Stratigraphy and paleoceanography of a topography-controlled contourite drift in the Pen Duick area, southern Gulf of Cádiz

Abstract

Abstract The northern part of the Gulf of Cadiz has and still is receiving a lot of attention from the scientific community due to (among others) the recent IODP Expedition 339. In contrast, its southern part, or the Moroccan margin has received far less attention, although mud volcanoes, diapiric ridges and cold-water corals are present in this region. The El Arraiche mud volcano field is characterized by a compressive regime creating several ridges and assisting the migration of hydrocarbon fluids towards the seabed surface. This study presents seismic and multibeam evidence for the existence of a contourite drift at water depths between 550 and 650 m along the southwestern flank of the Pen Duick Escarpment and Gemini Mud Volcano, within the El Arraiche Mud Volcano field. From the onset of the Quaternary, when the escarpment started to lift and the local mud volcanism initiated, contouritic deposition was initiated as well at the foot of both topographic obstacles. Initially, fairly low-velocity bottom currents gave rise to sheeted drift deposits, affected by the uplift of the escarpment or mud extrusion. From the Middle Pleistocene onwards, separated mounded drift deposits were formed due to intensified bottom currents. An Antarctic Intermediate Water origin is inferred as driving mechanism for the drift development, although glacial conditions are not yet well constrained. The influence of Mediterranean Outflow Water (MOW) cannot be substantiated here. Moreover, the changes recorded within this contourite drift differ from the MOW-dominated contourite depositional system in the northern Gulf of Cadiz, as drift deposits only occur as early as the base of the Quaternary (compared to the Early Pliocene for the north) and mounded drift deposits only occur from the Middle Pleistocene onwards (compared to the Early Pleistocene). Cold-water coral mounds have been observed within and on top of the sedimentary sequence at the foot of the Pen Duick Escarpment. This implies that environmental conditions in which cold-water corals thrive were not necessarily restricted to the top of the Pen Duick Escarpment.