INFLUENCE OF GEOLOGY ON RATES OF SEA LEVEL RISE IN THE GULF OF MEXICO

Sea-level rise has become a major environmental factor throughout the world. At the present time the global average rate of rise is about 2.5 mm/yr. There is a fairly high standard deviation in that rate depending on the geologic setting and conditions at a particular location. The coast of the Gulf of Mexico is experiencing a wide range of rates due to its wide range of geology. These rates range from the eustatic mean to more than four times that number. Much of this variation can be attributed to differences in the geology at various locations. Human activity is also a significant factor.

Both the Florida and Yucatan peninsulas are underlain by carbonate platforms. These carbonate rocks are soluble and produce karstic terrains but they do not compact and therefore these provinces experience the global rate of sea level rise of about 2.0-2.5 mm/yr. The rest of the Gulf of Mexico coast is underlain by terrigenous sand and mud of varying thickness and relative percentages. The thick fluvial channel deposits that accumulated during sea level lowstands compact at rates that depend on their thickness and the percentage of mud to produce changes of 4-5 mm/yr. Deltaic deposits that are dominated by mud may also be very thick and produce rates of sea level rise that exceed 10 mm/yr is some places; the Mississippi Delta being the most prominent.

Fluid content of coastal strata is also an important factor in relative sea level rise. Autocompaction discharges considerable water causing increased rates of rise. Withdrawl of fluids, both water and petroleum types, is also a significant contributor on the Mississippi Delta complex and in major metropolitan areas such as Houston.