Sedimentary Rocks Weathering Mechanical Weathering Types of

Lithification
Sedimentary Rocks
Weathering
The sediments that make up sedimentary rocks are produced by:
Sediments
Mechanical & Chemical Weathering
Deposition
Transport
Erosion
Weathering
http://www.teachnet-lab.org/ps101/bglasgold/rocks/EFCycleP2.gif
Types of mechanical aka physical
weathering
Mechanical Weathering
Chemical Weathering
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unloading – rx expand when overburden lessened
frost wedging – H2O expands 9% to ice
insolation – solar heating expansion
salt crystals
root wedging
seismic deformation
big point: some
minerals are more
stable than others…
Mineral
Stability
hydrolysis, oxidation,
dissolution, dehydration,
solutioning, bio-chemical
weathering
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Products of Weathering
Erosion & Transport
• Lithic (Rock) Fragments
(granite, basalt,schist, etc.)
• Dissolved Ions
(Calcium, Potassium, Sodium, etc.)
• Rust Minerals (Hematite, Goertite, etc.)
• Clay Minerals
Water
Wind
Ice
Gravity
(Bentonite, Montmorillonite, etc.)
• Residual Minerals
(Quartz, Orthoclase, Muscovite, etc.)
Common Depositional Environments
Lithification
Sediment
Marine shoreline and near-shore
environments
Cementation
Typical Cements:
•Calcite
•Quartz
•Iron oxide
Rock
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Types of Sedimentary Rocks
Sedimentary Rocks
Detrital or clastic Rocks
Chemical Rocks
Identification
vs.
Note: Use many of the same terms to describe
sediments & sedimentary rocks.
Only difference is lithification!
Difference: Texture
Detrital (Clastic Texture)
vs.
Chemical (Crystalline Texture)
Detrital Rock Composition
Detrital Rocks
• Lithic Fragments
• Quartz
• Clay Minerals
• Fossil Fragments
• Rust Minerals
• Orthoclase
• Muscovite / Biotite
Detrital Rock Texture
Clastic Texture
• Grain Size
• Grain Sorting
• Grain Rounding
• Sediment Maturity
Grain Size
•Gravel
2mm
•Sand
1/16 mm
•Mud - Silt
1/256 mm
•Mud - Clay
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Sorting
Detrital Rock Names
(Based Primarily on Grain Size)
Gravel -Sized:
Conglomerate
Sand Sized: Sandstone
Mud-Sized:
Mudstone
Siltstone
Shale
Gravel Sized Detrital Rocks
(Subdivided Based on Grain Roundness)
Conglomerate
Breccia
Maturity
Quartz Sandstone
Lithic Sandstone
Mature
•Well Sorted
•Well Rounded
•All Quartz
Immature
•Poorly Sorted
•Angular grains
•Mixed Composition
including clay
Arkose (Sandstone)
Sandstones
Greywacke
(Subdivided based
on maturity)
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Sandstones Under a Scope
Detrital Sedimentary Rock ID
Chemical Rock Texture
Crystalline Texture
• Coarse
• Fine
Chemical Rocks
(Names based mainly on composition)
Chemical Sedimentary Rocks
(Names based primarily on composition)
Composition
• Calcite
• Quartz (silica)
• Halite
• Gypsum
• “Carbon” / Plant
Remains
Basic Rock Name
• Limestone
• Chert
• Rock Salt
• Rock Gypsum
• Peat or Coal
Chemical Rocks (cont.)
Evaporites
Limestones
Crystalline
Limestone
Chert
Fossiliferous Limestone
Rock Salt
Chalk
Rock
Gypsum
Coal
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Sedimentary Rocks
Interpretations
What do Sedimentary Rocks Record?
•Source of sediment
•Erosion and Transport Agent
•Distance of Transport
•Depositional Environment
•Paleogeography/Tectonic Setting
Chemical Sedimentary Rock ID
Interpretation of Composition
Note About Detrital Rock
Color & Composition
• Grain Size
Smaller is often darker
Detrital Rocks:
• Source of sediment
• Exposure to Weathering
(Distance of Transport)
(Type of Climate)
• Composition
Carbon - black or brown
Quartz - tan, clear, white
Orthoclase – orange or pink
• Depositional Environment
Iron on land - red
Iron in deep, oxygen poor water - green
Detrital Rock Names
Interpretation: Grain Size
(Based Primarily on Grain Size)
• Gravel
Gravel -Sized:
Conglomerate
Sand Sized: Sandstone
Mud-Sized:
Mudstone
Siltstone
• High Energy
• River, Beach
• Sand
• River, Beach, Desert
• Silt
• Delta, Shallow Ocean
• Clay
• Low Energy
• Deep Ocean, Lake,
Swamp
Shale
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Interpretation: Sorting
Clast Supported Conglomerate
(River Deposits)
Interpretation: Transport Agent
Poorly Sorted Gravity and Glaciers (and Rivers)
Well Sorted
Water and Wind
Matrix Supported Conglomerate
(Glacial/Landslide Deposits)
Interpretation: Grain Roundness
2.2 Gyr Conglomerate
Short
“Modern”
Glacial Sediments
Limestone
Crystalline
Limestone
Interpretation:
Distance of Transport
Far
Formation of Limestone
Calcite Precipitates in
Warm Water
Water Under Low Pressure (Shallow)
Fossiliferous Limestone
Or
It is secreted by biological organisms
Clams, Mussels, Scallops, etc.
Corals
Foraminifera
Chalk
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Chalk
(Foraminifera)
Limestone Represents:
Shallow Tropical Ocean
Travertine
(Limestone)
Black Sea
Black Sea
Chert (Flint, Jasper, Agate…)
Diatom Skeletons
Chemical sed. rk formed
via silicious ooze in the
deep sea. Source of silica
= tests (tiny shells) of
radiolarians and diatoms
(which are made of silica)
Radiolarians
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Evaporites:
Bonneville Salt Flats, Utah
Rock
Gypsum
Chert
Represents
Deep Ocean
Rock Salt
Isolated,
Arid,
Salty
Sea/Lake
Peat and Coal
Swamp, Bog
Coal beds in Puget Group sedimentary rocks near Ashford
Sedimentary features and
structures
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beds
crossbeds
ripple marks
graded beds
fossils
mud cracks
raindrop imprints
etc
Channel fill
Sharon Conglomerate, Cuyahoga River valley,
Ohio
~315 Ma
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Crossbedded sandstone
dune deposition
by wind!
Planar cross beds
Sharon Conglomerate,
lower Pennsylvanian
Age (~315 Ma),
Cuyahoga River valley,
Ohio; interpreted as a
braided stream
sedimentary
environment (lens cap
~52 mm) – dune
deposition by water!
Zion National Park. Festooned cross beds deposited by wind.
How crossbeds form—migrating dunes!
Turbidity currents
aD:\digital_content\animations_library\0009.swf
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Modern mud
cracks
Ancient mud
cracks in shale
modern mud cracks,
Ceres Road 2007
flood-deposited muds
Current ripples in wet sediment,
Baja CA
Ripple marks in sandstone, Capitol
Reef National Park, Utah
Pat Pringle, photo
Ripple marks in tilted Puget Group sedimentary rocks
of Eocene age near Wilkeson WA
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Fossil shells in sandstone, CA
Fossil fish from Eocene Green River Shale in western
Wyoming
Fossil metasequoia leaf from rocks
several miles east of Packwood,
Oligocene age
Lithologic Indicators of Climate
http://www.scotese.com/
legend.htm
dipping beds in Centralia
Coal Mine, view to south
fossils from Skookumchuck
Formation
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<= Portunites triangulum Crab,
Eocene, Wahiakum Co., Washington
http://www.geo-tools.com/fossils.htm
More WA fossils!
http://orerockon.com/For_sale.htm
Dinosaur footprint, Tuba City, AZ
Sorting
Misc. Sedimentary Features
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Sorting
Roundness
Orientation: random vs. preferred
Color
Preferred orientation
Imbrication = strong current
 Current direction is
right to left
Color
• Black = reducing conditions (ex: pyrite,
MnO2, organic matter)
• Green = near oxidation/reduction margin
(ex: glauconite, chlorite)
• Red = oxidation (ex: hematite, “red beds”—
most of these are subaerial)
Color is a function of size and composition
Finer grained = truer colors
Weathering & matrix cement also influence
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Photo donated by Larry McMIllan
http://www.ci.tenino.wa.us/TeninoQuarry1_small.jpg
Eocene McIntosh Formation:
Tenino Sandstone
outcrop along rr tracks near Chehalis R., Galvin WA
Rock Units
• FORMATION– Extensive enough to show on a map
– Distinctive from neighboring rock units
– Named locally
• CONTACTS
– Sedimentary contacts – bounding surfaces
between two sedimentary units
Grand Canyon – an awesome place to see strata!
Monument Creek
Grand Canyon
The great unconformity
Track of 1984 debris flow
Bob Webb, photo, 1986
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Granite Rapid, Grand Canyon
volcanologist
for
Bob
Webb, photo, 1986
scale
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