Upper Oligocene to Quaternary sedimentary evolution of the Cantabrian continental margin (Eastern Bay of Biscay)

Abstract

Multibeam bathymetry, high and very high resolution seismic records were used to define a new seismic stratigraphy that offers fresh insights into the sedimentary evolution of the Cantabrian continental margin from Late Oligocene to Quaternary. The stratigraphic succession is divided by six main seismic discontinuities, whose seismic divisions are organized into a hierarchy on two different levels: seismic mega-sequences (C, B and A, from older to younger) and meso-sequences (C2, C1, B2, B1, A2 and A1). The facies architecture of the Cantabrian margin is characterized by shelf-margin deposits on the shelf break; open slope deposits locally intercalated with mass-flow deposits and isolated channels (braided and leveed), overspilling deposits, contourite deposits, scar and mass transport deposits, and scar and lobe deposits on the continental slope; and turbidite fans and to a lesser extent facies of scar and lobe deposits and basinal sheet-like turbidites on the continental rise. The sedimentary evolution is divided into three major phases that are conditioned by the main episodes of the regional Pyrenean tectonism: a first active stage (Late Oligocene – Earliest Miocene), a second stage where the activity deceases progressively from sea to land (Mid-Early Miocene – Middle Miocene), and a third quiescent period (Late Miocene – Quaternary). The detailed analysis of the interplay of the Alpine tectonism, global variations in eustasy and regional variations in climate, sediment supply and oceanography (variations in the MOW circulation) with the sedimentary products has permitted the definition of five different environmental scenarios whose detailed analysis has enable to state that the regional tectonics first and the climate secondly are the main drivers controlling the type and volume of sediment supply, and only when regional tectonics becomes quiescent the role played by the sea-level and the oceanography begins to be recognised in the margin architecture