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doi:10.2204/iodp.proc.339.101.2013

Preliminary scientific assessment

There can be no doubt that the expedition results have more than met our scientific objectives at the outset. The results are both expected in that they confirm many of our pre-expedition hypotheses and also unexpected in the wealth of new ideas and data that have arisen. We set out with five broad objectives. They have been addressed and met as follows.

  1. Understand the opening of the Gibraltar Gateway and onset of MOW.

We drilled to the Miocene at two sites, assessed the basal age of drift sedimentation caused by MOW, and evaluated the nature and effects of climate change in the patterns of drift sedimentation. We recognize clear evolution from proximal to distal sites.

  1. Determine MOW paleocirculation and global climate significance.

We penetrated most key Miocene-to-recent reflectors at one or several sites and therefore have been able to date these reflectors and confirm or refine our seismic stratigraphic framework accordingly. We have been able to understand and evaluate their link to paleocirculation variation and events with respect to MOW, as well as to the sedimentary and tectonic evolution of the whole region. We recognized orbital- and millennial-scale signals in the sedimentary record, which will be evaluated through subsequent work.

  1. Establish a marine reference section of Quaternary climate change.

We recovered a very complete record of sedimentation at the Shackleton site (U1385) dating back to ~1.4 Ma. Four holes were drilled and cored to 150 mbsf, allowing construction of two complete spliced records. Detailed sampling and subsequent study of this material will certainly increase the precision with which marine sediment records of climate change are correlated and compared with ice-core and other terrestrial records. It will also support and refine the proposals for further drilling on this margin.

  1. Identify external controls on sediment architecture of the Gulf of Cádiz and Iberian margin.

We have established the nature of sedimentation and timing of associated hiatuses by drilling and correlation between sites. This correlation has enabled us to further refine our understanding of the stacking pattern and evolution of the Quaternary drift deposits and to evaluate the nature of contourite cyclicity at different scales. Further detailed work on the contourite sediments will allow us to better understand the nature of bottom-current processes and contourite deposition and gain better insight into the sedimentary budget for contourite drifts. We have already established the key sources of sediment and their controls.

  1. Ascertain synsedimentary tectonic control on architecture and evolution of the CDS.

We have been able to accurately chart the chronology of neotectonic activity in the Gulf of Cádiz and to clearly see evidence of the varied effects of this activity, both on the alongslope (contourite) depositional system and on the downslope component. The timing and local effects of diapiric activity have been established; further work will allow closer refinement and understanding of these effects and of rates of movement.