Geoscience Reference
In-Depth Information
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Figure 5-20.
Vertical section in Key Largo Limestone, a
fossil coral reef that makes up the northern portion of
the Florida Keys, United States. This reef built up about
130,000 years ago when sea level was 5-8 m higher
than today. The head coral in growth position is about
half a meter across. Photo by J.S. Aber.
Figure 5-19.
Accumulation of salt on hydric soils. A.
Sodium-sulfate salt on mudl at adjacent to Frederick
Lake, southern Saskatchewan, Canada. B. Salt crust
including sodium and potassium chlorides at Dry Lake,
western Kansas, United States. Comb is
∼
5 inches
(12.5 cm) long; photos by J.S. Aber.
In modern soil classii cation, the order His-
tosols represents wetland soils; the root word
“histo” refers to plant tissues, as in peat and
muck soils. At the suborder level of classii ca-
tion, hydric soils are identii ed by the prei x
“aqu,” as in Aquoll, Aqualf, etc. Field criteria
for recognizing hydric soils are mostly conse-
quences of anaerobiosis, which is the combined
chemical and biological processes operating
within soils without oxygen. Four key elements
to consider are iron, manganese, sulfur, and
carbon. Iron and manganese may be reduced or
oxidized and removed or accumulated within
different portions of the soil. Sulfates may be
reduced to hydrogen-suli de gas, which gives off
a distinctive rotten-egg odor. In the absence of
Figure 5-21.
Coral reefs growing on sunken volcanoes
formed the Maldive Islands in the Indian Ocean. The
Maldives archipelago contains more than 1000 islands,
80% of which rise less than one meter above sea level.
Adapted from NASA space-shuttle photograph, June
1983, STS07-19-904.
