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Site U13861

Expedition 339 Scientists2

Background and objectives

An extensive contourite depositional system (CDS) was generated during the Pliocene and Quaternary by the action of Mediterranean Outflow Water (MOW) on the middle slope of the Gulf of Cádiz. In total, this CDS extends ~300 km alongslope from the exit of the Strait of Gibraltar (or Gibraltar Gateway) and a further 100 km around the West Iberian margin (e.g., Kenyon and Belderson, 1973; Gonthier et al., 1984; Nelson et al., 1999; Alves et al., 2003; Llave et al., 2007; Stow et al., 2002; Mulder et al., 2003; Habgood et al., 2003; Hernández-Molina et al., 2003; Hanquiez et al., 2007; Marchès et al., 2007; Roque et al., 2012). One of the main depositional features of this CDS is the Faro-Albufeira Drift (Gonthier et al., 1984; Faugères et al., 1985a), which is located at ~500–700 meters below sea level (mbsl) within Sector 4 (Fig. F1 and Fig. F12 in the “Expedition 339 summary” [Expedition 339 Scientists, 2013a]) of the CDS (defined by Hernández-Molina et al., 2003, and Llave et al., 2007) and has been generated by the upper core of MOW. This corresponds to an elongated, mounded, and separated drift (hereafter referred to as Faro Drift for simplicity), following the nomenclature of Faugéres et al. (1993), with a total length of 100 km, a maximum width of 20 km, and a maximum thickness of ~700 m.

The Faro Drift represents a classic example of middle-slope contourite deposits with a well-layered internal acoustic structure and an internal reflection configuration that onlaps and downlaps in an oblique upslope direction (Fig. F12 in the “Expedition 339 summary” [Expedition 339 Scientists, 2013a]). It is mainly composed of muddy, silty, and sandy sediments with mixed terrigenous and biogenic composition (Gonthier et al., 1984; Stow et al., 1986, 2002). The stratigraphic architecture of this drift and its relationship with the major structural features in the area has been described in some detail by previous authors (Faugères et al., 1985a, 1985b; Stow et al., 2002; Llave et al., 2001, 2006, 2007, 2011; Roque et al., 2012). In general, the drift shows laterally extensive, aggradational to progradational seismic depositional units with widespread discontinuities (Fig. F2).

Faro Drift has been developing along the midslope over the past 5 m.y. under the direct influence of MOW. It therefore contains the signal of MOW through the Strait of Gibraltar, reopened following tectonic adjustments at the end of the Messinian salinity crisis (Hsü et al., 1973; Sierro et al., 2008) and hence a clear record of Mediterranean Sea and MOW influence on the North Atlantic Ocean (Stow et al., 2011). The high rates of accumulation and expanded sedimentary records of drift deposits permit high-resolution examination of past environmental change (climatic and eustatic) (Llave et al., 2006; Voelker et al., 2006; Toucanne et al., 2007). On a smaller timescale, identified grain-size cyclicity is interpreted as representing cyclic changes in MOW strength (Fig. F3), suggesting MOW intensification during cold intervals in the Gulf of Cádiz (Llave et al., 2006; Voelker et al., 2006). During glacial periods, strengthened MOW sank to depths ~700 m deeper than today, impinging on the continental slope at 1600–2200 mbsl (Schönfeld and Zhan, 2000; Rogerson et al., 2005; Llave et al., 2007; Voelker et al., 2006; García et al., 2009). This enhancement of MOW also occurred during Heinrich events, Dansgaard/Oeschger stadials, and the Younger Dryas (Sierro et al., 2005; Llave et al., 2006; Voelker et al., 2006). Furthermore, post-Miocene tectonic activity has also played an important part in the morphological development of the seafloor, controlling multiple current pathways for MOW at each evolutionary stage (Nelson et al., 1999; Llave et al., 2007, 2011; García et al., 2009; Roque et al., 2012).

All the aforementioned work has demonstrated the importance of the Faro Drift for both paleoceanographic and contourite studies. However, despite this significance and despite it being one of the largest drifts in the world, it has never before been drilled for scientific purposes. Therefore, drilling the Faro Drift was a unique challenge for Expedition 339. Site U1386 (36°49.685′N, 7°45.321′W) on the Faro Drift (Figs. F1, F4) is a very important site and represents an opportunity for recovering a key Pleistocene and Holocene sedimentary succession formed under the influence of the upper core of MOW. This site is complementary to Site U1387, which is ~4.1 km southeast and targets a Pliocene and lower Pleistocene sedimentary record also formed by the upper core of MOW (Fig. F6 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]).


The major objective for Site U1386 was to recover at least a complete sedimentary contourite record deposited under the influence of the upper core of MOW for the last 1.8–2 m.y. on the Faro Drift. This record will allow us to investigate

  • The influence of the Gibraltar Gateway through the Quaternary,

  • MOW paleoceanography and its global climate significance during at least the last 1.8–2 m.y., and

  • The effects of climate and sea level changes on the sediment architecture of the contourite drift.

To achieve these major scientific objectives, it is essential to integrate the results at Site U1386 with a dense network of existing high- and medium-resolution seismic reflection profiles.

Specific objectives for Site U1386 include

  • Documenting the possible effects of the Gibraltar Gateway through the Pleistocene and hence determining the input variation of the influx of warm, saline intermediate water into the North Atlantic Ocean and the nature of change in the patterns of sedimentation and microfauna;

  • Reconstructing the main MOW paleoceanographic events for the Pleistocene and identifying the role of salt injection from MOW in the dynamics of North Atlantic Deep Water;

  • Focusing on high-resolution calibration of late Pleistocene–Holocene facies and the inferred environmental changes in terms of global rapid climatic events;

  • Evaluating the correlation and influence of cold periods (glaciations, terminations, and ice-rafting events) with MOW variation, testing the concept of cold period intensification of MOW;

  • Determining the sedimentary stacking pattern of Faro Drift in relation to changes in sea level and other forcing mechanisms, which can determine the potential role of variations in cross-sectional area of the Gibraltar Gateway;

  • Evaluating periods of drift construction, nondeposition (hiatuses), and erosion. The nature of sedimentation and timing of principal unconformities is one of the important objectives, especially for the mid-Pleistocene;

  • Determining the timing and extent of hiatuses and condensed sequences and attempting paleodepth reconstruction;

  • Evaluating the contourite deposition in relation to sea level variation and to the further development of a sequence stratigraphic model;

  • Quantifying the sediment budget and source for the contourite deposits; and

  • Calibrating and hence understanding the sedimentary cyclicity evident on the deposits, which can characterize their sedimentary expression and regional extent.

1 Expedition 339 Scientists, 2013. Site U1386. 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.339.104.2013

2Expedition 339 Scientists’ addresses.

Publication: 17 June 2013
MS 339-104