Weathering, Erosion & Soils / Sedimentary Rocks

This set goes over both the soils pptx and the sedimentary rocks pptx. It ignores the slides that the professor told us won't be on the test. This set has 140 flashcard, but the test will only have 20 questions.

As soon as a rock is on the surface…

It is exposed to the elements, and the various processes of weathering and erosion begin to affect it

Weathering

The physical breakdown and chemical alteration of Earth materials as they are exposed to the atmosphere, hydrosphere and biosphere

Erosion

Wearing or transporting away of soil and rock by other geologic agents, such as running water

Differential weathering

Weathering that occurs at different rates on rocks, thereby yielding an uneven surface

Why does differential weathering occur?

Rocks are not homogeneous all throughout. Differential weathering and differential erosion can combine to create fascinating features

Parent material

The rock being acted upon by weathering, which is disaggregated to form smaller pieces

How do you weather and erode rock?

The eroded material is transported elsewhere by water, wind, glaciers and marine currents

What does weathered and eroded rock turn into?

Sediment, which is the raw material for sedimentary rocks

At what point does eroded material become sediment?

The moment it is deposited

What are the types of weathering?

Mechanical and chemical

All surface and near-surface materials weather

True statement

Mechanical weathering

Physical forces break earth materials into smaller pieces that retain the composition of the parent material

Example of mechanical weathering

Granite might yield smaller pieces of granite, or individual grains of quartz, k-spar, plagioclase or biotite

Frost action

Involves water repeatedly freezing and thawing in cracks and pores of rocks

Why is frost action such an effective way to weather?

Water expands ~9% when it freezes, exerting great force on the rock

Frost wedging

The widening and extending of the cracks in the rock by repeated freezing and thawing

Pressure release

Mechanical weathering that consists of a process in which rocks that formed under pressure expand on being exposed at the surface

Exfoliation dome

Mechanical weathering that consists of a large, rounded dome of rock resulting when concentric (multiple) layers of rock are stripped from the surface of a rock mass

Thermal expansion and contraction

Mechanical weathering that consists of the volume of rocks changing as they heat up and cool down

Salt crystal growth

Mechanical weathering that consists of the formation of salt crystals widens cracks and dislodge particles, usually found in arid regions and coastal areas

Biomechanical

Mechanical weathering that consists of animals burrowing underneath or into, bringing up rock and soil to further weathering

What is a common result of biochemical weathering?

Plant roots grow into cracks in the rock and widen them

Chemical weathering

Changes that affect the composition of parent material

What is an example of chemical weathering?

The chemical and structural alteration of k-spar and plagioclase into the clay minerals

What agents are included in the process of chemical weathering?

Water, oxygen, acids and organisms

What is an example of the involvement of organisms in the process of chemical weathering?

Lichens derive their nutrients from rock, furthering chemical weathering

Solution

Chemical weathering that consists of ions separating in a liquid and the solid dissolving

What is an example of chemical weathering via solution?

Salt in water, and CaCO₃ in acid

Oxidation

Chemical weathering that consists of reactions with oxygen to form an oxide

What is an example of chemical weathering via oxidation?

One or more metallic elements combined with oxygen; 4Fe + 3O₂ = 2Fe₂O₃ → iron oxide (rust) hematite

Hydrolysis

Chemical weathering that consists of a reaction between a mineral’s ions and hydrogen, and hydroxyl (OH)

What is an example of chemical weathering via hydrolysis?

K-spar turns into the clay mineral, kaolinite clay, through hydrolysis

Why are ancient tombstones and buildings affected by chemical weathering?

They were built with limestone and acid rain reacts with it, eroding it over time

What are much better rocks to build tombstones and buildings?

Granite, diorite and quartzite

Regolith

A layer of sediment, pyroclastic material and residues formed in place by weathering that covers much of the Earth’s land surface

Soil

The part of the regolith that contains air, water, and organic matter that can support vegetation

What are the types of soil?

Residual and transported

Residual soil

Soils formed in place from the weathered material, usually located on top of the parent material being weathered

Transported soil

Soils formed after the weathered material was transported elsewhere, deposited, then converted into soil. Usually moved by wind and water

What does the soil profile consist of?

O, A, E, B and C horizons

Which horizons form soil?

O, A, E and B horizon

Which horizons form the bedrock?

C and R horizon

O horizon

Loose and partly decayed organic material, usually only a few centimeters thick

A horizon

Mineral matter mixed with some humus. It is mostly organic material and has intense biological activity, also called “topsoil”

E horizon

Zone of eluviation: process of leaching minerals by downward-moving water

B horizon

Accumulation of clay, iron, and aluminum from above. It has fewer organisms, also called “subsoil”

C horizon

Partially altered parent material and bedrock that usually grades downward into the unaltered parent material

R horizon

Unaltered parent material

What is the most important factor that controls soil formation?

Climate

Soils in humid regions tend to be…

Dark due to abundant organic material

Soils in semi-arid to arid regions have…

Less organic material and unstable minerals due to a lack of water

CaCO₃ can precipitate out of the soil as irregular masses called…

Caliche

Alkali soils supports little or no vegetation due to…

The precipitation of sodium salts in arid regions where water evaporated

Laterite

A very red soil that is formed in the tropics where chemical weathering is intense and leaching of most minerals is complete

What is laterite composed of?

Al-hydroxides, Fe-oxides and clay minerals

Why can laterite soil support lush vegetation but not agriculture?

There are no nutrients in the soil

Soil degradation

Any process that removes soil or makes it less productive, which is a serious problem that includes erosion, chemical deterioration and physical changes

Although erosion is a natural process…

Humans can accelerate the problem

How do humans accelerate erosion?

Removing natural vegetation by plowing, overgrazing exploitation of firewood, deforestation, etc.

What are the main drivers of erosion?

Wind and water

What can wind lead to?

Sheet erosion, rill erosion and gullies

Which erosion channel can be plowed over?

Rills

Which erosion channel cannot be plowed over?

Gullies

Chemical deterioration

When the soil is depleted of its nutrients and productivity decreases due to insufficient and inefficient use of fertilizers and clearing off of natural vegetation

Types of chemical deterioration

Salinization, pollution and compaction due to machinery and livestock

Salinization

Occurs when the concentration of salts increases, making it unfit for agriculture

Where does bauxite (Al-ore) form?

B horizon

Where can Banded Iron Formations (BIFs) be found?

In sedimentary iron deposits around the Great Lakes

Why can kaolinite deposits be found in the South, mainly in Georgia and Mississippi?

They accumulated a lot of k-spar overtime in the soil

What natural resources can be found in the soil?

Concentrations of iron (Fe), manganese (Mn), nickel (Ni), phosphates, tin, etc.

What marks the beginning of sedimentary rocks?

Weathering

What is involved in the origins of sedimentary rocks?

The physical disintegration and chemical deposition of pre-existing rocks (igneous, metamorphic and sedimentary)

Particle sizes

Gravel, sand, silt and clay

Mud

Mixture of silt and clay

Detrital sediment

Solid particles derived from other rocks

Chemical sediment

Chemicals derived from other rocks by means of inorganic chemical process, such as evaporating seawater, activities of organisms (CaCO₃), etc.

Diagenesis

Wide range of changes that affect sediments during their progress to become sedimentary rocks

When does diagenesis occur?

After the sediments are deposited and during lithification, but before any type of metamorphism

What are the diagenesis processes?

Mechanical, chemical and organic

Mechanical diagenesis

Physical re-working of the sediments

Chemical diagenesis

Precipitation, such as rain

Organic diagenesis

Bioturbation, such as when creatures burrow their way through sand

Rounding

As sediments are being transported, the particles collide and abrasion wears away the sharp corners

Sorting

As sediment is transported, the particles will differentiate themselves based on size

Where does sorting range from?

Poorly to very well

Well-sorted rocks tend to have…

More permeability

Poorly sorted rocks tend to have…

Low permeability

What do porosity and permeability control?

Water, oil and gas movement through the reservoir rock

Porosity

The open space between the grains

Permeability

The “connectedness” of the open spaces within a rock and the ability of fluids to move through it

Few spaces leads to…

Low porosity

Unconnected pore spaces leads to…

Medium porosity, impermeable

Connected pore spaces leads to…

High porosity, permeable

What is the first step in the process of sedimentary rock formation?

Erosion, weathered material is eroded and transported

What is the second step in the process of sedimentary rock formation?

Deposition, the transported material is deposited as loosely packed sediment

What is the third step in the process of sedimentary rock formation?

Compaction, overburden pressure and weight compact the sediments

What is the fourth step in the process of sedimentary rock formation?

Cementation, the now tightly packed sediments are cemented together

What are the most common cements?

Carbonate and silica

What agents can cement a sedimentary rock?

Siderite, limonite, silica, hematite and carbonate

What are the main types of sedimentary rocks?

Detrital, chemical and biochemical