Soils 205-90

Lecture 19- Parent materials, weathering, and soil forming factors

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Parent Material ¾¾¾weathering¾¾¾¾¾® Soil

primary minerals

secondary minerals

 Types of surficial deposits

I. Sedentary

formed in place = Residual parent material

 

II. Transported

Agent	Deposit
gravity ---------------	Colluvial
water ----------------	Alluvial
	Marine
	Lacustrine
ice ------------------	Glacial (till, moraine)
wind ----------------	Eolian

* Wide diversity within groups

A. Residual parent materials

1. develop from underlying rock

2. typically, long and intense weathering

3. wide distribution

- large variety of soils

- variable source and weathering processes

B. Colluvial debris

1. detached and moved down slope

2. often, coarse and stony

C. Alluvial deposits

1. Floodplains (Fluvial)

Mississippi flood plain and a soil profile showing the stratification due to different deposition events.

(a) meander vs flood

(b) particle size

- gravel and sands ¾® silt and clay

(c) terraces = old floodplain

(d) productivity

- usually, rich soils

- need drainage and protection

2. Alluvial fans

(a) gradient change from uplands = deposit

(b) porous = excessively well-drained

(c) common in mountainous and hilly regions

(d) can be quite productive

3. Delta deposits

Development on a delta soil

(a) in receiving body of water

(b) often, continuation of a floodplain

(c) properties - clayey and swampy are common

(d) historically important

(e) rich and productive

- need drainage, flood control

- wetlands and wildlife habitat

D. Marine sediments

1. oceans, seas, gulfs

2. generally, worn and leached

3. some - sandy; others - clay

4. require care to stabilize - subject to erosion and water action

E. Pleistocene Ice Age

1. Major influence on soil materials

2. Glacial till and moraines

Glacial till landscape and corresponding soil profile showing the heterogeneous particle size

(a) highly variable and heterogeneous

(b) properties reflect source

3. Glacial outwash and lacustrine deposits

(a) streams from glacial melt = alluvium

(b) lakes formed, when dried = lacustrine

4. Loess

(a) wind transported

- dry spells between glaciers

(b) source

- often glacial outwash materials

(c) texture - high in silt

(d) large regions

- N. and S. Idaho

- Great Basin

F. Eolian deposits

1. most important = loess

2. sand dunes

3. volcanic ash

G. Organic deposits

1. when plant growth > rate of residue decomposition

- mostly, wet and cold

2. "peat" soils

- very productive when drained

- wetland areas & wildlife habitat

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