SCSC 301: Ch 2 Soil Formation

weathering

biological, chemical, or physical process that destroys or decomposes rocks

weathering usually leads to

formation of regolith or soil due to 5 forming factors

physical weathering factors

abrasions by water/ice/wind, temperature, plants/animals

chemical weathering factors

hydration/hydrolysis, dissolution/acid dissolution, redox, complexation

weathering causes rocks and minerals to turn to

sand > silt > clay

weathering causes stable minerals to

gypsum < calcite < dolomite < Al silicates < Fe/Al oxides

what soluble materials does weathering release

Ca2+, Mg2+, K+, N+, SO42+

nature of rock determines what from weathering process

rate and products

types of rocks (parent material)

igneous, sedimentary, metamorphic

igneous rock

formed when molten lava cools

what is used for classification of rocks

Si content

minerals with high what are more easily weathered

Fe and Mn

Sedimentary rock

deposition and recrystallization of weathering products from other rocks

metamorphic rock

igneous or sedimentary rocks transformed by high heat or pressure

liquid magma + cooling/crystallization

igneous rock

igneous rock + compaction/cementation

sedimentary rock

sedimentary + heat/pressure

metamorphic rock

igneous + heat/pressure

metamorphic rock

metamorphic + weathering

sediments

metamorphic + heat/pressure

liquid magma

rock

naturally occurring aggregate of minerals

mineral

naturally occurring substance that has a characteristic composition, highly ordered atomic structure, and specific physical properties

rock chemical composition

no definite chemical composition

mineral chemical composition

definitely chemical composition

Abundance of elements in earths crust

O, Si, Al, Fe, Ca, Mg, Na, K

of the abundant elements in earths crust, which are acids

Al, Fe

of the abundant elements in earths crust, which are bases

Ca, Mg, Na, K

silicates

form clays

oxides

very insoluble

carbonates

somewhat soluble

phosphates

very insoluble

sufates

relatively soluble

halides

very soluble

primary mineral

minerals that have not been altered chemically from their initial formation

secondary mineral

recrystallized products from the breakdown and/or alteration of primary minerals

where are secondary minerals formed

near surface of earth

rock + physical breakdown

primary minerals

rock + chemical breakdown

secondary minerals

primary minerals + chemical breakdown

secondary minerals

6 chemical weathering reactions

dissolution, acid dissolution, reduction/oxidation, hydration, hydrolysis, complexation

dissolution

some minerals will dissolve in water

acid dissolution

weathering is accelerated by acid

acid enhances what reactions

hydration and dissolution

reduction/oxidation

electron is transferred to a new compound

oxidation

atom loses an electron

reduction

atom gains an electron

OILRIG

oxidation is loss, reduction is gain

hydration

intact water molecules can change the structure of minerals

hydrolysis

water molecules are split into hydroxyl and hydrogen ions at the mineral surface and part is absorbed into the mineral

complexation

Organic acids complex or chelate many metal cations and remove them from the mineral

soil

dynamic natural body having properties derived from the combined effects of climate, biotic activities, as modified by topography, acting on parent material over periods of time

ClORPT

climate, organisms, relief, parent material, time

parent material sequence

lithosequence

climate sequence

climosequence

biota sequence

biosequence

topography sequence

toposequence

time sequence

chronosequence

what does parent material determine

type of clay, texture

what does soil texture affect

water movement, soil acidity, plant nutrients

parent material forms in place

residual

parent material transported by gravity

colluvial

parent material transported by river

alluvial

parent material transported by ocean

marine

parent material transported by lake

lacustrine

parent material transported by ice

glacial

parent material transported by wind

Eolian

parent material formed by accumulated plant debris

organic

where does residual parent material form

in place from underlying rock

residual in warm/humid climates

soils leached and oxidized

residual in cool/drier climates

colored similar to rocks they developed from

how is colluvial parent material formed

sediment moved downhill by gravity

how is alluvial parent material formed

flowing water carries sediments deposited in 3 general classess

how do alluvial soils range

wide texture variety depending on energy of water transporting sediment

3 basic types of alluvial deposits

floodplain, alluvial fan, delta

marine parent material formation

beach or shore deposits

marine texture

vary from sandy to clayey

marine layering

horizontal

how much of texas soil is marine

1/3rd

lacustrine parent material formation

lake or shore deposits

lacustrine sediments

rich in clay and silts

lacustrine appearance

layered from annual deposition

glacial parent material formation

glaciers gouged earth and accumulated soil/rock

glacial till

materials deposited in place by ice

glacial till size

varies from boulder to clay

glacial outwash

coarse-grained alluvium, mostly gravel and sand, from flowing melt water

eolian parent material formation

wind picks up material and deposits it elsewhere

organic deposits development

wet areas where plant growth exceeds rate of residue decomposition

how does climate influence soil formation

acting on parent material controlling the nature and intensity of weathering, influences biota

two main variables of climate

effective precipitation, temperature

how does chemical weathering happen

water penetrates regolith and then translocates soluble weathering products out of profile

effective precipitation

Amount of rainfall that is actually penetrating into the regolith

increasing effective precipitation generally does what

increases clay/organic matter/acidity, lowers ratio of Si/Al

what does temperature increase

biochemical reactions

soil organisms influence

organic matter, biochemical weathering, profile mixing, soil erosion

topography

differences in elevation, slope and landscape position

steeper terrains have

shallow poorly developed soil profiles

how does topography affect vegetation

affects where plants grow by affecting water movement

what do topography and vegetation do together

affect soil formation

slope aspect

south facing slopes are warmer and lower in moisture than north facing

salt build up

in arid and semi-arid regions, salts accumulate in low lying areas