Geoscience Reference
In-Depth Information
59
25
142
444
30
100
31
133
131
56
110
256
1738
930
210
67
232
3000
286
1438
3228
113
290
150
28
17
18
154
42
Sediment Yield
(million tonnes per year)
Fig. 10.4 Volume of riverine silt supplied to continental shelves. (Adapted from Milliman & Meade 1993.)
Foraminifera). Other major producers of bio-
genic sediment are molluscs and bryozoans,
which feed on organic matter produced within
the water column by phytoplankton, and hence
ultimately also rely on light.
Given the above, shelves dominated by bio-
genic sediment production generally have low
rates of terrigenous input, because light inten-
sity is decreased by high rates of sediment input
and/or reworking by shelf processes. Globally,
major regions of tropical carbonate sedimenta-
tion include the seas off Indonesia, northern
Western Australia, the Bahamas and the Arabian
Gulf (Chapter 9), and there are some areas of
carbonate production in cooler waters, most
notably the Lacepede shelf, southern Australia
(James et al. 1992) but also in Brazil (Gischler &
Lomando 1999; Testa & Bosence 1999). There
are mechanisms for relatively rapid breakdown
of some biogenic sediments, through bioerosion
and solution, so that sediment production rates
need to be distinguished carefully from eventual
sediment accumulation rates (Buddemeier et al.
1974).
Many organisms in these environments are
highly environmentally specific, and thus have
potential to form part of assessments of the
'health' of modern ecosystems, or are potential
palaeoenvironmental indicators. Notable in this
regard are foraminifers and diatoms, but other
relevant fossils include dinoflagellate cysts, sponge
spicules, pollen, seeds, charcoal and ostracods.
There is, however, a general underutilization of
microfossil-based techniques in studies of mod-
ern environmental sedimentology. As an exam-
ple, the broad use of diatoms in environmental
science is well recognized (Stoermer & Smol
1999) and they are particularly useful in studies
of environmental pollution of freshwater lakes
and streams. Even in estuarine environments,
however, there are relatively few applied studies
using diatoms (Sullivan 1999), and there are even
fewer studies on continental shelves. Foramini-
fera are increasingly used in applied environ-
mental studies (Scott et al. 2001), but not yet for
open-shelf environments. There appears to be
insufficient work specifically designed to deter-
mine the tolerances of benthic marine micro-
organisms to various forms of pollution (Sullivan
1999). The environmental constraints upon many
larger organisms are also poorly documented.
For corals, there are some generally well-known
 
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