Episodic Burial and Exhumation along Atlantic Margins - Implications for Hydrocarbon Prospectivity

It is a common assumption that elevated passive continental margins (EPCMs) have remained high since rifting and breakup. Absence of post-rift sediments in the highlands is often taken as evidence of non-deposition, and the presence of high-level plateaux along many EPCMs is unexplained in many studies. However, the post-rift stratigraphic record in the adjacent sedimentary basins often contains significant unconformities and in some cases, post-rift, marine sediment crop out at high elevation. We present evidence of post-rift vertical movements along Atlantic margins and discuss how these movements affect the hydrocarbon prospectivity of these margins. We maintain that folds, reverse faults, reactivated normal faults and strike-slip faults that are typical of EPCMs, are a result of post-rift compression that leads to the formation of EPCMs, and that the necessary forces build up during changes in plate motion. One episode of uplift results in erosion of the region to produce a low-relief surface and a second (or more) episode(s) raises the plateau to its present elevation, after which fluvial and possibly glacial erosion dissects the plateau. Failure to realize that EPCMs are post-rift features have far-reaching implications for understanding basin development, hydrocarbon systems and the properties of the lithosphere itself.