Abstract

The SW Iberian margin holds an unmistakable signal of Mediterranean Outflow Water (MOW) following its exit through the Strait of Gibraltar. It also represents a key area for understanding the effects of tectonic activity both on evolution of the Gibraltar Gateway and on margin sedimentation, having major implications for global climate and oceanography. It was therefore targeted for drilling by IODP Expedition 339 – some of the principal results are presented here.

Following opening of the Gibraltar Gateway (5.33 Ma), it was a further 1 My before a weak MOW started to flow into the Atlantic (4.5- 4.2 Ma). It was not until the Late Pliocene (3.2-3 Ma) and early Pleistocene (2.4-2.1 Ma) that a marked enhancement of MOW circulation into the North Atlantic occurred, evidenced by two widespread depositional hiatuses, which determined significant changes in sedimentary style and dominant process. Significantly, MOW contributed to an enhancement of the Atlantic Meridional Overturning Circulation and, consequently, to global climate.

Tectonic controls on margin development are evidenced by the closure of the Atlantic-Mediterranean gateways in Spain and Morocco at just over 6 Ma, the opening of the Gibraltar Gateway at 5.3 Ma, downslope sediment transport and contourite drift evolution. Based on the timing of events recorded in the sedimentary record, we propose a tectonic pulsing in the region at a timescale of approximately 1 My, which we tentatively link with asthenosphere activity.

The Gulf of Cadiz is the world’s premier contourite laboratory and thus presents an ideal testing ground for the contourite paradigm. Following examination of over 4.5 km of contourite cores, the existing models for contourite deposition are found to be in good working order. Their further study has begun to allow us to resolve outstanding issues of depositional processes, drift budgets, and recognition of fossil contourites in the ancient record onshore. The expedition also verified an enormous quantity and extensive distribution of contourite sands that are clean and well sorted. These represent a completely new and important exploration target for potential oil and gas reservoirs.