173 Scientific Prospectus

Figure 3. Part of a new reduced-to-the-pole magnetic anomaly chart of the whole west Iberia margin produced in collaboration with the Atlantic Geoscience Centre, Dartmouth, Nova Scotia, Canada (Miles et al., 1996). The chart was made from a 5-km-gridded data set and is contoured at 25 nT. The main chart is based on over 400,000 sea-surface observations which were corrected to remove the effects of secular variation, high geomagnetic activity, spurious tracks, and systematic cross-over errors. Greater confidence in the quality of the resulting dataset allowed the use of the small contour interval. Leg 149 drilled to basement in this area (white dots); proposed sites are shown by squares. The data were reduced to the pole to clarify many features. Major linear trends in the anomalies are picked out by bold lines. The chart clearly shows the strong positive J anomaly which appears just west of 13° W and south of 41° 30'N. Between Site 897 and the continental shelf (~9° 15'W) and north of 41° N other less strong positive anomalies are associated with the shallow regions of Galicia Bank. South of ~41° N the chart can be divided into three distinct zones (bounded by the two broad N-S black bands) based on the character of the anomalies.

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