Journal of the Royal Society of Western Australia, 87(4), December 2004 
load of fine-grained particles such as diatoms, organic 
matter, or carbonate mud from peripheral zones into 
deeper water, and its settling on the basin floor as ooze; 5 
transport of fine-grained particles (such as diatoms) from 
a dried wetland floor towards the shore by aeolian 
processes to form low relief supra-littoral to littoral 
shoreline "mud" ridges; 6. the desiccation of any muddy 
margins of wetlands, and later in the dry season, the 
desiccation of the centre of wetlands if exposed; 7. local 
fluvial input (i.e., from local channels along the wetland 
margin, and that are consequent to the wetland shore); 8. 
groundwater discharge (seepage and percolation) to 
deliver fine-grained sediment in suspension and to 
initiate chemical changes; 9. groundwater fluctuation to 
initiate chemical changes; and 10. evaporation resulting 
in soil desiccation, and in changes in water chemistry. 
Examples of small-scale biological processes within 
wetlands include organic accumulation of detritus from 
flora and fauna (these include in situ peat beds, diatom 
deposits, and local shell beds), the contribution of calcitic 
mud by the disintegration of semi-calcareous charopyhtic 
algae, and bioturbation by flora and fauna (such as 
freshwater Crustacea, insects, tortoises, reptiles, 
amphibians, and mammals), and the root-structuring and 
burrow-structuring of sediments by the biota. 
Bioturbation by fauna such as frogs, bandicoots, ants, and 
freshwater Crustacea is particularly significant in the 
marginal facies of wetlands where interlayered 
sediments may be mixed, or the sediment becomes 
burrow-structured or burrow-mottled. Shoreline and 
peripheral vegetation also function in the role of 
sediment trapping, binding and root-structuring, and 
contributing directly to the sedimentary deposit as in situ 
deposits of plant material. 
Examples of small-scale chemical processes within 
wetlands include (1) the initiation of chemical changes 
due to sediment influx via seepage and percolation, (2) 
the initiation of chemical changes due to sediment 
transfer via vertical water fluctuations, and (3) changes 
in water chemistry due to evapo-transpiration. Chemical 
processes within wetlands that affect sediments include 
precipitation of minerals such as syntaxial overgrowths 
on grains, precipitation of minerals as intergranular 
cements (e.g., calcite), the stripping of clay and iron 
oxides from Pleistocene yellow sand grains under acidic 
conditions, precipitation of iron oxides, the precipitation 
of iron sulphides, and the transport of ions and nutrients 
throughout the sediment column. 
At the small scale, physical and chemical processes 
can often trigger biological responses which can then 
further influence sedimentation. With wave action on a 
standing body of water, for instance, the physical and 
chemical properties of surface water within wetlands in 
different geomorphic settings with different types of 
sediments in the basins, can determine the suspended 
sediment content or uptake of soluble material (viz., mud¬ 
sized phyllosilicate mineral content, carbonate mud 
content, and tannin content), which will affect turbidity 
and water quality, with concomitant influence on 
planktonic and benthic biota. 
Fire is another influence on stratigraphy, structure, 
texture, and composition of wetland sediments 
(Semeniuk & Semeniuk 2005b). Pyrosediments, a term 
coined in this paper, are secondary sediments, such as 
residues, formed as a result of the combustion of 
sedimentary materials. In natural settings, periodic fires, 
usually ignited by lightning in summer, may destroy 
peat beds and reduce a complex sequence of peats and 
other sediments to a more simple peat-free sequence. In 
modem times, fire may be anthropogenic or natural. By 
agency of fire, sand lenses can be introduced into a 
dominantly peat sequence by reducing to ash those trees 
with sand-constructed termitaria interior to their trunks. 
Fire in wetlands also can alter sediments texturally (e.g., 
it can fracture susceptible grains by intense heat to finer 
grain sizes, and can generate surficial breccia), and create 
specific types of pyrogenic surfaces and structures, such 
as fire-sculptured surfaces, baked surfaces, iron-oxide 
stained surfaces, and deep cracks, all of which influence 
development of subsequent sedimentary structures. 
Some of the buried surfaces and structures found in the 
subsurface in this study that had been generated as a 
result of fires are: buried fire-scarred (irregular to 
scalloped) surfaces; cracked surfaces (filled by later 
sediments, such as mud or intraclast breccia); in situ 
breccioid structures; and millimetre-scale lensoid 
structures resembling flaser layering (cf. Reineck & Singh 
1980). Fire can also alter wetland sediment composition: 
pyrite is transformed to iron oxides, biogenic silica is 
partly transformed to crystalline silica, and wood is 
transformed to ash of calcite, halite, sylvite, and 
anhydrite (later altering to gypsum). 
Diagenetic effects and overprints on wetland 
sediments and adjoining materials 
There are chemical, biological and physical diagenetic 
effects on wetland sediments, but the main effects are 
chemical. The chemical effects and overprints of 
diagenesis in wetland sediments include: 1. dissolution 
of shells and other carbonate grains; 2. precipitation of 
carbonates as isolated crystals, crystal aggregates, grain 
rimming cements, and nodules; 3. burning of wood, 
other vegetation,, and peat to generate calcite and 
anhydrite (and gypsum), and other minerals; 4. 
dissolution of diatoms and phytoliths; 5. precipitation of 
silica; 6. precipitation of iron oxides to form ferricrete; 7. 
precipitation of metal and metalloid sulphides (e.g., iron 
sulphides such as framboidal pyrite, or marcasite, or 
arsenopyrites) to impart a light grey to dark grey hue to 
sediments; and 8. reduction of iron oxide in envelopes 
around sand grains to form sulphides, imparting a light 
grey to dark grey hue to sediments and adjoining 
materials. Only carbonate dissolution, carbonate 
cementation/nodulation, silica solution and re¬ 
precipitation, and ferricrete cementation/ nodulation are 
described further here. 
In many wetland sediments, under conditions of 
acidic groundwaters, molluscan shells and carbonate 
intraclasts commonly exhibit varying degrees of surface 
corrosion. With molluscs, particularly within peats, there 
is gradation from entire shells through to pitted shells to 
heavily corroded shell and vestiges. Corrosion of 
carbonate intraclasts results in the pitting and 
development of micro-relief on their surface. Within 
carbonate sediments there is also re-precipitation of 
carbonate to form thin crusts, nodules, interstitial cement. 
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