ABSTRACT

The upper Cenozoic (last 15(10⁶) years) geologic evolution of the Louisiana Slope is the result of two interrelating processes: Louann Salt lateral southward extrusion by confining pressure of overlying Gulf Goast geosyncline sediments with a high-frequency pressure modulator provided by up to 10-fold fluctuations in amount of sediments deposited on shelfbreak and slope. Sediment fluctuations are caused by global climate, glacial and sealevel oscillations (of 50 m or less) with periodicities of 100,000 years and less. In the northern Gulf of Mexico, initiation and maximum growth of down-to-the-south growth faults along the shelfbreak, maximum sedimentation along the shelfbreak and Louisiana slope, coarsest sediment deposition, greatest sealevel lowerings, maximum salt tectonics and development of enclosed, silled intra-slope basins, maximum preservation of hydrocarbons and marine biological productivity, maximum sediment compaction and fluid migration appear to be synchronous; all occurred during global glacial maxima and sealevel lows. These processes combine either algebraically, positively or negatively, or synergistically. These, here enumerated, interrelated processes are geologic reality. The enumeration is for intellectual and model development convenience. Single processes may be quantified; then, included in future quantitative models. Knowledge and chronostratigraphy of any one process means that the remaining processes may be predicted.

During low sealevel, rapid, massive, and coarse deposition on underlying semi-plastic salt promotes salt flowage that activates regional faults and accelerates salt tectonics into creating enclosed intra-slope basins. These basins become anoxic and guarantee organic preservation. Increased organic production is caused by increased oceanic upwelling due to storminess of the Polar Front, shifted southward 30 latitude during glacial maxima. Increased organic preservation explains higher hydrocarbon concentrations entrapped during maximum structural and stratigraphic activity coinciding with glacial and sealevel low maxima.