Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
or displacive crystal aggregates: calcite and Mg-calcite 
locally cements carbonate; in some wetlands, aragonite 
has been precipitated within host carbonate sediments as 
an intergranular cement in intraclast and skeletal gravel 
and sand, or as a displacive radiating aggregate of 
acicular crystals within fine-grained carbonate sediment. 
Dolomite also locally has formed as a diagenetic mineral 
in a carbonate mud host sediment (similar to The 
Coorong; von der Borch 1976; Rosen ct al, 1989). 
The burning of wood, other vegetation, and sulphide- 
mineral-bearing peat in wetlands generates a range of 
minerals, evident in the ash: fine grained calcite, formed 
where Ca released in burning wood combines with C0 2 
also released during the combustion; anhydrite, where 
Ca released in burning wood combines with SO, released 
during the combustion (anhydrite later transforms under 
waterlogged conditions to gypsum); halite and sylvite 
(formed from the Na and K released in combustion), both 
of which dissolve in the ensuing wet season; crystalline 
silica formed from biogenic silica; and goethite and 
haematite formed by oxidation of pyrite (Semeniuk & 
Semeniuk 2005c). In this context, with the alteration of 
pre-existing materials to pyrogenic calcite, crystalline 
silica, goethite and haematite, pyrogenesis is a subclass 
of diagenesis. 
SEM show's that the biogenic silica of diatoms, sponge 
spicules and phytoliths also exhibit surface corrosion, 
and may be progressively chemically removed. In 
sediments where there is such dissolution, silica is locally 
re-precipitated, forming micro-botryoidal crusts and 
coatings to particles, indurating the sediment. 
Dissolution of biogenic silica and its localised re¬ 
precipitation as cements and nodules may occur in 
diatomites, carbonate sediments, and quartz sands. 
WETLAND BASIN 
highest high water 
KEY 
Wetland sedimentary fill 
(accretionary and Inflltratlonal) 
WETLAND SEDIMENT 
Zone of ferrlcrete 
(black = locally tightly cemented) 
Zone of reduced Iron (zone of pyitte. 
or other ferrous-bearing minerals) 
White quartz sand 
(= yellow sand bleached white); 
also zone of solution of calcite. 
If carbonates are present In basement 
ZONES OF DIAGENESIS 
SUPERIMPOSED ON HOST SEDIMENT: 
ARRANGED ACCORDING TO 
HYDROCHEMICAL FIELDS 
Yellow quartz sand basement host 
HOST SEDIMENT TO WETLAND 
BASIN, AND TO DIAGENETIC 
PRODUCTS 
Figure 15. Idealised diagram (not to scale) showing zones of diagenetic alteration under and around wetland basins resulting from the 
wetland hydrochemical fields interacting with the underlying and adjoining basement sand to illustrate that the products of diagenesis 
are separate from the sedimentary fill of a wetland basin. In this example, diagenetic zones focus on the chemistry of Fe, but similar 
zones may be devised for carbonate, silica, and phyllosilicate mineral components of the host sediments around and underlying 
wetlands. The asymmetry in the diagenetic zones is intended to show the effect of the directional plume of groundwater flow, with 
interdigitation reflecting lithological or hydrogeologic influences. 
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