Characteristics of estuarine sediments of the United States

The texture and composition of bottom sediments in the estuarine zones of the United States are a function of the geologic, bathymetric, and hydrologic settings in which they were deposited.On the northeast and northwest coasts, where sediment supply has been inadequate to fill many of the deep drowned river valleys or glacially scoured estuaries, clay and silt in the deep central parts of the bays most commonly grade shoreward and seaward into sand.On the Oregon and northern California coasts, where both sediment supply and tidal range are large, clay and silt are commonly swept from the deep channels and deposited on marginal tidal flats.On the gulf coast, where tidal ranges are small and where rivers transport abundant fine material to the coast, estuaries are generally shallow.Silt and clay near the center of these bar-built estuaries and lagoons grade into sand around the margins.Deltas are common in many of the gulf coast bays and have, in several, prograded across the estuarine zone onto the continental shelf.Most bottom sediments that accumulate in the estuarine zone consist of terrigenous detritus, biogenic debris, and pollutants.Organic carbon generally makes up less than 5 percent of the bottom sediments except in swampy areas, fjords, or where pollutants are abundant.Inorganic constituents are mostly quartz, feldspar, and clay minerals.In general, illite and chlorite are the most abundant clay minerals on the northeast coast; kaolinite predominates on the southeast Atlantic coast and in the eastern Gulf of Mexico; and montmorillonite is common along the coasts of the western Gulf of Mexico and the Pacific Ocean.Shell debris is locally abundant in many areas but is dominant only in areas far from terrigenous sources. CHARACTEEISTICS OF ESTUARINE SEDIMENTS IN THE U.Si.