A conceptual hydrodynamic model in the Holocene and upper Pleistocene beneath the<br>Louisiana wetlands is described in terms of salinity distributions. Porewater salinity is calculated<br>from electrical measurements, including resistivity soundings, electric logs, and electromagnetic<br>profiling. Electrical measurements support the primary, basin-wide groundwater flow model;<br>however, the data also indicate secondary contributions from expulsion of fluids under geopressure<br>along active growth faults and from original waters of deposition. Expulsion of water from<br>growth faults has been described previously for deeper sections of the Pleistocene, but has not been<br>reported for the Holocene or upper Pleistocene beneath the Louisiana wetlands. Porewater<br>chemistry variations beneath the coastal wetlands are a consequence of the following (in order of<br>importance): (1) environment of deposition; (2) a basin-wide, regional flow system; (3) expulsion<br>from deep-seated growth faults; and (4) pore water extrusion due to compaction. Water chemistry<br>in Holocene clays and muds is influenced primarily by the deposition environment. In Pleistocene<br>sands, the chemistry is a function of the other three factors.


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