ABSTRACT

The basinward salt extrusion along the Louisiana margin, with lateral and isostatic motions, creates mini-basins between rising salt ridges, generally along the upper and middle slope. Mini-basins grow with salt-withdrawal. Sedimentation includes gravity-driven, high-energy turbidity currents. Debris flows and slumps originate along the outer shelf/shelfbreak and descend the slope, depositing reservoir-quality graded beds on multiple time scales ranging from annual through 4th order, and punctuated by catastrophic (irregularly timed) turbidities and megaturbidities. Pelagic sediment accumulates between flows. Efficient sediment sorting yields clean sands in Bouma sequences. The source for the sand is ubiquitous. These sediments are found in numerous slope and continental-rise deposits; examples will be provided along with their seismic and well-log signatures. Neogene-Quaternary deposition along productive mini-basins results from 4th order sea-level oscillations of some 210⁴ to 10⁵ year durations, clustered into more easily recognizable 3rd order oscillations of approximately 10⁶ year durations, promoting energetic sediment movements and yielding reservoir-grade deposits. Trapping mechanisms within mini-basins are generally structural, aided by stratigraphy. Growth faults, basinward and counter regional, can bracket slope mini-basins. Active mini-basins are found along the present Louisiana slope and buried mini-basins are found beneath the continental slope and coastal plain.