DETAILED MAPPING OF THE JUNCTION OF THE LATE JURASSIC “STEP-UP” CONTINENT-OCEAN BOUNDARY OF THE NORTHERN US GOM WITH THE CONTINENT-OCEAN TRANSFORM ALONG THE EAST COAST OF MEXICO

The continent-ocean boundary (COB) of the northern Gulf of Mexico (GOM) or “step-up fault" separates Jurassic oceanic crust in the deep GOM from thinned continental crust bordering North America and the Yucatan Peninsula. We use a grid of 5500 km of 2D seismic reflection data to improve the location of the COB especially in the area of active, deepwater exploration of the northwestern GOM that spans the Mexico-US maritime boundary. The basement step-up fault that marks the COB extends as a deeply buried, continuous, and arcuate fault for a distance of 1300 km across the northern, US GOM. In the north-central GOM the step-up fault trends E-NE has a vertical relief ranging from 1 to 4 km, although thick salt obscures its presence in many areas. This prominent basement step forms a junction with the NNW-trending late Jurassic, right-lateral transform that forms an abrupt ocean-continent transform along the eastern margin of Mexico. Unlike the step -up fault formed within an extensional regime, the transform does not show a significant vertical trough and steps down in the basinward direction. For this reason the transform does not form structural ramp in the overlying sedimentary section as observed in the northern GOM.