GLG 362/598 Geomorphology

Soils in Geomorphology and Quaternary Research


Originally written by Lee Amoroso, September 2000

Soils definitions - it depends on whom you are talking to:

Geomorphologic:  loose, unconsolidated material on the surface of the earth.
Soil Science: the natural medium (weathered rock detritus) for the growth of plants.

Engineering/Environmental:all unconsolidated materials above bedrock.

Agricultural:  good or bad for growing crops (water retention, resistance to erosion, nutrient content)
 

Some just call it dirt.
 

Availability of soil data:

County soil surveys (USDA), geotechnical and environmental reports
 
 

Why study soils?

Geologists, geomorphologists, and Quaternary scientists are not simply interested in classification of soil types but also want to understand the processes that took place to create the soil and what record of past climate and geography may have been preserved.

Soils are characterized by horizons - recognizable zones of weathering (accumulation or depletion of material) that are created by physical, chemical, and biological processes. Soil horizons approximately parallel the land surface.

Principal soil horizons

O - uppermost, fresh to partly decomposed organic material

A - mineral soil mixed with decomposed organic material (dark color).  From 10 to 150cm in depth. Dominated by weathered mineral matter but has sufficient organic material to

       have darker color than lower horizons. Zone of leaching: elluviation taking soluble ions and clays lower. Desilicification: extreme leaching
       removing all soluble cations (mostly silica).

E - zone of maximum leaching of clay, iron, aluminum, and leaving behind residual minerals (lighter than A horizon).   Not present everywhere

B - zone of accumulation of clay, and iron/aluminum compounds. Soil structure development (prismatic, granular, blocky). Obliteration of rock structure. More intense colors than E or C horizons. Bt, is a reddish horizon seen in paleosols in the southwestern U.S. Of all the layers, as a zone of accumulation, B tends to preserve the best

       record of past soils.

C - relatively unweathered bedrock rubble. Saprolite: C

       horizon formed from bedrock-derived soil that maintains relist structures (layering, fractures).

from Jon Pelletier ( http://geomorphology.geo.arizona.edu//geos450/LECTURE4NEW/lecture4.html )
Overhead 1

The soil profile is not always so clear-cut, however. The photograph above shows an example of a "buried soil." The prominanet grey horizon just
below the head of the pick is a buried O horizon, and is underlain by a thick A horizon. The material above the buried O horizon is wind-blown
sediment deposited that was deposited on top of the older soil. Soil development within the wind-blown sediment has now given rise to A, B, and C
horizons in that material.  from Jon Pelletier ( http://geomorphology.geo.arizona.edu//geos450/LECTURE4NEW/lecture4.html )

Factors in soil formation: the soil equation S = f (p, cl, o, to, t) (Jenny, 1941)

Parent material

Climate

Organisms

Topography

Time

Soil properties vary with parent material

Soils formed on limestone are quite different from those that form on granite

Soil properties vary with climate

Soils from different climate regimes have different characteristics

Soil properties vary with time

An example: organic horizons can form in decades while high clay content soils can take 1000?s of years to develop.

Soil properties vary with organisms

The type of organisms (worms, ground squirrels, woodchucks) will determine the depth of bioturbation.
 
Soil properties vary with topography
Soil catena - soil characteristics that vary along a hillslope (even if it is all the same parent material). An illustration of the interaction between soils and landforms.
Affected by slope materials, water drainage, transport processes, chemical weathering
A catena is most recognizable when water movement and storage are dominant controls on soil formation.
Overhead 2

SELECTED TOPICS

Pedogenic (soil forming) regimes

Podzolization - leaching from A horizon to B horizon. Common in humid temperate climates, especially under forests.

 Laterization - high rainfall and temperature, intense leaching and oxidation, especially but not exclusively tropical regions.

Laterites are a good paleoclimate indicator. Australian bauxites are Paleocene age (57-66 Ma) when the climate was warm and moist.

Calcification - sub-humid to arid climates. The stage of development (of near-surface pedogenic carbonates) is an indicator of the age of the soil. This is discussed more fully later.
 

Age determination using soils

Weathering and other soild related processes have been used to estimate the age of surfaces and deposits

Weathering rinds - formed by oxidation of the exposed part of a clast or outcrop

Carbonate rinds - accumulation of CaCO3 on buried clasts

Surface roughness of rocks - usually increases with time

Microscopic etching of minerals - measure depth of etching

Depletion of chemical species - compare geochemical analysis of weathered vs. un-weathered materials
 
 

Some terms to know in studying soils and their use in geomorphology:

Paleosol - literally an old soil, depending on the author this may mean pre-Pleistocene or even older.

Relict soils, buried soils, and exhumed soils

 Relict - remained on the surface since formation

 Buried - soils buried by subsequent deposition (i.e. no further pedogenesis)

 Exhumed - buried and later uncovered
 

Soil chronosequence

- time is the variable considered, while the other soil forming factors (parent material, climate, organisms, and topography are assumed to be constant.

Used to develop a model to understand the depositional history and soil development of a deposit or series of deposits in a region.

(Vreeken, 1975)  identified four kinds of chronosequences:

1. Post-incisive - soils develop on deposits of different ages

2. Pre-incisive - a soil that develops on a deposit are buried by subsequent deposition

3. Time-transgressive without historical overlay - vertical stacking of sediments and buried soils

The buried soils indicate times of non-deposition

4. Time-transgressive with historical overlay - a combination of the first three

This is just a preview of an interesting and detailed subject.

 

Soil Definitions and Classification

How do we identify different soils and distinguish one from another? By the study of soil characteristics. The first step is to describe the soils.

A soil classification packet has been assembled from references that I (Lee) use when describing soils in the field. Also necessary are a hand lens, water, Munsell soil color charts, shovel or spade, and a trowel. A sieve set is useful to estimate the gravel percentage. We will learn how to use these tools in the laboratory session.

Package 1
Overhead 3
 
Soils have as many definitions as there are fields of study concerned with soil properties. Engineers consider soils to be any unconsolidated surficial material while geologists and geomorphologists consider soils to be rock detritus (alluvium or colluvium) that have weathered over a long period of time  (Ritter et al., 1995) . Soils are weathered sediments that differ from the parent materials in physical, chemical, morphological, and biologic characteristics  (Birkeland, 1984 ;  Hendricks, 1985) . The soil profile extends down to the unaltered parent material. Multiple soil horizons may be found in the subsurface making them difficult to separate and identify  (Birkeland, 1984) . Also, buried soil horizons can truncate geologic bedding, making them relatively easy to identify or can parallel bedding making them difficult to discern from the bedding  (Birkeland et al., 1991) .

Major soil groups

See Pelletier web site for a nice set of pictures and names:
 http://geomorphology.geo.arizona.edu//geos450/LECTURE4NEW/lecture4.html
Overhead 4

Aridisols and Entisols are the dominant soil orders on the basin floor in the Phoenix area. Aridisols are mineral soils with at least one diagnostic pedogenic or soil forming horizon, which have low concentrations of organic matter, and are dry for more than 6 months of the year. Aridisols are divided into Orthids that have little textural change with depth and have calcium carbonate throughout. Many Orthids have calcic horizons  Argids are Aridisols with accumulations of clay that was eluviated or transported from an upper horizon. Entisols are mineral soils with little or no evidence of development of soil horizons. Entisols are divided into Fluvents (recently deposited alluvium in floodplains and stream channels), Orthents (thin soils developed on steep slopes), and Psamments (sand or sandy loam soils)  (Birkeland, 1984 ;  Hendricks, 1985).
 
 

Carbonate Horizons - Parent Material, Topography, Climate, and Time Factors

Secondary carbonate accumulation in the soil profile is primarily due to calcium carbonate supplied by airborne dust, dissolved in infiltrating rainwater, and precipitated in the soil  (Machette, 1985; McFadden and Tinsley, 1985), although recent work in India has discounted the role of aeolian dust  (Choudhari, 1994) .Ruhe (1967)  showed that the carbonate in the K (calcic) horizons did not come solely as the result of weathering. If this were true, significant amounts of clay would also be created. Pedogenic carbonate horizons typically are approximately parallel to the land surface, their upper boundaries are within the range of the depth of wetting, and have distinct morphology  (Gile et al., 1981). The age of the geomorphic surface is related to the morphogenetic age of the carbonate horizon (Figure 3). Table 1 shows the carbonate morphology and estimated ages for the gravelly and non-gravelly soils found in southern New Mexico. Gravelly soils can develop significant carbonate accumulation and reduced permeability within 10,000 years.

Carbonate cemented river gravels in Mesa AZ:

Carbonate coatings on clasts:

Overheads 5 and 6

"to do Caliche is to do dust":

Package 2

Professor T. L. Pe'we':

See SCIENCE Ghost town reprint

 
 
 

References

Birkeland, P. W., 1999, ?Soils and Geomorphology.? Oxford University Press, New York., 3rd edition, 430 p.
Birkeland, P. W., Machette, M. N., and Haller, K. M., 1991, Soils as a Tool for Applied Quaternary Geology, pp. 63. Utah Geological and Mineral Survey, Salt Lake City, UT.
Bull, W. B., 1991, Geomorphic Responses to Climatic Change, Oxford University Press, New York.

Dorn, R. I., 1994, The role of climatic change in alluvial fan development. In ?Geomorphology of Desert Environments.? (A. D. Abrahams, and A. J. Parsons, Eds.), pp. 593-615. Chapman & Hall, London, U.K.

Gerrard, J., 1992, Soil Geomorphology, Chapman & Hall, London.

Gile, L. H., Hawley, J. W., and Grossman, R. B., 1981, Soils and Geomorphology in the Basin and Range Area of Southern New Mexico - Guidebook to the Desert Project, pp. 222 p. New Mexico Institute of Mining and Technology, Socorro, NM.

Hendricks, D. M., 1985, Arizona Soils, University of Arizona, Tucson, AZ.

Jenny, H., 1941, Factors of Soil Formation, Dover Publications, Inc, Mineola, NY.

Kraus, M. J., and Bown, T. M., 1986, Paleosols and time resolution in alluvial stratigraphy. In ?Paleosols - Their Recognition and Interpretation.? (V. P. Wright, Ed.), pp. 180-201. Princeton University Press, Princeton.

Machette, M. N., 1985, Calcic soils of the southwestern United States. In ?Soils and Quaternary geology of the southwestern United States.? (D. L. Weide, Ed.), pp. 1-22. Geological Society of America, Boulder, CO.

McAuliffe, J. R., 1994, Landscape evolution, soil formation, and ecological patterns and processes in Sonoran Desert bajadas. Ecological Monographs 64, 111-148.

McFadden, L. D., and Tinsley, J. C. (1985), Rate and depth of pedogenic-carbonate accumulation in soils. In ?Soils and Quaternary Geology of the Southwestern United States.? (D. L. Weide, Ed.), pp. 23-41. Geological Society of America, Boulder, CO.

Morrison, R. B., 1978, Quaternary soil stratigraphy - concepts, methods, and problems. In ?York University Symposium on Soils.? (W. C. Mahaney, Ed.), pp. 77-108. Geo Abstracts, Ltd., Norwich, England.

Ollier, C., and Pain, C., 1996, Regolith, Soils, and Landforms, John Wiley and Sons, New York.
 

Péwé, T. L., Péwé, E. A., Péwé, R. H., Journaux, A., and Slatt, R. M.,1981, Desert Dust: Characteristics and rates of deposition in central Arizona. In ?Desert Dust: Origin, Characteristics, and Effects on Man.? (T. L. Pewe, Ed.), pp. 169-190. Geological Society of America, Boulder, CO.

Ruhe, R.V., 1967, Geomorphic surfaces and surficial deposits in southern New Mexico, State Bureau of Mines and Mineral Resources, Socorro, NM, 66 p.

Selby, M. J., 1993, ?Hillslope Materials and Processes.? Oxford University Press, New York.

Watson, A., 1992, Desert Soils. In ?Weathering, Soils, and Paleosols.? (I. P. Martini, and W. Chesworth, Eds.), pp. 225-260. Elsevier, Amsterdam.

GLG 362/598 Geomorphology