Sed Strat Week 8 (cont)

chemistry

Solution

Dissolving of parent rock; addition of water and acids dissolves the rock into its original ions (limestone). Ions do not react with water

Common in polar solvents; most common reaction is carbonation, producing limestone pavement

Hydrolysis (decomposition reaction)

a molecule (primarily silicates) is cleaved into two parts by the addition of water. What results is H+ and OH- ions. Ions react with water instead of simply dissolving into solution, altering them

feldspar → kaolinite clay

Carbon dioxide in water (form of hydrolysis)

Carbon dioxide readily dissolves in water, producing a weak acid H+ donor (carbonic acid). This acid is consumed, producing alkaline solutions and consuming CO2

Pure water rarely acts as an

H+ donor, rarely resulting in full hydrolysis

Redox

atmospheric oxygen (O2) gains electrons and is reduced as mineral constituents lose electrons and are oxidized, producing new minerals

Oxidation is gain of O2, reduction is loss of O2

Oxidizing agent

removes electrons from another substance, and is reduced because it gains electrons (-)

Oxygen is an example

Reducing agent

transfers electrons to another substance, and is oxidized because it loses electrons (+)

Iron is an example

Hydration

process by which water molecules are added to a mineral to form a new mineral. Not hydrolysis. Accompanied by volume change

Plants enhance chemical weathering by

Retaining soil moisture, acidifying water by releasing CO2 and organic acids during decay

In weathering environments, minerals that are _____ are not stable, minerals _____ ARE

stable.

weathering, precipitating

Goldich series

Way of predicting stability of minerals at the surface. Inversion of Bowen’s series

A horizon (topsoil)

uppermost level of soil profile. Dark colored zone or organic accumulation that is decaying and mixing with mineral soil. Prone to leaching

B horizon (zone of accumulation)

Secondary level of soil profile. Composed of minerals with minimal organic content; most rock structures have been destroyed by soil processes

Enriched with cations (iron) and clay

C horizon

Lowest level of soil profile. Lies above bedrock (R layer) and can be deeply weathered, but relatively unaffected by soil-forming processes. Oxygen-poor

Accumulation of calcium and magnesium carbonates

Translocation (illuviation)

downward movement of clay and cations from A → B horizon. No leaching

Elluviation

Leaching of cations from A horizon, and moving them downward to B

Humification

transformation of raw organic matter (OM) into soil humus and soluble organic acids

Gleization

Reduction of iron under anoxic or anaerobic conditions to produce bluish to greenish gray waterlogged soil (gley). Seen in C horizon, preserves organic matter

Podzolization

downward chemical migration of Al, Fe, and/or organic matter within a soil profile

Lessivage

mechanical migration of clay-sized particles from the A to B horizon, producing a B horizon enriched in clay

Ferallitization

intense, deep weathering resulting in thick, uniform soil profiles depleted of exchangeable cations (tropics)

Calcification

accumulation of calcium (nodules) in the subsurface horizon near the depth of rainfall wetting in well drained soils of semiarid to subhumid regions

Salinization and desalinization

Accumulation or leaching of soluble salts (sulfates, chlorides) from salty horizons

Soil types

12 kinds; modern soils

Paleosols

buried or exhumed soil horizons that formed in the geologic past and represent ancient landscapes. May represent unconformities

Root traces

Evidence of exposure and colonization of plants. Branch and taper downward in webs, distinguishing them from burrows.

Evidence of paleosol, along with bioturbation

Cutan

Network of irregular cracks surrounded by more stable peds (aggregates of soil). Gives soil a hackly appearance

Glaebules (soil concretions)

Concentration of specific minerals to form hard, calcareous, ferruginous, or siderite nodules

Catena

Lateral variation in a paleosol or soil as a result of environmental change (rivers, elevation etc)