SEISMIC STRATIGRAPHIC RECORD OF TRANSPRESSION AND UPLIFT ON THE PASSIVE ROMANCHE TRANSFORM MARGIN, OFFSHORE GHANA

Recently available multi-channel seismic reflection data from offshore Ghana have been reprocessed to probe the eastern Romanche Fracture zone (RFZ) of the Equatorial Atlantic and associated sedimentary basins of the paleo- transform margin. The RFZ terminates landward into a submarine canyon, up to 2 km deep and >50 km wide, variably filled with submarine fans consisting of lobes of paleo-Volta delta. In contrast, the RFZ to the southwest is represented by a pronounced submarine escarpment juxtaposing continental and oceanic crusts. Three major sedimentary sequences have been identified from the seismic stratigraphy and calibrated with chrono- stratigraphic data from oil exploration wells. The pre-rift sequence consists largely of Paleozoic strata ranging in age from Devonian to Carboniferous and attains a thickness of up to 3 km. The overlying syn-rift sequence was deposited during the intracontinental wrench stage and consists of Aptian to Albian siliclastic strata with distinct continental facies. The seismic sections provide some of the clearest images yet of transpressional folding associated with continent-ocean transform displacement. Moreover they document uplift and subaerial erosion which we attribute to crustal thickening resulting from folding as well as heating and thermal expansion of the continental lithosphere by the migrating oceanic spreading center.