Abstract

Six thousand years of sediment accumulation and autocompaction in a transgressive valley-fill deposit are simulated numerically. Rates of accumulation of freshwater organic-rich mud, subtidal mud, and organic-rich mud of the modern salt marsh are specified by using existing sedimentologic, paleontologic, and geochronologic data. Processes of pore-water explusion and autocompaction are determined from finite-strain consolidation theory. Model parameters for subtidal mud facies are determined from laboratory consolidation tests. Model parameters for organic-rich deposits are determined by sampling equivalent modern sedimentary environments and by model calibration. Model calibration involves (1) reproducing the present distribution of void ratios measured in a 7.6 m Vibracore, (2) correctly calculating the preserved thickness of lithologic units, and (3) determining a history of elevation changes of the sediment surface that is consistent with the Delaware sea-level curve and the known sequence of paleoenvironments of Wolfe Glade, Delaware. The results indicate that preserved horizons in the 10 m Holocene section of Wolfe Glade have been lowered a maximum of 2.3 m. The rate of lowering due to autocompaction alone has been one-half to one-third of the rate of sea-level rise during most of the past 6000 yr. Numerical experiments suggest that organic-rich freshwater wetland deposits are primarily responsible for the extensive autocompaction at Wolfe Glade. Our approach may be used to correct Holocene coastal stratigraphic data for autocompaction, but careful model calibration (based in part on the stratigraphy) will usually be required.

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