weathering, soils and sedimentary rocks

why is weathering important?

provides sediment, contributes to soil formation, wears down mountains and shapes landforms

physical weathering

rocks→ smaller rocks. no change in chemistry. increase in surface area

chemical weathering

decomposition of rocks. bonds break and reactions alter/stabilize minerals

2 main processes of physical weathering

1) ice wedging

2) pressure unloading (exfoliation) (like an onion)

regolith

rock and mineral fragments produced by weathering that sit on top of solid rock

3 main processes of chemical weathering

1) dissolution

2) hydrolysis

3) oxidization

dissolution (chem weathering)

minerals completely dissolve into soluble ions in the reserve of water

hydrolysis (chem weathering)

minerals react with water to form new clay minerals and dissolved ion in water

oxidation (chem weathering)

minerals w iron react with oxygen → iron oxide

biological weathering(examples)

can be both phys and chemical. eg: tree roots, animal burrowing (physical) and lichens (chemical)

karst topography

landscape formed when acidic water dissolved limestone creating underground drainage systems, caves and sinkholes etc

2 primary controls of weathering rates

1) rock type/mineral composition

2) climate (temp, precipitation)

what is soil

thin layer covering most land surfaces. sits on regolith. bridge between life and rocks (plants grow in it)

why is soil important?

1) medium for plants to grow

2) ecosystem habitat (bugs!)

3) nutrient recycling

4) water filtration and storage

5) engineering medium?

what is soil made of (from most to least)

1) mineral matter 45%

2) water (25%)

3) air (25%)

4) organic matter (5%)

The 5 soil horizons:

o: organic matter

a: organic and mineral matter

e: eluviation and leeching (weird white silica layer with barely by organic matter)

b: zone of accumulation (clays, oxides, carbonates) red/brown

c: weathered rock

5 stages of sedimentary rock formation

weathering, transport, deposition, burial, lithification (compaction and cementation)

ways that sediments get from source to deposition basin

• rivers/streams

• mass wasting?

• glaciers

• wind

• ocean currents

clastic sedimentary rocks

formed from fragments of rocks or minerals

what does clast shape tell us? (round vs angular)

how mature the rock is (more round = more mature. travelled a farther distance)

compaction (lithification of sedimentary rocks)

as pile of sediment grows water is squeezed out and grains are forced closer together

cementation (lithification of sed rocks) (most common types?)

minerals from water stay as water is squeezed out. forms a cement that binds grains together (usually calcite or quartz )

chemical sedimentary rocks

formed from precipitation of dissolved ions in water. can be biogenic (eg corals→ limestone) or non-biogenic (eg evaporites: halite, gypsum)

atolls

coral reef forms around volcano. volcano sinks leaving pretty circular limestone island

deep sea chemical sedimentary rocks (example)

slow accumulation of silica from skeletons of microorganisms (eg chert “siliceous ooze”)

organic sedimentary rocks (example)

formed from dead remains of plants or animals. eg: coal

why are sedimentary rocks important?

resources: clay, groundwater, oil, gas, fossils

a record of past earth’s conditions