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Flashcards in Geology Midterm Deck (91):
1

Stratigraphy

Geological time record

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Stratigraphic Unit

-Includes strata that are distinguishable by physical, chemical or paleontological properties

-Units of time based on age of strata can make up a unit

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Strata

-Layer of igneous or sedimentary rocks formed on the surface

-Characteristics distinguish it from other strata

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Correlation

Relationship between seperate parts of a stratigraphic unit

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Lithologic Correlation

Correlation based on rock type

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Temporal Correlation

Correlation based on age

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Time-Rock Unit

-All strata deposited at a certain time

-Geological system = time-rock unit (Chronostratigraphic Unit)

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Time Unit

Interval where a time-rock unit is formed (Geochronologic Time Unit)

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Geologic System

Section of the geologic time scale

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Erathem

-Groups of eras (time units)

-Erathems subdivided into series, then further subdivided into stages

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Epochs / Ages

Corresponding time units for subdivided time-rock units

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Boundary Stratotype

Boundary between two systems, series or stages

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Biostratigraphic Unit

-Defined by fossil content

-Based on stratigraphic range of fossil taxa

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Stratigraphic Range

Vertical range in which species show up in a stratigraphic unit

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Biozone

-Fundamental biostratigraphic unit

-Lower and upper boundaries of the biozone are determined by the ranges of taxa

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Taxa

Group of one or more populations of an organism or organisms that form a unit

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Index / Guide Fossil

-Taxa that provide a reliable source for defining biostratigraphic zones

-Exhibits some or all characteristics:

1. Found easily in stratigraphic record

2. Easily distinguishable

3. Widespread and can be used to correlate rocks over a wide area

4. Narrow stratigraphic range

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Magnetic Stratigraphy

Correlation based on magnetic properties of rocks

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Polarity Time-Rock Unit

Time-rock unit where the Earth's polarity is either the same as it is now (Normal Interval) or the opposite as it is now (Reverse Interval)

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Chron

Polarity time-rock unit

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Rock Unit

-Groups, supergroups, formations and members

-Lithostratigraphic units

-Groups > Formations > Members

-Supergroups are made of multiple groups

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Lithology

Physical or chemical characteristics of a rock

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Stratigraphic Segement

-Vertical section of a rock unit

-May contain more than one rock unit

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Type Section

-Well-preserved section of a stratigraphic segment

-Defines the unit

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Regression

Shoreline migrates seaward

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Transgression

Sealine migrates shoreward

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Facies

Characteristics of a body of rock that represents a depositional enivronment

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Depositional Environment

Sediments, soils and rocks added to an environment

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Nicolaus Steno

-Discovered how to relatively age rocks

-His method only worked within stratigraphic segments

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William Smith

Discovered that fossils can be used to determine relative ages of unrelated rocks

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Baron George Cuvier

-First to discover species go extinct

-Did not make the hypothesis that new species come

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Geologic Systems

-Bodies of rock that contain specific fossils of flora or fauna

-Each geologic system corresponds to a geologic period

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Relative Age Dating

Age of rocks in relation to other rocks

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Absolute Dating

Actual numeric age of rocks

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Fossil Succession

-Helps determine relative age of rocks

-Vertical order of fossils in a stratigraphic segment

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Fossil Record

Key to determining Geological Time Scale

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Catastrophism

Belief that global floods were caused by supernatural forces

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Actualism

-Events explained in terms of fact and physical processes

-Replaced catastrophism in the nineteenth century

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Abraham Gottlob Werner

-Supported catastrophism

-Believed rocks formed from minerals that precipitated in a sea that occasionally flooded Earth

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James hutton

-Promoted actualism

-Believed scientific processes created / destroyed rocks

-Theory focused on geologic time

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Charles Lyell

-Popularized actualism with publication of 'Principles of Geology'

-What we see in the present is the key to the past

-Uniformitarianism

-Theory focused around geologic time

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Plate Tectonics

-Used to be called continental drift

-Unifying theory of geology
--Connects all current theories

-Predicts and explains geological phenomena

-Helps explain natural disasters, mountain formation, geography etc.

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Lithospheric Plates

-Sections of the lithosphere that move

-Some carry oceanic crust, others carry continental crust

-Plate tectonics

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Spreading Zones

-Plates move away from mid-oceanic ridges

-Forms new oceanic crust

-Plates move along the edges

-Also called Mid-Oceanic Rift

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Mid-Ocean Ridge

Heat from asthenosphere causes spreading zone to swell and separate

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Transform Faults

Surfaces where plates slide against one another

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Mantle Convection

-Hot material rises from asthenosphere

-Cools as it rises

-Denser material drifts closer to the crust

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Subduction Zones

-Places where plates descend (oceanic trenches)

-Caused by partial melting of upper mantle

-Subducted oceanic crust recycled

-Forms new sediment (accretionary prism)

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Divergent Boundaries

-Plates move apart

-Upwelling of magma creates new crust

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Convergent Boundaries

-Plates move closer together

-One plate moves on top of another

-Oceanic crust descends into mantle

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Plate Boundaries

-Associated with faulting

1. Normal faults - extension (divergent)

2. Reverse faults - compression (convergent)

3. Strike-Slip faults - plates sliding past one another (transform)

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Continental Drift

-Now called plate tectonics

-Rotation of Earth caused Pangea to split apart and drift towards the poles

-Created by Alfred Wegener

-This theory was too incomplete and thus had little relevance

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Crust

-Upper most layer of the Earth

-Hard

-Oceanic crust / mafic rock
--High in iron / magnesium

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Mantle

-Found below the crust

-Slush-like consistency

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Core

-Inner core is solid iron

-Outer core is liquid iron

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Moho Discontinuity

Boundary between the crust and the mantle

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Lithosphere

Crust and solid, uppermost mantle

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Asthenosphere

Upper, dutile mantle

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Big Bang

-Occurred 10B years ago

-Expansion > redshift > increase in light wavelength > galaxies move apart

-~ 2 Trillion galaxies

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Our Galaxy

-~ 100-400 Billion stars

-Formed <10B years ago

-Formed from gravitational collapse of dense gas clouds

-Stars form by condensing in spiral arms

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Sun

Formed by the collapse of a star

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Supernova

Exploding star

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Planets

-Formed from rotating dust clouds shortly after the sun formed

-Inner planets: Mercury, Venus, Earth, Mars

-Asteroid Belt

-Outer planets: Jupiter, Saturn, Uranus, Neptune

-Oort Cloud

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Meteorites

3 types:

1. Stony meteorites

2. Iron meteorites

3. Stony-iron meteorites
-Small asteroids

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Comets

-Made of ice and rock

-Come from Oort cloud beyond Neptune

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Early Earth

-Denser core

-Mostly molten iron

-Many meteorite attacks

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Earth Now

-Cooler

-Solid inner core, liquid outer core

-Slushy mantle and crust

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Moon

-Formed when a Mars sized body hit Earth and created debris

-Formed 30-60M years after formation of Earth

-Small, metallic core

-No magnetic field

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Mars

-Polar ice caps and dust storms

-Water in soil
--Used to contain a lot of water

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Atoms

-Electrons

-Nucleus (protons and neutrons)

-Neutral charge

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Atomic Number

= Number of protons

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Mass Number / Atomic Weight

= Protons + neutrons (nucleons)

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Isotopes

-The same elements with different atomic weights

-Vary in number of neutrons

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Chemical Bonds

-2 or more atoms form a molecule

-Reaction: formation of molecule

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Ion

-Charged atom

-Cation: positively charged

-Anion: negatively charged

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Ionic Bond

Atom loses electron to other atom

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Covalent Bonds

-Atoms share electrons

-Stronger bonds

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Crystal Lattice

-3D molecular structure of molecules

-Configuration related to size and number of ions

Note: some minerals (such as sapphires and rubies) are chemically the same, but impurities in their lattice will make them present as different minerals!

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Mineral Properties

Hardness, density, crystal habit (shape), colour etc.

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Mineral Types

-Over 4500 types

-2 dozen common types

-Silicates
--Silicon, oxygen
--Most common

-Carbonates, Sulfates, Halides etc.

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Igneous Rocks

-Defined by composition and crystal size

-Created by cooling magma

-Cooling rate defines crystal size
--Rapid: fine grain crystals
--Slow: coarse grain crystals

-Composition:
--Mostly silicates
--Felsic (granite)
--Mafic (basalt)

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Sedimentary Rocks

-Produced by weathering, erosion, depositions etc.

-Contains skeletal and shell material

-Siliciclastic rock
--composed of silicate minerals

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Conglomerate

Made from pebbles

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Clastic Rocks

-Rocks sorted by grain size

-Poorly sorted = mixed grain sizes

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Chemical Rocks

-Evaporites
--From seawater
--Halides and sulfates are common

-Chert / Silica (flint)

-Carbonate Rocks
--Sediments
--Mostly tropical / subtropical

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Sedimentary Structures

-Ripples formed by wind or water

-Cracks (synsedimentary deformation)
--desiccation
--intrastratal shrinkage
--sediment injection
--convolute bedding

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Lithification

-Process of sediments becoming rocks

-Neomorphism, replacement and dissolution

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Neomorphism

Recrystallization of CaCO3

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Metamorphic Rocks

Created using high temperature and pressure

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Metamorphic Grade

Level of pressure / temperature at time of alteration

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Sedimentary Environments

-Sediments created, deposited and recorded in oceanic or continental environments

-Accumulate in sedimentary basins

-Characteristics of rock provide evidence on how / when the rock formed

-Can contain paleosols (fossil soils) and lake (lacustrine) deposits