Structural control and tectono-sedimentary evolution of the Gulf of Cadiz, SW Iberia since the late Miocene: Implications for contourite depositional system

Abstract

The Gulf of Cadiz Contourite Depositional System (GCCS) developed due to the interaction of the Mediterranean Outflow Water (MOW) with the middle continental slope of the SW Iberian continental margin. The GCCS evolved in a complex tectonic setting within the foreland of the Betic Orogeny and near the Nubia-Eurasia plate boundary. This study used tectonostratigraphic analysis of an extensive 2D multichannel seismic reflection dataset to investigate how inherited basin configuration and tectonic activity controlled sedimentary stacking pattern and evolution of the GCCS. Three regional tectonostratigraphic units (U1-U3) were recognised in the margin. The younger seismic unit U3 corresponds to the Miocene-Quaternary foreland basin system where the contourite system is generated. Seismic analysis also detected the dextral strike-slip Gil Eanes Fault Zone (described herein for the first time), the Cadiz Fault, the Albufeira-Guadalquivir-Doñana Basement High and several diapiric structures. Integrated analysis of seismic profiles showing these tectonic structures with thickness and earthquake distribution maps suggest four tectono-sedimentary domains. The distinct characteristics shown by contourite features in the different domains, depends at broad-scale on the tectonic-control of the accommodation space (i.e., subsidence or uplift) and at local-scale on the presence of structural highs and fault-related depressions. Both influence bottom-current circulation and thus the evolution of the contourite deposits through the late Miocene and Quaternary. Three main stages have been recognised in the Gulf of Cadiz evolution: 1) the region was the western continuation of the Betic Corridor until the final re-opening of the Strait of Gibraltar (8–5.3 Ma). In this stage there is a predominance of turbidites or hemipelagic deposits, dependant on tectonic activity; 2) with the final re-opening of the Mediterranean-Atlantic connection there is the onset of the Pliocene- Quaternary contourite depositional system (5.3–2.0 Ma). Short-term changes in sedimentation during this stage, from contourite to turbidite deposits, indicate periods of increased tectonic activity; and 3) after the onset of the transpressive tectonic regime in the area (from 2.0 Ma), sedimentation became more homogeneous suggesting stable conditions (decrease of tectonic activity) with dominant contourite deposition. This work highlights the remarkable influence of structural features and tectonic events in controlling the seafloor relief and in turn in influenced the local oceanic circulation processes that controlling the morphology and sedimentary evolution of contourite systems.