The sandy channel–lobe depositional systems in the Gulf of Cadiz: Gravity processes forced by contour current processes V. Hanquiez a, ⁎, T. Mulder a , S. Toucanne a , P. Lecroart a , C. Bonnel b , E. Marchès a , E. Gonthier a a UMR/CNRS 5805-EPOC, Université Bordeaux 1, avenue des facultés, 33405 Talence cedex, France b Laboratoire de Modélisation et d'Imagerie en Géosciences UMR 5212, Université de Pau et des Pays de l'Adour, Bât IPRA, Avenue de l'Université, BP 1155, 64013 Pau Cedex, France abstract article info Available online 18 May 2009 Keywords: Gulf of Cadiz Mediterranean Outflow Water Contourite channels Sandy lobes Climate forcing The sedimentation in the Gulf of Cadiz (NE Atlantic Ocean) is significantly controlled by the Mediterranean Outflow Water (MOW). Along its pathway onto the continental slope, the MOW is canalized by contourite channels, some of them feeding gravity sandy channel–lobe depositional systems firstly recognized in previous study [Habgood et al., 2003. Deep-water sediment wave fields, bottom current sand channels and gravity flow channel–lobe systems: Gulf of Cadiz, NE Atlantic. Sedimentology 50(3), 483–510.]. Using very high resolution acoustic data and cores, a detailed characterization and a new evolution pattern of these channel–lobe depositional systems is established. Complex internal geometry of the lobes shows several depositional units revealing a polyphase evolution of these systems, with a general progradation punctuated by retrogradation and avulsion phases. A gravity origin controlled by contouritic processes and climatic changes is demonstrated for the feeding and the evolution of these sandy channel–lobe depositional systems. Climate oscillations, via the MOW variations, act as a major forcing of the activity of the channel– lobe depositional systems during the Late Quaternary. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Gulf of Cadiz (Eastern part of the Central Atlantic Ocean) extends from the Straits of Gibraltar (Spain) to Cape San Vicente (Portugal) (Fig. 1A). The oceanography and the sedimentation of the Gulf of Cadiz are influenced by a permanent current of warm and saline intermediate water mass (Mediterranean Outflow Water, MOW, Fig. 1A) flowing out the Mediterranean Sea along the upper and middle slopes between around 500–1400 m water depth towards the Atlantic Ocean (Madelain, 1970). Due to the predominance of contour currents in the upper and middle slopes of the Gulf of Cadiz, many studies focused on the contourite deposits (drifts), especially on their morphology and architecture (Faugères et al., 1985, 1994, 1984; Gonthier et al., 1984; Kenyon and Belderson, 1973; Stow et al., 1986, among others). Here, quality of very high resolution acoustic data set allows a new description of three channel–lobe depositional systems (Tasyo, Aveiro and Lolita systems, Fig. 1B), previously identified by Habgood et al. (2003), showing many similarities with the channel–levee–lobe complexes found in the deep sea turbidite systems (e.g., Deptuck et al., 2008; Normark, 1978; Normark et al., 1993; Walker, 1978). Originality of the Gulf of Cadiz lies in the absence of canyon upstream of the channel–lobe depositional systems (CLS). Based on the spatial organization and internal architecture of these lobe complexes, our study suggests a new evolution pattern for these depositional systems and shows a major role of the MOW on their evolution. 2. Regional background The study area is located within the overflow sedimentary lobe sector of the Gulf of Cadiz Contourite Depositional System (Hernández- Molina et al., 2003), which has been generated by the MOW, then controlled both by Pliocene and Quaternary environmental and paleoceanographic changes (Hernández-Molina et al., 2003, 2006). The lobe sector is characterized by the circulation of the Mediterranean Lower Water (southern branch of the MOW) which currently interacts with the sea floor down to 1400 m water depth (Hanquiez, 2006; Madelain, 1970). The Mediterranean Lower Water is channelled westward by the Main MOW Channel, (Mulder et al., 2003) and northward by the Cadiz Contourite Channel (Hernández-Molina et al., 2003)(Fig. 1). South of the Cadiz Contourite Channel and the Cadiz Valley (Hernández-Molina et al., 2003, 2006; Llave, 2004)(Fig. 1), and west of the Main MOW Channel, the Giant Contouritic Levee built by the overflow of the Main MOW Branch is observed (Mulder et al., 2003) (Fig. 1). Active secondary channels, such as the Gil Eanes Channel (Kenyon and Belderson, 1973), are present on the Giant Contouritic Levee and drain downslope a part of the MOW (Habgood et al., 2003; Hanquiez et al., 2007; Mulder et al., 2003)(Fig. 1). The Tasyo, Aveiro and Lolita CLS on which we focused in this study are described from the distal boundary of the Giant Contouritic Levee, and are consequently out of the present-day influence of the MOW. Their path developed in areas Sedimentary Geology 229 (2010) 110–123 ⁎ Corresponding author. Tel.: +33 5 40 00 34 35; fax: +33 5 56 84 08 48. E-mail address: v.hanquiez@epoc.u-bordeaux1.fr (V. Hanquiez). 0037-0738/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.sedgeo.2009.05.008 Contents lists available at ScienceDirect Sedimentary Geology journal homepage: www.elsevier.com/locate/sedgeo