Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
for humus material in the A horizon of soils. The zone of 
"muddy" sediment may develop as a material in its own 
right, immediately underlying the floor of a wetland, or 
may be a unit that is transitional between any accreted 
wetland sediment and the basement substrate. The 
"muddy" material that has formed by infiltration of 
wetland sediment into underlying basement materials is 
the product of infiltrational sedimentation. Any material 
that accumulates above the surface of basement materials 
is the product of accretionary sedimentation (Fig. 2C). 
Both may be present in the one wetland (Fig. 2D). 
Infiltrational material, accretionary material, and 
combined infiltrational/accretionary material are treated 
in this paper as wetland sediment. 
The processes leading to the development of wetland 
soils, and types of wetland sediments on the Swan 
Coastal Plain are summarised in Figure 3. 
Materials and methods 
A wide-ranging sediment sampling programme was 
undertaken at the surface of wetlands, in their 
stratigraphic sequence, across the width and along the 
length of the central Swan Coastal Plain in the different 
geomorphic, hydrologic and hydrochemical settings, in 
order to fully capture potential variability in these 
sediments. Samples were collected from hand cores and 
stratigraphic intervals in transects from some 143 
wetlands (Appendix 1). Stratigraphy of wetlands was 
determined by examination of dewatered trenches and 
excavations (to 4 m) in 17 wetlands, and shallow 
augering (to 5 m) in 70 wetlands. Additionally, in 35 of 
the wetlands, reverse-air-circulation coring to 30 m was 
undertaken. The cliff faces provided by dewatered 
trenches and excavations allowed direct observation and 
description of stratigraphy, sedimentary and biogenic 
A: Development of soils 
parent materials 
■ + + 
■ + + 
+ + + 
no accretion above this surface 
JL _ 1 
as well Illuviation and precipitation resulting 
from translocation downwards of material 
and solute generated by breakdown of 
parent substrate 
quartz 
sand 
granite 
S 58 S of physical, chemical, and 
sal weathering of parent material 
unification of surface, Involving 
coating of particles with humus; as well as 
Illuviation, precipitation of translocated 
material generated by breakdown of 
parent substrate). 
A horizon: zone of humification, 
- leaching, and extreme modification 
J.. of parent material 
B hortton: zone of ■uvtatton, 
precfclfatton, and moderate 
modWcatton of parent material 
C horizon: reiattvety unaltered 
parent material 
B: Development of infiltrational sediment deposits 
C: Development of accretionary sediment deposits 
^ ongoing vertical accretion 
of weMna sediment 
D: Development 
quartz sand 
debasement 
of infiltrational and accretionary sediment deposits 
Figure 3. Processes operating to develop wetland soils and wetland sediment. In (A), quartz sand and granite are used as examples to 
illustrate the development soils. 
143 
