Journal of the Royal Society of Western Australia, 87(4), December 2004 
, F ‘J, U r re f, EM Photomicrographs showing features of peat. A. Overview of sample from Willie Pool showing general fine-grained 
/ ^ n e p P ea j a ™ w desiccation in the SEM photograph is due to the vacuum process), phytoliths (arrow 2), and root fibres 
v f n n C r> *f US com P r * s ^ n g ^e peat at Leda Swamp, showing material riddled with fungal hyphae and cavities produced bv 
rl ' C ( lV | 1 \ j *. e lct structures of plant detritus, here riddled with fungal hyphae and cavities produced by bacterial activity. D 
Close-up of plant detritus from peat at Leda Swamp. K y y 
Structurally, the sediments are homogeneous to layered. 
Where sand-sized, the sediments grade from very coarse 
to medium sand. Compositionally, the sediments consist 
of whole and fragmented skeletons of molluscs, 
gastropods and/or pelecypods, and locally ostracods. 
The sediments commonly form layers in carbonate mud 
or peat deposits (Fig. 5J). 
Carbonate intraclast gravel and sand 
Carbonate intraclast gravel and sand are a cream or 
grey medium grained to coarse grained suite of 
sediments. They have homogeneous to layered structure, 
and local vesicular to fenestral structures (Fig. 5I-K). 
Texturally, where sand-sized, the grade is medium, 
coarse to very coarse grained. Compositionally, four 
types of intraclast are recognised: 1. clasts of calcilutite 
that essentially were dried, fragmented and reworked 
into intraclast sand; 2. clasts of carbonate cemented 
calcilutite, reworked into intraclast gravel and sand; 3. 
clasts of carbonate cemented intraclast sand (polycyclic 
intraclasts), reworked into intraclast gravel and sand; and 
4. clasts of carbonate cemented skeletal sand, reworked 
into intraclast gravel and sand. Carbonate intraclast 
gravel and sand has formed within wetland basins, and 
particularly along their margins, where desiccation has 
cracked and fragmented calcilutite deposits, and high 
water wave conditions have reworked and rounded them 
to form thin shoreline deposits (Fig. 4A). 
Diatomite 
Diatomite is light grey fine-grained sediment, though 
locally dark grey to brown in organic-rich layers. It is 
homogeneous to root-structured at the surface, and 
laminated to structureless at depth (Fig. 5L). Grey to 
dark grey to brown diatomite has disseminated organic 
matter and/or fine-grained pyrite. Diatomite consists of 
silt-sized to clay-sized diatom skeletons and particles 
(Fig. 10). It may have scattered (< 5%) quartz sand and 
quartz silt. Diatomite ranges from porous sediment with 
low bulk density (composed of whole and fragmented 
diatom tests) to a compacted, dense sediment with 
relatively higher density (composed largely of wholly 
fragmented tests). This latter sediment, as mentioned 
earlier, has the bulk properties of a quartz siltstone or 
silt deposit (i.e., not porous, but compact, and with a 
moderate bulk density unlike traditional "diatomaceous 
earth"). 
Diatomite intraclast gravel and sand 
Diatomite intraclast gravel and sand are a light grey 
medium to coarse-grained suite of sediments, composed 
of rounded fine gravel to sand-sized sized clasts of 
diatomite (Fig. 5M). Diatomite intraclast gravel and sand 
form within wetland basins, and particularly along their 
margins, where desiccation has cracked and fragmented 
diatomite deposits and high water wave conditions have 
reworked and rounded them to form thin shoreline 
156 
