1. Weathering
Weathering: physical and chemical breakdown of earth material (rocks and minerals) at or near the surface.
Includes disaggregation of parent materials, erosion and transportation of resulting clasts and sediments, and leads to deposition and lithification of these materials
Differential weathering: uneven weathering of heterogenous materials that leads to unique geologic structures such as hoodoos and arches

2. Mechanical Weathering
Physical processes cause weathering several ways:
Frost action: freezing and thawing in cracks and pores in rocks; high altitudes and latitudes
Pressure release: expansion of uplifted and exposed intrusive rocks; exfoliation domes such as Stone Mountain, GA, rock bursts in mines
Thermal expansion/contraction: differential reaction by rocks and minerals to daily or seasonal temperature changes
Salt crystal growth: occurs primarily in hot, arid regions
Biological actions: burrowing, root wedging

3. Chemical Weathering Processes that chemically alter parent material:
Solution/dissolution: occurs when ions separate in water due to the solvent properties of H20, example: dissolution of calcite in limestones by groundwater
Oxidation: occurs when oxides are formed by mineral ions combining with oxygen, example: Fe + O = hematite (rust)
Hydrolysis: free ions of H+ and OH- in water can replace ions in minerals, which are liberated to undergo oxidation, example: orthoclase weathers to kaolinite by loss of Al ions

4. Chemical Weathering
Chemical weathering operates on the surface of rocks and minerals, and can be observed in the difference between old and fresh surfaces of broken rock, controlled by:
Fractures: produce increased surface area in equal volume of rock
Climate: presence of water greatly accelerates weathering. Humid, warm climates have high weathering rates
Composition: stable minerals are resistant to weathering, example: Quartz; less stable minerals rapidly weather (Bowen’s reaction series)
One unique form of weathering is spheroidal weathering: rocks often weather into spherioids due to uneven weathering. 3X at points compared to flats

5. Soil Regolith: sediments that cover the Earth’s land surface
Soil: regolith composed of weathered minerals, air, water, and organic material; supports vegetation
all land-dwelling organisms dependent on soil
good farming soil composed of sediments (sand, silt, and clay), air, water, and humus.
Humus: carbon derived by bacterial decay of organic material

6. Soil profile Soil forms in characteristic layers:
Horizon O: thin subaerial layer, predominately organic material, including humus
Horizon A: weathered unstable minerals that provide nutrients, remnants of stable minerals such as quartz grains, a zone of biological activity.
Horizon B: where minerals leached from above accumulate (zone of accumulation)
Horizon C: unaltered to altered parent material

7. Sedimentary Rocks
Composed of sediments from weathering, chemical precipitation, and clastic material including fossil fragments
Sediments are produced by erosion or chemical means, then transported by physical processed such as wind, water, and gravity, and deposited as loose aggregates of particles.
Sedimentary particles are classified according to size: > 2 mm = gravel, 1/16-2 mm = sand, 1/256-1/16 mm = silt, < 1/256 = clay

9. Sedimentary Rocks
Depositional environment: describes the basin in which sediments are deposited, including: stream beds, lake bottoms, river deltas, coastal beaches, continental shelves, and sand dunes
Variations in transport duration and conditions produce characteristic sedimentary particles; abrasion reduces particle size, rounding wears away sharp angles, and sorting occurs during deposition
After deposition, sediments can be lithified by compaction and cementation to produce sedimentary rocks

10. Depositional Environments

11. Rounding of Sediments

13. Sedimentary Rocks
The most common cements in sedimentary rocks are the minerals calcite and silica, which are derived from weathering of rocks and transported by water
There are two major types of sedimentary rocks:
1) DETRITAL SEDIMENTARY ROCKS-composed of solid particles (detritus) derived from weathered parent rocks, classified according to size and include:
conglomerate: composed of gravel-sized particles, breccia refers to a conglomerate with angular clasts
sandstone: composed of sand-sized clasts of any composition, most common clast is quartz
mudrock: general term for sedimentary rocks with silt to clay sized clasts, varieties include: siltstones, mudstones, claystones, fissile = shale

14. Sedimentary Rocks
2) CHEMICAL SEDIMENTARY ROCKS: have a chemical origin and include:
limestone: the most common carbonate rock, composed of carbonate mud usually precipitated from shallow, warm marine waters, and often containing fossil fragments
coquina: type of limestone composed of fragmented seashells
oolitic limestone: contains small, spherical grains (ooids), concentric rings of calcite precipitated around a nucleus

15. Chemical sedimentary rocks
Other chemical sedimentary rocks are:
evaporites: composed of dissolved substances precipitated from evaporated water, examples: halite (NaCl) and gypsum (CaSO4.2H2O)
chert: microcrystalline quartz deposited as beds of microfossils (radiolarians and diatoms), often re-crystallized, includes flint and jasper

16. Sedimentary Rocks
Coal: derived from compressed, altered land plant remains:
peat: barely altered plant material
lignite: more fully altered, low grade coal (~70% carbon)
bitumin: or bituminous coal, higher grade (~80%), with little remaining evidence of plant material
anthracite: high grade, high carbon coal (up to 98% carbon)

17. Sedimentary structures
These are textural features formed by variation in deposition, and include:
bedding/strata: horizontal layers
graded bedding: vertical grain size change
cross bedding: bedding at angles to depositional surface
ripple marks: small dunes preserved on sand deposits, formed by moving fluids (air, water)
mud cracks: indicative of subaerial drying

18. Fossils remains of ancient life, found in sedimentary rocks
trace fossils: tracks, prints
body fossils: altered or unaltered remains of body parts such as bones, teeth or shells
microfossils: microscopic body fossils
biostratigraphy: correlation of sedimentary rocks using fossils

19. Resources in Sedimentary Rocks
clay, sand, and gravel
evaporite minerals: salt, gypsum, fertilizers
placer deposits: gold, silver, uranium
coal
petroleum/natural gas
iron (b.i.f.s)