Geology Department

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Geology 110 Syllabus

SEDIMENTARY ROCKS

 

Volcanoes Metamorphic Rocks

 

I. CLASSIFICATION

A. Detrital (clastic)--cemented fragments of pre-existing rocks
1. "Clastic" texture

2. Mechanical weathering--physical disintegration of rocks
B. Chemical and biochemical
1. Chemical--precipitate from water
a. Crystalline texture

b. Chemical weathering--chemical breakdown of rocks
2. Biochemical--form due to the activity of organisms
a. Clastic or crystalline in texture

II. WEATHERING

A. Mechanical weathering
1. Pressure release--rocks that are deeply buried are under stress, once stress is released, due to uplift and erosion, the rocks will crack
a. Average continental rocks
1 kilobar pressure = 4 Km depth
- Rock explosions in mines
2. Freeze/thaw--expansion and cracking due to freeze-thaw cycles

3. Burrowing of animals
a. 15,000 earth worms per acre of soil in Alabama

b. 15-20 tons of topsoil
4. Plant roots

5. Abrasion--rocks bumping into one another in rivers, streams, glaciers, deserts and shorelines .
B. Chemical weathering
1. Dissolution--rock material dissolves leaving no residue, everything ends up in solution
e.g. CaSO4 * 2H2O --- > Ca+2+ SO4-2+ 2H2O
gypsum solution

2. Carbonatization--CO2 is agent
e.g. H20 + CO2 --- > H2CO3
      rain + in atmosphere = carbonic acid
H2CO3 + CaCO3 --- > Ca+2 + 2HCO3-1
                calcite solution   + bicarbonate

3. Hydration--adds water
e.g. 2KAlSi3O8 + H2O + 2H+--- > 2K+ + Al2Si2O5(OH)4 + 4SiO2
     orthoclase plants/       kaolinite       solution
animals    (clay mineral)

4. Oxidation--O2 is the agent
e.g. 6H2O + 2Fe2+2SiO4 + O2--- > 4Fe+3(OH)3-1 + 2SiO2
                   olivine    limonite

5. Chemical stability and Bowens Reaction Series

III. CLASTIC SEDIMENTARY ROCKS

A. Tell us something about the environment of deposition

B. Sedimentary particles are derived from some "parent terrane" = provenance

C. Sandstone--"high - energy" environment = beach

IV. PATHWAY OF CLASTIC SEDIMENTARY ROCKS

A. Weathering

B. Transport--how particles reach a site of deposition
1. Fluid medium--water (liquid), ice, and wind
a. Three different mechanisms of transport by wind and streams
- Traction--rolling

- Saltation--bouncing

- Suspension--nearly floating
b. Particles are rounded and they lose mass

Roundness--measure of roundness of sedimentary articles
  • Angular
  • Rounded
  • Well-rounded
C. Deposition--depositional environments
1. Sorting--size distribution of grains due to selective transport

Grain size--basis of classification
pebble > 2mm conglomerate
sand 1/16 - 2mm sandstone
silt 1/256 - 1/16mm siltstone
clay < 1/256mm claystones or shales
Wind--pebbles are not moved, sands, silts, and clays are moved
a. Dust storm

b. Desert pavement
liquid water (fluvial)--variable sorter
D. Lithification--process of consolidating sediments
1. Cementation

2. Compaction

V. TYPES OF CLASTIC SEDIMENTARY ROCKS

A. Coarsest
1. Conglomerate

2. Breccia
a. Transport--conglomerate is more transported
B. Sand sized
1. Quartz sandstones (" orthoquartzite")
a. ~100% quartz

b. High-energy environment, like a beach

c. "Clean" or "mature" sandstone = well sorted, nearly monomineralic
2. Arkose
a. Feldspar clasts

b. Angular, poorly sorted

c. "Dirty" or "immature" sandstone

d. Provenance--granite or diorite = continental
3. Graywacke
a. Rock fragments

b. Formed around the bases of mountains

c. Provenance = core of mountain belt

d. Grey colored, clays

e. Dirty or immature
C. Silt sized--siltstone

D. Clay sized--shale
1. Fissility--a parting found in shales; the rx splits into tabular sheets along the fissility
Mudstone = siltstones + claystones vs shale

VI. PRIMARY STRUCTURES IN SEDIMENTARY ROCKS

Form during deposition
A. Stratification--layers in a sedimentary rx; called "beds", "strata", etc....

B. Turbidites--"graded beds" - fining upward sedimentary sequences

C. Ripple marks--periodic waves of sand
1. Flowing water or wind

2. Sands and silts

3. Cross beds--deposited in a nonhorizontal fashion

4. Sand dunes are like large ripples

5. Current flow

6. Two types of ripple marks
a. Asymmetrical

b. Symmetrical
D. Mudcracks--due to desiccation of mud

E. Fossils--evidence of past life
1. Mold

2. Cast

3. Trace fossils are most common

VII. COLOR OF SEDIMENTARY ROCKS

A. Reddish or pinkish = Fe2O3 (hematite)

B. Yellow or brown = FeO(OH) (limonite)

C. Grey or black = carbon, organic debris

VIII. CHEMICAL SEDIMENTARY ROCKS

A. Inorganic--precipitate from water
1. Evaporites= Louanne Salt (Jurassic Period ~ 140 m.y.)
1. Rock salt (NaCl)

2. Rock gypsum (CaSO4* 2H2O)
2. Playa--desert lake

3. Evaporite sequence--less soluble minerals precipitate first
normal
seawater
salinity
   
10x NaCl halite
10x CaSO4 anhydrite
4x CaSO4*2H2O gypsum
4. Lagoons--restricted exchange to the sea
a. Great Salt Lake, Utah

b. Gulf coast of U.S.
5. Limestones
a. Travertine

b. Micrite

c. Oolite
6. Secondary
a. Chert

b. Dolostone--forms due to diagenetic alteration of limestone
7. diagenesis--changes in sediments soon after their deposition
B. Organic
1. Limestones
a. Fossiliferous

b. Coquina

c. Chalk = Selma and Demopolis
Cretaceous Period ~ 120 m.y.
world-wide chalk deposits:
Dover, England

Paris basin
2. Coal--(increasing grade or rank)
a. Peat (low)

b. Lignite

c. Bituminous

d. Anthracite (high)

Carboniferous Period--280-350 m.y.

3. Chert--diatoms and radiolarians