Time-dependent flexural subsidence caused by Holocene and Late Pleistocene sedimentation in the Gulf of Mexico: New inversion modeling of vertical motion data

The rate of sedimentary deposition into the world's catchment basins abruptly increased during the transition from Pliocene to Pleistocene climate. Pleistocene periodicity in sedimentation rate has the distinct fingerprints of Milankovich orbital forcing periods 20,000, 41,000 and 100,000 years. We model time-dependent flexure of the Gulf of Mexico by continent-wide sediment transport rate variability over the past 4 Ma. Reconstructions of changes in sediment dispersal occurring during the Late Cenozoic indicate that glacioeustasy may also be a significant role along the shore of the Northern Gulf of Mexico Basin. We employ both spherically layered and self-gravitating viscoelastic models along with a half-space model of very high resolution. We also incorporate the long-wavelength background crustal motion associated with the main Laurentide deglaciation which produces a non-negligible bulge migration. The elastic lithospheric thickness and Maxwell time constants are tuned to both regional and global seismic tomography. The latter data are consistent with a rheologically stiffer than average sub-crustal environment. Hydro-isostatic loading is included in the modeling. Paleosealevel indicators, tide gauges and recent GPS results provide rich data sources for inverse modeling of the load history and solid earth rheology. The sediment rate changes are modeled, in part, as pulsed great megaflood erosional events known to be active during Glacial to Interglacial transitions. Although the model is relatively crude in both space and time, preliminary results indicate that the subsidence rate caused by long-term sedimentary changes could sustain subsidence rates dw/dt of roughly 1 - 12 mm/yr during the past 5,000 years over many hundreds of kilometers of coastline. Geodetic data in the Mississippi Delta region of southern Louisiana show subsidence at rates greater than 5 mm/yr, having many of the spatial characteristics predicted by the sedimentary load model. These data are interpreted in terms of a formal inverse approach and we report optimum solutions for sedimentary loading in for regions where it may be freed as a model parameter.