Chapter 9 & 10 - Geologic Time & Crustal Deformation
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| Absolute Age | where a number (yrs, min, sec) is assigned to the amount of time that has passed
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| Numerical Date | specify the actual number of years passed since an event occurred
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| Relative Age | where the AGE of a rock, fossil, or other geologic feature is measured RELATIVE TO ANOTHER FEATURE
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| Relative Dating | method used by geologists to determine the general SEQUENCE of geologic events from OLDEST TO YOUNGEST
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| Law of Superposition [Stratigraphic Principles] | in an UNDEFORMED SEQUENCE of sedimentary rocks, each bed is older than the one above and younger than the one below
[●YOUNG↓
●OLD↓
●OLDER]
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| Principle of Original Horizontality [Stratigraphic Principles] | layers of sediment are generally deposited in a horizontal position
rock layers that are flat have not been disturbed
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| Principle of Cross-Cutting [Stratigraphic Principles] | a rock unit must always be OLDER than any feature that cuts or disrupts it
features include: faults, igneous intrusions, folding, tilting
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| Principle of Inclusions [Stratigraphic Principles] | a piece of rock that is ENCLOSED within another rock
a rock containing an inclusion is always YOUNGER
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| Conformable Layers | layers of rock that have been deposited WITHOUT INTERRUPTION
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| Unconformity | BREAKS in the rock record
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| Formation | for the most basic rock division, constitutes a rock unit produced by UNIFORM or UNIFORMLY ALTERNATING CONDITIONS
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| How do unconformities form? | Long periods of NON-DEPOSITION
EROSION of material
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| Angular Unconformity [Unconformity] | TILTED or folded SEDIMENTARY rocks are OVERLAIN by FLAT-lying rocks ̷̷͞͞͞͞ ̷̷͞͞
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| Disconformity [Unconformity] | strata on either side of the unconformity are parallel
more difficult to identify
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| Nonconformity [Unconformity] | older METAMORPHIC or intrusive IGNEOUS rocks are OVERLAIN by younger SEDIMENTARY strata
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| Fossil | traces or remains of prehistoric life preserved in rock that are important inclusions in sediment and sedimentary rocks
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| Criteria for fossil preservation | Rapid BURIAL
Possession of HARD PARTS (skeletons)
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| Petrified (permineralization) [Fossilization] | "turned into stone"
the small internal cavities and pores of an organism are filled with precipitated matter
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| Mold/Cast [Fossilization] | shell or other structure is buried in sediment and then dissolved by ground water
the fossil only reflects the shape and surface marking of the organism and does not reveal any information regarding its internal structure
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| Carbonization [Fossilization] | preserving leaves and delicate animal forms that leaves behind a thin residue of an element
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| Impression [Carbonization: Fossilization] | if film of carbon is lost a replica of the surface may still show details
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| Amber [Fossilization] | preserving insects
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| Replacement [Fossilization] | cell walls and other solid materials are removed and replaced with mineral matter
microscopic detail can be preserved
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| Track [Trace Fossil: Fossilization] | footprints made in soft sediment and later lithified
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| Burrows [Trace Fossil: Fossilization] | TUBES in sediment, wood, and rock made by an animal
holes may later fill with mineral water
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| Coprolites [Trace Fossil: Fossilization] | fossil DUNG and STOMACH CONTENTS can provide information about food habits
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| Gastroliths [Trace Fossil: Fossilization] | highly polished STOMACH STONES used in grinding food by some extinct
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| Radioactive Decay | the SPONTANEOUS changes in the structure of atomic NUCLEI occur due to INSTABILITY in binding forces in nucleus
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| Alpha Decay [Radioactive Decay] | occurs when the NUCLEUS is TOO LARGE to be stable
EMMISION of 2 protons and 2 neutrons (an alpha particle which is, in fact, a He nucleus)
● Mass number is REDUCED by 4
◊ atomic number is REDUCED by 2
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| Beta Decay [Radioactive Decay] | occurs when there are TOO MANY NEUTRONS relative to the number of protons
An electron (beta particle) is EJECTED from the nucleus
● Mass number remains UNCHANGED
◊ atomic number INCREASES by 1
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| Electron Capture [Radioactive Decay] | occurs when there are TOO MANY PROTONS relative to the number of neutrons
An electron is CAPTURED by the nucleus and COMBINES with a proton to form a neutron
● Mass number remains UNCHANGED
◊ atomic number DECREASES by 1
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| Correlation Process | investigative process by which geologists ID and MATCH sedimentary strata and other rocks of the SAME AGES of DIFFERENT AREAS
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| The Principle of Fossil Succession [Correlation Process] | fossil organisms succeed one another in a DEFINITE and DETERMINABLE ORDER, therefore any TIME period can be RECOGNIZED by its fossils
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| What is the age of the Earth? | 4.5 BILLION years
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| Divisions of Geologic Time [Decreasing Order] | Eon -> Era -> Period -> Epoch
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| Where does C-14 come from? | Continuously produced in the UPPER ATMOSPHERE as a consequence of COSMIC-RAY BOMBARDMENT
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| Precambrian | 88% of Earth History
the vast amount of time that preceded the Paleozoic Era
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| Radiometric Dating | geologists use this technique to determine the age (a NUMERICAL age) of a rock
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| Atomic Number | element's identifying number
equal to the # of PROTONS (or electrons in an electrically neutral atom)
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| Mass Number | PROTONS + NEUTRONS
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| Force | tends to put stationary objects in motion or changes the motions of moving objects
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| Stress | term that structural geologists use to describe the forces that deform rock
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| Compressional stress | differential stress that SQUEEZES and SHORTENS a rock mass
crust is SHORTENED and THICKENED, producing MOUNTAIN terrain
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| Tensional Stress | pulls APART or ELONGATES a rock unit
STRETCHES and LENGTHENES rock bodies in upper crust by displacement along faults
displacement at depth by DUCTILE FLOW
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| Shear Stress | involves movement of one part of a rock body PAST another
can occur along FOLIATION SURFACES and microscopic features
can occur along LARGE SEGMENTS of crust
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| Differential Stress [ ≠ ] | stress applied UNEQUALLY in different directions
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| Confining Stress | rocks deeply buried are held together by the immense pressure and tend to flow rather than fracture
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| Compressional Stress : Tectonic Environment | CONVERGENT Plate Boundaries
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| Tensional Stress: Tectonic Environment | DIVERGENT Plate Boundaries
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| Shear Stress: Tectonic Environment | TRANSFORM Fault Boundaries
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| Ductile Deformation | BEND
once the elastic limit (strength) of a rock is exceeded, SHAPE IS CHANGED
does NOT fracture
type of solid-state flow
some chemical bonds are broken, WHILE OTHERS FORM
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| Examples of Ductile Deformation | Copper penny run over by a train
Modeling clay
Taffy
Beeswax
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| Brittle Deformation | BREAK
once the elastic limit (strength) of rock is exceeded, the rock BREAKS INTO PIECES
chemical bonds are broken
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| Examples of Brittle Deformation | Chalk dropped on hard surface
Glass objects
Wooden pencils
China plates
Bones
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| How do rocks at the earth’s surface behave? [Ductilely or Brittlely] | BRITTLE
Where temperatures are LOW rocks behave in a brittle manner and FRACTURE
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| How do rocks deep in the earth behave? [Ductilely or Brittlely] | DUCTILE
Where temperatures are HIGH rocks behave in a ductile manner and FLOW
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| What are strike and dip? | Strike and dip are measurements used to determine orientation (attitude) of rock layer or fault surfaces
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| Strike | TREND
compass direction of the line produced by the INTERSECTION of an inclined rock layer of fault with a horizontal plane
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| Dip | INCLINATION
the ANGLE of inclination of the surface of a rock unit or fault measured from a horizontal plane
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| Anticline [ ↑ ᴖ ] | UP-folded, or arched, sedimentary rock layers
oldest rock at the CENTER, youngest rock draped over them at the top
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| Syncline [ ↓ ᴗ ] | DOWN-folded sedimentary rock layers
oldest rock on the OUTSIDE, youngest rock in the center
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| Monocline [__ᴦ--] | large, STEP-LIKE folds in otherwise horizontal sedimentary strata
oldest rock is on BOTTOM, youngest rock is on top
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| Dome | UP-warping produces a circular or slightly elongated structure
oldest rocks of eroded dome in CENTER, youngest rock found on the outer part
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| Basin | DOWN-warping produces a circular or slightly elongated structure
oldest rocks found on the OUTER part, youngest rock found near the center
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| How do domes form? | Domes can form by magma intrusion
- Upward migration of salt formations produce salt domes
- Black Hills dome formed by up-warping
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| How do basins form? | A few structural basins are result of giant asteroid impacts
- Michigan and Illinois basins formed by large accumulations of sediment which caused crust to subside
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| Limb [Part of a Fold] | 2 sides of a fold
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| Axial Plane [Part of a Fold] | imaginary surface dividing fold
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| Hinge Line [Part of a Fold] | line drawn along maximum curvature of the fold
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| Plunge [Part of a Fold] | hinge line is at an angle
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| Reverse Fault | dip-slip faults where HANGING WALL moves UP relative to footwall
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| Normal Fault | dip-slip fault where HANGING WALL moves DOWN relative to footwall
lengthening of crust due to tensional forces
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| Strike-Slip Fault | displacement is mainly horizontal and parallel to strike of fault surface
classified as right and left lateral
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| Thrust Fault | reverse faults having dips less than 45°, so overlying block moves nearly horizontally over the underlying block
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| Hanging Wall Block | rock surface immediately ABOVE fault
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| Footwall Block | rock surface immediately BELOW fault
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