John M. Robalin1,
Harry H. Roberts2
(1) Marathon Oil Company, Houston, TX
(2) Coastal Studies Institute, Louisiana State University, Baton Rouge, LA
Abstract: Variation in deltaic architecture and stratigraphic attributes in the shelf-edge Lagniappe Delta System, Northeast Gulf of Mexico
During the last Pleistocene base-level fall, the shelf-edge Lagniappe Delta System constructed numerous, sand-rich delta lobes, with variable stratigraphic architecture, as the depocenter migrated from east to southwest. Different stratigraphic attributes recorded in two boring successions in conjunction with the temporal and spatial distribution of correlative facies in high-resolution seismic profiles record the switching loci of deposition. Differences in stratigraphic attributes, including lithology ratios, sedimentary structures, and low versus high- faunal diversities and abundances, and variations in deltaic architecture are accounted for by along-strike and -dip changes in accommodation and sediment supply.
In the eastern area of the shelf-edge delta system, at least five different depocenter positions have been mapped beyond a paleo- break in the shelf. As the depocenter prograded beyond this large shelf-gradient increase, high accommodation and relatively high rates of sediment supply resulted in construction of broad, arcuate fluvial/wave influenced delta lobes. As the depocenter migrated west and southwest, decreasing amounts of sediment supply in the shelf-edge area of the eastern delta resulted in the progradation of a storm-influenced, wave-modified, strike-elongate delta lobe, sourced both along strike and dip. During this same time, the repositioned west-to-southwest depocenter encountered decreased paleo- shelf gradients. In response to this reduced accommodation the still relatively high sediment-supply main depocenter constructed numerous, multi-lobate, fluvially-dominated delta lobes.
Previous interpretations that the eastern Lagniappe Delta was built during the early rising-stage of the last glacial maximum/sea-level lowstand and is comprised of backstepping progradational geometries are not supported by the findings of this study.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana