Environmental Engineering Reference
In-Depth Information
by long-distance transport of suspended fine particles. Each turbidite can be recognized
through a fining-upwards sequence of gravel → sand → mud, as the respective particles
settle out over time. Sediment sequences several kilometres thick form in the slope-rise
area in this way.
Abyssal plain sediments are usually isolated from adjacent slopes in the 'quietest'
parts of the ocean and accumulate extremely slowly. They are primarily undisturbed
biogenic muds 0·5-1·0 km thick, forming at rates of 0·1-4 cm ka
−1
, illustrating the
profound stability of these areas. Fractionation of the stable isotope composition of
oxygen in sea water and organic carbonate provides some of the best long-term records of
recent Earth history. The ratio of
18
O/
16
O in water is temperature-dependent. The lighter
isotope
16
O is taken up preferentially when sea water evaporates, enriching the remaining
water in heavier
18
O. Water retention in ice sheets sustains the difference and leads to
enrichment of
18
O in marine carbonates and
16
O in ice sheets. Both environments thus
record global temperature and ice volume.
GEOLOGICAL RESOURCES
applications
Human prehistory is defined by the fashionable geological materials used by early
societies. The Palaeolithic- Mesolithic-Neolithic progression of 'Stone Ages' charts
early technology from the earliest known humans to just 4000 years ago, witnessing the
slow improvement in stone tools to the later development of clay-using ceramic pots. The
first use of metals in the subsequent Bronze and Iron Ages extended well into the
historical period, 1500 years ago, and just 300 years ago our ancestors started the new
'Iron and Steel Age' of the Industrial Revolution. It is estimated that 50-100 tonnes of
rock material are now consumed each year for every person living in an advanced techno-
industrial society. Higher standards of living and rapid industrialization in other parts of
the world create an inexorable rise in world-wide consumption, as the following annual
global mining and quarrying extraction rates show:
aggregates
(
sand
,
gravel
,
construction stone
,
etc.
) 7·5 billion tons,
limestone
(
cement
) 1·4 billion tons,
iron ore
1
billion tons,
clays
200 million tons,
rock salt
(NaCl) 190 million tons,
non-ferrous metal
ores
90 million tons (of which
manganese
,
aluminium
,
chromium
and
copper
account for
60 per cent and
titanium
,
nickel
,
magnesium
,
zinc
and tin account for just 6 per cent).
Energy demand adds 4·5 billion tons of
coal
and 3·5 billion tons of
crude oil
to these
figures.
Systematic, dynamic links between geological environments and their representative
rocks and structures have been the focus of this chapter, together with Chapters 10 and
11. The products of past geological environments in Britain can be assessed in terms of
their resource potential (Figure 1). Few geological resources are 'consumed' literally, and
scarcely any are used directly from the ground. Instead we segregate, concentrate, clean
or refine them to be fit for use in the required form, quantity and quality. Mineral
concentrations vary, as the following average quantities of discarded rock waste per ton
of usable minerals show: manganese 2·75 tons,
aluminium
(from
bauxite
) 3 tons,
chromium
3·2 tons,
iron
4 tons,
copper
250 tons,
gold
1 million tons.
All these processes also consume energy, much of it to produce high-temperature
melts. Wastes are discarded at every stage, from mining to manufacture and after their
useful life
We recycle some materials or extend their useful life but the slow rate of
