Impact of Sub-Seismic Scale Salt-Controlled Deformation on Deep-Water Flow Processes and Deposits: Insights from the Jata and Burgoa Minibasins, Basque Country, Spain

Active salt tectonics and resultant topography strongly influence deep marine sediment gravity flow behaviours and resulting depositional architecture. However, most studies have focused on seismic scale interaction between salt diapir growth and the adjacent stratigraphy. Salt-controlled deformation and its effects on deep-water flow processes, on lateral scales of tens to hundreds of metres during the fill of salt withdrawal basins, is poorly understood. In the Basque–Cantabrian Basin of northern Spain, the Bakio Diapir separates the Jata and Burgoa minibasins. The late-stage fill of these minibasins is represented by the ~1700-meter-thick Late Albian–Early Cenomanian Black Flysch Group. The Black Flysch Group is a prograding submarine fan succession that provides an excellent opportunity to understand the impact of salt diapir growth on sediment gravity flow processes. A field-based study has revealed that, metre-scale displacement synsedimentary normal faults and mass transport deposits associated with slope failure formed dynamic seabed topography that influenced overriding flow behaviour. Bed-scale heterogeneity increased as fault topography caused low concentration flows to become more erosive, entraining muddy substrate which increased flow concentration, cohesive forces and the deposition of transitional flow deposits and hybrid beds. The synsedimentary fault growth was also responsible for large scale architectural changes evidenced by the juxtaposition of proximal lobe facies with channel fill facies across faults. These findings enhance the understanding of depositional architectures and the facies distributions at sub-seismic scale within salt minibasins.