QUATERNARY SOILS: characterization and dating of buried soils used to date and correlate pluvial sequences, glacial chronologies, etc.; and to provide paleoclimatic inferrences

SOIL MORPHOLOGY: HORIZONS

• O Organic matter accumulation (dark), but not formed by illuviation of organic matter
  
• A Mineral horizons at surface or below O horizon, characterized by accumulation of humified organic matter, or by cultivation
  
• E Mineral horizons with eluvial loss of silicate clay and/or aluminum leaving a concentration of quartz sand and silt
  
• B Mineral horizon formed below A, E, or O by illuvial deposition of clay, iron, aluminum, humus, carbonates, gypsum or silica. Or characterized by removal of carbonates; presence of sesquiozides; granular, blocky, or prismatic structure reflecting autogenic clay
  
  clay, iron + aluminum oxides, carbonate
• Bkm (or k, C) Carbonate horizon (caliche)
  
• C Parent Material - less effected by soil-forming processes
  

SOIL ORDERS:

ENTISOL  no (?) soil development INCEPTISOL moderate devel. (A1) ARIDISOL limited development MOLLISOL thick dark A1 SPODOSOL light A2, Fe and Al in Bir ALFISOL forest soils A2 ULTISOLS crystalline clays low bases OXISOLS highly weathered soils VERTISOLS playa, cracking soils HISTOSOLS peats CATENAS (Morrison, 1967) facies changes in soils example elevational changes higher elevation = more OM in A higher elevation = less Cca

RATE OF SOIL FORMATION
Horizons weakly or strongly developed depending on several factors that effect rates of chemical and physical processes

SOIL = f(C,O,R,P,T)
Dokuchaev Equation (Jenny, 1961)


• CLIMATE
  • moisture - rates of eluviation, illuviation
    
  • temperature - rates of chemical reactions, oxidation, clay formation
    
• ORGANISMS
  • soil chemistry pH, nutrients, eluviation
    
  • tilling, mixing of horizons
    
• RELIEF
  • erosion - deposition
    
  • micro-habitat moisture and temperature
    
• PARENT MATERIAL
  • texture of parent material - soil moisture, aeration
    
  • chemistry - base content, carbonates, iron, clays
    
  • more than one parent material I, II, III
    
  • example: loess, coluvium over aluvium (CO₃), volcanic ash = A₂
    
• TIME
  • length of time = degree of development
    example: Central and Southern Rocky Mountains (Shroba and Birkland 1983)
    
    0-300 yr little formation, some organic in A1
    1000-2000 yr some oxidation of C (Cox) no "B"
    3000-5000 yr color change in B (Bs) but no clay (Bt)
    10,000 yr Bt (illuvial clay) developed
    

CARBONATE ACCUMULATION (Gile and Hawley, 1966) STAGE I thin discontinuous coatings on pebbles STAGE II continuous coatings, calcareous loose matrix STAGE III cementation

FOSSIL SOILS Soils that formed in the past Processes that led to formation no longer operation RELICT SOIL: at surface, +/- modified by modern soil or be remnant of former time example: red, argillic B near Tucson BURIED SOIL: past soil beneath modern soil e.g. histosols beneath loess in U.S. Midwest e.g. soils visible in arroyos may be modified by current soil forming processes if shallow some buried horizons may not be visible (A1)

PALEOCLIMATE

inferring past climate from morphology of fossil soil
e.g., "Altithermal soil" intense weathering warmer, wetter ?

climate vs biota vs time etc.
e.g., "Sangamon" soil actually two interglacials

STRATIGRAPHIC CORRELATION

soil morphology used to correlate stratigraphic sequences
e.g. Morrison's chronology for western U.S.
e.g. alluvial chronology and Altithermal Soils

Soils Readings

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