/VC evolution of facies associations. Contempo raneous fossiliferous turbidite-pelagic sequences that surround the volcani c succession allow paleobathymetry to be estimated on the basis of biofacie s, Sites with the highest rate of volcanic emission correspond to an averag e depth of 900 m; sites with thinner volcanic pile accumulated at a minimum depth of 1100 m, The facies sequence established in this work and the processes involved in its formation are comparable with the sequences and processes described in other submarine basic volcanic systems. Consequently, the depositional mode l for the Errigoiti Formation can perhaps serve as a reference model for th is type of volcanic system.