159 Preliminary Report
Côte d'Ivoire-Ghana Transform Margin,
Eastern Equatorial Atlantic

The information contained within this report is proprietary and cannot be quoted or published elsewhere without the permission of ODP.


Leg 159 drilled a series of four sites (Sites 959-962) within continental crust adjacent to the continent-ocean transition along the transform passive margin of Côte d'Ivoire-Ghana (CIG). This leg represents the first application of deep-sea drilling to the tectonics of transform- margin development. A series of tectonized Albian sediments documents an early phase of intra-continental transform motion. The deep-water lacustrine sequence passed into a progressively more marine sequence as breakup continued, probably as part of a pull-apart basin system. The coexistence of compressional and extensional features, as well as rarer strike-slip faults, shows the intense deformation that affected a broad zone of the continental margin at that time. Subsequent inversion of the pull-apart basin into the Marginal Ridge occurred during the Cenomanian- Turonian. The period of maximum uplift of the ridge is shown by the development of shallow-water reefal carbonates and associated high- energy coarse, clastic sediments of Turonian-Santonian age. Tectonic models of transform margins indicate that, following continental breakup, an active ocean-continent transform phase is ended by the migration of an active oceanic spreading center along the margin. Transfer of heat from the spreading ridge is predicted to cause major uplift and may correspond to this phase of shallow-water sedimentation. Subsequent cooling of the continental lithosphere would produce subsidence. Post- Santonian sedimentation at Site 959, situated on the flanks of the Deep Ivorian Basin, was marked by a deeper water, organic-rich, black-shale facies that continued until the late Paleocene. In contrast, Sites 960, 961, and 962, which are closer to the crest of the CIG Marginal Ridge, show hiatus and condensed claystone facies with glauconitic hardgrounds for this time. This ridge may have acted as a sill to the Deep Ivorian Basin, where free circulation with the open Atlantic was restricted. A major unconformity seen at all four sites in the upper Paleocene may mark the end of rapid thermal subsidence of the margin, but may also reflect changes in current activity at that time. Much of the Eocene and Oligocene is represented by pelagic siliceous sedimentation, with slumping off the uplifted ridge crest seen at Site 959. Neogene sedimentation is dominated by a hemipelagic clayey nannofossil sedimentation, except at Site 962, which accumulated clay alone because of its position below the carbonate compensation depth (CCD). Study of the Neogene sediments at Sites 959 and 960 is expected to yield a rare, high-resolution (1,000-10,000 yr) record of the intermediate-water history in the Eastern Equatorial Atlantic, with implications for paleoceanographic changes during glacial/interglacial cycles.

To receive the complete electronic copy of this report please select one of the following:

  • Text 136K (graphics not included)
  • WordPerfect (graphics not included)

  • Acrobat(text and graphics)
  • Acrobat Reader

    For comments or additional information please select one of the following

    Publication Distribution

    Publications Feedback

    Adobe and Acrobat are Copyright © 1994,1995 Adobe Systems Incorporated.