Geology G100 Quick review for Test

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Geology G100 Quick review for Test 2
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Sedimentation and Sedimentary Rocks

• What is a sedimentary rock?

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Sediments

• Sediments are loose fragments of solid
  materials- pre-existing rocks, remains of
  organisms, and precipitation of minerals
• Sediment textures- size, shape, and arrangement
• are determined by transportation and depositional
  processes
• Sorting
• selecting particle based on size, shape and
  density
• Shape
• angular or irregular grains become rounded
• longer travels lead to more rounding of grains

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From Sediments to Sedimentary Rocks

• Pressure, heat, and underground circulating
  water produce changes in rocks- known as
  Diagenesis
• Lithification- conversion of loose sediments into
  solid sedimentary rocks
• Compaction- weight of overlying materials
• Cementation- mineral precipitated in pore spaces
• Recrystallization- less stable minerals change to
  new stable minerals

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Sedimentary Structures

• Physical features that reflect condition of
  deposition
• (how and where?)
• Beddings (stratification)
• sediments in distinct layers- separate
  depositional environments
• Graded beddings
• deposition occurs in relatively quiet waters
• Cross bedding
• sedimentary layers at an angle to underlying
  layers
• Ripple marks
• small surface ridges- produced by water or wind
• Symmetrical Asymmetrical
• Mud crack
• muddy sediments that dry and contracts
• Bioturbation
• No drawing provided ?

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Classification of Sedimentary Rocks

• Detrital and Chemical
• Detrital- based on grain size
• Mudstone- clay and silt size- constitute gt 50
  of all detrital sedimentary rocks
• Shale- clay and silt size particles- parallel
  layers- fissility
• Siltstone- silt size particles
• Sandstone- quartz arenite, arkose (with 25
  feldspar), graywacke (lithic, dark fragments
  fines)
• Breccia- angular gravel size particles
• Conglomerate- rounded gravel size particles

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Sed. rock Classification contd.

• Chemical- organic and inorganic
• Organic- derived from living organism/biogenic
• Limestone and chert- composed of skeletal remains
  of animals
• coal- carbon rich remains of terrestrial plants
• Inorganic Sedimentary Rocks
• Direct precipitation from water
• e.g. Limestone, chert
• Evaporation of saline water
• evaporite- gypsum, halite, dolostone

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Sedimentary Environments

• Continental
• rivers, lakes, caves, desert, glaciers- mostly
  detrital
• Transitional- coastal- along ocean shores
• estuaries and deltas
• Marine
• shallow-above continental shelf (lt 200m (700))
• deep- beyond the continental shelf
• Sedimentary Facies- sediments deposits at the
  same time but in different environments as a
  horizontal continuum of distinct rock type

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Metamorphic Rocks

• Altered rocks

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Definitions

• Metamorphic rock is formed when existing rocks
  change due to subjection to pressure and or
  temperature
• Any rock can undergo metamorphism
• Metamorphism is the process by which heat,
  pressure, and chemical reactions deep within the
  earth alter the mineral content and or structure
  of existing rock without melting it down

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What Drives Metamorphism

• Heat
• Accelerate pace of chemical reactions
• Pressure
• Lithostatic (confining)- rock becomes smaller and
  denser
• Directed- minerals become aligned- Foliation
• Circulating Fluids
• Ions in water- change mineral composition
• Parent Rocks
• Original rocks composition will affect the
  outcome of metamorphism

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Types of Metamorphism

• Contact
• Heat is the dominant factor
• Area affected generally smaller than regional
  metarmorphism
• Regional are two types with extensive coverage
• Burial- occurs in deep sedimentary basins- no
  plate tectonics involved
• Dynamothermal- occurs where converging plates
  squeeze a rock caught between them
• Others
• Hydrothermal- involves hot water from magma
• Fault-zone- rocks grinding past one another
• Shock- meteorites strike
• Pyrometamorphism- lightning

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Metamorphic Rock Types

• Foliated- based on type of foliation
• Slate- fine grain
• Phyllite- fine grain with sheen
• Schist- has split appearance
• Gneiss- layers/bands of minerals
• Non-foliated- based on mineral composition
• Marble
• Quartzite
• Hornsfel
• Mixed Rock
• Migmatite- indicates partial melting

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Metamorphism Temperature Pressure

• Information about degree to which a
  metamorphic rock differs from its parent material
• Metamorphic Grade-
• low (200-400) slate
• high (500-800) gneiss
• Index minerals/metamorphic Zones are used to
  determine metamorphic condition of temperature
  and pressure
• Chlorite, muscovite-low grade (low P/T)
• Garnet, staurolite- intermediate
• Sillimanite- high grade (high P/T)

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How old is the Rock?

• How can we tell the age of rocks?
• Geochronology

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Geochronology

• Geochronology is the study of time in relation
  to earths existence
• Relative Dating
• Determines how old a rock is in relation to its
  surrounding
• Numerical Dating (Absolute Age?)
• Determines actual age in years

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Relative Dating

• Relies on Key Principles such as
• Uniformitarianism- the present is key to the past
• Original horizontality
• Sediments deposited in horizontal layers
• Superposition
• Youngest rocks are on top (assuming no tectonic
  activity)
• Cross-cutting relationships
• Cut layer is older than cutting rock
• Faunal succession
• Organisms succeed one another in recognizable
  reproducible pattern
• Unconformity
• Represents a break (gap) in the rock record

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Numerical Age

• Isotope Dating relies on the rate of decay of
  radioactive isotopes within a rock
• Radioactive isotopes have nuclei that
  spontaneously decay emitting or capturing a
  variety of subatomic particles
• Decaying radioactive isotope- parent isotopes
  decay to form daughter isotopes
• Half-life- is the time it takes for half the
  atoms of parent isotope to decay
• Some radioactive isotopes with daughter products
• U-238 gt Pb-206 K-40 gt Ar-40 C-14 gt N-14

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Factors Affecting Isotope Dating Results

• Isotope dating is more useful for igneous rocks
• Clock is set when igneous rock crystallizes
  locking the radioactive isotopes within its
  crystal lattice
• Rock/Mineral must be a closed system
• Atoms of parent and daughter are still present in
  rock/mineral being dated
• Condition of parent Material
• Fracture, weathering and migrating ground water
• Age of Substance
• Enough measurable daughter isotope, use
  appropriate radioactive isotope

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Other Numerical Dating Techniques

• Fission Track
• High speed particles emitted during radiation may
  pass through crystal leaving tears within the
  crystal- the older the rock, the more fission
  tracks
• Dendrochronology (Tree-Ring dating)
• Annual growth rings
• Varve- deposited layers of lake-bottom
• Paired layers of sediments
• Lichenometry
• Lichens grow at a fairly constant rate
• Cosmogenic isotopes
• Used in dating land features

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Geologic Time Scale

• Contrasting several dating techniques
  chronicling Earths history to produce a geologic
  Time Scale
• Geologic Time Scale- divided into Eons, Eras,
  Periods, and Epoches
• Phanerozoic Eon (evidence of life began) divided
  into three eras
• Paleozoic (ancient life) dominated by marine
  invertebrates
• Mesozoic (middle life) dominated by reptiles
• Cenozoic (recent life) dominated by mammals

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The Earth moves

• Its not an earthquakebut the earth materials

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Mass Movement

• Process that transports Earths materials
  downslope by the pull of gravity
• Friction, strength, and cohesiveness of materials
  resist mass movement
• Angle of slope (sloppiness), water content, lack
  of vegetation, and biological disturbances
  enhance mass wasting

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Causes of Mass Movement

• Steepness of Slope
• Faulting, folding, river cut, glacial, coastal
  wave create steep slope
• Composition of Material either promotes or
  resists mass wasting
• Solid /Unconsolidated
• Vegetation- lack of which promotes mass wasting
• Water Content- increases weight of material and
  reduces friction between planes of weakness
• Human/Other Disturbances

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Triggers for Mass Movement Events

• Natural Triggers
• Climatic- torrential rains and snow melt
• Geologic- earthquakes and volcanic eruptions
• Human-Induced Triggers
• Oversteeping of slopes- excavation
• Overloading- excess water, building, and other
  construction
• Deforestation/overgrazing of vegetation
• Loud noise- trains, aircrafts, blasting

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Mass Wasting Types

• Classification is based on composition and
  velocity
• Creep- slowest form
• Slides- move along a plane of weakness
• Slumps- move along concave slip surfaces
• Flows- rocks and soils have with excess water
• Falls- fastest type
• Landslide is a general term for downslope
  movement

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Reducing Mass Movement

• Avoiding
• Predicting mass movement
• Terrain analysis, field visit, eye
  witness/recorded accounts
• Vegetation- over grazing, harvesting
• Preventing
• Develop Prevention Plan
• Enhance Forces that Resist or Reduce forces of
  mass wasting
• Structural Approach- reduce slope
• Non-Structural Approach- tree, chemical stability

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Study for Test 2

• Use the class notes/textbook and the links
  provided in the syllabus.
• Its an open book test and the Honor System
  prevailsno help from any one, no collaboration

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Some key words for Test 2

• Some key words for test 2
• Cementation, crystallization, Compaction
• Transportation of sediments results in..
• Rock salt, sandstone, siltstone, coal, arkose,
  graywacke
• Quartzite, marble, slate, schist, migmatite,
  order of metamorphism
• Types of metamorphism, parent materials of some
  metamorphic rocks
• Relative age and principles of Superposition,
  original horizontality, faunal succession,
  cross-cutting, unconformities, radiometric
  dating, half life..