Seismic pre-site survey for an IODP site on the Cape Verde Plateau
Geophysics
Final Report Abstract
The IODP full-proposal 973 ‘Neogene climate of NW Africa’ has the following main objectives: i) NW African climate in a warmer world, with emphasis on wind systems, dust supply, precipitation and vegetation, ii) High productivity, ecosystem and sediment transport response to climate perturbations. Sediment cores should be retrieved at five locations between Cape Bojador southeast of the Canary Islands and the deltas of Senegalese and Gambian rivers, including the Cape Verde Plateau. Good seismic information exists for most of the proposed sites, while no modern data were available for the Cape Verde Plateau. ODP Site 659 was drilled on the Cape Verde Plateau during ODP Expedition 108 in 1986, and the results of that site indicate that Miocene sediments can be drilled in relatively shallow subsurface depths. The aim of this project was to identify new IODP drilling site where the Plio-Pleistocene is thinner and the Miocene is thicker than it is at ODP Site 659. This study is based on new high-resolution seismic reflection data that was collected during RV MARIA S. MERIAN Cruise MSM87 in late 2019. During this cruise, we collected 28 seismic profiles with a total length of ~1000 km. The seismic data is mainly characterized by wellbedded, sub-parallel and sub-horizontal reflectors. Two lines crossing ODP-Site 659 allowed a detailed stratigraphic characterization of the reflectors. The Pleistocene- Pliocene boundary as well as the Pliocene-Miocene boundary can be clearly identified and traced on the seismic data. In most areas on the Cap Verde Plateau, the Plio-Pleistocene sediments appear to have a relatively constant thickness of approx. 0.18 s TWT (~140 m assuming a velocity of 1600 m/s). South-East of ODP Site 659, the Pleistocene- Pliocene sediments appear to thin to 0.08 s TWT (~60 m assuming a velocity of 1600 m/s). This site (NWAFR-14A) represents an optimal drilling location and was selected as primary site on the Cape Verde Plateau. The shallow water depth (2850 m) and the shallow burial of the Miocene deposits will permit full recovery (piston coring) of Miocene strata with well-preserved calcareous microfossils. Two alternate sites were selected based on the seismic data. The new data are an important contribution the IODP full-proposal 973 ‘Neogene climate of NW Africa’. The sites were well accepted by the site-evaluation panel and the proposal was sent out for external review.
Publications
- (2020) Seismic pre-site survey for an IODP site on the Cape Verde Plateau. 80. Jahrestagung der Deutschen Geophysikalischen Gesellschaft (virtual meeting)
Wilckens, H., Krastel, S.
