Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
description of sand and mud fractions under a 
stereoscopic binocular microscope and petrographic 
microscope. 
Fifthly, scanning electron microscopy (SEM), and 
associated analyses, were undertaken for a subset of the 
32 wetland sediment standards and 30 other sediments 
to determine the crystal form and characteristics of the 
fine-grained constituents to ascertain their ultrastructure 
and hence their origin, and to confirm the nature of the 
silt-sized and clay-sized opaline silica and amorphous 
silica from their X-ray diffractometry patterns. During 
the SEM, images of fields of view 100-200 pm in size 
were obtained using back-scattered electron emissions 
(BSE) in order firstly to map the distribution of average 
atomic number, which was used as a surrogate to 
determine the consistency of element distribution, and 
hence consistency of the distribution of particle types, 
and also to map the distribution of selected elements 
(specifically C, Ca, Mg, Al, and Si as indicators of organic 
matter, calcite/aragonite, Mg-calcite, phyllosilicate 
minerals, quartz, and diatoms, respectively). This 
provided a method for evaluating the homogeneity, for 
instance, of the carbon content of peat, or the diatom 
content of diatom-bearing peat. Additionally, routine 
spot analyses of 5 to 6 particles within each SEM field of 
view, some 100-200 pm across, with particle selection 
based on the heterogeneity of the SEM image, or 
heterogeneity of the BSE field, or on particle shape, were 
undertaken using Energy Dispersive Spectroscopy (EDS), 
which allowed for determination of relative element 
content of individual particles. With this method, 
elemental content of particles, combined with 
information on their shape, allowed identification of 
diatoms, very fine and ultrafine-grained diatom 
fragments, sponge spicules, invertebrate skeletons/tests 
and their fragments, quartz silt, mud-sized phyllosilicate 
minerals, organic carbon, plant detritus, calcite, and 
framboidal pyrite. 
To assist with identification of particle sizes < 63 mm 
in size under SEM, standards of several mollusc species, 
ostracods, and Chara species and other carbonate- 
impregnated filamentous algal species were prepared for 
XRD and SEM analyses. The XRD analyses provided data 
on the range of mineralogic types that comprise skeletal 
grains, information particularly useful in interpreting the 
origin of mud-sized carbonate particles. The SEM and 
associated EDS analyses of known skeletal grains 
provided micromorphologic, microstructural, and 
ultrastructural standards for comparisons with wetland 
sediment particles, and provided information for the 
various mollusc species, crustaceans, and Chara on the 
range of their composition in terms of calcite and 
aragonite content, their Mg content in low Mg calcite and 
high Mg calcite, and in terms of Mg, Sr and Pb content in 
aragonite cements. 
In the field, during appropriate seasons, various large- 
scale and small-scale physical and biological processes, 
instrumental in developing sediment types, were 
observed within and adjacent to wetlands. These 
processes, such as wave action, sheet wash, bioturbation 
by fauna, and desiccation, provided information on some 
of the mechanisms of sediment particle generation, and 
the development of sedimentary structures and sediment 
types. 
Regional geologic and geomorphic setting 
The Swan Coastal Plain is the Quaternary surface of 
the Perth Basin (Playford et al., 1976). The Plain 
comprises distinct large-scale landforms which are either 
arranged subparallel to the Darling Scarp or the coast, or 
are associated with major rivers. These landforms 
correspond to the main sedimentary formations in the 
region (Woolnough 1920; McArthur & Bettenay 1960; 
Playford et al., 1976; McArthur & Bartle 1980a,b; 
Semeniuk & Glassford 1987, 1989; C A Semeniuk 1988; 
Semeniuk et al ., 1989; Geological Survey of Western 
Australia 1990; Semeniuk 1995): 
• Pinjarra Plain: flat to gently undulating alluvial fans 
fronting the Darling Scarp and Darling Plateau 
(underlain by sand, laterite, and the Precambrian 
rocks), as well as floodplains and various sized 
channels; underlain by the Guildford Formation (clay, 
laterite, sand, muddy sand); 
• Bassendean Dunes: undulating terrain of low 
degraded dunes (varying in relative relief from 20 m 
to almost flat), and interdune flats and basins; 
underlain by the Bassendean Sand (quartz sand) of 
Pleistocene age; 
• Spearwood Dunes and Yalgorup Plain: large-scale, 
linear, near-continuous subparallel ridges (c 60m 
relief) and intervening narrow and steep-sided 
depressions, or narrow plains; underlain by 
Pleistocene limestone (aeolianite and marine 
limestone) blanketed by quartz sand; 
• Quindalup Dunes: Holocene coastal quartzo- 
calcareous sand dunes, beach ridge plains, tombolos 
and cuspate forelands. 
The units relevant to this paper are the Bassendean 
Dunes, which are ergs formed during glacial periods, the 
Spearwood Dunes, which were composite ergs, i.e., 
quartz sand desert ergs formed during glacial periods, 
and calcareous coastal ergs formed during interglacial 
periods (Semeniuk & Glassford 1988; Glassford & 
Semeniuk 1990), and the Pinjarra Plain. In these settings, 
there are two main lithologic/stratigraphic units that 
either adjoin or underlie wetlands: 1. Pleistocene quartz 
sand, and 2. Pleistocene limestones. 
Pleistocene quartz sand is typically yellow, but varies 
from white to orange to locally red. Yellow sand forms 
thick formations landward of Pleistocene limestones on 
the coastal plain, but extends as sheets covering these 
limestones, along unconformities within the limestone, 
and underlies the coastal limestones (Allen 1981). The 
yellow sand is mostly homogeneous, but locally there is 
large-scale, aeolian cross-layering (Glassford & Semeniuk 
1990). Towards the contact with Pleistocene aeolian 
limestones to the west, the yellow sand contains scattered 
limestone lenses (Semeniuk & Glassford 1988). Yellow 
sand is typically composed of quartz, with moderate to 
trace amounts of feldspar, and minor kaolin, goethite, 
and heavy minerals (Prider 1948; Glassford & Killigrew 
1976; Glassford 1980). Yellow quartz sand grains have a 
thin coating of kaolinite clay and quartz silt impregnated 
with goethite (yellow) and/or haematite (red) (Glassford 
1980). Goethite-pigmented kaolinite and quartz also 
comprise the < 90 pm fine-grained interstitial material to 
yellow sand (Glassford 1980). 
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