SedStrat

sedimentology vs. stratigraphy

Sedimentology:

• Classification, origin, and interpretation of sedimentary rocks

• Concerned with physical (textures, structures, minerology), chemical, and

biological properties of the rocks

Stratigraphy:

• Science of rock strata

• Age relationships and chronological arrangement of strata, successions

(stacking patterns), correlation and stratigraphic order of beds

3 types of sedimentary rocks

siliciclastic

chemical/biochemical

carbonaceous

weathering

the in situ decomposition of rocks and minerals at the Earth’s surface

6 components of physical weathering

 freeze-thaw

 thermal expansion

 salt weathering

 wetting and drying

 release of overburden (unloading)

 other processes (biological activity, etc.)

Processes of Chemical Weathering (6)

hydrolysis

hydration and dehydration

oxidation

solution

ion exchange

chelation

3 products of weathering

1. Source rock residuals

2. Secondary minerals

3. Soluble minerals

humus

decayed remains of animal and plant life (organic matter in soil)

Controls of Soil Formation (5)

climate

time

parent material

plants and animals

slope

soil profile: O zone, A zone, E zone, B zone, c zone

O zone: loose and partly decayed organic matter

A zone: mineral matter and humus

E zone: zone of eluviation and leaching

B zone: accumulation of clay transported from above

c zone: partially altered parent material

paleosols and how to recognize them

paleosol: buried, fossilized soil

diagnostic features: root traces, soil horizons, peds and cutans

peds and cutans

network of irregular planes formed by clay skins (cutans) that surround more stable aggregates of soil (peds).

glaebules

hard chemical concentrations of minerals in a soil

flow type depends on (3 things)

-Roughness of the bed

– Velocity of the fluid

– Viscosity of the fluid

Reynolds number tells you…what two values?

less than 500=laminar

greater than 2400=turbulent

unknown between the two values

viscous sublayer

Molecular adhesion causes particles of the flow to remain stationary right above the boundary. Successive layers of the fluid slide over lower layers.

boundary layer

the region of the flow that is slowed due to frictional resistance from the bed/sides of the flow

-Most sediment transport occurs within this zone

transport (erosion) requires two things:

entrainment

sustained movement

4 sediment transport pathways

Bedload (water):

• Constant or intermittent contact with the bed

Suspended Load (water):

• High above the bed

• Settling velocity < shear velocity

Dustload (wind)

Ice- coarse poorly sorted material

4 major dispersive forces in gravity flows

1. Turbulence

2. Upward escape of fluid

3. Grain-to-grain interactions

4. Support by a cohesive matrix

turbidity current sediment concentrations

Low Sediment Concentration-(~ < 1 % sediment by volume)

High Sediment Concentration-(~1 - 10 % sediment by volume)

bouma sequence

low to high:

graded sand and gravel

Parallel laminated sands

ripple laminated sands

parallel laminated muds

bioturbated mud….?

Debris flow

cohesive matrix provides dispersive force

• Cohesive strength of matrix prevents larger grains from settling out

Poorly sorted, Matrix supported deposits

sediment gravity flow (2 ways)

Grain-to-grain interactions (fronts of dunes)

Upward escape of fluid (quicksand example)