IODP Proceedings    Volume contents     Search


Site U13891

Expedition 339 Scientists2

Background and objectives

Integrated Ocean Drilling Program (IODP) Site U1389 (36°25.515′N, 7°16.683′W; 644 m water depth) is located in Sector 3 of the contourite depositional system (CDS) (channel and ridge sectors defined by Hernández-Molina et al., 2003, and Llave et al., 2007a) on the northwest side of the Guadalquivir diapiric ridge (Figs. F1, F2). This is an important site for the recovery of a late Pliocene and Pleistocene succession under the influence of the lower core of Mediterranean Outflow Water (MOW).

This sector is located in the central area of the middle slope between Cádiz and Faro, at 800–1600 meters below sea level (mbsl) (Fig. F3), and was first studied by Nelson et al. (1993, 1999) and Baraza et al. (1999), who originally described it as the “Ridge and Valley Province.” The sector has been described in more detail recently by several authors (Mulder et al., 2002, 2003; Habgood et al., 2003; Hernández-Molina et al., 2003, 2006; Hanquiez et al., 2007; Llave et al., 2007a; García et al., 2009).

The sector includes some prominent morphostructural features, including the Guadalquivir Bank; the Doñana, Guadalquivir, and Cádiz diapiric ridges; and numerous isolated diapiric highs and mud volcanoes (Fig. F3) that are caused by recent tectonic activity (Maldonado et al., 1999; Maestro et al., 2003; Somoza et al., 2003; Medialdea et al., 2004, 2009; Fernández-Puga et al., 2007; Zitellini et al., 2009). Some of the diapiric ridges occur as a distinctly linear and segmented seafloor relief with a general northeast–southwest trend, whereas others are buried and show an undulating deformational pattern of topographic highs and lows. In this scenario, a complex pattern of erosive features occurs, composed of four types of submarine valleys: contourite moats, contourite channels, marginal valleys, and large isolated furrows (Hernández-Molina et al., 2003, 2006; Llave et al., 2007a; García et al., 2009). As many as nine contourite channels have been identified in this sector by García et al. (2009), with the five larger ones known as the Cádiz, Guadalquivir, Huelva, Diego Cão, and Gusano Channels (Figs. F3, F4). These channels are asymmetrical in cross section, with lengths ranging from 10 to >100 km, widths ranging from 1.5 to 10 km, and depths ranging from 10 to 350 m, and the incisions are generally greater on the northern flanks (Figs. F4, F5).

Within the contourite channel, the floors are characterized by very high backscatter, representing scoured diapirs, outcrops of rock, and rubble partially covered by longitudinal bedforms and regularly spaced dunes (Hernández-Molina et al., 2006; Stow et al., 2009, in press). Nelson et al. (1993) identified gravel and shelf lags in the eastern channels and sand in western channels. Contourite channels are broadly S-shaped in plan view, with northwest-southeast–oriented alongslope segments veering to northeast-southwest–oriented downslope segments, caused by the interaction of bottom currents with the irregular morphology of the slope and diapiric ridges (Figs. F3, F4). Several marginal valleys with irregular morphology and a northeast–southwest orientation are noted behind the adjacent diapiric ridge flank, whereas other marginal valleys identified by García et al. (2009) have much more irregular trends. Erosive contourite channels and marginal valleys are present over a broad deformed sheeted drift. This drift represents the main depositional morphology in this sector (Figs. F4, F5), but some patch drifts can be also identified behind local topographic obstacles. The distribution and characteristics of these erosive features allowed García et al. (2009) to propose a new and more precise scheme for the MOW circulation pattern. This scheme includes a main alongslope circulation responsible for the excavation of the contourite moat and channels and a secondary downslope circulation responsible for the erosion of marginal valleys and isolated furrows.

Based on seismic data through the Quaternary period, Llave et al. (2007a) and García et al. (2009) reported important depositional and oceanographic changes associated with tectonic events related to the aforementioned morphostructural features, coeval with the mid-Pleistocene revolution and marine isotope Stage 6. In these two periods, realignment of the diapiric ridges and their segmentation as the result of neotectonic effects led to the development of new local gateways. These affected the distribution of the different branches of the MOW, and hence, the distribution of associated contourite channels. As a result of these tectonic changes, some mounded, elongated, and separated drifts were buried (Figs. F6, F7) under the influence of the lower core of MOW. These are preserved in the sedimentary record (Llave et al., 2007b).


The major objective for Site U1389 was to recover a sedimentary contourite record through the late Pliocene and Pleistocene (see F17 in the “Expedition 339 summary” chapter [Expedition 339 Scientists, 2013a]) under the influence of the lower core of MOW (Stow et al., 2011). This record will allow us to investigate

  • The influence of the Gibraltar Gateway through the Pliocene and Pleistocene in the proximal to middle part of the contourite system;

  • MOW paleoceanography for the late Pliocene to Holocene;

  • The effects of long- and short-term climate and sea level changes on the sediment architecture of the contourite drift in this sector of the CDS; and

  • The stacking and evolution of the previously identified buried, mounded, elongated, and separated drifts developed under the influence of the lower core preserved in the sedimentary record (Llave et al., 2007b).

Specific objectives for Site U1389 include

  • Drilling through the sheeted drifts and buried mounded drift succession and into late Pliocene sediments and hence dating the most important intervals for contourite sedimentation in the proximal to middle part of the CDS;

  • 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;

  • Determining the sedimentary stacking pattern and evolution of the buried, mounded, elongated, and separated drifts and the inferred tectonics and/or environmental changes;

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

  • Determining the contourite sequence of facies 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 drift construction, non-deposition (hiatuses), and erosion; and

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

1 Expedition 339 Scientists, 2013. Site U1389. 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.339.107.2013

2Expedition 339 Scientists’ addresses.

Publication: 17 June 2013
MS 339-107