Passive Margin Architecture in the Atlantic Basins
Hermann Lebit¹ and Luke Jensen²
¹ ENI Petroleum, Houston, Texas 77002
² Shell International E&P, Houston, Texas 77056
Post-rift tectonic stresses are considered insignificant at passive margins assuming
the underlying oceanic and continental lithosphere have thermo-mechanically reequilibrated
since onset of seafloor spreading. Thus sedimentation input remains the
major (gravitational) driving forces sculpturing the passive margin architecture. Two
end-member modes are suggested for gravity-driven instabilities along these margins:
(i) load-driven outflow of sediment sequences above a detachment horizon due to progressive
sediment input from prograding delta wedge; and (ii) mass wasting processes
dominate margins with moderate sedimentation, due to sustainable slope gradients resulting
from basinward subsidence. These processes might become significantly amplified
when evaporite layers add a salt (channel) flow component to the system. Prograding
delta systems drive gravitational collapse by growth faulting in the shelf sections.
Rapid burial of these sequences may trigger salt withdrawal and lateral fluid migration.
Normal faults usually bottom out at basal décollements that translate into outboard contractional
regimes, dominated by thin-skinned fold belts, which form prolific hydrocarbon
provinces in the Atlantic Basin, including Gulf of Mexico. Sequential kinematics
restoration along regional seismic sections demonstrate equilibrium between extension
in the shelf region and corresponding shortening near the toe
of the slope with bulk displacement
rates one order of magnitude less than those in tectonic belts. However, localized
dramatic flow rates (channel flow) are evidenced by rapid lateral salt extrusion (salt
canopies). Mechanics of passive margin sequences is analogous to gravitational flow in
ice sheets and allows to model displacement fields in sedimentary wedges.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012