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Site U13911

Expedition 339 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site U1391 is located on the West Iberian margin (37° 21.5322′N, 9°24.6558′W) and represents the most distal site within the contourite depositional system (CDS) explored during Expedition 339 (Fig. F1, F2). It is situated over a large plastered drift on the middle slope terrace from Sector 5 of the CDS (the canyons sector in Stow et al., 2011, previously defined by Hernández-Molina et al., 2003, and Llave et al., 2007). This site represents an opportunity for recovering a sedimentary record for the Quaternary and Pliocene caused by Mediterranean Outflow Water (MOW) deposition on the southwest Portuguese margin (see Fig. F21 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]).

Regional work has determined the tectonic and stratigraphic evolution of this part of the margin. These previous studies identified that the sedimentary record of the southwest Portuguese margin spans from the Late Triassic through Quaternary and consists of Mesozoic rift and postrift sediments deformed during the Cenozoic alpine compression (Terrinha et al., 2003). Major unconformities/hiatuses generated during this tectonic inversion phase separate Late Cretaceous from middle Eocene sediments and late Eocene from early Miocene sediments (Alves et al., 2003; Pereira et al., 2011). The present-day morphostructural attributes of the margin are the result of the middle Miocene uplift of fault blocks inherited from the Mesozoic rifting phases. This structural compartmentalization of the margin controlled its tectonic and sedimentary evolution during the Pliocene and Quaternary transpressive regime because of the activity of some structures located near Site U1391, such as the São Vicente Canyon and Horseshoe faults to the south, the Pereira de Sousa fault to the north, and the Marquês de Pombal fault to the east (e.g., Alves et al., 2000; Terrinha et al., 2003; Zitellini et al., 2004).

In this morphostructural context, contourite features developed over the middle slope as a northward extension of the CDS from the Gulf of Cádiz. As no previous work has been published on contourite sedimentation along this margin, the results from this site are very important for increasing the knowledge of margin evolution. The plastered drift at this site is one of a series of contourite features formed under the influence of the northern branch of MOW as it continues north along the Iberian margin and beyond (Iorga and Lozier, 1999; Serra et al., 2010). These include those along the middle slope of the northwest Portuguese margin (Alves et al., 2003; Pereira and Alves, 2011), the Galicia Bank and Galician slope (Ercilla et al. 2009, 2010, 2011; Bender et al. 2010; Mena et al. 2010), Ortegal Spur (Hernández-Molina et al. 2009), Le Danois Bank or “Cachucho” (Ercilla et al. 2008; Iglesias, 2009; Van Rooij et al. 2010), and the Porcupine slope (Van Rooij et al., 2003).


The major objective for Site U1391 was to recover a sedimentary contourite record for the Pliocene and Quaternary deposited under the influence of MOW along the West Iberian margin (see Fig. F21 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]). This record will allow us to investigate more specific objectives including

  • The influence of the Strait of Gibraltar (or Gibraltar Gateway) through the Pliocene and the Quaternary in the West Iberian margin,

  • MOW paleoceanography and its global climate significance during the last 4 m.y.,

  • The effects of climate and sea level changes on the sediment architecture of the plastered drift on the middle slope off Portugal, and

  • The sedimentary stacking pattern of the plastered drift in relation to changes in sea level and other forcing mechanisms.

To achieve these major scientific objectives, it is essential to integrate the results from Site U1391 with a network of existing seismic reflection profiles from the Portuguese margin and to correlate these with results from the Gulf of Cádiz.

1 Expedition 339 Scientists, 2013. Site U1391. In Stow, D.A.V., Hernández-Molina, F.J., Alvarez Zarikian, C.A., and the Expedition 339 Scientists, Proc. IODP, 339: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.339.109.2013

2Expedition 339 Scientists’ addresses.

Publication: 17 June 2013
MS 339-109