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Observations on Structural Styles in the Northern GOM (Flextrend Area)


Significant contributions on the Gulf of Mexico ROHO and slope minibasin salt tectonics were made in the 1990s and provided critical insight into the lateral movement in shallow salt basins. Most conclusions are based on 2D and early 3D seismic data prior to reverse-time migrations, full wavefield inversion, and anisotropy corrections. This study investigates the transition from ROHO dominated salt systems to slope mini basin systems, and the salt flow behavior in an area along the shelf break of the Northern GoM. The results are based on a reprocessing program during which most recently developed seismic processing tools were deployed in combination with new concepts of model building in order to enhance the subsurface images of complex salt and mini basin geometries.

The results indicate multiple layers of ROHO style systems are present at various layer in the sub-surface, which are related to Miocene to Pliocene salt movements, driven by the migrating depo-systems along the paleo shelf. The shallowest RoHo level reveals classic up-dip, extension those transients into basal, low angle detachments/welds of the translation zone, and down-dip contraction with local thrusts and salt cored anticlines at the frontal part of the individual basins. The principal kinematic direction of theses RoHo systems has northwest to southeast orientation. Salt rollers in associated faults are easily interpreted as is salt present in associated extensional and compressional faults of the shallower ROHO systems in the area. All of these features are excellently imaged by enhanced high end reprocessing, which also extent the imaging capability further down section and beyond the shallow salt layers.

The well imaged deep ROHO basins are delineated by the basal detachment surfaces and salt structures associated with faults either controlled by local extension or contraction. The deeper ROHO-like systems differ in trend and appear to be oriented north-northwest to south-southeast.

Active diapirs piercing the mini basin sequences are rare, but locally reaching shallow sequences and affect the sea bottom morphology.

The RoHo and slope mini basins are concentrated in elongated domains which are separated by salt free corridors. The concentration of mobile salt presumably resembles the original salt sheet that existed prior to the formation of the mini basins. The intervening areas are imaged as ultra-deep mini basins with continues sediment fill to more than 12 km depth.