Surface 9: Weathering, Regolith, & Soils

Regolith

• weathering mantle + any transported material resting above it

• includes soil, saprolite, and highly weathered rock

• driven by inputs, outputs, transfers, & transformations of energy

Weathering profile

• a vertical section through soil and rock showing different zones of weathering

• includes layers → unweathered rock at the bottom → partially weathered rock → soil on top

Weathering front

• boundary between fresh and weathered rock

Weathering profile (top to bottom)

mobile zone → saprolite → saprock (all regolith) → || weathering front|| → fresh bedrock

Blockfield formation

• intense frost weathering of exposed bedrock

• large expanses of coarse and angular rock rubble

Duricrusts

• include all cemented terrestrial soils and sediments forming near the Earth’s surface as hard nodules or crusts

• e.g. Ferricrete, Laterite

Midlatitude Soil Profile

• O → litter + decomposed animal & plant remains → organic

• A → humic horizon

• E → eluvial horizon

• B → illuvial horizon → A to C = topsoil

• C → unconsolidated material → subsoil

• R → consolidated bedrock

Soil landscape systems

• emphasizes the dynamic links between soil and other Earth systems

Geopedology

• investigates the joint development of soilscapes and landscapes

Dynamic Denudation Theory

• implies that the textural contrast between A and B horizons is due to the action of animals and plants rather than due to eluviation and illuvation of fine materials

Bioturbation

• the topmost portion of the weathered mantle is subject to mixing by organisms that live in the soil

Weathering patterns (factors + effect)

• climate → influences all types of weathering

• temperature → high temp = more chemical weathering

• water storage & movement → more moisture = more chemical weathering

• variability temp. → high variability = more freeze thaw cycles

Neoformation

• the process of forming entirely new secondary minerals (such as clay minerals) from the dissolved components carried in the soil solution, rather than just transforming existing minerals.

Leaching (define)

• the natural process where water (from rain or irrigation) percolates downward through the soil profile, dissolving and transporting soluble nutrients, minerals, and organic matter from the upper layers (topsoil) to deeper layers or out of the soil system entirely.

Types of Leaching

• weak → 2:2 and 2:1

• moderate → 1:1

• intense → allitization → Al oxides

Weathering zones

• Allitization → intense leaching → humid tropics

• Kaolinization → seasonal leaching → seasonal tropics

• Smectization → weak leaching → arid, semi-arid, temperate

• Little Chemical weathering → hyper-arid

• Podzolization → boreal climatic zone

• Ice-cover → presence of ice sheets

Local factors affecting clay formation

• Topography and drainage → more drainage = more minerals removed = more weathered clay

• Rainfall → more rain = more weathering

• Parent material → type of clay is dependent on parent rock

• Age → older = more weathered

• Geological events → e.g. new magma → newer rock = less weathered soils

Anthropopedology

• the study of the impacts that humans have on soils

Types of human affected soils

• anthrosols → formed by long-term agriculture

• technosols → contain manmade material