Geoscience Reference
In-Depth Information
Time-scale (years)
0.01
0.1
1
10
100
1,000
10,000
100,000
Climatic and
sea-level change
Spit/barrier retreat
or progradation
Mass movement
of cliffs
Fig. 1.1
Time-scales
over which different
geomorphological
processes operate within
a hypothetical coastal
environment. (Adapted
from Woodroffe 1992.)
Storm reworking
and erosion
Changes in
beach profile
Tidal erosion
and deposition
the sedimentary landforms discussed also inevit-
ably represent the products of longer-term sedi-
ment accumulation. Hence, in each chapter these
may encompass the daily processes of sediment
transport and reworking, through to the effects
of rapid climatic and sea-level change (Fig. 1.1).
In this context, short-term changes (
mental sedimentology. This chapter also outlines
the magnitude and frequency of predicted shifts
in global climatic and environmental conditions
that have relevance to the development of both
terrestrial and marine sedimentary systems over
the coming century. These include issues such as
sea-level change, global warming and changes in
temperature, precipitation and storm frequency,
and thus provide a framework for discussion
within the respective chapters.
1 yr) within
a coastal sedimentary environment may, for
example, include the processes of tidal erosion
and deposition, seasonal changes in beach pro-
files or morphological change due to storm events;
in the short-to-medium term (
<
10 yr), mass
movement of unstable cliffs, spit progradation,
or barrier breaching; and in the medium-term
(up to 100 yr), coastal landform progradation,
changes in delta morphology, or coastal retreat.
Superimposed upon these processes may be a
range of anthropogenic activities (e.g. sea-wall
construction, sand dredging or contaminant
inputs), which may influence not only the dy-
namics of the sedimentary system, but also the
associated floral and faunal components of the
system. Many of these biological components
(e.g. dune plants, mangroves or corals) are often
of sedimentological significance in their own
right, either as sources of sediment or as agents
of sediment trapping and stabilization.
This introductory chapter reviews the funda-
mentals of sediment production and the principles
of sediment transport and deposition. In addi-
tion, consideration is given to the types of issues
that are discussed in the respective chapters, and
which help to define the discipline of environ-
<
1.2
SEDIMENT PRODUCTION AND SUPPLY WITHIN
SEDIMENTARY ENVIRONMENTS
The composition of sediments that accumulate
within individual sedimentary environments is
primarily a reflection of three main factors:
1
the sediment source;
2
the processes of sediment transport and
deposition, which determine whether sediment
is retained or transported through a specific
environment (these mechanisms are outlined in
section 1.3);
3
the chemical processes operating within the
sediment or water column, for example, car-
bonate and evaporite precipitation, chemical
diagenesis.
In terms of the initial supply of sediment into a
sedimentary system, three basic sediment types
can be delineated. These are: (i) detrital minerals,
(ii) biogenic or organic sediments and (iii) anthro-
pogenic particles and compounds.
