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Abstract

A segment of seismic profile A-3 across the equatorial fracture zones is shown. In addition to Shell seismic, a large number of Lamont-Doherty sparker profiles were used to complete the structure map.

The Romanche fracture is one of a group of transform systems that separates the Jurassic Central Atlantic from the Cretaceous South Atlantic. These fractures reflect a major indentation in the Pangea breakup pattern.

The Central Atlantic north of the St. Paul Fracture began to open during Early Jurassic and formed an open ocean basin, 4,000 km (2,485 mi) wide, surrounded by extensive carbonate shelves when the South Atlantic began to open up in Aptian-Albian time.

Typical for all three fracture systems are 25 to 50 km (15.5 to 31 mi) wide trenches with steep south flanks and relatively gentle north flanks. The north flank of the Romanche fracture appears to be tectonically disturbed and there is evidence for reverse faults and some folding.

Line A-3 crosses the Romanche fracture 400 km (248.5 mi) to the east of the Mid-Atlantic ridge. Unlike other fracture systems, which become inactive away from the transform segment, the region between Romanche and St. Paul fractures shows signs of repeated tectonic activity up to Recent times.

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