Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
wetlands, mineralogic types and particle types of 
calcilutite can be stratigraphically monotonous 
throughout the wetland sediment sequence. On the other 
hand, a wide range of carbonate mineralogic types and 
particle types can occur stratigraphically interlayered or 
form a graded sequence within the one wetland basin, 
either because of fluctuating water chemistry, reflecting 
changing hydrochemical, biotic, and climatic influences, 
or because of long-term evolving hydrochemistry within 
the wetland basin, for instance, evolving from freshwater 
conditions to hypersaline conditions, with attendant 
long-term changes in biota, hydrochemical processes, 
and diagenesis (Coshell & Rosen 1994; Machlus 2000 ). 
Against this variable backdrop, the calcilutites within 
wetland basins on the Swan Coastal Plain encountered in 
this study are mainly calcitic and mostly derived by 
breakdown of charophytes and invertebrate biota, and 
while SEM studies show that there is some diagenetic 
precipitation of carbonate within a pre-existing carbonate 
sediment host (radiating crystals of acicular aragonite 
embedded in calcilutite exemplify this), there has been 
no evidence for in situ chemical precipitation of mud¬ 
sized carbonate as intrabasinal sediment. However, in the 
more saline carbonate basins such as the Coogee Suite or 
the Cooloongup Suite (Semeniuk 1988), calcilutites 
exhibit complexity in mineralogy and particle types: 
there is biogenically derived carbonate mud formed by 
breakdown of charophytes and invertebrate fauna; there 
is authigenic precipitation of carbonates formed within 
the sedimentary body (displacive crystal aggregates, or 
as crusts and cements of aragonite, Mg-calcite, or 
dolomite), and there is diagenetic replacement of pre¬ 
existing carbonate sediment. These aspects of carbonate 
sedimentation and diagenesis, however, will be the 
subject of a later paper. 
As noted above, pyrogenesis creates new sediment 
types, e.g., diatomite, or quartz sand, new textures, and 
new minerals, but in all cases the process acts on pre¬ 
existing sediment. Mostly, pyrogenic processes modify 
or transform particles within sediments, or create new 
structures in a pre-existing sediment. In this context, 
pyrogenesis is viewed as subclass of diagenesis. 
The categorisation and description in this paper of 
wetland sediment types will assist wetland scientists, 
administrators and planners to address one of the 
fundamental attributes of wetlands, and indeed, an 
attribute which defines and delineates wetlands, i.e., 
"hydric soil" (noting that we use the term "hydric soils" 
here without implication that all materials that underlie 
wetlands are wetland "soils")- The limit of "hydric soils" 
or wetland sediments delineates the boundary of a 
wetland in combination with two other determining 
factors, the presence of surface or near surface water, and 
the presence of hygrophyllic flora or fauna (Tiner 1999). 
The boundary of a wetland determined by the occurrence 
of wetland sedimentary deposits, or "hydric soils", 
becomes increasingly important during periods of 
natural water level fall, when the characteristics of the 
water regime such as water presence and longevity are 
intermittently or cyclically altered or erratic. Wetland 
sediments are also an important characteristic in wetland 
inventories and classifications, and in an hierarchical 
classification system, it is one of the criteria for assigning 
wetland types to suites (Semeniuk 1988). 
The focus on the different sediment end members and 
mixtures described above, should provide a basis for 
understanding the dynamic nature of wetlands as they 
develop, through deepening, infilling, and responding to 
changes in hydrological and hydrochemical regimes 
(Semeniuk 2005). Given that many of the sediment types 
represent particular environmental settings, either in terms 
of hydrochemistry or location within the basin, viz., centre, 
or margin of basin, some of the sediment types can be 
used to infer palaeo-environments and to reconstruct past 
hydrochemical and climatic conditions. Also, given their 
strong palaeo-environmental implications, the sediment 
within a basin also can signal the nature of mechanisms 
contributing to the current ecological balance, as well as to 
predict hydrological pathways, recharge and discharge 
mechanisms, and provide fundamental hydrogeological 
information critical to the proper design of buffer zones to 
protect wetlands. 
When sediment types are related to geomorphic and 
geological setting, they can further be used in a predictive 
capacity to provide clues about the regional and local 
wetland processes which may be taking place in 
previously unstudied settings. If sediment types have 
changed, as evidenced in the wetland fill, this may 
provide insights into wetland stability and/or 
identification of potential risk factors. 
Wetland sediments provide a powerful tool in the 
reconstruction of wetland history in the Holocene, 
particularly if used in conjunction with fauna, flora, 
pollen, microcharcoal, and diagenetic products. In this 
context, recognising the sedimentary products of former 
processes provides an important key to the unravelling 
of Holocene palaeo-environmental, palaeo-ecological and 
palaeo-climatic history. For example, the marginal facies 
represents a distinct hydrochemical and hydrological 
condition, and such facies recurring as tongues along the 
wetland margin, or as buried sheets extending across the 
wetland basin provides information on former wetland 
conditions. Similarly, the occurrence of shell beds (or 
laminae), or the incursions of sand into the wetland 
margin by fluvial processes or by sheet wash, or the 
regular influx of quartz silt laminae in the stratigraphic 
sequence by, say, aeolian processes, signal important 
events in the history of accretion within a wetland, and 
the recognition of the processes and products of 
intrabasinal versus extrabasinal sedimentation becomes 
an important part of the stratigraphy of wetlands. 
Acknowledgements: This work is part of the R&D endeavour of the V & C 
Semeniuk Research Group, registered as VCSRG R&D Project #3 with 
Auslndustry (the Commonwealth Government R&D Board). The 
specialised laboratory work was undertaken in a number of institutions. 
The SEM, EDS, and ancillary work was carried out using CSIRO Bentley 
Laboratories, Western Australia, with the assistance of Peter Austin and 
Rick Hughes. XRD work was carried out at the Chemistry Centre 
University of Western Australia during the 1980s, and at the CSIRO 
Bentley Laboratories in more recent years. During the 1980s, laboratory 
combustion work was carried out by Envirochem P/L. VCSRG P/L and 
the Wetlands Research Association Inc. contributed to page costs of this 
publication. 
References 
Allen A D 1979 The hydrogeology of Lake Jandabup, Swan 
Coastal Plain, Western Australia. West Australian Geological 
Survey Annual Report 1979, p. 32-40. 
173 
