Journal of the Royal Society of Western Australia, 87(4), December 2004 
forming small nodules (of induration), or interstitial 
grain-coating fine-grained cement. 
Ferricrete is common in wetlands as an indurated 
sheet overprinting sandy wetland fills at levels of the 
water table and below. The ferricrete is a mixture of 
goethite, X-ray amorphous iron oxides, infiltrated 
kaolinite, and silica silt. Where it occurs as a weakly 
indurated overprint, it forms laminated rims interstitial 
to sand grains. Well-indurated ferricrete consists of a 
complex of laminated iron oxides, kaolinite, and quartz 
silt filling the sand interstices. 
There also are diagenetic effects on the materials 
underlying and adjoining the wetland sediments, but 
these strictly are processes and products associated with 
acidic and Fe-enriched water derived from wetlands on 
underlying basement materials (Fig. 15). It is useful to 
clearly separate the products of diagenesis on basement 
materials, and diagenetic effects on wetland sediments, 
from primary wetland sediments themselves. These 
diagenetic effects include the bleaching of yellow sand 
on the margins and beneath wetland basins, and the 
translocation of mud-sized phyllosilicate mineral 
particles and fine quartz silt down the profile or into a 
wetland. Thus, while wetland sediments may fill a basin, 
there also is a halo effect of diagenetic alteration from the 
base and margins of the wetland into the underlying 
materials. Pre-Holocene host sediment under wetland 
terrains, for instance, are commonly bleached to white 
sand, with incomplete bleaching resulting in mottled 
white, cream, yellow and orange coloured sand. The host 
sand is yellow to orange quartz sand where the sand 
grains are coated by goethite-impregnated kaolinite skins 
(as described above). The bleached sand is quartz sand 
stripped of the goethite, kaolinite and quartz silt. The 
mud-sized phyllosilicate mineral particles and fine 
quartz silt are translocated to elsewhere in the profile, 
and the goethite is chemically translocated to precipitate 
as an iron oxide to form ferricrete. This style of alteration 
around wetlands was described in Figure 10 of Glassford 
& Semeniuk (1990) for yellow sand proximal to and at 
the water table. 
Origin of sedimentary particles and wetland 
sediments 
The origin of wetland sediment particles and wetland 
sediment types is diverse, ranging from intrabasinal to 
extrabasinal, from terrigenous to biogenic sources, and 
for the intrabasinal, biogenic, and chemically modified 
sediments, from in situ accumulations to reworked 
deposits (Fig. 16). 
The sedimentary particles and the accumulated 
deposits can be initially categorised as intrabasinal and 
extrabasinal, then further differentiated as infiltrational 
or accretionary. Wetland particles and sediments can also 
be differentiated as terrigenous ( i.e ., derived from 
terrestrial sources, such as quartz sand and mud-sized 
phyllosilicate mineral particles), or biogenic (i.e., derived 
from biological sources such as peat, carbonate sediment, 
and siliceous diatoms). In this context, peats, calcilutite. 
D: INTRABASINAL, INTRACLASTIC 
(desiccation, cementation, 
fragmentation, reworking) 
Dl: peat Intraclasts 
D2: dlatomlte Intraclasts 
D3: carbonate Intraclasts 
C: INTRABASINAL, BIOGENIC 
ACCRETIONARY 
(accumulation within basin) 
Cl: plants to form peat 
C2: diatoms to form dlatomlte 
C3: Charo to form calcilutite 
C4: shells to form skeletal gravel/sand 
A: EXTRABASINAL, TERRIGENOUS 
(delivery of quartz sand, quartz silt, 
phyllosilicate clay, goethite mud) 
Al; fluvial 
A2: sheet wash 
A3: aeollan 
A4: groundwater seepage 
A5: basal bioturbation 
B: INTRABASINAL, BIOGENIC 
INFILTRATIONAL 
(Infiltration of biogenic sediment 
into underlying sand at base of 
sedimentary fill) 
B1: Infiltration via gravitational water 
B2: Infiltration by bioturbation 
Figure 16. Origin, categories and composition of wetland sediments. 
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