PMDEP
Parent material mode of deposition

The mode of deposition of mineral materials and undifferentiated organic materials is shown by a single alpha code whereas the origin of specified organic material is given by a numeric, two-digit code (ref: Tarnocai, 1984; ECSS, 1987; NWWG, 1987).

Mineral materials and undifferentiated or unspecified organic materials:

CODE CLASS
     DESCRIPTION

A

Alluvial
Sediment, generally consisting of gravel and sand with a minor fraction of silt and clay. The gravels are typically rounded and contain interstitial sand; alluvial sediments are moderately to well sorted and display stratification. Examples are channel deposits, overbank deposits, terraces, alluvial fans, and deltas.

B

Bog
Bogs consist of unspecified organic materials formed in an ombrotrophic (nutrient-poor) environment caused by the slightly elevated nature of the bog which dissociates it from nutrient-rich ground water or surrounding mineral soils. Near the surface, materials are usually undecomposed (fibric), yellowish to pale brown, loose and spongy in consistence, and entire sphagnum plants are readily identified. These materials are extremely acid, with low bulk density and high fibre content; at lower depths they become darker, compacted, and somewhat layered. Bogs are associated with slopes or depressions on topography with a water table at or near the surface in the spring and slightly below it during the rest of the year. They are usually covered with sphagnum mosses, but sedges may also grow on them. Bogs may be treed or treeless and many are characterized by a layer of ericaceous shrubs.

C

Colluvial
Massive to moderately-well stratified, nonsorted to poorly sorted sediments with any range of particle sizes from clay to boulders that have reached their present position only by direct, gravity-induced movement (except snow avalanches). Processes include slow displacements such as creep and solifluction and rapid movements such as earth flows.

D

Residual
Unconsolidated, weathered, or partly weathered mineral soil material that accumulates by in situ disintegration of bedrock.

E

Eolian
Sediment, generally consisting of medium to fine sand and coarse silt particles, which is well sorted and poorly compacted. It may be massive, or show internal structures such as cross bedding or ripple laminae. Individual grains may be rounded and show signs of frosting. These materials have been transported and deposited by wind action. Examples are dunes, shallow deposits of sand and coarse silt, and loess.

F

Fluvioglacial
Material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. Deposits are stratified and may occur in the form of outwash plains, deltas, kames, eskers, and kame terraces.

H

Marsh
Mineral wetland or peatland that is periodically inundated by standing or slow-moving water. Surface water levels may fluctuate seasonally, with declining levels exposing drawdown zones of matted vegetation or mudflats. Waters are rich in nutrients, varying from fresh to highly saline. Substratum usually consists of mineral material, although in some places it consists of well-decomposed peat. Soils are predominantly Gleysols, with some Humisols and Mesisols. Marshes characteristically show zonal or mosaic surface patterns composed of pools or channels interspersed with clumps of emergent sedges, grasses, rushes, and reeds, and are bordered by grassy meadows and peripheral bands of shrubs or trees. Submerged and floating aquatics flourish where open-water areas occur.

I

Folic
Upland organic material.

L

Lacustrine
Sediment, generally consisting of either stratified fine sand, silt, and clay deposited on the lake bed, or moderately-well sorted, stratified sand and coarse materials that consist of near lake shore or beach deposits. These materials have either settled from suspension in bodies of standing fresh water or accumulated at their margins through wave action.

M

Morainal
Sediment, generally consisting of well-compacted material that is nonstratified and contains a heterogeneous mixture of sand, silt, and clay particles and coarse fragments in a mixture that has been transported beneath, beside, on, within, or in front of a glacier but not modified by any intermediate agent. Examples are basal till (ground moraine), lateral and terminal moraines, rubbly moraines of cirque glaciers, hummocky ice-disintegration moraines, and pre-existing, unconsolidated sediments reworked by a glacier so that their original character is largely or completely destroyed.

N

Fen
Fens consist of unspecified organic materials formed in a minerotrophic environment due to the close association of the material with mineral-rich waters. The material is usually moderately-well to well decomposed, dark brown to black, with fine- to medium-sized fibres; decomposition often becomes greater at lower depths. The materials are covered with a dominant component of sedges, but grasses and reeds may be associated in local pools.

O

Organic
A layered sequence of more than three undifferentiated types of organic material (>30% organic matter by weight).

R

Rock
A consolidated bedrock layer that is too hard to break with the hands (>3 on Mohs' scale) or to dig with a spade when moist.

S

Swamp
Minerotrophic wetlands with the water table at or above the peat surface. The dominant unspecified organic materials are forest and fen peat formed in a eutrophic (nutrient-rich) environment due to strong water movement from the margins or other mineral sources. The material is usually moderately well to well decomposed and has a dark brown to reddish brown matrix; the more decomposed materials are black. It has an amorphous or very fine-fibred structure containing a random distribution of woody fragments and trunks of coniferous tree species. The vegetation cover may consist of coniferous or deciduous trees, tall shrubs, herbs, and mosses; in some regions sphagnum mosses are abundant.

T

Anthropogenic
Materials modified by people,including those associated with mineral exploitation and waste disposal. They include materials deposited as a result of human activities or geological materials modified artificially so that their physical properties (structure, cohesion, compaction) have been drastically altered. Examples are areas of landfill, spoil heaps, open-pit mines and levelled irrigated areas.

U

Undifferentiated
A sequence of more than three types of genetic mineral materials outcropping on a steep erosional escarpment. This complex class is to be used where units relating to individual genetic materials cannot be delimited separately at the scale of mapping. It may include colluvium derived from the various genetic materials and resting upon the scarp slope.

V

Volcanic
Volcanic pumice and ash.

W

Marine
Unconsolidated deposits of clay, silt, sand, or gravel that are well to moderately well sorted and well to moderately well stratified (in some places containing shells). The deposits have settled from suspension in salt or brackish water bodies or have accumulated at their margins through shoreline processes such as wave action and longshore drift. Nonfossiliferous deposits may be judged marine if they are located in an area that may reasonably be considered to have contained salt water at the time the deposits were formed.

Specified organic materials:

CODE CLASS
     DESCRIPTION

11

Fibric sphagnum
Sphagnum organic material having a fibric (slight) degree of decomposition in which the fibric materials are readily identifiable as to botanical origin. The peat is usually undecomposed (or fibric), light yellowish brown to pale brown, and loose and spongy in consistency with the entire sphagnum plant being readily identifiable.

20

Fibric sedge and moss
Sedge and brown moss organic material having a fibric (slight) degree of decomposition. The peat is composed dominantly of sedge (Carex spp.) and brown mosses (Depranocladus spp.). It is usually slightly decomposed and brown to dark brown; consistency is variable and ranges from loose to matted. The material commonly contains large amounts of very fine sedge roots.

21

Mesic sedge
Sedge organic material having a mesic (intermediate) degree of decomposition. The peat is composed dominantly of sedge (Carex spp.) and is moderately decomposed and matted. The sedge leaves are readily identifiable by the naked eye. This material commonly contains large amounts of very fine roots of the above species.

22

Mesic woody sedge
Woody sedge organic material having a mesic(intermediate) degree of decomposition. The peat is composed dominantly of sedge peat (see code 21) with subdominant amounts of woody materials.

23

Mesic woody forest
Woody forest organic material having a mesic(intermediate) degree of decomposition. The peat contains significant amounts of woody materials derived from both coniferous and deciduous tree species. In general, wood fragments are easily identifiable in this peat.

25

Mesic sphagnum
Sphagnum organic material having a mesic (intermediate) degree of decomposition.

31

Humic sedge
Sedge organic material having a humic (most advanced) degree of decomposition in which most of the material is humified and there are few recognizable fibres.

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Non applicable

effective Version 1.0 Contact: Peter Schut