6.2 - Critical Zone Formation Flashcards
What forms the critical zone?
Weathering rock
What is the definition of soil?
Soil is the collection of natural bodies on earth’s surface containing living matter and supporting, or capable of supporting plants.
It’s upper limit is the atmosphere (air) or water, and its lateral margins it grades to deep water or barren areas of rock and ice.
It’s lower limit is normally considered to be the lower limit of the common rooting zone (root zone) of the native perennial plants, a boundary that is shallow in the deserts and tundra and deep in the humid tropics.
Pedogenesis = soil formation
What is pedogenesis
The formation of soil.
Late 19th century = Hillard (USA) and Dukuchaev (Russia) independently suggested that pedogensis is principally controlled by vegetation and climate.
What soils are most common throughout the UK?
- Inceptisols = barely developed soils
- Spodosols (aka podsols) = formed under coniferous forests
- Histosols = high in organic matter (eg. Peat bogs)
- Mollisols = Grasslands soils
What is the critical zone grouped into?
The CZ is grouped into horizons
O = Humus or organic (It is the topmost layer of decomposing leaves and lots of organic matter.)
A = topsoil (It is a mineral soil, which contains lots of roots, microbial activity, worms and minerals for growing plants
E = Eluviated layer or exit layer (Soils are well developed which show leached portion of ‘A’, the source region of clay Fe, Ai. Materials, minerals, organic matter, and clays exit the soil profile)
B = subsoil (It is highly weathered bedrock, with accumulation of clay/iron oxides from weathering. Minerals from upper horizons stop here.)
C = parent material (It is poorly weathered bedrock, with some accumulation of soluble products. It is the earth’s surface that soils develop from)
R = bedrock
What is CLORPT?
CLORPT is a mnemonic for Hans Jenny’s (1940’s) famous state equation for soil formation
Soil = f(cl,o,r,p,t)
- CLimate (primarily precipitation and temperature)
- Organisms (living biota, vegetation, micro- and macro organisms)
- Relief (topography: slope, aspect and landscape position)
- Parent material (geological or organic precursors to the soil)
- Time (duration of exposure of parent material
In general these processes DO NOT function independently
What is it called when one of the CLORPT influences is dominant?
In certain situations one of the soil-forming factors may exert a dominant influence of the formation of a set of soils.
Climosequence = when Climate influence is dominant
Biosequence = when organism influence is dominant
Toposequence = when relief influence is dominant
Lithosequence = when parent material influence is dominant
Chronosequence = when time influence is dominant
What are soil characteristic strongly influenced by?
Soil characteristics are strongly influenced by lithology and geological structure.
- Especially the chemistry and mineralogy of soils
How is parent material classified?
Soil “parent materials” are classified based on the initial location of soil precursors
Are they local (in situ) or transported from elsewhere?
1) In situ parent materials are classified as either residual or organic
Residual = rocks and minerals
Organic = plant debris
What is residual material?
It is inorganic parent material developed in place from weathering of underlying rock.
If the climate is warm and humid:
- Residual parent material is strongly leached and oxidised
- Bright red and yellow colours
Examples of this are Laterite and saprolite
Laterite = iron oxide/ clay layer rich in acid leached (but insoluble) elements like Fe, Mg, Si
Saprolite = it is isovolumetric, retains most original rock texture, but in warm/humid environments is oxidised, with the accumulation of soluble elements
What are laterites?
Laterite = iron oxide/ clay layer rich in acid leached (but insoluble) elements like Fe, Mg, Si
They are very common building material in sub-tropics/tropics. Hot and humid environments create oxidising conditions. This leads to red/orange rock from iron oxidisation
They are also a large source of aluminium, iron, and nickel ores
What is saprolite
Saprolite = it is isovolumetric, retains most original rock texture, but in warm/humid environments is oxidised, with the accumulation of soluble elements
Saprolite from a cool and dry environment = isovolumetric, it retains original rock texture and most of the chemistry. IT IS GREY
- Saprolite can be derived from granite in a dry, cold region
Saprolite from granite in a hot and humid environment = IT IS RED/ORANGE
Saprolite behaves differently in environmental conditions. Deep weathering causes many secondary/supergene ores of economic interest in subsoil horizons
What are examples of secondary/supergene ores?
- Bauxite And iron ores in laterites
- Saprolitic gold, supergene copper, uranium and many heavy metals in saprolites
Where is lots of peat formed across the globe?
Peat is most extensive in cool climates where precipitation is > evaporation and where drainage is poor.
About 75% of the worlds peat lands occur in northern Canada and Russia.
Organic parent material/deposits = peat
How is peat formed?
It is formed in wet places with poor drainage, and where decomposition of plant debris limited due to the lack of O2
(Organic matter accumulates in the soil without decaying due to lack of oxygen)
