2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 25
Presentation Time: 8:00 AM-4:45 PM

Margin Tectonics of Northern Gulf of Mexico Coastal Plain, Shelf, and Slope Proposed to Impact Basement and Mantle

LOWRIE, Allen, Consultant, 238 F. Z. Goss Road, Picayune, MS 39466 and JENKINS, Linda, Consultant, 2403 Hillsdale Road, Picayune, MS 39466, alowrie@webtv.net

“Margin tectonics” is a published explanation of the northern Gulf of Mexico coastal plain, shelf, and slope's intermittent basinward migration. With normal faulting in the rifted basement and prograding sediment wedge, the motion is subsidence and extension, a net movement basinward. The extent of the most landward continental margin is fall-line faults. That the margin is intermittently migrating basinward suggests that fluid migration routes remain open. Also, such margin-wide attributes indicate that this region of several physiographic/geologic provinces is interrelated and is operating as a unit. Maximum migration and deformation are located over shelf and slope with diminishing rates farther away.

Principal constant force input is gravity. Downslope motion causes earthquakes (brittle fracture) and slow/silent earthquakes (plastic deformation). Earthquakes generate “instantaneous” energy that accelerates ongoing geologic processes. Slow/silent earthquakes move sediment volumes, reorienting mass location and further movements/dynamics. Instantaneous pressure waves from meteor impacts and great earthquakes act as margin-wide energy inputs. Catastrophic glacial lake collapse deposition creates events that last less than a year and deposition rate changes of 3 to 4-5 orders of magnitude. These low-frequency, pressure-generating events create pressure waves. Margin evolutionary processes generate energies that drive tectonic growth.

Within margin progradation, there is aggradation and progradation with sea-level oscillation. The maximum deposition loci oscillates across the margin, changing compression onto the basement. Following isostacy basement depression, given the changing sedimentary cover, thicknesses could vary 60-90% of sediment cover. With successive sediment accumulation, the basement continues to be depressed. These basement-depth-related changes vary basement impact onto overlying sediments with heat, geothermal and geochemical fluids.