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.