One square nautical degree within the active part of the Romanche Fracture Zone was surveyed at about long 17°W during the 1988 Equamarge II cruise of the R/V Jean Charcot to the equatorial Atlantic. SeaBeam mapping and seismic-reflection profiles of the trench and adjacent northern and southern transverse ridges emphasize the contrast between the apparent simplicity of the major morphostructural lineaments and the complexity of the second-order features. The vertical displacement associated with the main strike-slip movement of major oceanic transform faults is clearly illustrated by positive topographic anomalies of the transverse ridges. The bathymetric map and samples collected confirm that the flat-topped northern transverse ridge actually emerged at a time when peridesertic climate shaped basaltic basement into ventifact pebbles coated with desert varnish.

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