Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
"spongolitic diatomite". Similarly, peat may contain a 
significant proportion of diatoms and their fragments, 
and these sediments are termed "diatomaceous peat". 
Mixtures of peat, sponge spicules and diatoms are 
referred to as spongolitic diatomaceous peat. 
To complete the picture of the variability and 
occurrence of wetland sediments of the central Swan 
Coastal Plain, it is worthwhile to note that within the 
Quindalup Dunes calcilutite, peat, carbonate muddy 
sand (to be discussed later), and quartzo-calcareous sand 
occur as sediment types in the Becher Suite (Semeniuk 
2005), calcilutite, peat, carbonate muddy sand, intraclast 
gravel and sand, and stromatolitic boundstone occur at 
Lake Waiyungup, Lake Cooloongup and Lake Richmond 
of the Cooloongup Suite, and calcilutite, peat, carbonate 
muddy sand, and quartzo-carbonate sand occur in the 
Peelhurst Suite (Semeniuk 1988). 
The wetland sediments are described below in terms 
of: colour; structure (layered, laminated, wispy 
laminated, homogeneous or structureless, root- 
structured, burrow-structured, bioturbated, texture- 
mottled, colour-mottled, fenestral, bubble-structured or 
vesicular, brecciated; see Table 3); fabric (grain-support, 
mud-support; cf. Dunham 1962); texture (grainsizes of 
gravel, grades of sand, and mud); and composition 
(quartz sand, kaolinitic clay, iron oxides, carbonate mud 
or sand, skeletons, and opaline silica and X-ray 
amorphous siliceous frustules and skeletons). Some of 
the field settings of wetland sediments are shown and 
described in Figure 4. Annotated selected cores of 
sediments showing overall lithologic appearance and 
structure are shown in Figure 5. Selected 
photomicrographs of sediment dispersed on slides, and 
of SEM images are presented and described in Figures 6- 
11. The geographic, geomorphic and consanguineous 
setting of the 32 wetland sediment standards, and the 
results of detailed microscopy and analyses of these 
sediments, in terms of sand versus mud content, organic 
carbon content and carbonate content of the mud 
fraction, and the mineral composition of the mud 
determined by XRD, are provided in Appendices 2 & 3. 
Peat 
Peat is a black to grey, and in certain horizons, brown 
sediment. It is mainly homogeneous to root-structured, 
and in upper near-surface layers weakly laminated to 
compositionally layered, to fibrous; some layers at depth 
in peat profiles also are laminated. Texturally, peat 
consists of fine-grained organic matter < 63 pm in size, 
and larger root fibres, stem fibres, plant detritus particles 
and scattered (< 5%) quartz sand and quartz silt. Local 
deposits may contain minor amounts of freshwater 
snails, or their comminuted fragments. There is also a 
presence of fine-grained iron sulphide (evident as pyrite 
framboids in SEM, and detected as pyrite and marcasite 
in XRD), and occurrence locally of arsenopyrites. Cores 
through peat show an upper layer of partly decomposed 
leaves, stems, twigs, and roots that grades down within 
30 cm, and locally within 100 cm, into fine-grained to 
fibrous organic material that has scattered plant material, 
and non-fibrous organic matter. In some peats, at depth, 
branches, twigs, and logs are still preserved in the fine¬ 
grained organic accumulation. Near the surface, root 
holes and burrows may have oxidation haloes 
surrounding them. The surface of peats that dry out are 
polygonally cracked, with desiccation cracks descending 
locally down to 20 cm into the peat. 
In the upper parts of peat, within 10-30 cm of the 
surface, where the plant material is not wholly decayed, 
various types of vegetation contributing to the deposit 
can be recognised, e.g., the leaves of Melaleuca 
rhaphiopltylla and M. cuticularis, and the leaves, stems and 
rhizomes of Baumea articulata and Typlia spp (Fig. 5A-C). 
Roots and plant fibres are also common in these upper 
layers. Grain-mount microscopy and SEM show peat to 
be composed of plant detritus in various stages of fungal 
and bacterially induced structural breakdown (Fig. 8). 
For instance, large particles are riddled with fungal 
hyphae. 
SEM and petrographic microscopy of many 
homogeneous or structureless, fine-grained, black to dark 
grey peat-like materials show them also to have a 
significant component of diatoms and/or sponge 
spicules, and siliceous phytoliths. Where diatoms and 
sponge spicules are abundant, the peats become 
diatomaceous or spongolitic peat. Sponge spicules and 
diatoms in peat range from complete spicules and 
frustules to largely fragmented particles. 
Since peat can grade into organic matter rich diatomite 
and organic matter rich calcilutite, the lithological 
boundary of peat is set at > 75% content of organic matter 
(as dry weight), and sediments containing 74%-50% 
organic matter mixed with diatoms, or calcilutite, are 
termed diatomaceous peat and calcilutaceous peat 
respectively (see later). The content of organic matter as 
dry weight in some typical peats is presented in Table 4. 
Multiple values of organic matter content reflect 
variablity of peat composition spatially, where samples 
have been collected at a number of sites within a large 
wetland, or from several proximally located small 
wetlands within the same consanguineous suite, or 
collected stratigraphically at the one site. 
Peat intraclast gravel and sand 
Peat intraclast gravel and sand are a black to grey 
coarse-grained suite of sediments, ranging from breccias. 
Table 4 
Content of organic matter in some typical peats on the Swan 
Coastal Plain (for co-ordinates of locations see Appendix 1) 
Location of sample 
(ordered south to north) 
% organic matter 
Australind wetlands 
94,75 
Riverdale wetlands 
80,90 
Lake Mealup 
96 
Wawa Swamp 
75 
Forrestdale Road Swamp 
78, 88, 77 
Leda Swamp 
95 
Karrinyup Road Swamp 
90,75,90 
Lake Gwelup 
78, 83, 84, 83, 89,95, 
Lake Goolelal 
90 
Beenyup Swamp central 
78,79 
Beenyup Swamp south 
79, 80, 81, 80, 81, 80, 95 
Waluburnup Swamp 
89 
Ellenbrook Swamp 
89, 83 
Melaleuca Park 
90,75 
151 
