Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
Figure 11. SEM photomicrographs of diatomaceous peat. A. Overview showing abundance of whole and fragmented sponge spicules, 
200-250 pm in size (arrow 1), scattered diatom fragments (arrow 2), and the fine-grained organic matter that dominates the sediment, 
here showing cracking by desiccation (arrow 3), as a result of carbon-coating under vacuum in the SEM process. B. Close-up of typical 
fragments of diatom frustules, 5-20 pm in size (arrow 1), in various stages of disaggregation, and fine-grained plant detritus with 
layered internal structure (arrow 2). C. Overview of interstitial sediment of peaty sand from a wetland basin in the Ellenbrook area 
showing diatom fragments (arrow 1), plant remains and fibres (arrow 2), and phytoliths (arrow 3). D. Close-up showing diatoms in 
various stages of fragmentation from 20 pm in size to < 1 pm in size, and plant detritus (arrows). 
the biogenic mud-sized sediments (i.e., peat, diatomite 
and calcilutite), and between quartz sand and mud-sized 
components. 
In the sediments dominated by biogenic mud-sized 
components, there may be a gradational series of 
sediment types between peat, diatomite, and calcilutite, 
i.e., organic matter, diatoms and carbonate mud are 
mixed together to form a variety of mud-dominated 
sediments. Sponge spicules generally are not abundant 
enough in the wetland sediments to form spongolites, 
and hence in this paper are not considered to be an end- 
member biogenic sediment type. In this study they were 
most abundant in a thin layer of peaty sediment at Lake 
Gwelup, contributing c. 50% of particles to the sediment; 
in this context, the sediment is a spongolitic peat. A 
simplified classification and nomenclature of the three 
end-member biogenic fine-grained sediment classes and 
the sediments produced as mixtures of organic matter, 
diatoms and carbonate mud is presented in Figure 12A. 
The sediment types formed in this manner are: 
diatomaceous peat, calcilutaceous peat, organic matter 
enriched diatomite, organic matter enriched calcilutite, 
organic matter enriched diatomaceous calcilutite, 
diatomaceous calcilutite, and calcilutaceous diatomite 
(rare). The classification presented in Figure 12A involves 
only mixtures of biogenic mud-sized components and 
not mixtures of mud-sized and sand-sized components. 
Analyses from some 100 fine-grained wetland sediments 
are superimposed on the ternary diagram in Figure 13A 
to illustrate the variability in composition of these types 
of wetland sediments. 
Generally, kaolinitic mud does not form significant 
mixtures with the biogenic muds. However, if there is 
admixed organic matter, carbonate mud, diatoms and 
kaolinite mud, the following nomenclature is proposed. 
With > 75% kaolinite, the sediment is kaolinitic mud. 
With 50-75% kaolinite, and diatoms or organic matter 
comprising the remaining 25-50% of the sediment, the 
sediment is termed diatomaceous kaolinitic mud, 
organic-matter enriched kaolinitic mud, or organic- 
matter enriched diatomaceous kaolinitic mud. With 25- 
50% kaolinite mud, the term "kaolinitic" becomes an 
adjectival descriptor to be added to one of the various 
mud sediment terms illustrated in Figure 12A, e.g., 
kaolinitic organic matter enriched diatomite, or kaolinitic 
diatomaceous peat. Where the mud component is not 
kaolinite, the term "phyllosilicic mud" replaces 
"kaolinitic mud". 
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