. The ecology of delta marshes of coastal Louisiana : a community profile . 100 50 OCCURRENCES/100 YEARS Figure 12. Tide levels at Shell Beach, in the Pontchartrain-Lake Borgne basin, associated with nine major storms (Wicker et al. 1982). brought down by the Mississippi River created a major sedimentary basin, and many of the subsurface deposits, especially those that formed in localized centers of deposition, have been prolific hydrocarbon-produci ng reservoi rs. In more recent geologic times, changing sea levels associated with the advance and retreat of inland glaciers during the Pleistoce
. The ecology of delta marshes of coastal Louisiana : a community profile . 100 50 OCCURRENCES/100 YEARS Figure 12. Tide levels at Shell Beach, in the Pontchartrain-Lake Borgne basin, associated with nine major storms (Wicker et al. 1982). brought down by the Mississippi River created a major sedimentary basin, and many of the subsurface deposits, especially those that formed in localized centers of deposition, have been prolific hydrocarbon-produci ng reservoi rs. In more recent geologic times, changing sea levels associated with the advance and retreat of inland glaciers during the Pleistocene Ice Ages have strongly influenced the sedimentary patterns off the coast. In order to understand the development of the present-day coastal wetlands it is necessary to view the progradation of the delta and its adjacent coastal plains in relationship to several time scales. These scales range from the long periods of geologic time associated with changing sea levels to the changes in the last 100 years in the patterns of minor subdeltas that foniied the most recent deltaic lobe, the Balize Delta. In addition, the heavy sediment load deposited by the river during the last several million years has caused excessive subsidence. This factor has to a large degree controlled the construction rate and the rate of coastal wetland loss throughout much of the recent geologic history. Pleistocene Sea Levels During the Pleistocene Epoch, some - million years long, sea level fluctuated several times. Most authorities agree on at least four major low sea-level stands and four or five high level stands. In addition to these major changes in sea level, numerous more rapid fluctuations took place. The minor changes in level undoubtedly affected the development of the delta marshes, but in the younger Pleistocene deposits it is extremely difficult to document the pre- cise changes. At the lower sea-level stands, the ocean surface was 150 - 200 m below its present level. During the hig
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Keywords: ., bookcentury1900, bookcollectionbio, booksubjectwetlandslouisiana
