LOWER MISSISSIPPI RIVER DELTA DEEP-SEATED SUBSIDENCE RATE DYNAMICS, BIAS, AND SPATIAL-TEMPORAL DEPOCENTER COMPLEXITIES THROUGH THE NEOGENE

Southern Louisiana coastal wetland loss has been well documented and largely attributed to a combination of vertical land-surface subsidence and eustatic sea level rise. Land-surface subsidence and the vertical motion of local strata represents the synthesis of a number of geologic processes operating at different spatial-temporal scales and depths. Shallow-seated processes, including the compaction of coastal organic-rich Holocene strata, have long been thought to dominate the historic-period subsidence record with rates on the order of 1-25 mm/yr. Deep-seated processes, including compaction of pre-Holocene strata, isostatic response to Holocene sediment loads, growth fault motion, and glacio-isostatic forebulge collapse, dominate Lower Mississippi valley subsidence data below the Holocene-Pleistocene contact with assessed rates of 0-2 mm/yr.

New chronostratigraphic data compiled from over 225,000 wells across the Gulf of Mexico (GOM) reveal a remarkable, negative log-log ‘Sadler’ relationship between shallow and deep-seated subsidence processes. Additionally, substantial northern GOM fluvial depocenter shifts and sediment supply signatures may be discerned through the Neogene coincident with sequence boundaries. This improved understanding of Lower Mississippi River Delta deep-seated subsidence rate variability, dynamics, and measurement bias begins to unravel the spatial-temporal complexity inherent in fluvio-deltaic systems and related clastic basin-fill successions providing critical baseline model constraints for more accurate coastal wetland loss estimates, regional Holocene sea level curves, and future engineered flood control solutions.