Semeniuk & Semeniuk: Wetland sedimentary fill - particles, sediments, classification 
sedimentation are examples of synsedimentary 
phenomena. The term synsedimentary also is commonly 
applied to a particular stage of diagenesis in which there 
is alteration of sediment contemporaneously or 
penecontemporaneously with sedimentation 
(precipitation of sulphides and cementation by carbonate 
mineral are examples of synsedimentary diagenesis). The 
term diagenesis (and diagenetic ) refers to the physical, 
biological, and chemical processes, acting alone or in 
concert, that overprint sediments after accumulation, and 
products resulting from these processes. Precipitation of 
carbonate within sediment to develop indurated layers, 
for instance, is a diagenetic phenomenon, and the 
precipitate may be referred to as “diagenetic carbonate", 
noting that diagenetic carbonate thus is distinct from any 
sedimentary carbonate material that has been derived 
from accumulating skeletons (“biogenic carbonate"), or 
that derived by chemical precipitation. Sediment fabric 
terms, such as grain-support, mud-support, grainstone 
and boundstone, are after Dunham (1962). 
The term “organic matter" is used in the sediment 
descriptions in this paper to refer to the range of 
materials of various particle sizes that are derived from 
plants. Organic matter ranges from relatively fresh 
material, to particles in various stages of decomposition 
(structural and biochemical breakdown, mediated by 
microbiological and fungal processes) to elemental 
carbon. 
Sediment versus soil 
The approach in this paper is from a sedimentary 
perspective, i.c., the materials accumulated in wetlands 
are sediments and are described from this sedimentary 
viewpoint. However, to avoid the confusion in the 
literature between the notions of “sediment" and “soil", 
a range of terms in relation to materials underlying 
wetlands are stipulatively defined below. “Sediment" 
refers to accumulated material that either has formed 
wholly within the wetland (autochthonous, intrabasinal 
sediment, i.e., that formed inside the basin), or has been 
transported into the wetland (allochthonous, extrabasinal 
sediment, i.e., that formed outside the basin). The term 
can be applied to individual sediment types or to inter- 
layered deposits. Thus, carbonate mud is a type of 
wetland sediment, and peat is a type of wetland 
sediment, since they both form as intrabasinal 
accumulative deposits. “Sedimentary" refers to any 
material accumulations that have formed as sediments. 
“Sedimentary fill" refers to the total aggregate of deposits 
filling a wetland basin. “Stratigraphic" and 
“stratigraphy" refer to the accumulated sequence of 
sediments. 
“Soil" in this paper refers to the altered material near 
or at the surface of any pre-existing sediment or rock 
body that has been biologically, chemically, or physically 
modified under extant conditions (Buol et ai, 1973; 
Arnold 1983; Jackson 1997), e.g., the weathering of the 
surface of the Bassendean Sand (Playford & Low 1972) 
on the Swan Coastal Plain, or the surface weathering of 
granite. Soils generally are not accretionary but 
degradational (Hunt 1972), though some authors place in 
the realm of soil the thin layer of fresh to decomposed 
organic matter accumulated above the mineral material 
(parent body), designated as the “O horizon", even if it 
has accreted to several centimetres in thickness (Buol et 
al, 1973). Soils that have formed under past climatic or 
hydrologic conditions, and are not therefore extant, are 
palaeosols. 
In this context, wetland sediments are the primary 
accumulates within a wetland basin, and not physical, 
chemical or biogenic alteration products of pre-existing 
material, and if soils are developed on them, the wetland 
soils will be near surface alteration of those primary 
materials (Fig. 2A). Thus, a wetland basin filled with 
white carbonate mud is filled with carbonate sediment, 
and the grey carbonate surface mud layer, say, 10 cm 
thick, of humified root-structured material at its surface 
is the wetland soil. Pre-existing Pleistocene quartz sand, 
e.g., the Bassendean Sand underlying a wetland is the 
basement material (note: the term “basement" here refers 
to the floor of the wetland basin and is not to be confused 
with the notion of basement referring to Precambrian 
rocks). Where such quartz sand immediately underlies 
the wetland floor, and there is no development of 
wetland sediment, the surface grey sandy layer, say, 10 
cm thick, of humified root-structured material developed 
on the sand is the wetland soil. 
The term “soil" carries the implication that any 
layering developed within it (e.g., the A, B and C 
horizons, or the Al, A2, and K horizons) has developed 
as a result of internal horizontal partitioning 
(“horizonation", cf. Buol et al., 1973) as a result of 
leaching, export (removal), or redistribution of materials 
physically, chemically, and biogenically within the soil 
profile on a pre-existing parent material. As such, 
chromatic, compositional or textural “layering" in the soil 
profile is the result of pedogenic processes, and the 
horizontal differentiation therein is interrelated. Stratigraphic 
sequences, e.g., interlayered accumulations of 
diatomaceous mud, biogenically derived organic matter 
and carbonate mud, are the result of the addition and 
accumulation of material generated within a basin and 
from the water column, and are not alterations or 
modifications of pre-existing materials. These 
horizontally-oriented differentiations are due to 
sedimentary accretion under differing regimes of water 
chemistry, or climate, or biotic assemblages, and are not 
internally interrelated. As such, the application of the 
term “soil" to stratigraphically layered material in a 
wetland accumulated from the intrabasinal processes is 
not correct. 
In contrast to these definitions and concepts outlined 
above, practitioners in geomorphology, soil science, and 
wetlands tend to have a wider view of the term “soil", 
and would use it to refer to all the materials that underlie 
wetlands, and thus would apply the term to sediments, 
sedimentary-fill, stratigraphic sequences, and diagenetic 
products. 
Commonly, in wetlands, there is addition of fine¬ 
grained wetland sediment (e.g., organic matter, diatom 
mud, carbonate mud, or mud-sized phyllosilicate 
minerals) by infiltration or bioturbation into any 
underlying porous basement substrate, such as sand or 
gravel. This process may result in a “muddy" sand or 
gravel (Fig. 2B). The fine-grained material is interstitial to 
the sand or gravel grain-support framework (Dunham 
1962), and not merely grain-coating, as is often the case 
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