ABSTRACT

Along the northern Gulf of Mexico, the deglaciation phase of a Plio-Pleistocene glacial cycle produced up to a 10-fold increase in waters available for sediment transportation to continental margins. With lowered sea levels during glacial maxima, sedimentary pulses are deposited along the shelfbreak and on the slope. High energy deposition promotes foundation instability. Growth faults then originate along the shelfbreak. Increased lithostatic pressure due to rapid deposition on underlying un- and semi-consolidated sediments, semi-plastic salt and marine clays promote flowage that accelerates compaction, fluid migration, growth fault movements, and salt tectonics.

Sedimentary depositional cyclicity of deca- and centenary-millennia are recorded throughout the Phanerozoic. Planetary orbital motions, controlling the amount of incoming solar radiation and of 20,000, 40,000, and 100,000 year duration, are the apparent cause of these depositional cycles via climate/ sea-level fluctuations.

When sea level is low, sediments are deposited about or beyond the shelfbreak. Increased lithostatic pressure promotes movement on the fault, deposition on the down-thrown block, accelerated compaction of sediments and fluid expulsion and migration. When sea level is high, sediment deposition is along the upper and middle shelf. Fault activity should be minimal or none. Thus, those geologic episodes which record greatest amount of down-thrown block growth may also be periods punctuated by bursts of large sea level lowerings. Onshore Louisiana hydrocarbon production is usually greatest from those portions of maximum growth along down-thrown blocks.