Geology 101 Exam 2 Study Guide
If a nuclear weapon was detonated in the air above an exposed rock surface, the rocks would undergo what type of metamorphism:
shock metamorphism
Foliated rocks include...
slate, phyllite, schist, and gneiss
Rainwater is naturally...
slightly acidic
As distance of transport increases, grains become...
smaller and more rounded
Phanerozoic
"Visible life"- the most recent eon, began about 540 million years ago
Numerical Age
the age of a geologic feature given in years
Period
the basic unit of geological time in which a single type of rock system is formed.
Geologic Contact
the boundary between two adjacent rock units
Geochronology
the branch of geology concerned with the dating of rock formations and geological events
shock metamorphism
the changes that can occur in a rock due to the passage of a shock wave, generally resulting from a meteorite impact (also lightning)
Hydrolysis
the chemical breakdown of a compound due to reaction with water.
depositional environment
the conditions in which sediment was deposited
Holocene Epoch
the current epoch of geologic time which began 10,000 years ago; post-glacial period
metamorphic aureole
the distinct belt of metamorphic rock that forms around an igneous intrusion
The term recrystallization refers to:
the formation of new mineral crystals without melting
If a 5 million year old granite contains rock fragments of basalt, you can conclude that
the granite is younger than the basalt fragments
metamorphic grade
the intensity of metamorphism that formed the rock
Eon
the largest division of geologic time
isograd
the line on a map along which an index mineral first appears
protolith
the original rock from which a metamorphic rock formed; "parent rock"
The Principle of Superposition
the principle that in a series of stratified sedimentary rocks the lowest stratum is the oldest
metasomatism
the process by which a rock's overall chemical composition changes during metamorphism because of reactions with hot water that bring in or remove elements
compaction
the process by which sediments are pressed together under their own weight
metamorphism
the process in which one type of rock changes into metamorphic rock because of chemical processes or changes in temperature and pressure
Sandstone strata and a mass of granite are observed to be in contact. Which statement is geologically correct?
the sandstone is older if it shows evidence of contact metamorphism
subsidence
the sinking of regions of the Earth's crust to lower elevations
Sedimentary rock can help you determine...
the type of environment that was present at its creation
Isotopic Dating
the use of naturally occurring radioactive elements to determine the ages of rocks
When sedimentary rocks are mature...
they are usually smaller and about as changed as they are going to get.
When sedimentary rocks are immature...
they still closely resemble the rocks they came from.
Phase Change
transforms one mineral into another mineral (a polymorph) with the same composition but a different crystal structure. On an atomic scale, _________ involves the rearrangement of atoms.
If you measure the amount of parent atoms and daughter atoms in a mineral and find that the mineral contains 75 daughter atoms and 25 parent atoms, how many half-lives have occurred?
two
How many half-lives must elapse before 75% of parent isotope decays to the daughter isotope?
two half-lives
The Law of Superposition states that:
undisturbed sedimentary rocks are oldest on the bottom
Which one of the following parent-daughter isotope pairs is commonly used for numerical dating of minerals and rocks?
uranium-lead
The main agent of mechanical weathering is:
water
The Principle of Cross-Cutting Relationships
younger features cut across older features
The Principle of Crosscutting Relationships states that:
younger geologic features cut across older ones
Radiometric dating can't easily find exact ages for rocks between the ages of....
100,000 years to 10 million years
The half-life of an isotope is 10,000 years. If 12.5% of the parent isotope remains in the rock by the time it is dated, how old is the rock?
30,000 years
Carboniferous Period
354 to 290 mya. refers to the rich coal deposits found in rocks of this age.cooler period, much of the land covered by forest swamps. Very large plants and trees became prevalent. amniotic egg, which prevents dessication of the embryo inside.
What is the oldest dated whole rock?
4 billion years old
How old is the Earth?
4.54 Billion Years old
Based on current data, the age of the Earth is about ____________.
4.6 billion years
Unconformity
A break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.
Cambrian Explosion
A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geologic history; recorded in the fossil record about 545 to 525 million years ago.
contact metamorphism
A change in the texture, structure, or chemical composition of a rock due to contact with magma.
Oxidation
A chemical change in which a substance combines with oxygen, as when iron oxidizes, forming rust
Stratigraphic Column
A diagram representing a series of rock layers
stress
A force that acts on rock to change its shape or volume
travertine
A form of limestone that is deposited by hot springs or as a cave deposit; calcite is coming out of a water solution
Thermal Fracture
A form of weathering brought about by expansion and contraction of the outer surface of a rock caused by intense temperature fluctuations
Chert
A hard, compact, fine-grained sedimentary rock formed almost entirely of silica (quartz). Formed in colder waters.
dune
A hill or ridge of sand piled up by the wind
delta
A landform made of sediment that is deposited where a river flows into an ocean or lake
Greenstone
A low-grade granoblastic rock produced by the metamorphism of mafic volcanic rock and containing abundant chlorite, which accounts for its greenish cast
phyllite
A low-grade, fine-grained metamorphic rock with a foliation caused by the preferred orientation of very fine-grained mica. Has a sheen, unlike slate. Tend to be green.
Geologic Map
A map showing the distribution of rock units and structures across a region.
metaconglomerate
A metamorphic rock produced by metamorphism of a conglomerate; typically, it contains flattened pebbles and cobbles.
Uniformitarianism
A principle that geologic processes that occurred in the past can be explained by current geologic processes
Stratigraphic Formation
A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region.
migmatite
A rock formed when gneiss is heated high enough so that it begins to partially melt, creating layers, or lenses, of new igneous rock that mix with layers of the older gneiss.
sandstone
A sedimentary rock formed by cementing grains of sand over time. Formed from moderate energy.
shale
A sedimentary rock formed by the deposition of successive layers of clay. It is the most common sedimentary rock.
evaporite
A sedimentary rock formed of material deposited from solution by evaporation of water in a lake or ocean. Halite and Gypsum are examples of this.
metamorphic facies
A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.
bed
A single layer of sediment or sedimentary rock with a recognizable top and bottom
Radioactive Decay
A spontaneous process in which unstable nuclei lose energy by emitting radiation
Radioactive Dating
A technique used to determine the actual age of a fossil on the basis of the amount of a radioactive element it contains
fossil
A trace of an ancient organism that has been preserved in rock.
slate
A type of low grade Metamorphic rock that was once shale rock formed by heat and pressure. Most common metamorphic rock. Harder than shale, won't fall apart in water.
metamorphic rock
A type of rock that forms from an existing rock that is changed by heat, pressure, or chemical reactions.
sedimentary rock
A type of rock that forms when particles from other rocks or the remains of plants and animals are pressed and cemented together
Cross bed
A vertical slice cut into a ripple or dune caused by a current of air or water moving in one direction.
Acid Enhanced Dissolution
Acid added to water makes it easier to dissolve rocks
Where is the thickest sedimentary basins?
Along continental margins
foliation
An arrangement of minerals in flat or wavy parallel bands.
Carbonate Platform
An extensive flat, shallow area where both biological and nonbiological carbonates are deposited.
sedimentary structure
Any kind of bedding or other feature (such as cross-bedding, graded bedding, or ripples) formed at the time of sediment deposition.
Which clastic rock is rich in feldspar particles?
Arkose
Isotope
Atoms of the same element that have different numbers of neutrons
Rain picks up CO2 gas from the atmosphere as it falls; this causes the rain to:
Become slightly acidic
At what temperatures do metamorphic rocks usually form at?
Between 250 and 850 degrees celsius
Coarse Grained Rocks
Boulder, Cobble, Pebble Include: Breccia, Wacke, Conglomerate
Which are the three most common cementing agents for sedimentary rocks?
Calcite, Silica, Iron Oxide (hematite)
What forces create a metamorphic mineral assemblage?
Change in temperature and/or pressure, application of compression or shear, and interaction with hydrothermal fluids
hydrothermal metamorphism
Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock.
Very Fine Grained Rocks
Clay Includes: Mudstone (can't easily break apart), shale (brreaks along bedding), and claystone
Which of the following rocks is composed of marble sized detrital sediment?
Conglomerate
What is the difference between conglomerate and breccia?
Conglomerate has rounded edges, breccia has sharp edges and angles. Both are formed from high energy events.
What type of metamorphism would you expect to find adjacent to an igneous intrusion?
Contact
What is necessary during rock formation for a geologist to be able to use radioactive dating on a rock?
Daughter isotope must be excluded during solidification and the daughter isotope must be trapped and not allowed to escape.
Where is bluschist formed?
Deep in the ocean where temperatures are low but pressure is high; in accretionary prisms.
A chemical weathering process in which polar water molecules surround individual ions.
Dissolution
What are the divisions of geologic time?
Eon > Era > Period > Epoch
True or False? A mineral can be numerically dated as long as it trapped lots of stable daughter atoms when it formed.
False
True or False? Foliation is the direct result of recrystallization along bedding planes.
False
True or False? Hydrolysis involves the reaction of iron and oxygen in pyroxene.
False
True or False? Shock metamorphism occurs only through lightning strikes.
False
True or False? The mineral Trinitite is diagnostic of intermediate-grade metamorphism.
False
Geologists separate metamorphic rocks into what two groups?
Foliated and nonfoliated rocks
The parallel alignment of mica in a metamorphic rock is an example of ______.
Foliation
Fossil Succession
Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.
Phanerozoic Eon
Fossils are found in rock
Unloading Fracture
Fracture caused by pressure being removed from a rock
Cooling Fracture
Fracture caused by the cooling of rock
Which of the following metamorphic rocks cannot form from a dolostone?
Gneiss (What can be formed: stretched pebble conglomerate, mylonite, marble)
What are some other methods for dating materials?
Growth rings in trees and seasonal layers in glaciers
Bicarbonate
HCO3-
This mineral commonly forms when sea water evaporates.
Halite
Great Extinction
Happened after cretaceous period, mammals become dominant.
Which of the following minerals will be least affected by chemical weathering?
Hematite
What is migmatite a mixture of?
Igneous and metamorphic rock
conglomerate
In the water, clasts bang into each other and into the riverbed, a process that shatters them into still smaller pieces and breaks off their sharp edges. As the clasts are carried downstream, they gradually become rounded pebbles and cobbles. When the river water slows, these clasts stop moving and form a mound or bar of gravel. Burial and lithification of these rounded clasts produces ______________________.
Arkose
It is generally formed from the weathering of feldspar-rich igneous or metamorphic, most commonly granitic, rocks, which are primarily composed of quartz and feldspar. Created with moderate energy.
What is the parent rock for marble?
Limestone
What is contact metamorphism?
Localized metamorphism caused by intense heat from intruding magma, like the intrusion of a dike into the country rock.
What is the difference between low, intermediate, and high grade rocks?
Low grade rocks are formed at low temperatures. High grade rocks are formed at high temperatures. Intermediate rocks are formed at temperatures between low and high.
Banded Iron
Magnetite/hematite layered with chert
gneiss
Metamorphic Foliated rock- formed from granite; has dark and light bands, hard, durable
What can be found at mountain ranges?
Metamorphic rocks can be found at mountain ranges
Quartenary Period
Modern day plants and animals; rise of modern humans
Fine Grained Rocks
Mud, Silt Include: Siltstone
Precambrian
Name for the time in earths early history that accounts for ninety percent of earth's time, but only cellular organisms lived.
How does an angular unconformity form?
Older rocks are tilted, eroded, and then overlain by younger rocks.
Coal Process
Peat > Lignite > Butiminous Coal > Anthracite Coal
deposition
Process in which sediment is laid down in new locations.
erosion
Processes by which rock, sand, and soil are broken down and carried away (i.e. weathering, glaciation)
Acid Rain
Rain containing acids that form in the atmosphere when industrial gas emissions (especially sulfur dioxide and nitrogen oxides) combine with water.
What are the features of metamorphism?
Recrystallization, phase changes, metamorphic reactions, pressure solutions, and/or plastic deformation. If hydrothermal fluids bring in or remove elements, we say that metasomatism has occurred.
hornfels
Rock that undergoes metamorphism simply because of a change in temperature, without being subjected to differential stress.
Medium Grained Rocks
Sand Include: Arkose, Sandstone
Example of Stratographic Sequences
Sandy Sediment > Muddy Sediment > Limey Sediment
clastic (detrital) sedimentary rock
Sedimentary rock that forms when fragments of preexisting rocks are compacted or cemented together.
chemical sedimentary rock
Sedimentary rock that forms when minerals precipitate from a solution or settle from a suspension.
Stratigraphic Group
Several adjacent stratigraphic formations in a succession.
This type of sedimentary rock forms when mud is lithified.
Shale
Low to High Grade Metamorphism Changes (Foliated)
Shale (protolith) > Slate > Phyllite > Schist > Gneiss > Migmatite
Most common minerals that cement sediment together are (in order from strongest to weakest)
Silica, calcite, hematite
Felsic materials weather...
Slowly; they are generally resistant to weathering.
Relative Age
The age of a rock compared to the ages of rock layers
Tectonic Fracture
The breaking down of a rock from tectonic forces
Trinitite (also known as atomsite or Alamogordo glass)
The glassy residue left on the desert floor after the plutonium-based Trinity nuclear bomb test on July 16, 1945, near Alamogordo, New Mexico. The glass is primarily composed of arkosic sand composed of quartz grains and feldspar that was melted by the atomic blast. It is usually a light green, although color can vary. It is mildly radioactive but safe to handle.
An isograd indicates what?
The location at which an index mineral first appears.
Frost Wedging
The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices
preferred orientation
The metamorphic texture that exists where platy grains lie parallel to one another and/or elongate grains align in the same direction.
Pleistocene Epoch
The most recent epoch of the Late Cenozoic Ice Age, beginning about 1.8 million years ago and marked by as many as 20 glaciations and interglaciations of which the current warm phase, the Holocene epoch, has witnessed the rise of human civilization.
exhumation
The process (involving uplift and erosion) that returns deeply buried rocks to the surface.
Bioturbation
The process by which organisms rework existing sediments by burrowing through muds and sands. Example: roots, burrowing animals
cementation
The process in which minerals precipitate into pore spaces between sediment grains and bind sediments together to form rock.
Stratigraphic Correlation
The process of matching up strata from several sites through the analysis of chemical, physical, and other properties.
lithification
The process that converts sediments into solid rock by compaction or cementation.
metamorphic zone
The region between two metamorphic isograds, typically named after an index mineral found within the region.
Geologic History
The sequence of geologic events that has taken place in a region.
Closure Temperature
The temperature at which parent and daughter isotopes can no longer escape from a mineral, so the ratio of parents to daughters can be used for isotopic dating.
Mechanical (Physical) Weathering
The type of weathering in which rock is physically broken into smaller pieces. It does NOT change the chemical composition of a rock.
Organic activity can cause mechanical weathering, true or false?
True
True or False? All metamorphic changes to a rock occur in the solid state.
True
True or False? Atoms within a mineral are moved during dynamic recrystallization.
True
True or False? Intermediate grade metamorphosis of slate produces schist.
True
mudstone
Very fine-grained sedimentary rock that will not easily split into sheets.
What is necessary for chemical weathering?
Water
regression
When relative sea level falls, the coast migrates seaward—we call this process ______
transgression
When relative sea level rises, the shoreline migrates inland—we call this process ______________.
sorting
____________ of clasts indicates the proportion of clasts in a rock that are the same size.
shield
a broad region of long-lived, stable continental crust where sedimentary "cover" either was not deposited or has been eroded away so that Precambrian "basement" rocks are exposed
Sinkhole
a circular depression formed when the roof of a cave collapses; a cavity in the ground, especially in limestone bedrock, caused by water erosion and providing a route for surface water to disappear underground
diagenesis
a collective term for all the chemical, physical, and biological changes that take place after sediments are deposited and during and after lithification
coal
a combustible black or dark brown rock consisting mainly of carbonized plant matter, found mainly in underground deposits and widely used as fuel. It is a rock but NOT a mineral.
sedimentary basin
a depression, created as a consequence of subsidence, that fills with sediment
turbidity current
a downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension
Alluvial Fan
a fan-shaped mass of material deposited by a stream when the slope of the land decreases sharply
Index Fossil
a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
Turbidite
a graded bed of sediment built up at the base of a submarine slope and deposited by turbidity currents
Fossil Assemblage
a group of fossil species found in a specific sequence of sedimentary rock
graded bed
a layer of sediment, deposited by a turbidity current, in which grain size varies from coarse at the bottom to fine at the top
quartzite
a metamorphic rock composed of quartz and transformed from a protolith of quartz sandstone; it is extremely durable
The Principle of Inclusion
a rock body that contains inclusions of preexisting rocks is younger that the rocks from which the inclusions came from
Limestone
a sedimentary rock consisting mainly of calcium that was deposited by the remains of marine animals. This is the second most common sedimentary rock.
oil shale
a soft, fine-grained sedimentary rock from which oil and natural gas are obtained.
Era
a subdivision of geologic time that divides an eon into smaller units of time.
Epoch
a subdivision of the geologic timescale that is longer than an age but shorter than a period.
dolostone
an abundant carbonate rock composed primarily of dolomite and is formed from limestone where groundwater replaces some calcium with magnesium.
Geologic Column
an arrangement of rock layers in which the oldest rocks are at the bottom
A disconformity is ___________.
an erosional surface between horizontal layers of sedimentary rocks
Radioactive Element
an unstable element that breaks down into a different element
The following texture indicates high-grade metamorphism:
banded
sedimentary structures include...
bedding, cross-bedding, graded bedding, ripple marks, dunes, and mud cracks.
The half-life of carbon-14 is about 6000 years. Assume that you have unearthed a preserved tree that died 15,000 years ago. How much of the original amount of C-14 would remain today?
between one-fourth and one-eighth
Landslide deposits that become lithified (cemented together) form what type of sedimentary rock?
breccia
Which of the following minerals is most susceptible to weathering by dissolution?
calcite
Decaying matter can...
cause a rock to go through chemical weathering faster
Recrystallization
changes the shape and size of grains without changing the identity of the mineral making up the grains
The four major classes of sedimentary rocks are...
clastic rocks, biochemical rocks, organic rocks, and chemical rocks
breccia
coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting
When used to describe a sedimentary rock, "detrital" means:
composed of rock fragments that have been transported, deposited, and cemented
The Las Vegas valley is ringed by mountains. When it rains in the mountains flash floods carry tons of clastic sediment down narrow slot canyons, and then deposit the sediment on alluvial fans at the mouth of the canyon. What kind of sedimentary rock would you expect to form on the alluvial fans?
conglomerate
What type of intrusive features are examples of cross-cutting relationships?
dikes, sills and plutons
Types of Chemical Weathering
dissolution, oxidation, hydrolysis
Cenozoic Era
era that began about 66 million years ago, known as the "Age of Mammals"
siltstone
fine-grained sedimentary rock generally composed of very small quartz grains
regional metamorphism (tectonic burial)
formation of metamorphic rock bodies that are hundreds of square kilometers in size
Types of Mechanical Weathering
frost wedging, salt crystal growth, sheeting/unloading, biological activity
Which of the following lists has one rock from each major category (igneous, sedimentary, metamorphic) that contains quartz?
granite, sandstone, gneiss
Which of the following metamorphic rocks forms from mafic volcanic rocks?
greenstone
Plastic Deformation
happens when a rock becomes warm enough to behave like soft plastic, so the minerals within it can change shape without breaking.
Pressure Solution
happens where the surface of one mineral grain pushes against the surface of another, under conditions that allow a water film to exist between the grains. The grains preferentially dissolve at the surface of contact and the resulting ions migrate away, through the water film. The ions may precipitate on the sides of grains that aren't being pushed together.
Limestone is mainly composed of the mineral calcite, whereas chert is mainly composed of quartz. Knowing this, what characteristics would be most useful in trying to differentiate between the two?
hardness
Which mineral causes red colored rocks around the Vegas area?
hematite
Non-Foliated rocks include...
hornfels, quartzite, marble, greenstone, and some mylonite
Which of the following is not a type of mechanical weathering?
hydrolysis
Paleozoic Era
immediately after Precambrian; organisms developed hard parts
An older rock that is entirely surrounded by a younger rock is called a(n):
inclusion
Which term denotes fossils of particular organisms that were distributed widely but lived for only a relatively brief interval of geologic time?
index fossils
Geologist track the distributions of different grades of rock by looking for...
index minerals
What characteristic is key to identifying a rock sample as a conglomerate?
large rounded grain
The Principle of Original Horizontality
layers of sediment are generally deposited in a horizontal position; therefore, undisturbed sedimentary rock layers are found in horizontal beds.
strata
layers of sedimentary rock
Half-Life
length of time required for half of the radioactive atoms in a sample to decay
Mud rocks are created at _____ energy.
low
Smaller pieces of rock are more easily moved, therefore...
mechanical weathering facilitates chemical weathering by creating more surfaces
marble
metamorphic rock that was once limestone; often used for sculptures
schist
metamorphic, foliated, lots of mica, intermediate grade
thermal metamorphism
metamorphism caused by heat conducted into country rock from an igneous intrusion
burial metamorphism
metamorphism due only to the consequences of very deep burial; mostly get low-grade rocks under this
dynamic metamorphism
metamorphism that occurs as a consequence of shearing alone, with no change in temperature or pressure; happens along fault
When you fire up a kiln, a pot recrystallizes and clay turns into...
mica
Mesozoic Era
middle life (245-144 million years ago); rise of mammals and dinosaurs; the rise of birds; extinction of dinosaurs, rise of flowering plants
What property is used to classify non-foliated metamorphic rocks?
mineral composition
metamorphic mineral
new minerals that grow in place within a solid rock under metamorphic temperatures and pressures
What is foliation?
parallel orientation of platy minerals caused by metamorphism
"Biochemical" sedimentary rocks:
precipitate in response to biologic activity
Metamorphic foliation can be defined by....
preferred mineral orientation (aligned inequant crystals) or by compositional banding
This concept states that a rock containing fossils of very early life forms is older than one containing dinosaur fossils.
principle of faunal succession
Which relative dating principle states that fragments inside of a more extensive rock unit are older than the more extensive rock?
principle of inclusion
Which relative dating principle states that the youngest layer in a sedimentary rock sequence is on the top of the sequence and the oldest layer is at the bottom of the sequence?
principle of superposition
Mafic materials weather...
quickly
Which of the following is not a type of unconformity (gap in the rock record)?
reconformity
Type of metamorphism that involves both high heat and high pressure over a large area.
regional
Stratigraphic Sequences
relative dating technique; observing patterns of materials in a stratigraphic column to order them in time. Sites with multiple occupations at different times
ripple mark
relatively small elongated ridges that form on a sedimentary bed surface at right angles to the direction of current flow; symmetrical ones found in beaches or tidal flats, bidirectional flow; asymmetrical ones are found in dunes, water or wind flowed in one direction
Metamorphic Reaction (Neocrystallization)
results in growth of new minerals that differ from those of the protolith. During _________________, chemical reactions effectively "digest" minerals of the protolith, so the chemicals can go into the production of new minerals.
Salt Wedging
rock disintegration caused by the crystallization of salts from evaporating water
turbidite
rock that forms from a graded bed of sediment built up at the base of a submarine slope and deposited by turbidity currents
Why is sandstone deposited on beaches while shale is deposited in deeper water?
sand-sized grains require higher-energy environments for transport
What is the parent rock for quartzite?
sandstone
Geologic Time
scale used by paleontologists to represent evolutionary time
Geologic Time Scale
scale used by paleontologists to represent evolutionary time
Volcanic ash can help find the age of what?
sedimentary rock
biochemical sedimentary rock
sedimentary rock formed from material (such as shells) produced by living organisms; forms from the remains of plants or animals.
How are shale and basalt different in hand sample (both can be featureless and dark)?
shale is softer than basalt, and can be easily scratched with a nail
