1. Parent Material

a. resistance of parent material to weathering

b. texture

c. mineral stability

2. Time

a. rates of weathering

b. degree of weathering

• in rocks

  • historic time: tombstones & other cultural features

  • over thousands of years: weathering rind thickness

• in soil

  • rate of CaCO₃ depletion

  • observe mineral & chemical composition of soil

c. clay minerals

• formed primarily by recombination of silica, alumina and metal cations released during weathering

• 1:1 layered clays (kaolinite)

• 2:1 layered clays: smectite (montmorillonite), illite, vermiculite, chlorite

• alteration of clay minerals

  • progression: primary minerals to 2:1 layered clays to 1:1 layered clays to hydrous oxides of iron and aluminum

3. Climate

a. affects type and rate of weathering

b. affects biota

4. Organisms

a. aid physical and chemical weathering

5. Relief (topography)

a. microclimate affected by orientation & altitude

b. influence of slope: soil catena

1. Decipher sequence of events; relative ages

a. time is critical for profile formation

b. soil forming factors change over time

c. polygenetic soils: profile characteristics reflect more than one set of soil forming factors

2. Guidelines for interpreting soils

a. law of superposition: younger beds overlie older beds; younger beds truncate older beds

b. law of ascendency & descendency: higher surfaces are older than lower surfaces

• these first two laws allow relative dating of surfaces & help predict the areal distribution of surfaces

c. the composition of surface & subsurface materials and the geomorphology of a site control the hydrology of the site

3. Paleosols

a. relict soils: soils that have remained at the surface since their initial formation

b. buried soils: soils formed on an ancient surface & subsequently buried; not affected by current pedogenic processes

c. exhumed soils: formerly buried, but subsequently exposed to current pedogenic processes

 

• five soil forming factors: parent material, time, climate, organisms, relief

• affect soil characteristics

• comparisons of soils may allow:

  • relative dating; important for reconstructing past sequences of geomorphic events

  • estimating past environmental conditions that may have influenced geomorphic processes