GEOL

Using the relationships between rock units, it is possible to assign relative times to what we see in nature. Relative dating is where one set of rocks is compared to another to determine which is older or younger.

James Hutton

"The key to the present is the past"-processes that act today, acted the same way in teh past.

He is credited with being the first person to recognize geologic history through rock relationships.

1. Original Horizontality: All sedimentary sequences form as flat, horizontal beds. Aby tilting or folding must occur AFTER the rock is formed.

2: Superposition: The oldest rocks are always on the bottom and the youngest are on teh top.

3. Lateral Continuity: Sedimentary deposits will extend out laterally in all directions. Eventually they will thin out or be terminated by the edge of a basin.

Any structure that cuts another must be younger that what it cuts.

An unconformity is where part of the rock record is missing.

This type occurs between two parallel rock beds, both sedimentary

This type is also between two sedimentary rock beds, but in this case, both rock units are NOT parallel. The upper units will be horizontal and the lower units will be tilted.

This type occurs between two DIFFERENT types of rock. Non=Not the same.

This applies to any rock unit containing pieces of another rock. The rock unit is younger than the pieces.

Best fossils for dating are Index Guide fossils. These are fossils of organisms that are known to have existed for only limited time periods.

Decay occuring at a specific rate. This is the time it takes for half of the radioactive parent atoms to be converted into stable daughter atoms.

1. Alpha Decay: The isotope will lose 2 protons anad 2 neutrons. As a result, the atomic number will change by 2 and the atomic mass (protons plus neutrons) will change by 4.

2. Beta Decay: The isotope will lose 1 electron. This electron is given off by a neutron, which causes it to change into a protron. Resulting in a positive change of one to the atomic numner, but no change in mass.

3. Electron Capture: This is the opposite of beta decay. Isotope gains an electron, converting a protron to a neutron. Resulting in a negative change of one to the atomic numner and no change to the atomic mass.

Closed System. This means that niether the parent nor the daughter atoms can escape.

• Eons
• Eras
• Periods
• Epochs

PreCambrian. It accoutns for 87% of all geologic time.

When rocks are changed from their original shape or relationship, they have been deformed.

It is caused by stress.

Stress is a FORCE applied to a rock.

Strain. This is the changing of the rock,

1. Compression: This type of stress pushes the rocks together. Causes shortening and thickening of the rock.

2. Tension: This type pulls the rocks apart. Causes lengthening and thinning of the rock.

3. Shear: Two opposing forces act parallel to one another to displace rock. The rock just pushes past each other, with no change in shape.

Once the stress is removed, the rock returns to its original shape with no changes.

The rock is BENT permanently. This type is found deep in the Earth, where temperatures are high. The result is Folds.

The rock is BROKEN permanently. This type is foound at shallow depths, near the surface, where temps are low. The result is Faults and Fractures.

This is the compass direction of the intersection of a bed with the horizontal plane defined by the Earths surface. It is always measured from NORTH.

This is the angle between the horizontal and the top of an inclined bed. It is always measured perpendicular to strike.

All folds consist of two lembs and an axis plane. Fold is bending. There are different types depending on how the rocks are bending.

This is a hill shaped (sad face), upward-bowing fold. The limbs are being bent down in respect to the axial plane. THE OLDER UNITS WILL BE AT THE CENTER OF THE FOLD.

This is a basin/bowl shaped, downward-bowing fold. The limbs are being bent up in respect to the axial plane. THE YOUNGER UNITS WILL BE IN THE CENTER OF THE FOLD.

In sequences.

If tilted away from vertically, this can create over-turned or asymetrical folds.

If tilted away from horizontally, this can create a plunging fold.

Domes occur through upwarping of the underlying rock.Caused also by intrustions like laccoliths.

Thought of as a double syncline and show the same characteristics: youongest rocks will be in the center and the dips will point in towards the center.

This is a fold that is only a small bend or flexure int he rocks. It essentially is only half a fold (mono=one).

Fractures in the rock with no associated motion. They are caused by cooling and pressure release and also horizontal and vertical pressure on teh rocks.

Fractures in the rock WITH motion.

Motion in these faults is UP and DOWN

Faults caused by tensional stress-the rocks are being PULLED apart.

Faults caused by compressional stress-the rocks are being PUSHED together. The hangingwall goes UP relative to the footwall.

Motion in faults is BACK and FORTH.

Combination of Dip-Slip and Strike-Slip. Visible of motion is viewable on both the map view and cross-section views.

Earthquakes occuring when energy in rocks is released.

Through Seismic waves

P-waves: Theses are PRIMARY waves and occur first in a PUSH-PULL motion.

S-waves: These are SECONDARY waves, they happen second in a UP_DOWN motion. They cannot travel through liquid.

1. Focus: This is the actual position where the quake occured. It is located below the ground and the seismic energy dissipates from this point in all directions.

2. Epicenter: This is the point on the surface directly above the focus. This is the position given in media reports.

1. Modified Mercalli Scale: This is based on intensity and damage. This scale is purely visual, with no instruments needed.

2. Richter Scale: Based on magnitude, the actual energy released during the earthquake. Determined by the difference in arrival times of the P wave and S wave and the size of the waves recoreded on the seimogram. There is not a steady progression in size from one number to the next.

Very close to p[late boundaries.

Occurs in unconsolidated, wet sediments. During a quake, dry sediments will shake into a more tightly consolidated arrangement.