20. PALEOMAGNETIC RESULTS FROM HOLES 959D AND 960A, CÔTE D’IVOIRE-GHANA TRANSFORM MARGIN1 Simon Allerton2 |
This paper reports paleomagnetic results from minicores taken from Ocean Drilling Program Holes 959D and 960A, drilled on the marginal ridge of the Ghana-Côte d’Ivoire Transform Margin. As initially indicated by shipboard studies, many samples were too weak to measure, and many that were measurable did not carry a stable remanence. Despite these problems, a significant number of reliable measurements were obtained from three units: Unit III of Hole 959D, and Subunits IVB and VB of Hole 960A. The sediments from Unit III of Hole 959D and Subunit IVB of Hole 960A appear, from formation microscanner data and seismic reflection profiles, to dip gently north-northwest, away from the marginal ridge. In the absence of any other method of reorienting the data from core to geographic coordinates, the data from these units were reoriented by rotating the dip-direction measured in the core to the regional dip direction (assumed to be 330°). Stable magnetizations from Unit III of Hole 959D probably represent the combination of steep drilling-induced overprints, and shallow, generally northerly directed components that may correspond to either a recent overprint or an earlier magnetization. The limited number of reliable directions from Subunit IVB of Hole 960A have shallow inclinations, and are dominantly directed to the north after the azimuthal correction is applied. It is not possible to discriminate whether this component was formed before or after tilting. Subunit VB of Hole 960A lies beneath an angular unconformity. A different approach was applied to the stable components of these rocks: the stable component was rotated to a common direction (assumed north), and the resulting bedding orientations were considered. Results can either be interpreted as folding about an axis orthogonal to the marginal ridge, or a sequence of reversals. The former is considered more likely. |
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