Post on 05-Jan-2016
Color, Trace Fossils, Weathering, and Soils
• Causes of Color
• Common Trace Fossils
• Weathering Processes
- Physical Weathering
- Chemical Weathering
• Weathering Products
- Soils
- Paleosols
Text: Manual p. 15, 89; Boggs Ch.1, 114-122
Causes of Color
yellow goethite, jarosite cement
brown Fe-oxides cement
red Fe-oxides cement, coatings
purple hematite (coarse) cement
pink K-feldspar, hematite cement, framework
white kaolinite, gypsum, no organics
cement, bleaching
green glauconite, chlorite, illite cement, framework
black organics, oil, heavy minerals, pyrite, Mn-oxide
cement, framework
color mineral occurrence
Color, Trace Fossils, Weathering, and Soils
• Causes of Color
• Common Trace Fossils
• Weathering Processes
- Physical Weathering
- Chemical Weathering
• Weathering Products
- Soils
- Paleosols
Text: Manual p. 15, 89; Boggs Ch.1, 114-122
Trace Fossils
Ichnofacies (Boggs, p. 118)
En
viro
nm
ent
Color, Trace Fossils, Weathering, and Soils
• Causes of Color
• Common Trace Fossils
• Weathering Processes
- Physical Weathering
- Chemical Weathering
• Weathering Products
- Soils
- Paleosols
Text: Manual p. 15, 89; Boggs Ch.1, 114-122
Physical Weathering
• no change in mineral / chemical composition
Physical Weathering: Break-down rock into smaller pieces
Physical Weathering
1. Granite
2. Partially-Weathered Granite
3. Granite Grus
• roots / lichens • freeze-thaw
• wet-dry
• hot-cold
Physical Weathering
Physical Weathering
Physical Weathering
Exfoliation
Enchanted Rock batholith
http://www.governor.state.tx.us/
Physical Weathering
Spheroidal Weathering
Costa Rica
Physical Weathering
Painted Desert, Utah
Gullying
Bryce Canyon
Physical Weathering
Chemical Weathering
• alter chemical and mineral composition
• disrupt fabrics
Chemical Weathering: Dissolution and/or crystallization of new minerals
Chemical Weathering
Feldspar + H+ + H2O kaolinite + silicic acid + K+ or Na2+
Hydrolysis: H+ breaks down silicates
Chemical Weatheringpyrite
Oxidation / Reduction: O alters Fe silicates and S minerals
http://web.wt.net/~daba/Mineral/index.htm
pyrite
pyrite hematite
silicate mineral Fe-oxide
Chemical Weathering
Fe-oxide Stains
(E. McBride)
Bastrop, TX
Chemical Weathering
Solution: dissolve in water
pyrite
http://www2.nature.nps.gov/(E McBride)
Limestone Karen Rills
calcite / dolomitegypsumhalite
Physical/Chemical Weathering
bench
slopecliff
Differential Weathering
Grand Canyon
Physical/Chemical Weathering
Differential Weathering
“Toadstools” Utah
Physical/Chemical Weathering
Differential Weathering
burrows
Color, Trace Fossils, Weathering, and Soils
• Causes of Color
• Common Trace Fossils
• Weathering Processes
- Physical Weathering
- Chemical Weathering
• Weathering Products
- Soils
- Paleosols
Text: Manual p. 15, 89; Boggs Ch.1, 114-122
• clastic sediments
• residues (source rock)
• secondary minerals
• ions in solution
Weathering Products
Soils and Sed. Rocks
Weathering Products
Terrigenous Clastic Sediments
Weathering Products
EvaporitesDeath Valley, CA
www.geol.binghamton.edu/faculty/lowenstein/dv/deathvalley.html
Chemical Sediments
Cements
(M. Campbell)
Soils
• mineral residues
• rock fragments
• organics
Horizons
Soil Profile
http://www.cjnetworks.com/
Soils
Horizons
Soil Profile
http://www.cjnetworks.com/
O - organic matter
A - topmost mineral horizon
E - (eluvial) leaching
B - (illuvial) accumulation
C - weathered bedrock
R - bedrock
Soils
• bedrock
• time
• climate
• topography
Pedocal Soils
Pedalfer Soils
30 inches of rain per year
http://www.mhhe.com/earthsci/geology/mcconnell/wss/soil.htm
Soils
Soils
• color
• texture
• structure
• consistency
• contacts
SoilsTexture
columnar
crumb platy
blocky
SoilsStructure
Classes Description
Non-plastic A roll 4 cm long and 6 mm thick that supports its own weight held on end cannot be formed.
Slightly plastic A roll 4 cm long and 6 mm thick can be formed and, if held on end, will support its own weight. A roll 4 mm thick will not support its own weight.
Moderately plastic A roll 4 cm long and 4 mm thick can be formed and will support its own weight, but a roll 2 mm thick will not support its own weight.
Very plastic A roll 4 cm long and 2 mm thick can be formed and will support its own weight.
Consistency: Plasticity
Soils
Standard USDA Soil Description Form
Soils
Color, Trace Fossils, Weathering, and Soils
• Causes of Color
• Common Trace Fossils
• Weathering Processes
- Physical Weathering
- Chemical Weathering
• Weathering Products
- Soils
- Paleosols
Text: Manual p. 15, 89; Boggs Ch.1, 114-122
Paleosols
Paleosols
• colors (red, green, purple)
• root casts
• caliche
• vertical streaks
• mottled bedding
Paleosols
Paleosols Painted Desert, AZ
Root Casts
Paleosol, near Hunt, TX
Paleosols
Paleosols
vertical streaks (bleaching)
(E. McBride)
Paleosol Bastrop, TX
Paleosols
(E. McBride)
“terra rossa” fill
Reference
Soil Survey Manual, 1993, Soil Conservation Service, USDA Handbook 18.