Environmental Engineering Reference
In-Depth Information
Figure 12.17
Hydrothermal circulation around a mid-ocean
ridge, indicated by solid arrows. Ocean water circulates as
far as the cracking plane, above which layered ocean crust is
stretched and cracked.
solids and 4 × 10
12
kg of solutes, or derived from marine erosion of the coast itself.
Heavy minerals such as gold (Au), copper (Cu) and tin (Sn) settle out as
placer
deposits
among the shelf sediments. Biogenic rain-out of dead marine organisms and their
chemical derivatives increases in importance away from the shore. They are the
predominant source of abyssal sediments, flooring 62 per cent of deep-ocean basins as
calcareous
(calcite/aragonite) and
siliceous
(silicate) muds derived from the skeletal parts
of plankton. Carbonate mud is three to four times more abundant and is referred to as an
ooze
if over 30 per cent is derived from diatoms and coccoliths (marine microorganisms).
Silicate solutions are less depth- and temperature-sensitive than carbonates, so
precipitated silicates are found in deeper and colder ocean areas. Carbonate rocks are
associated with tropical/warm-temperate oceans today, with a contrasting silicate mud
belt in the southern (Antarctic) ocean (Figure 12.18). Silurian, Carboniferous and Jurassic
limestones and Cretaceous
