Powerpoint Presentation Physical Geology, 10e

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Sediment and Sedimentary Rocks, plus Metamorphic
RocksChapter 6 and 7
Objectives Know the source area for sedimentary
material Understand sediment transportation How
does sediment change to sedimentary rocks Know
the types of sedimentary rocks
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Relationship to Earths Systems
Atmosphere Most sediments produced by
weathering in air Sand and dust transported by
wind Hydrosphere Water is a primary agent in
sediment production, transportation, deposition,
cementation, and formation of sedimentary
rocks Biosphere Biological activity key to
formation of sedimentary rocks Petroleum and coal
resources have biological origin
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Sediment
Sediment Classified by particle size
Boulder - gt256 mm Cobble - 64 to 256 mm Pebble -
2 to 64 mm Sand - 1/16 to 2 mm Silt - 1/256 to
1/16 mm Clay - lt1/256 mm
Gravel
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Sediment Source Area
Chemical Weathering Feldspar Mica to
clay Calcite to calcium and bicarbonate ions
in solution Olivine to Fe or Mg oxide
residues Halite to salt water Physical
Weathering
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From Sediment to Sedimentary Rock
Transportation Movement of sediment away from
its source, typically by water, wind, or
ice Rounding of particles occurs due to abrasion
during transport Sorting occurs as sediment is
separated according to grain size by transport
agents, especially running water Sediment size
decreases with increased transport distance Poor
sorters of sediment glaciers Well sorted
grains that are sorted are of similar size
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From Sediment to Sedimentary Rock
Deposition Settling and coming to rest of
transported material Accumulation of chemical or
organic sediments, typically in water. Chemical
deposition can be controlled by temperature,
pressure, or chemistry of a solution Environment
of deposition is the location in which deposition
occurs Deep sea floor Beach Desert dunes River
channel Lake bottom
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From Sediment to Sedimentary Rock
Preservation Sediment must be preserved, as by
burial with additional sediments, in order to
become a sedimentary rock On land preservation
more erosion, less likely Sea preservation
better environment Lithification General term
for processes converting loose sediment into
sedimentary rock.
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Sedimentary Rocks
Produced from weathering products of
pre-existing rocks or accumulated biological
matter Detrital rocks Chemical rocks Organic
rocks Sedimentary rock types and sedimentary
structures within the rocks give clues to past
environments Fossils in sedimentary rocks give
clues to the history of life Important resources
(coal, oil) are found in sedimentary rocks
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Types of Sedimentary Rocks
Detrital sedimentary rocks Chemical
sedimentary rocks Organic sedimentary rocks
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Clastic Sedimentary Rocks
Breccia and Conglomerate Coarse-grained clastic
sedimentary rocks Sedimentary breccia composed of
coarse, angular rock fragments cemented
together Conglomerate composed of rounded gravel
cemented together Sandstone Medium-grained
clastic sedimentary rock Types determined by
composition Quartz sandstone - gt90 quartz
grains Arkose - mostly feldspar and quartz
grains Graywacke - sand grains surrounded by
dark, fine-grained matrix, often clay-rich
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Clastic Sedimentary Rocks Fine Grained
Shale Fine-grained clastic sedimentary
rock Splits into thin layers (fissile) Silt- and
clay-sized grains(1/3 and 2/3) Sediment
deposited in lake bottoms, river deltas,
floodplains, and on deep ocean floor Siltstone Sli
ghtly coarser-grained than shales Lacks
fissility Mostly Silt grains Claystone
Predominantly clay-sized grains
non-fissile Mudstone Silt- and clay-sized grains
massive/blocky Lack lamination and non fizzile
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Chemical Sedimentary Rocks
Carbonates Contain CO3 as part of their chemical
composition Limestone is composed mainly of
calcite Most are biochemical, but can be
inorganic Often contain easily recognizable
fossils Chemical alteration of limestone in
Mg-rich water solutions can produce
dolomite Chert Hard, compact, fine-grained,
formed almost entirely of silica Can occur as
layers or as lumpy nodules within other
sedimentary rocks, especially limestones Evaporite
s Form from evaporating saline waters (lake,
ocean) Common examples are rock gypsum, rock salt
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Seven kinds of Chemical Sedimentary Rock
Travertine intergrown calcite crystals Oolitic
Limestone tiny beadlike spherical grains
of calcite. Dolostone an aggregate similar to
calcite/will fizz in powdered form/has Mg in
structure(tougher) Rock gypsum aggregate of
gypsum crystals Rock salt aggregate of halite
crystals Chert crystals are not visible at
all Ironstone composed of hematite, limonite,
or other iron bearing minerals.
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Biochemical(organic) Sedimentary Rocks
Limestone composed of animal skeletons
(seashells, corals) Peat compacted deposit
of brown plant fragments Bituminous Coal
black rock composed of charcoal or brittle
shiney layers of carbon.
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Detrital (clastic) Sedimentary Rock
Mudstone if its fizzle, its called shale. It
can be called siltstone or claystone depending
on its make up. Sandstone composed mostly of
detrital sand-sized particles quartz sandstone
mostly quartz arkose mostly feldspar graywacke
composed of a mixture of sand-sized and
mud-sized grains Breccia Angular gravel sized
grain, poorly to moderately sorted. Conglomerate
rounded to well-rounded, poorly to moderately
sorted.
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Organics in Sedimentary Rocks
Coal Sedimentary rock forming from compaction
of partially decayed plant material Organic
material deposited in water with low oxygen
content (i.e., stagnant) Oil and natural
gas Originate from organic matter in marine
sediment(diatoms and algae) Subsurface cooking
can change organic solids to oil and natural
gas Can accumulate in porous overlying
rocks Follow a similar process as coal, but is in
marine environment (continental shelves) Sandy
layers are great collection places for oil and gas
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Sedimentary Structures
Sedimentary structures Features within
sedimentary rocks produced during or just after
sediment deposition Provide clues to how and
where deposition of sediments occurred Bedding Ser
ies of visible layers within a rock Most common
sedimentary structure Cross-bedding Series of
thin, inclined layers within a horizontal bed of
rock Common in sandstones Indicative of
deposition in ripples, bars, dunes, deltas
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Sedimentary Structures
Ripple marks Small ridges formed on surface of
sediment layer by moving wind or water in shallow
environments. Graded bedding Progressive change
in grain size from bottom to top of a bed as
they enter a body of water that is standing
still. Mud cracks Polygonal cracks formed in
drying mud Fossils Traces of plants or animals
preserved in rock Hard parts (shells, bones)
more easily preserved as fossils
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Formations
Formation Often based on rock type, but not
limited to it. There has to be some observable
characteristic to make it recognizable. Such as
sedimentary layer, limestone beds, can be
separated by fossil types, and igneous or
metamorphic layer. Contact is the boundary
surface between the two different rock types.
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Sedimentary Rock Interpretation
Sedimentary rocks give important clues to the
geologic history of an area Source area Locality
that eroded and provided sediment Sediment
composition, shape, size and sorting are
indicators of source rock type and relative
location Study of direction and
distance Depositional environment Location where
sediment came to rest Sediment characteristics
and sedimentary structures (including fossils)
are indicators Examples glacial valleys,
alluvial fans, river channels and floodplains,
lakes, deltas, beaches, dunes, shallow marine,
reefs, deep marine
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Plate Tectonics and Sedimentary Rocks
Tectonic setting plays key role in the
distribution of sedimentary rocks Occurrence of
specific sedimentary rock types can be used to
reconstruct past plate-tectonic settings Erosion
rates and depositional characteristics give clues
to each type of tectonic plate boundary
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Metamorphism, Metamorphic Rocks, and Hydrothermal
RocksChapter 7
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Metamorphic Rocks

• Metamorphism refers to solid-state changes to
  rocks in Earths interior
• Rocks produced from pre-existing or parent rocks
  in this way are called metamorphic rocks
• Geologically they are blocks of relatively light
  weight rock(felsic) that " float" above sea level
  on the earth's hot plastic interior. This can be
  found east of The Rockies and west of the
  Appalachians.

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Factors Controlling Metamorphic Rock
Characteristics

• Temperature during metamorphism
• Pressure during metamorphism
• Confining pressure applied equally in all
  directions
• Pressure proportional to depth within the Earth
• increases 1 kilo bar(1000x atmospheric press)
  per 3.3 km of burial within the crust

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Factors Controlling Metamorphic Rock
Characteristics

• Texture and mineral content of metamorphic rocks
  depend on
• Parent rock composition
• Temperature and pressure during metamorphism
• Confining and differential pressure
• Effects of tectonic forces
• Effects of fluids, such as water(exchange of
  Ions)
• Metasomatism
• Parent rock composition

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Factors Controlling Metamorphic Rock
Characteristics

• Tectonic forces (Differential Stress)
• Often lead to forces that are not equal in all
  directions (differential stress)
• Planar rock texture of aligned minerals produced
  by differential stress is known as foliation
• Foliation increases with pressure and time
• Three types of textures

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Factors Controlling Metamorphic Rock
Characteristics

• Fluids
• Time

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Metamorphic Rock Classification

• Classification based on rock texture

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Types of Metamorphism

• Contact (thermal) metamorphism
• High temperature is dominant factor
• Produces non-foliated rocks
• Occurs adjacent to magma bodies intruding cooler
  country rock
• Occurs in narrow zone (1-100 m wide) known as
  contact aureole
• Rocks may be fine- (e.g., hornfels) or
  coarse-grained (e.g., marble, quartzite)

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Types of Metamorphism

• High pressure is dominant factor
• Regional metamorphism
• Results in rocks with foliated textures
• Prevalent in intensely deformed mountain ranges
• May occur over wide temperature range
• Higher pressure and temperature will produce
  increased metamorphic grade
• Prograde metamorphism of shale produces

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Types of Metamorphism

• Partial melting during metamorphism produces
  migmatites
• Migmatites
• Shock metamorphism is produced by rapid
  application of extreme pressure
• Meteor impacts produce this
• Shocked rocks are found around and beneath impact
  craters

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Plate Tectonics and Metamorphism

• Regional metamorphism associated with convergent
  plate boundaries
• Pressure proportional to depth
• Temperature varies laterally at convergent
  boundaries
• Isotherms bow down in sinking oceanic plate and
  bow up where magma rises
• Wide variety of metamorphic facies

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Hydrothermal Processes

• Rocks precipitated from or altered by hot water
  are referred to as hydrothermal
• Common at divergent plate boundaries
• Hydrothermal processes
• Metamorphism
• Metasomatism
• Formation of hydrothermal rocks
• Water passes through rocks and precipitates new
  minerals on walls of cracks and in pore spaces
• Metallic ore deposits often form this way (veins)