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Site U13881

Expedition 339 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site U1388 (36°16.142′N; 6°47.648′W) is located on an extensive sandy sheeted drift of the proximal sector (Sector 1; proximal scour and ribbons sectors defined by Hernández-Molina et al., 2003, and Llave et al., 2007) of the contourite depositional system (CDS) close to the Gibraltar Gateway (Figs. F1, F2, F3). This site represents an opportunity for recovering part of the late Pliocene and Pleistocene succession close to the gateway in order to identify key paleoceanographic changes in Mediterranean Outflow Water (MOW) and to evaluate the influence of the gateway. Site U1388 is 6.5 km southwest of the oil company exploratory well MPC-1 (dry well), where samples older than Quaternary were recovered in 1982.

This sector is located in the southeastern area between Cádiz and the Strait of Gibraltar and is characterized by a smooth contourite terrace oriented alongslope between 500 and 800 meters below sea level (mbsl) (Figs. F1, F2; see also Fig. F15 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]). It was first described by Kenyon and Belderson (1973) and later by Nelson et al. (1993), Habgood (2002), and Habgood et al. (2003), all of whom consider it as the proximal part of the CDS. It is an extensive area (~100 km long and 30 km wide) dominated by an abrasional surface with high backscatter intensity (Fig. F2).

Several erosive scour alignments with a northwest–southeast orientation, smooth V-shaped expression, and truncated reflectors are evident in seismic profiles (Fig. F4). In the northwest part of this sector, distinct depositional features at the surface include a sequence of longitudinal bedforms (also oriented northwest–southeast), ripple marks, sand ribbons, and sediment waves (Kenyon and Belderson, 1973; Nelson et al., 1993; Hanquiez et al., 2007).

Oil company data show an exceptionally thick (~815 m) sandy sheeted drift (see Fig. F15 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]) composed of sand-rich horizons that average 12–15 m in thickness (Buitrago et al., 2001) intercalated with finer grained sediments. In addition, a sand bank was identified by Akhmetzhanov et al. (2002) and Akhmetzhanov (2003) at the southeast boundary of this sector.

The Gibraltar Gateway has a very special role in Mediterranean–Atlantic water mass exchange, which is associated with the highest bottom current velocities known anywhere in the study region (nearly 300 cm/s). This is also one of the most important oceanic gateways worldwide, enabling overflow and circulation of MOW to the Atlantic Ocean (e.g., Serra, 2004; Legg et al., 2009; Serra et al., 2010). The proximal sector within the CDS of the Gulf of Cádiz results from MOW generating strong and turbulent bottom currents, which contour the slope between 300 and 1000 mbsl (Kenyon and Belderson, 1973; Habgood et al., 2003; Hernández-Molina et al., 2003, 2006, 2011). Its velocity decreases from a maximum of 240 cm/s immediately west of the Gibraltar Gateway to ~75–100 cm/s near the northern end of the Cádiz sand sheet (Fig. F5). Beneath the highest velocity zone there is a broad abrasional surface and erosive scours, but as current velocity decreases, sand ribbons and wave fields develop. MOW divides into an upper and lower core at the northwest end of this sector, as described by Madelain (1970).


The major objective for Site U1388 was to recover a sedimentary contourite record for the late Pliocene to the Holocene deposited under the influence of the overflow of MOW close to the Gibraltar Gateway (Stow et al., 2011b). This record will allow us to investigate

  • The influence of the Gibraltar Gateway through the Pliocene and Pleistocene,

  • MOW paleoceanography and its global climate significance, and

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

Specific objectives for Site U1388 include

  • Drilling through the sheeted drift succession and into late Pliocene sediments and hence dating the most important intervals for sandy contourite sedimentation in the Gulf of Cádiz;

  • Evaluating the nature of change in the patterns of sedimentation and microfauna from the late Pliocene through the Holocene;

  • Documenting the possible effects of the Gibraltar Gateway through the Pliocene and Pleistocene and hence determining the input variation of MOW influx;

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

  • Focusing on the diagnostic criteria for sand-rich contourite deposits on sheeted drifts and the inferred environmental changes;

  • Evaluating the correlation and influence of cold/warm periods with MOW variation;

  • Determining the sedimentary stacking pattern of the sandy sheeted drift in relation to changes in sea level and other forcing mechanisms, thereby determining the potential role of variations in cross-sectional area of the Gibraltar Gateway;

  • Evaluating periods of sheeted drift construction, nondeposition (hiatuses), and erosion;

  • Evaluating the sandy contourite deposition in relation to sea level variation; and

  • Calibrating and therefore understanding the sedimentary cyclicity evident on the sandy contourite deposits, thereby characterizing their sedimentary expression and regional extent.

In addition to these objectives, improved knowledge of sand-rich contourite deposits will have significant implications, both in the establishment of a facies model for sandy contourites (Stow and Faugères, 2008; Viana, 2008) as well as in consideration of their potential as a future deepwater hydrocarbon exploration target (Buitrago et al., 2001; Llave et al., 2005; Akhmetzhanov et al., 2007; Viana et al., 2007; Viana, 2008; Stow et al., 2011a; Brackenridge et al., 2011).

1 Expedition 339 Scientists, 2013. Site U1388. 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.).

2Expedition 339 Scientists’ addresses.

Publication: 17 June 2013
MS 339-106