Journal of the Royal Society of Western Australia, 87(4), December 2004 
Pleistocene limestones in near-surface sections mostly 
are composed of an overlapping series of aeolianites, 
with local lenses, wedges and thin sheets of intercalated 
marine units. These limestones have been referred to the 
Tamala Limestone, the Tims Thicket Limestone, the 
Kooallup Limestone, and the Peppermint Grove 
Limestone (Playford et al, 1976; Semeniuk & Johnson, 
1982,1985; Searie & Semeniuk, 1985; Semeniuk 1995). The 
aeolianites are large-scale cross-layered, mainly medium 
sand-sized quartz, skeletal lithoclastic grainstone, 
cemented by sparry calcite and micritic calcite (locally 
forming calcrete). Limestone surfaces are mantled by 
yellow quartz sand, penetrated by pipes filled with 
yellow sand, and dissected by karst features. 
Wetlands on the Swan Coastal Plain 
A wide range of basin wetland types occur on the 
Swan Coastal Plain, varying in size, shape, water 
characteristics, stratigraphy and vegetation (Semeniuk 
1988; Semeniuk et al, 1990). Dependent on setting, 
wetlands can range from large linear lakes to small, 
round or irregular, seasonally damp wetland basins; 
from fresh water to hyposaline (brackish) to saline; from 
basins which perch surface water to those which are 
recharged by groundwater; with vegetation cover which 
can vary from herbland to forest. These attributes are 
determined by regional features such as geology, 
geomorphology, soils, climate and hydrology, and local 
physical/ chemical processes such as groundwater flow 
and karstification. While there is a large variety of 
wetland types across the Swan Coastal Plain, using 
criteria of size, shape, patterns of clustering, water 
quality, substrates, and maintenance processes, they can 
be aggregated into natural groupings that are termed 
consanguineous suites (Semeniuk 1988). 
In this paper, the wetlands for sediment study have 
been drawn from the following consanguineous suites: 1. 
Yanchep Suite, 2. Balcatta Suite, 3. Coogee Suite, 4. 
Stakehill Suite, 5. Bibra Suite, 6. Jandakot Suite, 7. 
Riverdale Suite, 8. Gnangara Suite, 9. Mungala Suite, and 
10. Bennett Brook Suite (Semeniuk 1988). Site 
descriptions of these settings and a description of the 
wetlands from which the 32 sediments were studied in 
more detail are provided in Appendix 2. 
Types of sediment fills 
Sedimentary particles 
A variety of particles comprise wetland sediments, 
ranging from those that are biogenic, siliciclastic, to 
abiotic intraformationally-generated. Biogenic particles 
include whole shells, frustules, tests, and skeletons (e.g., 
molluscs, diatoms), disintegrated remains of biota (e.g,, 
diatoms, charophytes), to decayed plant remains and 
detritus. There is a large range of organisms that inhabit 
wetlands of the Swan Coastal Plain (Hembree & George 
1978; John 1981, 1993; Balia & Davis 1993; Davis et al, 
1993; Helleren & John 1994; Maly et al, 1997; Chessman 
et al, 2002), and in the arena of invertebrates and 
microscopic plants, many make conspicuous and/or 
significant contributions to the wetland sediments as 
skeletal remains (e.g., the calcareous remains of molluscs 
and ostracods, the siliceous remains of freshwater 
sponges, the siliceous remains of diatoms, and siliceous 
phytoliths). There also are other organic particles that 
contribute mainly to the surface sediments of wetlands; 
e.g., the chitonous tests of insects. However, while some 
of these latter biogenic particles can occur in the shallow 
stratigraphic sequences, many of the exoskeletons of 
invertebrate fauna, such as chitonous tests, do not 
survive synsedimentary diagenesis or shallow burial 
diagenesis. Only particles that are preserved in the 
sedimentary record have been described here. 
XRD and EDS of shelly biota and Cluira and carbonate- 
impregnated filamentous algae show the following: 
molluscs, depending on species, may be wholly calcitic, 
or Mg-calcitic, or interlayered aragonitic and calcitic 
(similar to the mineralogy of marine molluscs; cf Bathurst 
1971); ostacods are calcitic, or aragonitic and calcitic; 
Chara may be calcitic, Mg-calcitic, or aragonitic; and that 
carbonate-impregnated filamentous algae have mediated 
precipitation of calcite or Mg-calcite as crusts on their cell 
walls. The implications are that carbonate sediments 
composed of, or derived from these biota will have a 
similar range in mineralogy. 
Grains of pollen, spores, phytoliths, and microcharcoal 
(Clarke 1988; Faegri et al, 1989; Odgaard 1992; Meunier 
& Colin 2001) also occur in wetland sediments, and are 
important in the analyses of sediments and stratigraphic 
sequences for palaeo-environmental studies and 
palaeoclimatic reconstructions. However, while their 
occurrence is noted, they do not contribute enough 
material to the sediments to be recognised as distinct 
wetland sediment types. 
A note is made here on the use of the terms "clay 
mineral", "phyllosilicate", and "phyllosilicate clay" for 
particles that comprise the fine-grained component of 
many wetland sediments. The term "clay" has two 
meanings in the Earth Sciences (Jackson 1997). One has a 
grainsize connotation denoting particles < 4 pm. The 
other is as a rather imprecise mineralogical term, viz., 
"clay mineral", intended to cover categories of layered 
silicates (hence "phyllosilicate clay") such as kaolinite, 
smectite, illite, halloysite, and montmorillonite (Kerr, 
1959; Sinkankas 1964; FitzPatrick 1983), based on an 
assumption that it is finely crystalline layered silicates 
that dominantly comprise "clay-sized" minerals. 
However, as described later, calcite, quartz, goethite, and 
feldspar can occur as clay-sized particles, but they are 
not viewed traditionally as "clay minerals", and hence 
the term "clay mineral" is not appropriate for use in this 
paper. The range in grainsize of kaolinite further 
complicates the use of the term "clay mineral" because in 
the wetland sediments of this study kaolinite manifests a 
variety of grainsizes: it can be very fine (< 1 pm), and 
hence conforming with the notion of being a "clay-sized" 
mineral, but can range up to medium silt size. 
Additionally, some micas, such as muscovite, can be 
comminuted to silt or clay-sized and hence occur in the < 
63 pm fraction. Given these problems, the term "clay 
mineral" is not used in this paper, and while the term 
"phyllosilicate" is used to refer to the mineral group of 
layered silicates, it is not used in association with "clay" 
as it is often traditionally used. Kaolinite, white mica 
(muscovite), hydrobiotite, and montmorillonite, 
occurring in wetlands sediments, are referred to as 
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