Page 143 - (DK) Ocean - The Definitive Visual Guide
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SHELF DEPOSITS
The Mississippi River flows into the sea
through a network of channels. As its
silt-laden waters reach the sea, sediments
fall out along the continental shelf.
Geology of the Continental Shelf
Shelf deposits can be extremely thick. For example, those off eastern
North America are up to 9 miles (15km) deep, and have been
accumulating and compacting for millions of years. A cross-section here
reveals ancient sediments other than those deposited by rivers and glaciers,
HUMAN IMPACT
including carbonates, evaporites, and volcanic materials. Carbonates are
COASTAL POLLUTION largely produced by marine life in shallow tropical seas. Evaporites are
salts resulting from seawater
For many years, coastal seas have evaporation in shallow
been used as a convenient dump
for human waste. Even the most basins or on arid coastlines.
remote seashores are now littered Evaporite deposits create
with plastic. More insidious is domes in overlying
invisible pollution: nutrients and sedimentary rocks, trapping OCEAN ENVIRONMENTS
pathogens from sewage; heavy oil and gas.
metals, organohalogens, and other
toxins from industrial and
agricultural effluents; radioactive DREDGED TREASURE
waste from power stations; and Metals such as gold, tin, rare earth
hydrocarbons from effluents, oil elements, and aggregates for the
spills, and other sources. building industry are extracted by
dredging continental shelves.
