Plate Tectonics (the unifying theory in Earth Sciences) Summary Data and Questions
Definition: Theory that large segments or plates of the lithosphere move relative to one another
A. Continental Drift Hypothesis
Although Suess (1885) noted similarities of Glossopteris flora and glaciation and named the southern supercontinent Gondwana, Alfred Wegener is credited with developing the hypothesis of Continental Drift. He suggested
a super-continent of Pangea that formed in the Paleozoic that subsequently split apart.
Evidence:
1. Continental fit
2. Glacial evidence
3. Similarities of rock sequences (compositions and types including coal distribution)
4. Mountain ranges of the same age and rock type on different continents
5. Fossil evidence (Glossopteris flora, Mesosaurus, Cynognathus, Lystrosaurus)
This evidence, though persuasive, lacked a means to describe how the continents moved.
B. Plate Tectonics (move to a theory)
Evidence plus a mechanism:
1. Paleomagnetism
a. Polar wandering
b. Magnetic reversals (striping) on the sea floor; led to idea of seafloor spreading
2. Age of ocean floor materials
3. Distribution of earthquakes
4. Distribution of volcanoes
5. Hot spot “trails”
C. Types of Plate Boundaries (see Table 2.2): Know locations and examples, types of rocks, stress
regimes, and types of geohazards
1. Divergent (spreading ridges, split apart)
2. Convergent (colliding margins)
3. Transform (strike-slip)
D. Plate Names (the big seven and there are many smaller ones), Rates of Movement (mm’s to
cm’s per year), and Mechanisms of Movement (convection cells and slab push/pull models)
E. Resources
1. Where do they occur and why? At what plate boundaries?
2. Types of resources: How does the previous and current distribution of plates dictate the occurrence of oil and gas,
coal, copper, gold, metals, etc.
3. Where would you look for these resources?
F. Questions for Your Consideration
1. Where are active hazardous earthquakes and volcanoes today? Where would I go to find the most exciting
geology?
2. Where are most of our resources located? What are the controls on their distribution?
3. Are there different rock types on continents and ocean floors, and if so, Why?
4. How does a hot spot reveal information to support the Plate Tectonics Theory?
G. Interior of the Earth: Composition and How do we Know and what is the significance?
1. The Earth is composed of many “layers” but you should know the main 4 including their composition, thickness
etc.:
a. Lithosphere (continental and ocean) – the thin outer shell
b. Mantle - plastic
c. Outer Core - liquid
d. Inner Core – solid
2. How do we know the composition and liquid vs. solid?
Earthquake waves, seismic waves and models, nuclear explosions, meteorites
How do we know what is
inside the earth and why do
we care?
How do we know?
1.
2.
3.
Seismic data
Earthquakes
Magma and rock comp.
Why do we care?
1.
2.
3.
4.
Heat of the earth
Geothermal energy
Geomagnetism
(magnetic field protects us)
Location of resources
We only know directly about the
“skin” of the Earth; but even that
upper 5 – 40 km is continuously
in motion leading to the formation
of ocean basins, mountains, and all
of the features we observe.
Granite: Light in color w/ less
dense minerals like quartz,
feldspar, mica
(Grain density = 2.8 g/cc)
Basalt and peridotite: Dark in
color w/ dense minerals like
olivine, augite
(Grain density = 3.1 g/cc)
Earth Materials: Minerals, Rocks, and Sediments
Mineral Definition:
1. Must occur naturally
2. Must be inorganic
3. Must be a solid
4. Must possess an orderly internal structure; atoms must be arranged in a definite pattern
5. Must have a Definite chemical composition that varies within small limits.
Ex. Graphite – lubricant, pencil lead, golf – C
Halite – Salt – NaCl
Quartz – used for glass, computer chips - SiO2
Talc – baby powder – Mg3Si4O10(OH)2
(Are coal, pumice, and/or cubic zirconia minerals?)
ELEMENTS (Basic building block of minerals:)
a. 112 elements, 92 are naturally occurring.
b. Only eight make up the bulk of minerals and represent 98% (by weight) of the continental crust.
What are the most abundant elements on or in the earth? Or is it the same thing? The interior has more Mg, Ni, Fe and less Al, Na,
K because of early differentiation (density)
CRUSTAL (ELEMENTAL) COMPOSITION
ELEMENT
Oxygen
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
All Others
SYMBOL
O
Si
Al
Fe
Ca
Na
K
Mg
% BY WEIGHT
Mineral
46
28
8
5
4
3
3
2
>1
Percent in Crust
Plagioclase
Quartz
Orthoclase
Pyroxene
Micas
Amphiboles
Clay minerals
Other silicates
Nonsilicates (calcite/halite, etc)
39
12
12
11
5
5
5
3
8
Properties of Minerals
1. Crystal Form – external expression of the orderly internal arrangement of atoms.
Ex. Quartz (hexagonal) with pyramidal shaped ends
2. Hardness – measure of the resistance of a mineral to scratching
Use MOHS Scale of Hardness
Relative Scale
Hardest
10
9
8
7
6
5
4
3
2
1
Mineral
Diamond
Corundum
Topaz
Quartz
Feldspar
Apatite
Fluorite
Calcite
Gypsum
Talc
Hardness of Common Objects
6.5 Ceramic Streak Plate
5.5 Glass Plate
3.5 Copper Penny
2.5 Fingernail
3. Color – obvious feature of minerals but not truly diagnostic (inclusions)
Ex. Olivine – green; Quartz – clear, smoky, amethyst (purple), rose; sulfur – yellow
4. Luster – appearance or quality of light reflected from surface of mineral
a. Metallic – pyrite, galena, magnetite
b. Non-metallic – vitreous (glassy, quartz), silky (talc), earthy (soft hematite)
5. Streak – color of mineral in powdered form. Use streak plate.
Ex. Hematite – red to reddish brown/gray
6. Cleavage – tendency of mineral to break along planes of weak bonding. All minerals do not have cleavage; some
fracture such as quartz.
Ex. Calcite – 3 directions not at 90°, muscovite – 1 perfect direction
7. Tenacity – resistance a mineral offers to breaking (brittle, ductile, elastic, malleable, etc.)
8. Specific Gravity – compares weight of a mineral to the weight of an equal volume of water
9. OTHER: Magnetism – magnetite; Double Refraction – calcite; Malleability – gold; Taste – halite; Feel – talc, graphite;
Smell – sulfur; Reaction to HCl – calcite, dolomite
The BIG FIFTEEN: Rock-forming Minerals you MUST know
Ferromagnesium (also called Mafic) Silicates (Fe, Mg, Si, Al, O)
Olivine
(Mg, Fe)2SiO4
Pyroxene
Ca, Mg, Fe, Al silicate
Amphibole
Hydrous Na, Ca, Mg, Fe, Al silicate
Biotite
Hydrous K, Mg, Fe silicate
Primarily Occurs In:
Ig., meta rks
Ig., meta rks.
Ig., meta rks.
All rk. types
Non-Ferromagnesium (also called Felsic) Silicates (Si, Al, Na, K, O)
Quartz
SiO2
K-feldspar
KalSi3O8
Plagioclase
Ca(Na)Al2Si2O3
Muscovite
Hydrous K, Al silicate
Clay minerals
Various
All rk. types
All rk. types
All rk. types
All rk. types
Soils, sed rks
Carbonates
Calcite
Dolomite
CaCO3
CaMg(CO3)2
Sed. rks
Sed. rks
Sulfates
Anhydrite
Gypsum
CaSO4
CaSO4.H2O
Sed. rks
Sed. rks
Halides
Halite
NaCl
Sed. rks
Sylvite
KCl
Sed. Rks
--------------------------------------------------------------------------------------------------------------------------------------------------------------Rock Cycle and Rock Types
Rock – solid aggregate of mineral particles (mostly). Some rocks are composed of volcanic glass (obsidian) and of organic
particles (peat, coal, skeletal limestone).
Rock Cycle – conceptual model that explains how all rocks are formed (cooled from magma, cemented grains), transformed (heat
and pressure), destroyed (broken down to grains), and/or re-formed as a result of environmental factors and natural processes.
All rock-forming materials come from:
a. Earth’s Mantle – molten rock: magma or lava
b. Organisms – plants and animals
c. Fragmentation/Chemical Decay of Other Rocks – sediments
d. Space
Three Rock Groups (Identification of rock types rely on their Composition and Texture; form and color)
Igneous – formed when magma or lava cool to a solid state, either glass or masses of intergrown mineral crystals
Sedimentary – formed when fragments of plants, animals, or other rock are compressed or cemented together; or when masses of
mineral crystals precipitate from water
Metamorphic – rocks are changed from one form to another (transformed) by intense heat, pressure, or by the action of fluids.
North Carolina Mineral and Rock Facts: (Go to website: www.geology.enr.state.nc.us/ for additional information)

N.C. has 310 minerals (3700-4000 in the world)

First gold rush in 1799 near Charlotte (17lb. nugget found)

N.C. official state rock is granite; state precious stone is emerald

Mineral industry is $1billion industry in N.C.

N.C. leads nation in production of feldspar (most common mineral in earth’s crust and used to make ceramics and abrasives),
mica (filler in paints, plastics, cosmetics, drilling mud), and high purity quartz (glass, industrial materials, computer
components; chips in silicon valley and in the Palomar telescope)

Dimension stone (like granite for building faces and monuments); ?largest in Mt. Airy in world

Other important minerals/rocks in N.C.
Phosphate (Aurora quarry: fertilizer, feed, ceramics)
Common clay (bricks and tiles)
Olivine (refractory liner; only in N.C. and Washington)
Aggregate (sand and gravel for roads and construction)
Peat (organic matter for soil additive, filtering, and energy)
Name 10 rocks/minerals/soils/sediments that are resources and their uses. Five should include quartz, feldspar, coal,
clay, lime/limestone.
Igneous Rocks
Igneous (“Fire”) Rocks – formed by the cooling of molten rock.
Magma – molten rock below surface
Lava - molten rock at the surface
Why doesn’t molten rock stay at depth? Liquid is less dense than rock confining it so confining pressure and low density
causes the molten material to squeeze up through weak points in earth’s lithosphere.
1. Intrusive – magma cools below the surface. Large crystals can form because of slow-cooling.
Types of Intrusive Bodies
bedding
A. Batholiths – very large (~100 km2)
C. Dikes – cut across bedding
B.
Sills – sheet-like, parallel to
2. Extrusive – magma cools at the surface. Rapid cooling either leads to small or no crystal formation from
lava. Explosive forms are the geohazards.
Types of Extrusive Bodies
A.
Lava flows
B. Pyroclastics (ash, flows, etc.)
The location, type of material, and hazard potential of intrusives, lava flows, and volcanic activity is primarily dictated by plate
tectonics.
Formation of Igneous Rocks: There are 3 locations where igneous rocks form that bring them near or to the surface
of the earth.
1) Mid-oceanic ridges (Divergent) 2) Subduction zones (Convergent)
Ex. Mid-Atlantic Ridge (Iceland)
Ex. Japan, Western S. America
3) Hot Spots
Ex. Hawaii, Yellowstone
Geologic hazards associated with volcanoes are concentrated along these areas though the type of magma (amount of
gas it contains and whether it is felsic or mafic) controls the explosivity of the volcano. This too is controlled by plate
tectonics. Spreading centers and hot spots have lower hazard potential than volcanoes at converging boundaries.
Why do we have different kinds of magma?
1) Source material - spreading centers and hot spots are more mafic, subducting zones are more felsic
2) Bowen’s Reaction Series – cooling of magma leads to a predictable igneous rock composition
as different minerals crystallize at different temperatures. As minerals form they are removed
from the melt changing composition. At what temperature would you melt a rock?
Classification of Igneous Rocks
Three Properties
1) Mineralogic composition,
2)Color Index (mostly controlled by minerals),
3)Texture
Minerals: Eight minerals (rock-forming minerals) occur most commonly in igneous rocks.
A. Felsic (light colored) – quartz, potassium feldspar, muscovite, plagioclase (Na mostly)
B. Mafic (dark colored) – biotite, amphibole, pyroxene, olivine
C. Intermediate – contains both felsic and mafic minerals
2. Color Index (CI) – percentage (by volume) of mafic minerals in the rock. Used as a rough measure of the amount of mafic and
felsic minerals. Know minerals!
3. Texture – description of components of rocks including their sizes, shapes, and arrangement. Intrusives usually cool slowly and
have large crystals; Extrusives rapidly cool and fine-grained
Textural Terms
1) Phaneritic – coarse-grained crystals (1-10 mm)
2) Aphanitic – fine-grained crystals (requires hand lens or scope to see: <1 mm)
3) Glassy – no crystals
4) Pegmatitic – very coarse-grained (>1 cm)
5) Porphyritic – two distinct crystal sizes
Phenocrysts are large crystals (larger than matrix or groundmass). May have phenocrysts in aphanitic or
phaneritic textures.
Porphyritic indicates two different cooling rates. Larger crystals formed more slowly and then cooling rate
increased to have smaller crystals.
6) Vesicular – trapped gas bubbles leave “holes” in rock. May have many or few.
7)
Pyroclastic – rocky material broken and ejected during eruption; may contain ash (<2 mm), cinders (2 – 64 mm), or
bombs (>64 mm).
Classification of Igneous Rocks
STEPS: Identify the rock’s texture, dominant material (Aphanitic, phaneritic, glassy), Identify the mineral composition and color index
(determine felsic, intermediate, mafic so light minerals are felsic and dark are mafic), Add qualifying terms such as porphyritic (name
phenocrysts if possible) or vesicular.
Igneous Rock Questions you Should be able to Answer for Lab and Lecture
Everyone should of course be able to completely diagram and explain in detail the rock cycle – I mean
detail. How about drawing it on the back of this sheet?
1. Where do igneous rocks form and occur?
2. a. What are the types of volcanic geohazards? Name at least two areas that have been impacted by a
volcanic geohazard in the last 20 years.
b. Does the U.S. have any potential volcanism geohazards?
3. What are the best properties to use to classify igneous rocks?
4. Why are some rocks light and some rocks dark? Be specific.
5. I have three rocks (I think they are igneous). Let me describe them to you and you tell me where they
were formed, how, and give me a possible mineral composition and rock type.
a. Very small crystals, black
b. Some large crystals (plagioclase) in a finely crystalline matrix (dark)
c. Vesicles throughout rock (dark, except on the surface which is brown – why would it be brown?)
6. There are upwards of 4000 minerals in the world, or some such huge number. However, if you know
the rock forming minerals you will be able to make most of our rocks. What are those rock-forming
minerals?
7. THOUGHT Questions:
A mineral resource is a concentration of a naturally occurring material in or on the crust of the earth in a
form that may be currently or potentially extracted economically. U.S. mineral raw materials are worth $32
billion annually. Igneous processes (e.g. plate tectonics) concentrate many minerals such as gold,
diamonds, copper, magnetite, etc. Why do you think there are these “exotic” minerals with igneous rocks?
If many of these are related to plate boundaries, why was N.C. the site of the most gold production in the
U.S. prior to the California Gold Rush in 1848-49?
Rock Cycle and Rock Types
Rock – solid aggregate of mineral particles (mostly). Some rocks are composed of volcanic glass
(obsidian) and of organic particles (peat, coal, skeletal limestone).
Rock Cyle – conceptual model that explains how all rocks are formed (cooled from magma, cemented
grains), transformed (heat and pressure), destroyed (broken down to grains), and/or re-formed as a result
of environmental factors and natural processes.
All rock-forming materials come from:
1) Earth’s Mantle – molten rock: magma or lava
2) Space – meteorites
3) Organisms – plants and animals
4) Fragmentation/Chemical Decay of Other Rocks – sediments
Three Rock Groups (Identification of rock types rely on their Composition and Texture; form and color)
Igneous – formed when magma or lava cool to a solid state, either glass or masses of intergrown mineral
crystals
Sedimentary – formed when fragments of plants, animals, or other rock are compressed or cemented
together; or when masses of mineral crystals precipitate from water
Metamorphic – rocks are changed from one form to another (transformed) by intense heat, pressure, or
by the action of fluids.
Sediments and Sedimentary Rocks
Sediment – loose grains or chemical residues derived from inorganic (rock and mineral) and organic (plants and
animals) materials, and/or from chemical precipitates (halite, gypsum).
The formation of sediments, other than the precipitates, is from the weathering of pre-existing materials (rocks, trees,
shells)
Weathering – breakdown of pre-existing rocks and sediments
1. Physical (mechanical) – break larger particles into smaller ones (cracking, abrading)
Ex. Break granite into rock fragments and minerals, shells into smaller pieces, logs into plant fragments
2. Chemical – dissolution or decomposition
Ex. Halite dissolves to salty water, calcite decomposes to calcium and bicarbonate, feldspar from granite
decomposes to clay minerals
Sedimentary Rocks are consolidated sediments composed of organic or inorganic materials, or chemical
precipitates. Hardening of sediments to rock occurs by:
1. Compaction – grains pack closer together: Sand ---- Sandstone (Compaction and cementation)
2. Cementation – precipitates such as calcite, halite, silica, etc. “glue” the sediments or grains
together
3. Precipitation of crystals from aqueous solutions, often form crystalline masses
Ex. Salt in Solution ---- Evaporation of Water ---- Halite (solution to crystal)
Composition and Texture of Sediments and Sedimentary Rocks
Sediments have different COMPOSITIONS based on their origin and different TEXTURES because of how
they are transported and then deposited. These are the two keys to the Description, Identification, and
Interpretation of Sedimentary Rocks.
COMPOSITION
Types and abundance of grains that make up sediment or sedimentary rock.
1. Detrital (Clastic or Terrigenous) – decomposed pieces of pre-existing rock. Includes rock
fragments, mineral grains (quartz, feldspar, micas), and clay minerals (decomposed
feldspars and other minerals).
Ex. Breccia, conglomerate, sandstone, siltstone, shale
2. Biochemical – remains of organisms such as shells (corals, forams, clams, etc.) and plants
EX. Skeletal limestone, peat, coal
3. Chemical – composed mostly of intergrown mineral crystals precipitated from aqueous
solutions (halite, gypsum, calcite, dolomite)
Ex. Chemical limestones (travertine, micrite, oolites), Dolostones, Gypsum, Chert, and Halite
Texture – description of a sediment’s or sedimentary rock’s constituent parts and their sizes, shapes, and
arrangement.
1. Grain size – particle size. Usually relate size to energy of transport and deposition (larger equals higher energy)
Gravel – grains larger than 2 mm (pebbles, boulders)
Sand – grains 62 um to 2 mm. Feel gritty like sandpaper
Silt – grains 4 – 62 um. Grains are mostly too small to see
Clay - <4 um. Feel smooth, not gritty. Clay is used both for size and as a mineral
2. Shape – Transport and abrasion changes the grain shape from more angular to rounded
3. Sorting – different energy levels (velocities) transport different size particles. Velocity variations will segregate
different sizes. Larger particles may be transported with higher energy, when velocity drops, large sizes settle.
4. Roundness – degree that abrasion has removed edges (repeated transport and movement)
Other Definitions
1. Sedimentary structures – characteristic feature formed during or just after deposition (mud crack, track, ripple,
burrow)
2. Fossils – remains or traces of past life
3. Sedimentary facies – sediment w/ characteristic properties (lithology, fossils)
4. Formation – mappable rock unit w/ characteristic properties (lithology)
Although many sedimentary rocks will have textural properties like those described above, the detrital
rocks most commonly possess those properties (sandstone, conglomerate). Many of the biochemical and
chemical rocks have crystalline textures or interlocking growth forms.
Crystalline Texture – interlocking network of crystals
Classification of Sedimentary Rocks
1. Determine the rock’s general composition Identify the kinds of grains and abundances
a. Clastic (detrital, terrigenous)
b. Biochemical
c. Chemical
2. Determine the rock’s texture (Size, sorting, angularity)
3. Name the rock (use composition, texture, and other special features)
4. Determine how the rock was formed and where it was deposited.
Where Do These Sediments and Rocks Form?
Sedimentary Environment – geographically limited area where sediments are deposited (river, beach, delta, reef,
deep sea) and preserved. It is characterized by a certain energy regime (currents, waves, river flow) and chemical
equilibria (tropics or temperate, water composition, aridity).
One of the goals of geology is to interpret the earth’s history. This requires being able to interpret what the rocks tell
us about geologic processes and environments of deposition that occurred in the past. How do we do that?
OBSERVE ------- DESCRIBE ------- INTERPRET
1. Know the properties and distribution of sediments today
2. Apply those observations and interpretations to the rock record.
Ex. Beach Sand Today (typical sandy beach; there are others)
Waves sort the sand, uniform grain size and removal of clays (energy)
Waves abrade and round the sand (energy)
Quartz is most stable mineral, “most” beach sands are predominately quartz (composition).
Contains whole and broken shell fragments (composition)
Beaches are linear features (coast-parallel)
So how do I know the Beach Sand of Yesteryear
Look for moderately sorted, rounded, clay-free, quartz-rich sandstone with shell fragments
and the shape of the deposit in the subsurface will be a linear sand body geometry
FOSSILS – (dug up) remains or evidence of ancient plants or animals that have been preserved in the rocks of the
earth’s crust; these mostly represent hard parts. May be actual remains, altered hard parts (petrified), molds or casts
of organisms, carbonized, tracks or other evidence. These may be critical to recognizing ancient sedimentary
environments (there will be few shark teeth in a river deposit).
Sedimentary Rocks – Questions for Consideration
1. Do you remember what rock forming minerals are the dominant ones in granite?
Stone Mountain, North Carolina, like Stone Mountain in Georgia is composed of granite. Trace the changes that may
occur to a piece of igneous rock as gravity takes it to the sea. Can I form a really good beach sand from it and what
would it look like? What are the major mineral components on beaches and are they always the same? In other
words, is it possible to have a limestone, basaltic, or even a clayey beach?
2. Where is the origin of that most important of minerals, salt – halite – NaCl? Of course the ocean is salty (35 parts
per thousand or 3.5% salts; all of it is not halite) but what about Great Salt Lake. Why are either of these “salty”? Did
you know there is a Morton Salt Plant on the edge of the Great Salt Lake right next to the mountains and right next to
where the Winter Games are being held? How can that lake be salty with all that snow?
By the way, did you know that there are thousands of feet of halite under the Gulf of Mexico and under the
Mediterranean Sea? If seawater is only 3.5% salts, how could you ever accumulate 1000’s of feet of salt?
3. It takes a village to raise a child, it takes a huge swamp/forest to make some coal. The U.S. is blessed with an
abundance of coal (second only to the former Soviet Union in resource supply), enough to provide electricity to us for
hundreds of years. A few coal thought questions.
a. What are the stages in coal formation and what is required (yes I know a lot of trees)
b. Why does coal occur much more in certain geologic periods and in certain areas than in others? And why isn’t
there any coal before the Silurian Period?
c. Old coal-burning power plants are one of the big issues in North Carolina. There is a law being considered in the
legislature right now (Smokestack Law – it was passed, unbelievable) concerning curbing the emissions from these
plants. Do you know what the issues are with the use of coal?
4. Although I love igneous and metamorphic rocks, if you consider the thin outer veneer of the earth, sediments and
sedimentary rocks cover ~3/4 of the earth’s land surface and most of the ocean basins. And they either are
composed of or contain most of our important resources (salt, aluminum, iron ore, uranium, a little gold, and the less
exotic but very important lime, gypsum, and stones for construction). They also contain the fossil fuels (oil, gas, coal)
and our groundwater, not to mention where do your crops grow? What factors lead to the concentration and storage
of these resources in sediments and sedimentary rocks?
Sedimentary Rocks and Resources
Sedimentary rocks contain many of our mineral and rock resources and practically all of our coal, uranium, and hydrocarbons (gas
and oil). In addition, much of our groundwater is contained in sedimentary aquifers such as the High Plains Aquifer (Ogallala),
Edwards Limestone, and the Castle Hayne Limestone here in N.C.
Questions:
1. What are the properties of sediments and sedimentary rocks that allow them to contain these resources? The
textural properties of the sediments/rocks are most important. In general, though it matters whether the rocks are
highly cemented or not and whether there is dissolution, rocks with larger grain sizes and better sorting make better
aquifers and reservoirs. Why? Can you explain it?
2. What types of sediments and/or sedimentary rocks would be the best for aquifers and hydrocarbon reservoirs?
3. In order to produce oil and gas there must be a source rock (organic rich) and in order for a reservoir to contain
these fluids they must have pores/void space. But if I don’t want the fluids to escape they must be trapped by a
structure and/or by a sealing rock will not allow the fluids to migrate out. What type of rock would be a good sealing
rock?
4. In the Groundwater Model, what would make the best aquifer (contains and transmits water) and the best
aquiclude/aquitard (prevents water movement)? Explain the movement of the water and contaminants in the model.
Fossils, Preservation, and Importance
Fossil (dug up) – remains or traces of animals or plants that are preserved by natural causes. Variously
explained as being grown from seed, devices of the Devil, and not until 15 th century was the origin
accepted that they were prehistoric organisms. Of course there was still 300 years of theological and
scientific argument of whether the fossils result from the Flood.
Paleontology – study of fossils
Preservation depends on:
1)
2)
3)
Original composition of the organism
Environment of deposition
Forces acting on the remains after death
QUESTIONS:
1) Most fossils are found in sedimentary marine rocks, WHY?
2) Many of our most famous dinosaur fossils are in river, floodplain, and lake deposits, WHY?
3) If I find a shark’s tooth in Raleigh or a coral in Tennessee, what were the environments there at some
time in the past?
Methods/Style of Preservation
1) Soft parts – difficult, parts must be protected from being eaten or decay.
a. Ice or Soil
b. Amber
c. Oil
2) Original “Hard Parts” of Organisms
Minerals resist weathering or may slightly change.
a. Shells (clams, oysters)
b. Teeth and bones
c. Woody tissue
3) Altered “Hard Parts” of Organisms
Hard parts undergo change after death; determined by organism composition and the
environment
a. Petrified (turned to stone)
b. Carbonization – decomposition leaves carbon film. Coal
c. Molds – shell dissolves leaving an impression of shell form
d. Casts – mold fills with another material
4) Traces of Organisms
a. Tracks and trails
b. Coprolites and gastroliths
c. Burrows
Why are Fossils Important?
1) When, Where, and How organisms lived
2) Interpretation of the depositional environment for possible resources
3) Development history of the earth
4) Correlation of rock layers, particularly using INDEX fossils
The Grand Canyon is several miles wide with layers of rock on either side; how would I know if I was
looking at the same rock from side to side. Think about practical applications for this type of data
(correlation) elsewhere.
Metamorphic Rocks
Metamorphic (changed form) Rocks – alter preexisting rocks (parent rock or protolith) by physical and/or
chemical means; these processes do not mean that the rock melts.
1)
Heat, 2. Pressure, 3. Chemicals (fluids and gases)
Three Types of Metamorphism
1. Contact – more local; occurs adjacent to igneous intrusions and along fractures filled with hot fluids
(hydrothermal). Thin zones that change rapidly away from heat/fluid source.
2. Regional – large areas; formed by:
a. Major igneous intrusions, b. Extreme heat and pressure from burial, c. Widespread
migration of chemical fluids
3. Dynamic – associated with fault (fractures with movement) zones; high differential pressures.
What controls and where do you get Meta Rocks?
Must have heat, pressure, chemicals – Plate boundaries and hot spots are excellent places to have these factors
present.
Ex. East Coast including North Carolina Piedmont
1. N. Amer. Collided with Africa and Europe in the Paleozoic, large pressure led to large scale metamorphism
2. Rifting of these continents (~230 m.y.) led to igneous intrusions (heat and fluids) that caused contact
metamorphism
Primary Textures of Metamorphic Rocks (Description of mineral sizes, shapes, and arrangement)
1. Foliated – parallel (or approx. parallel) layering of platy minerals (mostly micas) formed by realignment of
minerals in the rock by pressure and/or recrystallization
a. Slaty cleavage – nearly perfect, planar layering of fine-grained minerals. Product of low-grade metamorphism.
Common form: SLATE
b. Phyllitic texture – wavy foliation of fine-grained minerals that exhibit a shiny luster. Product of low-grade
metamorphism. Common form: PHYLLITE
c. Schistosity – parallel to subparallel foliation of medium- to coarse-grained platy minerals (mica, chlorite) or
alignment of prismatic crystals (amphibole). Product of intermediate to high-grade metamorphism. Common form:
SCHIST
d. Gneissic texture - parallel to subparallel foliation of medium- to coarse-grained platy minerals in alternating layers
of different compositions: banded look w/ ferromagnesium minerals making dark and felsic or carbonate minerals
making the light bands. Product of intermediate to high-grade metamorphism. Common Form: GNEISS
2. Non-Foliated – no obvious layering of platy minerals
a. Cataclastic texture – fracturing and crushing, often has hydrothermal veins. BRECCIA
b. Granular texture – randomly oriented, often visible crystals.
1. Sandy: QUARTZITE
2. Crystalline: MARBLE
3. Smooth: ANTHRACITE
Mineralogic Composition (Types and Abundance)
Mineral composition of parent rock may change or stay the same (rearrange texture) during metamorphism.
Describe the rock by its textural type and use the components (minerals) to describe the composition.
Ex. Garnet mica schist (Schist texture, mostly mica, some garnet; minerals listed in order of increasing %)
Metamorphic Grade measure of the intensity of metamorphism (how rock differs from parent rock). The grade may
change, based on proximity or distance from high Tº or Pressure.
Metamorphic Facies is body of rock with certain INDEX minerals that characterize a particular grade of
metamorphism (pressure and Tº control)
Classification of Metamorphic Rocks
1. TEXTURE (Determine if it is foliated or nonfoliated
2. COMPOSITION (Determine mineralogy; list minerals in order of increasing abundance)
3. Determine rock name (gneiss); give qualifiers to further describe it (biotite quartz gneiss)
(History, Maps, Rocks, Maps, Stratigraphy, and Structure)
The complex geologic history of North Carolina, though only approximately 1.8 billion years (based on the oldest rocks
found to date), various rock types, and physiographic features of the state illustrate many of the fundamental principles
and issues of geology. From continents colliding (mountain building forming much of the Piedmont and Blue Ridge) to
continents splitting (rifting to form Triassic Basins), from sea level highs to lows (forming the Coastal Plain), from the
formation of resources (phosphate, gravel, granite, feldspar, bricks, etc.) and fossils (dinosaurs, giant sharks, giant
ground sloths, etc.) to the ever changing landscape of the state caused by weathering and erosion, river movements, and
coastal processes; the provinces (Blue Ridge, Piedmont, and Coastal Plain) of N. C. have many different geologic origins
and properties.
North Carolina Facts:
Size:
Population:
People/ mi2:
Name:
State Tree:
State Flower:
State Bird:
State Rock:
State Gemstone:
State Soil:
2
48,711 mi
8,541,221 (2004)
175
Tarheel State (reference to tar/pitch/turpentine industry)
Pine
Dogwood
Cardinal
Granite (igneous felsic rock, formed in the Paleozoic; Mt. Airy largest open-faced granite quarry in
the world)
Emerald (Blue Ridge province found associated w/ pegmatites)
Cecil (located in Piedmont, formed mostly from weathering metamorphic rocks)
A brief history of time for N.C.
1. Several collision and rifting events in the Proterozoic
2. Primary formation of the Piedmont, Blue Ridge, and the Appalachian Mountains during the Paleozoic Mt. Building
events:
a. Taconic (Ord. – Sil.: 470 – 440 m.y.)
b. Acadian (Dev. – Carb.: 380 – 340 m.y.)
c. Alleghanian (Late Carb. – Permian: 330 – 270 m.y.)
3. Late Triassic rifting 200 – 180 m.y. (formation of failed rift basins: Deep River and Dan River)
Alluvial fans, Lake deposits, red beds, minor coals, dinosaurs. And of course some igneous intrusives.
4. Formation of the Coastal Plain (Jur. to Recent). Repeated rises and falls of sea level led to stacked marine and
nearshore continental deposits
5. Final rise following the last glacial event (~18,000 yrs. ago has led to current coast shape and barrier islands)
6. Previous continental collisions, rifting and sea level fluctuations have led to the general NE-SW trend of rock units
in N.C. The various rock types and topography define the physiographic boundaries of the Blue Ridge, Piedmont,
and Coastal Plain. The contact of Coastal Plain sedimentary rocks with Piedmont metamorphic rocks form the Fall
Line.
Physiography

N.C. is divided into three provinces: Blue Ridge (Mountain) (10%), Piedmont (45%), and Coastal Plain (45%). These
subdivisions are based on landforms but the rocks are very different as well (part of which control the landforms)

The Coastal Plain is low gradient w/ maximum elevations of 600’. The surface has thick soils developed though older
rock outcrops locally and along streams. There is a general trend of older rocks inland and younger rocks near the
coast. Black water rivers, large estuaries and barrier islands are prominent features of this province.

The Piedmont contains the most varied rock types and is separated from the Coastal Plain by the fall line – rock and
gradient change. Elevations range up to 1500’.

The Blue Ridge contains all 3 rock types (ages >1 to 0.5 b.y.) and abundant (43) peaks over 6000’. The highest is
Mt. Mitchell at 6,684’.
Information for Geologic Maps/Structure/Stratigraphy
Stratigraphy – study of layers of sediment and rock and how they were deposited.
1) Principle of Original Horizontality – sediments are originally deposited as near horizontal sheets. If they are at a
high angle that means they have been deformed.
2) Law of Superposition – The oldest rock is at the bottom and the youngest is at the top (true unless severe
structural deformation)
3) Law of Faunal Succession – fossils change with time.
Index fossil – key fossils, used to represent named subdivisions of the geologic time scale
4) Principle of Cross-Cutting Relationships – any feature that cuts across a rock or sediment must be younger than
what it cuts across.
5) Lateral continuity, 6) Principle of Inclusions, 7) Baked zones
Geologic Cross Section – a cutaway view of the earth. It’s like digging a trench and looking at the sides of the trench.
The cross section shows how the rocks are arranged, what they are, and even the surface topography.
Structural Geology – how rocks deform after they were originally deposited. Stresses such as compression, tension,
and shear cause these deformations.
Ex. Outcrop shows deformation, what type of stress caused it?
Types of Structures: Unconformities, Faults, Folds
Unconformity – rock surface that represents gap in the geologic record either by removal of sediment by erosion or
non-deposition
a. Disconformity – unconformity between parallel strata
b. Angular – unconformity between non-parallel strata
c. Nonconformity – stratified sedimentary rock deposited on igneous or metamorphic rock.
Faults – a break in the rock, shown by offset of layers or rock types. There is either vertical and/or lateral offset
a. Normal – footwall moves up relative to hanging wall
(Form in a tensional regime such as divergent zones/rifts)
b. Reverse – footwall moves down relative to hanging wall
(Form in a compressional regime such as convergent zones)
Thrust – low angle reverse fault
c. Lateral or strike-slip – lateral movement of rock
(Form in Shear stress regime as at transform boundaries)
Folds – upward or downward arching of layers of rock. Folds have limbs on each side of axis (axial plane), elongate
in plan view, may plunge (angle between fold axis and horizontal)
a. Anticline – convex fold, oldest rocks in middle
b. Syncline – concave fold, youngest rocks in middle
More circular forms
c. Dome – upward arch, strata oldest at center
d. Basin – downward arch, strata youngest at center
Strike – compass direction (bearing) of a line formed by the intersection of horizontal plane and an inclined surface
Dip – angle between horizontal plane and inclined surface. Dip is measured perpendicular to strike
Geologic Map – shows the distribution (describes rock types and age) of rocks at or near the surface (sometimes the maps ignore
the surficial recent material). The colors represent ages/rock types/formations
Formations - mappable rock units
Ex. Castle Hayne Limestone in North Carolina; Coconino Sandstone in Grand Canyon
Boundaries between these formations are called contacts.
Block diagram – combination of the geologic map and the geologic cross section.