GEGN 101 Exam 2 part 1 Rocks/Errosion/and Geo time scale

Know the main physical properties used to identify minerals and their characteristics.

Color, specific gravity, luster, crystal form, cleavage/fracture, hardness, streak (color of streak on porcelain), effervescence.

Know what to call liquid hot rock underground versus on the surface, and when they solidify what general crystal size results from each.

*Magma*: underground, cools slowly, larger crystals

*Lava*: surface, cools quickly, small crystals

Know what to call an igneous rock that cooled and crystallized underground.

Intrusive/plutonic

Know what to call and igneous rock that cooled and crystallized on the surface.

Extrusive/volcanic

Know the seven principal igneous rock textures and their definitions.

1. Glassy: no crystals

2. Aphanitic: crystals too small to see (under 1mm crystals)

3. Phaneritic: visible crystals (1mm to 2.5cm)

4. Pegmatitic: crystals are larger than 1 inch across

5. Porphyritic: large crystals surrounded y small crystals

6. Vesicular: full of bubbles

7. Pyroclastic: composed of ash and rock fragments from explosive eruptions

What is the most common molecule in magma and lava?

Most common molecule: Silica (SiO2)

What are the two most common gasses dissolved in magma?

Most common dissolved gasses: H2O and CO2

Know the names of the phaneritic, aphanitic, and glassy igneous rocks which form from each magma type.

Basaltic (Mafic)-low silica

Andesitic (Intermediate)-medium silica

Rhyolitic (Felsic)-high silica

On the Bowen's reaction series, what are the first minerals to crystallize from a typical magma, and what is the last to crystallize?

First: Olivine and calcium-rich plagioclase

Last: Quartz, Muscovite Mica, and Potassium Feldspar

Besides the order in which minerals crystallize from a melt, what other two pieces of information does the Bowen's reaction series give us?

Tells us:

-order which minerals will melt when heated

-which minerals are most likely to be stable at the surface.

Define and identify *country rock*

Magma intrudes into, layered sedimentary rock

Define and identify *plug* (volcanic neck)

Center remnant of an eroded volcano

Define and identify *sill*

Tabular and parallel to country rock

Define and identify *dike*

Tabular and *not* parallel to country rock

Define and identify *baked zone*

Burned area around a magma body

Define and identify *xenolith*

Piece of country rock inside a piece of igneous rock

Know how to tell the difference between an igneous sill and a lava flow that has been buried.

An igneous sill has a baked zone on the top and bottom. Lava flows have more bubbles toward the top.

Define rock

Any solid mass of mineral or mineral-like matter that occurs naturally

What are the 3 types of magma and which has the highest and lowest of the following: viscosity, gas content, silica content, ability to form pyroclasts (explosiveness)

*Mafic (Basaltic):*

Least silica, least viscous, least gas, least pyroclasts

*Intermediate (Andesitic):*

Mid silica, mid viscous, mid gas, mid pyroclasts

*Felsic (Rhyolitic):*

High silica, high viscous, high gas, high pyroclasts

Define weathering

Breaking apart of rock into smaller pieces (sediment)

Define erosion

Movement of sediment from one place to another

Define deposition

Placement of sediment at new location

Define lithification

Turning loose sediment into sedimentary rock

What are the 2 different types of weathering? What causes them? What type of material do they result in?

*Chemical:*

Rocks dissolved (in H2O) into individual molecules

Effective if H2O is acidic

*Mechanical:*

Rock is physically broken into smaller pieces

Happens from impact, heat expansion, frost weathering

What are the 4 agents of erosion? Which is most important on Earth?

*Water*

Wind

Gravity

Ice

Only glaciers can move uphill

Know the 3 ways of transporting (eroding) weathered material in water

*Bed load:* Rolls/bounces along bottom of river

*Suspended load:* Turbulence in water keeps particles in water and off bottom

*Dissolved load:* Rock is dissolved into molecules and ions in solution

Know the 2 types of deposition and the names of the 2 types of sedimentary rocks they produce

Chemical deposition --> Chemical sedimentary rock

Clastic deposition --> Clastic sedimentary rock

What happens to the lakes that we create by building dams? What happens directly downstream?

Lakes fill up with silt (lake siltation)

Erosion occurs directly downstream

Know the names for the different relative sizes of detritus and the name of the rock made from the lithification of each size classification

Clay (Mud) --> Mudstone/Shale

Silt --> Siltstone

Sand --> Sandstone

Pebble { }

Cobble { Conglomerate (round); Breccia (sharp) }

Boulder { }

Know the environment of deposition for each clastic sedimentary rock

Pebble = Floods, debris flows, mountain streams

Sand = Base of mountainous areas, fast moving stream beds, beaches

Silt = Slow moving/still water to deposit, near shore

Clay = Still water to drop out, deep calm water far from shore

*Need high energy to move large particles and low energy to move small particles*

What is the most common characteristic of chemical sedimentary rocks?

Monomineralic

Know the names for the major chemical sedimentary rocks based on their mineral composition

*Carbonates:*

CaCO3 --> Limestone

(Ca,Mg)CO3 --> Dolestone

*Silicates:*

SiO2 --> Chert (Flint, Jasper, Agate)

*Evaporites:*

Rock salt --> Halite

Rock Gypsum --> Gypsum

Know the environment of deposition for the evaporites and carbonates

*Evaporites:*

Require body of water with high evaporation rate

Usually need a "closed basin" where water can run in but not out

*Carbonites:*

Limestone forms very slowly and will get overwhelmed by any clastic particles

Need water with no clastics either far from shore or in sheltered bays

What happened at Lake Peigneur, L.A.?

What was being mined there?

What happened to the lake?

Who's fault was it?

Salt and oil were being mined

Lake drained into salt mine because oil miners drilled a hole through the mine roof

Texico read their map wrong and drilled into the salt mine

Know how sorting, roundness, and size of clastic particles can help determine environment or distance of erosion

If well sorted --> Consistent energy level

If moderaterly sorted --> Energy level fluctuates within a certain range

If poorly sorted --> Energy levels fluctuate drastically over time or material has been deposited all at once by ice

Rounding/Size: Tell you about distance of erosion

Farther --> Rounder and smaller

Closer --> Sharper and bigger

Know the 3 ways lithification takes place

*Compaction:* Burying sediment

*Cementation:* Gluing together with minerals

*Recrystallization:*

Significance of rhythmic layers

Rhythmic change in the environment of deposition

*Transgression = Sea level rise*

*Regression = Sea level fall*

Significance of cross bedding

Unidirectional flow that is concave in the direction of flow

Sharp angle on top

Low angle on bottom

Significance of graded bedding

Small sediment is on top, coarse sediment is on bottom

There was a violent event to stir sediment up and this event ended fast

Significance of ripple marks

Unidirectional flow --> Asymmetric ripples

Bidirectional flow --> Symmetric ripples

Ripples are up

Significance of mud cracks

There is mud

Cracks pinch down, widen up

What is the only feature that can not give original up direction?

Rhythmic Layering

Know the importance of sedimentary rocks to fossil preservation

Pretty much the only rock you'll find fossils in

What does the name "metamorphic" mean, and what is the definition of a metamorphic rock?

Means "changed shape". Defined as a rock that has undergone chemical and/or physical changes in the solid state.

What are the two main types (scales) of metamorphism?

1) *Contact metamorphism*: small scale metamorphism usually caused when magma burns the surrounding country rock.

2) *Regional metamorphism*: large scale metamorphism usually caused by tectonic pressure.

What are the factors that make an igneous or sedimentary rock turn into a metamorphic rock?

1) Heat

2) Pressure

3) Chemical Reactions with hot fluid

Know the three ways that a rock can *physically* change in the solid state during metamorphosis.

1) Reorientation of rod or plate shaped minerals

2) Recrystallization of minerals resulting in less but larger grains

3) Creation of new minerals: some index minerals can tell you what pressure and heat conditions the rock reached

Know the two main types of metamorphic rock textures.

-Foliated: rod or plate shaped

-Non-foliated: minerals have no dimension

What do you call a rock that partially melted?

Migmatite

What are the names of foliated rocks that have: microscopic, small (almost to barely visible), and large (visible) mica grains, and what is the name of the foliated rock with a dark/light banded pattern?

Foliated Rocks

*Slate*: microscopic crystals

*Phyllite*: crystals have said so that they are almost visible, gives off shiny appearance

*Schist*: crystals have grown large enough to see

*Gneiss*: magic and felsic minerals have separated to make dark and light bands

What are the names of the two most common metamorphic rocks, what minerals make up each, what is the most common parent rock for each, and what physical test could you use to distinguish them?

Non-foliated

*Marble*: effervesces with HCl, limestone parent rock, hardness of 3

*Quartzite*: does not effervesce with HCl, sandstone parent rock, hardness of 7

What is the general term for contact metamorphic rocks?

Hornfels

How does "shocked quartz" get created on Earth?

Meteor impacts

What are the two main types of contacts between rock formations?

1) Sharp contact

2) Gradational contact

Know the definitions of the terms "strike" and "dip" as they are used in structural geology, know how to measure strike and dip, and know how to read a strike and dip symbol on a geologic map.

*Strike*: direction of line that is formed by the intersection of the plane of the rock bed with a horizontal surface (determined by the RHR).

*Dip*: direction which the steepest angle is formed between the plane of the rock bed and the horizontal surface.

Symbol "T" with down indicating downhill

Know the three types of stress.

Compression, tension, shear

Know the three types of strain.

Brittle, ductile, elastic

Features that result from stress and strain, and the types of folds and faults possible with each type of stress and strain:

| *Brittle* | *Ductile* | *Elastic*

*Compression* | Reverse fault | folding |

*Tension* | Normal fault | boudinage |

*Shear* | Strike-slip faults | Monoclinal fold |

Know which wall is the foot wall, hanging wall, and which direction they move for each type of fault.

Can walk on the foot wall. Hanging wall above the foot wall.

Compression, reverse fault: hanging wall up, foot wall down

Tension, normal fault: hanging wall down, footwall up

What about geologic structures makes them important to oil exploration?

They make oil traps

Laws of relative age dating

1) *Law of Original Horizontality*: most rocks laid down flat, and tilted only later during geologic events

2) *Law of Superposition*: oldest rocks are on the bottom

3) *Law of Lateral Continuity*: most rock beds don't end suddenly when laid down

4) *Law of Cross-Cutting Relationships*: a rock being cut by another rock or feature is older than that rock or feature

5) *Law of Inclusions*: if rock A includes a piece of rock B, then rock B is older than rock A.

6) *Law of Fossil Succession*: fossil assemblages change in an ordered succession through time

Various forms of "up indicators"

*Graded bedding*: fossils such as tree stumps, animal burrows, root traces

*Stratigraphic superposition*: channel fill, cut out beds and fill with younger beds

*Cross bedding*: sediment deposited on a slight slope in water or air

*Mud cracks*: cup up

*Rain drops*: dimples in mud or in sediment imprints of mud

*Infilled voids*: sediment fills lower half, crystals can fill upper half

*Flute and Scrapes*: casts and molds

*Vesicles*: appear at the top of lava flows

Define fossil

A remnant, impression, or trace of an organism of past geological ages that has been preserved in the Earth's crust.

Define trace fossil

When the organism itself is not preserved but only evidence of its existence (dinosaur tracks, worm burrows, coprolite)

Who was the person who developed the principle of fossil succession? Where/when did he work? What did he do? Why else is he famous?

William Smith, surveyor, early 1800s, mapped the whole country of England's geological formations.

What are index fossils?

Tell you what part of the geologic history the rocks were formed in. A good index fossil exists for a limited period of geologic history, is easily preserved, and can be preserved in many different sedimentary environments.

What are ecological indicator fossils?

A fossil that can tell you where you are

Define unconformity

A break in the record; missing time

What are the 4 types of unconformities?

*Angular:* Angled beds with sediment on top

*Disconformity:* Parallel beds that got cut by sediment

*Nonconformity:* Bottom is intrusive igneous/metamorphic, top is young sediment

*Paraconformity:* Parallel beds with no evidence of erosion

Reproduce Geologic Time Scale

Just do it

What feature of life history marks the boundaries of periods?

Mass extinctions

What feature of life history marks the boundaries of eras?

Mass extinctions ( >50% )

Know the 3 types of radioactive emission and how/if they transmute one element into another

*Alpha Emission:* 2 protons and 2 neutrons get thrown out (# - 2)

*Beta Emission:* 1 proton gets added from electron emission (# + 1)

*Gamma Emission:* High energy photon emission (# + 0)

Half Life

Time for half of population of parent to decay into daughter

i.e. Half life = 10 years, initially had 100% parent and 0% daughter, now have 6.25% parent

Thing is 40 years old

What assumptions are made in the "absolute dating" method?

Rock or mineral system is closed

Initial ratio of parent to daughter must be determined

Half life must be constant through time

Measurements of parent and daughter must be accurate (need minimum amount)

A realistic value must be applied to daughter amount (can't be too small)

What rock types are most and least useful for radiometric

dating?

Most: igneous

Leat: Sedimentary

What other physical aspect of a rock can be used to constrain its

age.

The rock's position in the rock layers (stratigraphy) can be used to constrain its age.

Superposition: In undisturbed layers, older rocks are below younger rocks.

Cross-cutting relationships: A feature that cuts through a rock is younger than the rock it cuts.

How old are the oldest rocks and minerals in the world, and

where do they come from?

Oldest minerals: About 4.4 billion years old — zircon crystals found in the Jack Hills of Western Australia.

Oldest known rocks: About 4.0 billion years old — found in the Acasta Gneiss Complex in the Northwest Territories, Canada.

Where were the oldest fossils found, and how old are they?

Stromatolites that are 3.5 billion years old in westeran austrlia

What is the oldest evidence of life and how old is it?

It is possible that we have a fossil that is 3.7-3.8 billion years old and thats from greenland

Radioactive decay

N(t)=N(0)e-λt

T ½=ln2/λ=0.693/λ=0.693τ