Journal of the Royal Society of Western Australia, 87(4), December 2004 
structures, and sediment types under wetlands. Artificial 
exposures were described in 12 un-named wetland basins 
at Osborne Park, Bullcreek, and Forrestdale, as well as in 
excavation trenches in Lake Gwelup, Little Carine 
Swamp, Lake Pinjar, and Karrinyup Road Swamp. 
Sediments from trenches, excavations, and cores were 
described in the field in terms of colour, structure, fabric, 
texture, and composition. 
Short cores of in situ sediment were obtained from a 
range of wetlands to study surface and near-surface 
sedimentary structures and micro-structures. These short 
cores were obtained by pushing 10 cm diameter PVC 
pipes, 10-30 cm long, into the substrate, retrieving them, 
and returning them to the laboratory. At some 30 sites, 
75-100 cm long cores also were obtained. In the 
laboratory, the cores, generally in a water saturated state, 
or at least with pellicular water, were frozen for storage 
and ice-hardening. The cores later were longitudinally 
sliced while frozen to cleanly expose the stratigraphy and 
sedimentary structures. One half was returned to frozen 
storage as archive material; the other half was 
photographed, and used in further analyses. 
In the laboratory, the samples of sediment were 
described and analysed using five progressive levels of 
detail to provide a comprehensive view of the variety of 
sediment types. 
Firstly, the large range of surface sediments, 
stratigraphic samples, and hand cores from all the 
wetland sites, involving several hundred samples, were 
examined and described as to colour, texture, and 
composition, and categorised according to their sand and 
mud content ( i.e., clean sand, muddy sand, sandy mud 
and mud) following the grain-support versus mud- 
support concept of Dunham (1962). With the aid of a 
stereomicroscope and a light transmitting microscope the 
presence of carbonate in sand and mud was determined 
(with dilute HC1), carbonate intraclasts, carbonate 
skeletal tests and their fragments, plant material (stems, 
roots, fibres, leaves), quartz sand, quartz silt, lithoclast 
sand, carbonate mud, invertebrate skeletal debris, and 
sponge spicules (as monaxons), and mud-sized 
phyllosilicate minerals were identified, and sediment was 
assigned to size fraction categories of gravel, or coarse, 
medium, fine or very fine sand, muddy sand, or mud. 
Secondly, examination of sand grain mounts and mud 
particle mounts, where sand and mud-sized fractions, 
respectively, are dispersed in a fluid medium on a glass 
slide (Swift 1971), and thin sections, under a polarising 
petrographic microscope was undertaken on a selective 
basis for c. 200 samples. Under a petrographic microscope 
with high power for resolving mud-sized particles, 
grains in the sand and mud particle mounts were 
categorised in types based on their size and shape, and 
their crystallinity and mineralogy determined on their 
colour, refractive index, cleavage, and birefringence (Kerr 
1959). With this method, very fine-grained plant remains, 
diatoms and their fragments, various types of siliceous 
monaxon sponge spicules (megascleres, microscleres, and 
gemmoscleres; cf. Williams 1980), siliceous phytoliths 
(Meunier & Fabrice 2001), and various invertebrate 
skeletons (cf. Williams 1980), in addition to the grains 
noted above, were identified. Thin section study of 
epoxy-impregnated sediments, and of any hard layers in 
the wetlands was undertaken under a petrographic 
microscope for about 100 selected samples. 
Thirdly, the content of organic matter and calcium 
carbonate in a range of black, dark grey, and brown 
sediments was determined in some 100 samples using a 
variety of peats, peaty sediments, and dark grey fine¬ 
grained sediments - the problem of determining organic 
matter content was not an issue for carbonate-mud- 
dominated sediments or diatomite-dominated-sediments. 
The samples were divided in three sets of subsamples. 
One set was processed by combustion at 550° C and then 
at 1100° C. Another set was prepared as mud particle 
mounts for examination under a petrographic 
microscope. The third set was processed by acid 
digestion (using dilute HC1) to estimate the content of 
CaCO v Since loss of weight on ignition at 550° C can be 
due to loss of organic carbon, loss of sulphur liberated as 
S0 2 from sulphides (if sulphide was present in the 
sediment), and other volatiles liberated from the 
combusting organic matter, it may not be a direct 
measure of the content of organic carbon or even organic 
matter. Additionally, the loss of weight on ignition at 
1100° C may not be a direct measure of primary CaC0 3 
content since some CaC0 3 could have been generated 
from organic matter rich sediments during their 
combustion at 550° C. Hence, some independent 
calibration of sediment composition was undertaken for 
organic-matter rich sediments and dark grey sediments. 
This involved the point counting procedure, and 
chemical analyses, mentioned above. Mud particle 
mounts were point-counted under a petrographic 
microscope to estimate their content of organic matter, 
carbonate, quartz silt, diatoms, sponge spicules, and 
phytoliths, and the data compared to the results from the 
combustions to assess within the sample the amount of 
organic matter, biogenic silica, and carbonate mud. After 
combustion, opportunity also was taken to examine the 
ash as grain mounts and mud particle mounts under a 
petrographic microscope as these residues commonly are 
comprised of the concentrated remains of biogenic silica. 
Fifty selected pre-combustion samples and their 
combustion residues were analysed by mass 
spectrometry (using ICP-MS) and XRD to determine their 
elemental nature (Na, K, Ca, Mg, Fe, As, Cd, Pb, S and 
Si) and mineralogy (carbonate minerals, quartz, biogenic 
silica, pyrite, marcasite, arsenopyrites, goethite, 
haematite), respectively, as a record of wetland sediment 
geochemistry. The results of the content of Fe and S, and 
their correlation, also provided another internal 
assessment of the contribution of sulphide minerals to 
loss on ignition at 550° C. 
Fourthly, more detailed systematic analyses were 
undertaken for some 32 selected samples obtained from 
various locations and depths for the purpose of typifying 
a range of muddy sediment types, and particularly muds, 
sandy muds, and muddy sands. In this paper, these 
samples are referred to as the "wetland sediment 
standards". These analyses involved all the procedures 
outlined above as well as sieving to quantitatively 
determine sand versus mud content, acid digestion and 
furnace combustion to determine the content of carbonate 
and organic matter, respectively, of the mud and sand 
fractions, X-ray diffractometry (XRD) to determine mud 
fraction mineralogy, and routine photography and 
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