Late
Pleistocene Shelf-Edge Deltas and Growth Faulting in the Northeast Gulf
of Mexico: The Early Development of Shelf Margin Reservoir Systems
Fillon, Richard H.1, Harry H.
Roberts2 (1) Earth Studies Group, New Orleans, LA (2) Coastal
Studies Institute, Louisiana State University, Baton Rouge, LA
Seismically imaged clinoform sets in the
northeast Gulf
of Mexico
define deltas that prograded to the shelf edge during periods of lowered sea
level. Two shelf margin deltas, one associated with marine isotope stage 2 (~19
kaBP), and one associated with marine isotope stage 8 (~270 kaBP) are
especially well imaged and have been cored by research boreholes. The
architecture of this delta complex is calibrated to corrected radiocarbon age,
marine isotope stages, biostratigraphic markers, paleoecologic water depth
estimates, and sediment properties. The clinoform tops of the younger delta lie
at about -90 m water depth, covered only by a thin veneer of transgressive
deposits, while the clinoform tops of the older delta lie beneath 185 m of
water and 50 m of sediments, downthrown ~145 m to a shelf edge growth fault.
Using this high-resolution dataset we are
investigating how growth faulting affects the post depositional geometry and
sourcing of shelf margin sand bodies, a major and very prolific reservoir type
in the northern Gulf of Mexico. While located near the surface these
sand bodies are relatively leaky, receiving large volumes of fluids from
downdip sources, via linked thin distal turbidite beds. Fortuitously, the
stacking relationship of growth faulted shelf-edge deltas places the leaky
portions of older deltas beneath thick accumulations of vertically sealing
prodeltaic strata related to middle shelf deltas of intermediate age. Further,
it appears that the overlying prodeltaic strata are prevented from transmitting
fluids laterally updip into coeval, and potentially
leaky, middle shelf deltaic facies by displacement on the growth fault.