Geology 1010 Exam #2

Sedimentary Processes

Step 1 - Weathering

Step 2 - Erosion

Step 3 - Deposition

Step 4 - Lithification

Physical Weathering

Plant roots + frost wedging

Chemical Weathering

More common in many environments.

Chemical reactions involved.

Feldspar + H2O + H2C03 -> Kaolinite + Dissolved ions

Saprolite formation

Erosion

Processes by which rock, sand, and soil are broken down and carried away (i.e. weathering, glaciation). Requires energy.

Deposition

Process in which sediment is laid down in new locations. Requires a basin, accomodation space, subsidence, and layers.

Lithification

The process that converts sediments into solid rock by compaction or cementation.

Types of Sediments

Detrital/Clastic, Chemical, Biogenic

Detrital/Clastic

Sorting, rounding, grain size is key

Chemical

Form via chemical reactions

Dissolution and re-precipitation

Saltwater evaporation

Usually comprised of 1 major mineral type

Biogenic

Chalk

Limestone

Coal

Mass Wasting Causes

Angle of Repose

Lack of Moisture

Excessive Moisture

Lack of Vegetation

Excessive Vegetation

Types of Mass Wasting

Rockslides

Creep

Prevention of Mass Wasting

Risk Assessment maps

Drainage control

Retaining walls

Rock bolts

Expensive to build/impliment changes but damage is more costly

Return on prevention?

$10-$2,000 per $1

Case Study: Thistle, UT

1983 slide caused $200mil in damage, deemed preventable if $0.5mil had been spent on drainage systems.

Causes of Metamorphism

Temperature, pressure, metasomatism

Temperature

Geothermal gradient

Avg. 30℃/km

Typical Range: 20-60℃/km

Pressure

Pascals and Bars - 1 Bar = Atmospheric Pressure at the surface

Confining pressure - the stress that a material experiences uniformly from all sides as a result of the weight of material above and around it

Directed pressure - a type of force on an object where the pressure is not equal in all directions, causing deformation and changes in the object's texture

How much pressure is needed?

Most metamorphic rocks form at 10-30km depth (mid-lower crust). 6-18 miles.

Metasomatism

Addition or loss of elements new minerals form with only some of the original elements. Ores.

Types of Metamorphism

Contact, regional, fault, shock, seafloor

Metamorphic Conditions

Metamorphic grade, index minerals, metamorphic facies

Types of Metamorphic Rocks

Foliated and Non-foliated

Foliated

Slate, schist, gneiss

Non-foliated

hornfels, quartzite, marble.

Tectonic Forces

Tensional, compressional, shearing.

Responses to tectonic forces

Brittle, ductile

Responses can vary based on: Rock type, T/P, Speed of deformation

Classifying folds, based on three things

Shape, age of the layers relative to each other, and geometry.

Synform and Antiform, Anticline and Syncline

Horizontal and Plunging folds

Faults

Inches to 100s of miles

Classified by slip direction

Dip-Slip Faults

Inclined fault plane

Normal Fault

Reverse Fault

You must ID the hanging wall vs. foot wall before determining if it's normal or result

Thrust fault

Strike-Slip Faults

Horizontal movement

Left lateral

Right lateral

What causes earthquakes?

Motion along faults

Time 1: Stress < Friction

Time 2: Stress ~ Friction

Time 3: Stress > Friction

How frequent are earthquakes?

Small ones are quite common.

Earthquake Movements

Focus vs. Epicenter

Foreshocks - Small quakes that occur in the same area before a large quake.

Aftershocks - Earthquakes that follow the largest shock.

3 types of Seismic Waves

Primary waves

Secondary waves

Long, surface waves

Measurement and Detection

Three devices per lab

Key to finding the focus is that the different waves travel at different speeds.

How big was the earthquake?

Mercalli Index

Richter Scale

Moment Magnitude

Risks and Mitigation

Faults occur in sets

Deep quakes occur in specific locations

Prediction is difficult because ever fault is different

Building codes

Reinforced concrete

Liquefication

A phenomenon where earthquakes shaking causes water-saturated soil to behave like a liquid.

Fossils

Any preserved remains, impression, or trace of a living organism from a past geological age

Stratigraphy

The branch of science that studies rock layers (strata) and their layering (stratification)

Unconformities

A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

Why is there a gap?

Run out of sediment

Run out of accomodation space

Erosion

3 types of Unconformities

Disconformity, nonconformity, angular unconformity

Disconformity

A type of unconformity in which the beds above and below are parallel.

Nonconformity

An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.