Geology Exam II

Sedimentary Rocks

Formed from the transported, deposited and lithified weathering products of rocks and biological material

Covers 75% of earths surface

Sediments

Weathered and transported products (solid and dissolved) of other rocks as well as biological materials

Erosion

General term for the processes by which rock is broken down and the products moved
Includes weathering and transport

Weathering

The breaking down of rocks

Transport

Moving of products
Includes gravity, wind, ice, and liquid water

Deposition

The process of sediment accumulation that occurs when transport of solids or dissolved species ceases

Lithification

Process of turning deposited sediments into stone through compaction, cemnetation, precipitation and/or recrystallization

Physical Weathering

The breaking of rocks with physical means including wind/water abrasions, root wedging, freeze/thaw and thermal expansion

Chemical Weathering

Breaking of rocks by chemical means including disolution, oxidation/reduction and hydrolysis

Impact/Abrasion

Things knocking rocks together and breaking them apart

Root Wedging

Roots growing into cracks of rocks and eventually splitting them apart

Freeze / Thaw

Water seeping into cracks of rocks then freezing and expanding making bigger cracks in rock

Thermal Expansion

When flakes are spalled off from heat. Heat makes outside of rock more mallable but inside is cold so it breaks off

How Physical and Chemical Weathering Work Together

Physical breaks up rocks, making more surface area for chemical weathering to attack!

Water and Temperture

Most important factor in controlling rate of chemical weathering

Transportation By Glaciers

Ice melts so material the glacier was carrying is deposited

Transportation By Gravity

It falls. Like duh.

Transportation By Wind

It blows things making it move

Transportation By Water

When it evaporates the dissolved load is deposited
When it slows down the solid load is deposited

Name for Pebble (or larger) sized grains

Breccia (angular)
Conglomerate (Rounded)

Name for Sand sized grains

Sand stone

Name for Silt sized grains

Silt stone

Name for Clay sized grains

Shale (Or clay stone)

Depositional Enviorment

Physical, biological and chemical conditions (that is, the enviorment) at the time sediments are deposited

Sedimentary Facies

A distinctive group of characteristics within a sedimentary unit (including sedimentary structures, grain size, and rock type) that allow one to infer the depositional enviorment

Sedimentary Structures

Features in sedimentary rocks that reflect some aspect of the depositional enviorment

Metamorphism

Textural and compositional changes in ricks due to increased temperture and pressure

Metamorphic Rocks

Rocks changed by heat and/or pressure

Important Factors in metamorphism

1. Pressure (Confining or directional)

2. Temperture

3. Parent rock (protolith) composition

4. Fluids

5. time

Types of Metamorphism

1. Mountain Belt

2. Contact

3. Subduction Zone

Foliation

Parallel orientation of platy minerals (like micas) or elongated grains in some metamorphic rocks
Usually breaks parallel to this orientation

Contact Metamorphism

Metamorphism caused by magmatic intrusions. Intrusions bring in a lot of heat to relatively shallow, cool, depths and also give off fluids. The rocks in contact witht he intrusion are changed ( = Metamorphosed)

Shock Metamorphism

Results from extreme, short-lived, high pressures

Mountain Belt Metamorphism

increases in both heat and pressure

Subduction Zone Metamorphism

Low Temperature and high pressure

Principles of stratigraphy

Putting things in order / Relative timeline

Original Horizontality and Lateral Continuity

Sedimentary rocks are originally laid down in horizontal (or almost horizontal) layers
Layers continue laterally until they run into a discontinuity, grade into something else or pinch out

Superposition

Oldest layers on bottom and younger layers get piled on top
Only requirement is to find which side is “up” and which is “down”

Cross-Cutting Relationships

Features that cut across layers are younger than the layers they cut across
Includes Magmatic intrusions, faults and erosion

Faunal Succession

Way to tell time using fossils since creatures lived at different times

Fossil organisms succede one another in a definite order.

Relative Datitng

Placing events/rock units/organisms in a chronological sequence, using principles of stratigraphy

Catastrophism

If the geologic column accumulated over biblical timescales, forces of tremendous violence and magnitude that surpass anything experienced in nature are predicted/required

Uniformitarianism

Theory that changes in Earth’s crust were the result of continouis and uniform processes

Absolute Dating

Estimating an age for an event, rock unit, and/or organism’s range in years

Calculation for absolute age

Time = Total / Rate

Isotope

atoms of the same element (that is, same # of protons) but with different numbers of neutrons

Half life

Time it takes for half of a radioactive isotope to decay

Radiometric Dating

Way to tell age on decay of radioactive material

The Percentage of radioactive atoms that decay during a half life is always the same (50%)

Stress

The force that causes rocks to deform (confining - pressure)

Can be tensional, compressional and shear stress

Strain

The deformational response to stress

Can be…
Elastic Deformation

Brittle Deformation

Ductile Deformation

Pressure

Type of stress where the force is equal in all directions

Compression

Type of stress where it is pushed together

Tension

Type of stress where it is pulled apaet

Shear

Type of stress where it is pulled in 2 directions on different sides

Elastic

When deformation happens due to strain but strain and deformation will go away when the stress is removed

Ex. Tennis Ball

Brittle

Permanent breakage

Ex. Disposable Fork

Ductile

Permanent bending or flowing

Ex. Clay Ball

Favored at higher temps, slower deformation rates, softer minerals with planes of weakness and higher pressure

Factors that affect whether a rock will break or bend

1. Temperature

2. Time / Deformation Rate

3. Composition

4. Confining Pressure

Hinge

Position on fold where curvature is greatest

Axial plane

plane that contains hinges in successive layers

Limb

Sides of the fold with lower curvature

Anticline

Fold where limbs are inclined (dip) away from the hinge

Syncline

Fold where limbs are inclined (dip) toward the hinge

Monocline

Fold where one incline between two levels, like a carpet draped over a step

Basins

Fold with a center towards which rock layers are inclined (dip)

Looks like a bowl

Dome

Fold with a center away from which rock layers are inclined (dip)

Plunging antilcline & syncline

Its a anticline or syncline but the hinge goes down towards earth

Anticlines “close” in the direction of plunge

Synclines “open” in the direction of plunge

Fracture

General term for when there is a break in a rock

Joint

A fracture across which little or no movement has occured (e.g. cooling joints - Devil’s Tower, expansion - Yosemite)

Hanging Wall

Overhead

Foot Wall

Under Foot

Fault - Normal

A fracture across which significant movement has occured

A fault in which the hanging wall moves down, relative to the foot wall

Fault - Strike Slip

One piece goes forward while the other either stays or go backwards

Can be Right lateral or Left Lateral

Fault - Reverse

A fault in which the hanging wall moves up, relative to the footwall

Earthquakes

Vibrations of the earth caused by the rupture and sudden movement of rocks that have been strained beyond their yield points

Elastic Rebound

The mechanism for earthquake generation

1. Rock strength and friction fault prevents movement

2. elastic deformation in fault blocks

3. force of friction (and/or rock strength) exceedes; Fault ruptures

4. Rocks rebound or spring back to their deformation state

Epicenter

The point on earths surface that lies vertically above the focus

Focus

Center of energy release and site of first movement on a fault

Seismic Waves

They are produced by earthquakes thgat propagate radially from the surface.

The types are…

1. Body Waves

2. Surface Waves

Body Waves

They travel through the earths interior. There are 2 types

1. Primary - Compressional, travel through all states of matter, the fastest

2. Secondary - Shear, can only go through solids

Surface Waves

Seismic waves that travel on the surface of the earth

Do the most damage

Seisometers

Produce a record of the arrival and size of seismic waves

Seismograph

The record produced by a seisometer

Mercalli Scale

Scale based on the damage of an earthquake. Ranges from 1 to 12.