Chapter 6 Flashcards
Define weathering, parent material, soil and erosion.
-Weathering: Physical breakdown and chemical alteration of earth material
•From exposure to the atmosphere, hydrosphere, amd biosphere
- Parent material: Rocks and minerals acted on by weathering
- Soil: Modified weatheres materials
-Erosion: Removal of soil and rock by geological agents such as running water, wind, glaciers, and marine currents, from their source area
•Deposited as sediments, which is the raw material for sedimentary rocks
•Sedimentary rocks make up only 5% of the crust, but cover two thirds of Earth’s surface and most of the seafloor
Sedimemtary rocks cover how much of the Earth’s surface?
Two-thirds
What is differential weathering? What is the difference between mechanical and chemical weathering? Do they proceed at the same time?
-Occurs at different rates even in the same area and results in irregular surfaces.
•Mechanical and chemical weathering proceed simultaneously
- Mechanical weathering: Disaggregation of Earth materials by physical forces into smaller pieces that retain the compostition of the parent material
- Chemical weathering: Decomposition of rocks by chemical alteration of parent material
- They proceed simultaneously
List and explain the different types of mechanical weathering.
-Frost action
• repeated freezing and thawing of water in cracks and pores of rocks
• water expands by about 9% when it freezes
• widening and extending of cracks in rocks by frost wedging
•Talus: Angular pieces of rocks that accumulate at the base of the slope
-Pressure release
• outward expansion of rocks form at depth that are under tremendous pressure
~ outward expansion occurs when the rock is exposed at the surface and pressure is released
~ results in sheet joints: Fractures parallel to the exposed rock surface
•Exfoliation domes: Large round Masses left when she joint bounded slabs of rock slipped off the parent rock
-Thermal expansion and contraction
•Rock volume changes as rocks heat up and then cool dowm
- When heated rocks more on the outside than the inside
- Differential expansion of minerals: Dark minerals absorb heat faster than light colored ones
- Surface expansion can cause fracturing
-Salt crystal growth
• formation of crystals exerts enough force to widen cracks and dislodge particles
• Easy in porous rocks such a sandstone
~ Also occurs in other rocks with an interlocking mosaic of crystals
• Takes place mostly in the hot arid regions
-Living organisms
• Burrowing animals mix soil and sediment particles
• root wedge themselves into cracks in rocks and wide in them

What are the agents of chemical weathering?
• Atmospheric gases • Water • Acids • Organisms ~ Wax with lichens undergo more change than those without
Define solution
-ions of a substance separate any liquid and a solid substance dissolves
Why is water an excellent solvent? What do acid do to most minerals? Give an example
-Water is an excellent solvent because its molecules have an asymmetric shape.
-Acids breakdown most minerals
-Example: calcite
•Water can be made acidic by dissolving the ions of carbonic acid
What is oxidation reaction? What does it form when water is present? What mineral group is oxidation important in?
- Reaction with oxygen to form oxides
- Reaction forms hydroxides when water is present
- Important to ferromagnesian silicates
What is hydrolysis? In what direction does the alteration of rocks and minerals occur?
•H+ and O H- of water react with a mineral’s ions
~Hydrogen ions actually replace positive ions in minerals
- Example: Potassium feldspar produces clay minerals and soluble salts
- It occurs from the outside inward
List and explain the five factors that control the rate of chemical weathering
-Presence of fractures
•Fractures promote chemical weathering
-Surface area
•Small particles have larger surface areas compared to their volume than do large particles
-Climate
•Temperature, rainfall, and evaportation
~Conditions affect the presence of vegetation and animal life
-Parent material
•Some minerals are more susceptile
~Mineral stability is the opposite of the minerals’ order of crystallization in Bowen’s reaction series
-Spheroidal weathering
•Corners and edges of rocks are more affected by weathering
Define regolith, soil, and humus
- Regolith: Layer on Earth’s land surface consisting of sediment, pyroclastic materials, and the residue formed in place through weathering
- Soil: Regolithconsisting of air, water, and organic matter that supports vegetation
•Good farming soil
• Compries 45% solid, weathered particles
~Includeds sand and silt sized mineral grains and clay minerals
•Rest of its volume consists of voids filled with air or water or both, along with humus
-Humus: Carbon that forms by bacterial decay of organic matter
What is the difference between residual and transported soil
- Residual soils: Accumulated weathering residue is converted to soil in the same area of its formation
- Transported soils: Weathering residue is transported elsewhere, deposited, and then converted to soil
Define each of the five soil horizons in order from top to bottom
-From top to bottom, soil horizons are designed O, A, E, B, and C
•Boundaries between horizons are transtional, and in some cases E is not present
•Horizon O is only a few centimeters thick and comprises organic matter
•Horizon A is also called topsoil
~More organic matter than B, C, and E
~Intense biological activity because plant roots, bacteria, fungi, and worms are abundant
~Mature soil consists mostly of clays and chemically stable minerals
•Horizon E
~ Contains little carbon with most of the small particles removed
~Results from eluviation, a process of leaching of minerals by downward moving soil water
•Horizon B or subsoil
~Zone of accumulation: Soluble materials from horizon A form irregular masses
~Fewer organisms and less organic matter than horizon A
•Horizon C
~Little organic matter
~Partially altered bedrock grades down info unaltered bedrock
~Minerals and rock fragments of parent material are easy to identify here
Discuss the factors involved in soil formation
-Climate: Is most important as it affects temperature and precipitation
•Precipitation affects leaching of soil
•Soluble minerals are taken into solution and precipitated in horizon B as irregular masses of caliche
What is a laterite soil? Where are they found?
-Laterite soil: Red soils that are composed largely of aluminum hydroxides, iron oxides, and clay minerals
•Vegetation depends mostly on the surface layer of organic matter
-Found in the tropics, where chemical weathering is intense
What does soil fertility depend on?
-Soil fertility depends on organisms
•They provide humus when they die and decompose by bacterial action
•Burrowing animal mix soils and create channels for gases and water
What is relief?
-Relief: Difference in elevation between high and low points in a region
•Climate changes with elevation
Discuss the two ways that slope influences soil formation
-Slope influences soil formation in two ways:
•Slope angle: Steep slopea have little
or no soil
~Weathered materials erode faster than soil-forming processes operate
•Slope direction: Effects of temperature and sunlight on the soil
What is soil degradation? Discuss the three processes involved in soil degradation
-Any process that removes soil or reduces its productivity
•Includes ersion, chemical deterioration, and physical changes
*The three processes are:
-Erosion: Ongoing natural process that humans accelerate
• Human practices that cause erosion: Plowing, overgrazing, deforestation, and over exploitation for firewood
• Erosion by running water: Sheet erosion and rill erosion
~ Real erosion forms tshallow channels called reels and deeper channels called gullies
-Chemical deterioration
• Nutrient depletion from intensive agriculture
•Salinization: Increased salt concentration in soil
•Contamination with toxic substances
-Physicsl deterioration
•Soil is compacted by weight of heavy machinery and livestock
~Plants have a more difficult time emergent from such soil
~ Water does not readily infiltrate, causing greater runoff
Discuss the relationship between weathering and various natural resources
• Soil supports agriculture and is also important economically
• Laterite sometimes produce bauxite, an aluminum ore, that accumulates in a horizon B
• residual concentrations from chemical weathering form deposits of:
~Iron
~Manganese
~Nickel
~Phosphate
~Tin
~Clays
~Diamonds
~Gold
Define sedimentary rocks detrital and chemical sediments
-Sedimentary rocks
• Any rock made of sediment
• Weathering, erosion, and deposition or fundamental to the origin of sediments and sedimentary rocks
-Detrital sediment
•Solid particles from other rocks
~Detrital sediment is transported some distance from its source
-Chemical sediment: Comes from chemicals derived from rocks that were extracted from solution by inorganic chemical processes or by the activities of organisms
•Chemical sediment forms in the area where it is deposited
What is the depositional environment?What are three depositional settings?
-Depositional environment: Site where physical, biologic, and chemical processes yield a distinctive sedimentary deposit
-Three depositional settings
•Continental
•Transitional (on or near seashores
•Marine
Discuss the process of lithification be sure to equal the definition of compaction and cementation
-Lithification: Turning sediments into sedimentary rocks by compaction, cementaion, or both
•Compaction: Reduction of of the volume of the deposit and core spaces
•Cementation: Involves the precipation of mineral in pore spaces
~Common cements: Calcium carbonate and silicon dioxide
Define a detrital (clastic) sedimentary rock. What are clast? What is the relationship between transport distance and grain size?
-Detrital (clastic) sedimentary rocks:
•Made up of solid particles such as gravel, sand, silt, amd clay
• Clastic texture: Composed of particles or fragments called clasts
• Range from very course to very fine
• Boulder, cobble, pebble, sand, silt, and clay
• As transport distance increases, grain size decreases
- Clastic texture: Composed of particles or fragments called clasts
- As transport distance increases, grain size decreases
