--> ABSTRACT: Model of Upper Cenozoic Geologic Evolution of Louisiana Slope, by Allen Lowrie; #91042 (2010)

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Model of Upper Cenozoic Geologic Evolution of Louisiana Slope

Allen Lowrie

The late Cenozoic (last 15 million years) geologic evolution of the Louisiana slope is the result of two interrelating processes: (1) lateral southward extrusion of the Louann Salt by confining pressure of overlying Gulf Coast geosyncline sediments and (2) high-frequency pressure modulation provided by up to ten-fold fluctuations in amount of sediments deposited on shelf break and slope. Sediment-supply fluctuations are caused by global climate, glacial, and sea level 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 shelf break, maximum sedimentation along the shelf break and Louisiana slope, coarse sediment deposition, maximum salt tectonics, development of enclosed silled intraslope basins, maximum preservation of hydrocarbons, marine biological productivity, maximum sediment compaction, and fluid migration appear to be synchronous. All of these occur during global glacial maxima and sea level lows. These processes combine either algebraically, positively or negatively, or synergistically. These 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 mean that the remaining processes may be predicted.

During lowstands of sea level, rapid, massive, and coarse deposition on underlying semi-plastic salt promotes salt flowage that activates regional faults and accelerates salt tectonics into creating enclosed intraslope 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° of latitude) during glacial maxima. Increased organic preservation explains higher hydrocarbon concentrations entrapped during maximum structural and stratigraphic activity coinciding with glacial and sea level low maxima.

AAPG Search and Discovery Article #91042©1987 GCAGS and GC-SEPM Section Meeting, San Antonio, Texas, October 28-31, 1987.