Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
Lake 
Pinjar 
Illustrating transition between 
diatomite and sand 
Ellenbrook 
area 
Illustrating transition between 
peat and sand 
Lake 
Forrestdale 
illustrating transition between 
calcilutite and sand 
o 
1 
2 
3 
CD 
transition 
zone 
diatomite 
dlatomaceous 
quartz sand 
quartz sand 
peat 
peaty 
quarfz sand 
quartz sand 
diatomite 
diatomaceous peat 
transition 
zone 
quartz sand 
calcilutite 
calcilutaceous 
quartz sand 
quartz sand 
Figure 14. Examples of typical transitions of fine-grained wetland sediment (diatomite, peat, and calcilutite) into underlying basement 
sand to form ''muddy" sand (specifically, diatomaceous sand, peaty sand, and calcilutaceous sand, respectively). 
Suggested use of descriptors 
The various sediment types described above can be 
discriminated further by use of adjectival descriptors, the 
most important of which are the subdominant to minor 
grain content, the sedimentary structures, colour or tone, 
and sand grain-size. For example, as noted earlier, 
sponge spicules do not form "spongolite" as an end- 
member sediment type, but they may comprise a 
conspicuous and/or subdominant proportion of peat and 
diatomite. In this context, their presence is noted by an 
adjectival descriptor, viz., spongolitic peat, or spongolitic 
diatomite. Similarly, if diatoms make a conspicuous 
contribution to the sediment, the descriptors 
"diatomaceous" are added to the primary sediment term, 
e.g. f diatomaceous kaolinitic muddy sand. Using 
sedimentary structures, for instance, calcilutite can be 
separated into laminated calcilutite, massive calcilutite, 
mottled calcilutite, and peat can be separated into 
massive peat, fibrous peat, laminated peat. Sediments 
and soils may be characterised by their colour or tone 
(e.g., dark grey, cream, yellow), with the caveat that 
colour and tone may be a primary sediment attribute 
(e.g., the colour of accumulated charophytes), or may be 
the result of diagenesis (e.g., formation of fine-grained 
pyrite). Sand and gravel deposits may be divided into 
grades of grain-sizes (using terms of Wentworth 1922), 
e.g., medium carbonate intraclast sand, or coarse peat 
intraclast sand. 
The protocol for ordering the descriptors where there 
are a range of particle types contributing to, say, the 
muddy fraction, the name of the most abundant particle 
type is placed closest to the core sediment term. Thus, a 
spongolitic phytolithic diatomaceous muddy sand is 
muddy sand with mud-sized particle abundance diatoms 
> phytoliths > sponge spicules. 
Processes affecting and influencing 
sedimentation in wetlands 
Large-scale and small-scale processes influence 
wetland sedimentation on the Swan Coastal Plain. They 
are instrumental in directly contributing sediment to 
wetland basins, in influencing and altering the structures 
of sediments, and effecting changes texturally and 
compositionally. The large-scale processes are 
sedimentary, geomorphic and hydrological, while the 
small-scale processes encompass the physical, biological 
and chemical. 
At the large scale, the geomorphic/geologic setting 
has an influence on the type of physical and chemical 
processes that operate within the wetland. For example, 
the geomorphic/ geologic setting affects sedimentation 
through direct input of sediment, but also by 
determining the type and impact of sediment 
transporting agents that will be present, such as fluvial 
influx or aeolian contribution. The large-scale 
geomorphic/geologic setting also influences the 
hydrological and hydrochemical setting of a wetland, 
and this influences the development of various chemical 
environments for surface and ground waters. For 
instance, wetlands in a terrain of yellow quartz sand 
receive quartz sand into the basin through aeolian 
transport, whereas wetlands in terrains near Holocene 
coastal dunes may receive quartzo-calcareous sediment 
through a similar agent or through encroachment of 
dunes. Wetlands in quartz sand terrains will have a 
different groundwater chemistry to those in limestone 
terrains. 
At the smaller scale, physical processes operating in 
and around wetlands that influence sedimentation and 
sedimentary products include: 1. sheet wash from the 
adjoining uplands to provide sediment fill into the 
wetland; 2. aeolian deposition and deflation (aeolian 
delivery of extrabasinal particles is evident as quartz silt 
and quartz very fine sand scattered in central basin 
deposits of peat, calcilutite, and diatomite); 3. wave action 
in standing water during high water periods to effect 
sediment winnowing, transport and the development of 
peripheral low-relief sandy beachridges or beaches, and 
the wave reworking of any sandy shores of wetlands that 
are bordered by sand terrain; 4. transport as a suspension 
163 
