ABSTRACT

The northern Gulf of Mexico/Louisiana offshore is described as a new sub-class of passive margin basins: a salt-floored basin. The prerequisite is that there was a period of salt deposition during the transition from fresh water deposition to salt water deposition. This salt layer then serves as a lubricating/separating layer along which over-riding "shallow" sediments migrate and/or prograde basinward over underlying "deep" sediments. Shallow means shelf and upper slope whereas deep sediments are from lower continental rises and abyssal plains. The characteristics of a lubricating/separating layer are salt welds and salt units comprised of myriad shapes. A salt-floored basin's ocean-side would be a "salt nose", a paleo-Sigsbee Escarpment complex, which exists when enough terrigenous sediments have accumulated on the landward/up-dip side to extrude the now buried and semi-plastic salt. The extruded salt nose becomes a down dip, basinward migrating "front".

A salt-floored basin is different from the two existing hypotheses describing major salt movement along the Louisiana margin. The hypotheses involve: a) salt rising buoyantly from mid-Jurassic crust and later deformed laterally, and b) salt extruded down-dip into the "deepest" basin with salt becoming buoyant on over-riding basement highs while migrating basin-ward. The salt-floored basin concept provides a "constant" salt nose migrating basinward as the basin expands.

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