Development of the Cote d'Ivoire-Ghana transform margin; evidence from the integration of core and wireline log data

Author(s): Goncalves, C. A.; Ewert, L.
Author Affiliation(s): Primary:
LENEP/UENF, Laboratorio de Engenharia e Exploracao de Petroleo, Rio de Janeiro, Brazil
Other:
Quantsci, United Kingdom
Volume Title: Core-log integration
Volume Author(s): Harvey, P. K., editor; Lovell, M. A.
Source: Geological Society Special Publications, Vol.136, p.375-389; Core-log integration, London, United Kingdom, Sept. 1996, edited by P. K. Harvey and M. A. Lovell. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719. ISBN: 1-86239-0169
Note: In English. 19 refs.; illus., incl. 1 table, geol. sketch maps
Summary: The primary objective for drilling the Cote d'Ivoire-Ghana Transform Margin during ODP Leg 159 was to assess the sedimentary and deformation processes resulting from the different stages of continental break-up and related transform tectonism. In view of the structural importance of the leg, integration of logging and core data is important to help understand the main tectonic and deformation events that occurred. The effect of the transform deformation can be seen in physical properties data, for instance the porosity data derived from index properties measurements. Major breaks in porosity are associated with the tectonized lower Cretaceous and Cenozoic boundary, a trend also reflected in the P-wave velocity measurements. At each site, core and well log data show the presence of a major unconformity between the Cretaceous and Cenozoic, marked by an offset in porosity, density and P-wave data. The physical properties of log data are also heterogeneous, reflecting variations in consolidation, age and lithology. Another interesting aspect covered by core-log integration was the structural relationship within the sediments. As well as the direct measurements made on cores, in situ structural measurements have been obtained using the Formation MicroScanner (FMS; Mark of Schlumberger) logging tool in two of the holes. The measurements cover the Eocene to Turonian-upper Santonian limestones. Bedding planes dip predominantly towards NW-NNW and show an increase with depth which can be interpreted to be the result of steady subsidence of the Deep Ivorian Basin. Break-outs and fracturing were also observed. Break-out occurrences depend on sediment type and their axes are perpendicular to the maximum compressive horizontal stress east-northeast west-southwest. Fracturing occurs as normal and reverse microfaults, with dispersion of dips and azimuth directions in these zones. The presence of fault zones are also correlated with changes in the physical properties of the sediments.
Year of Publication: 1998
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Africa; Body waves; Cenozoic; Continental margin; Cores; Cretaceous; Deep drilling; Deep-seated structures; Drilling; Elastic waves; Electrical logging; Eocene; Faults; Formation MicroScanner; Ghana; Ivory Coast; Leg 159; Mesozoic; Ocean Drilling Program; P-waves; Paleogene; Plate tectonics; Porosity; Rifting; Santonian; Sedimentary rocks; Seismic logging; Seismic waves; Senonian; Strike-slip faults; Tertiary; Transform faults; Turonian; Upper Cretaceous; Well-logging; West Africa
Coordinates: N030000 N040000 W0020000 W0030000
Record ID: 1999021037
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