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Geology 3550
Sedimentation &
Stratigraphy
Weathering
Weathering
Weathering is …..
I Controls
III Products
II Mechanisms
IV Temporal
Patterns
Mechanical
Chemical
I Controls on Weathering
• Source Rock
• Climate
• Topography
• Tectonics
Fractures are very important
Surface Area Effects
Not all rocks are created equal……
~1900oC
Low
Temperature
high
Bowen’s Reaction Series
~500oC
GRANITE
* Quartz – SiO2
* Orthoclase (K-spar) – KAlSi3O8
Albite (Na plag) – NaAlSi3O8
Muscovite
Biotite
BASALT
* Pyroxene – Mg,Fe,Ca,Na,Al (Si2O6)
* Anorthite (Ca plag) – CaAl2Si2O8
Olivene – Fe/Mg2SiO4
Relative Stability of Common Rocks
low
high
Limestone
Dolostone
Siltstone
Sandstone
Basalt
Granite
Chert
Quartzite
I Controls on Weathering
• Source Rock
• Climate
• Topography
• Tectonics
temperature, moisture, plants
Water is a polar molecule
Hydrogen Bonds
Covalent Bonds
Water is the
“universal
solvent”
Inverse relationship between topographic
relief and weathering
Slope
steep
gentle
weathering
little
intense
II Mechanisms of
Weathering
Mechanical
• Physical
Exfoliation
Frost Wedging
Impacts
Spheroidal
Weathering
•
Biological
Root
Wedging/Plucking
The Importance
of “Plants”
Physical Weathering –
Root Wedging
(Also important in chemical weathering –
Organic acids and CO2 generation)
II Mechanisms (cont.)
Chemical
• Inorganic
Hydrolysis
Carbonation
Solution
Oxidation
Hydration
Halmyrolysis
Water is very important
CO2 is very important
Hydrolysis Reactions
Al silicate + H2O + CO2 ---> clay + Si (SiO2 or H4SiO4)
(e.g. Orthoclase/K-spar -- KAlSi3O8)
Note: H2O + CO2 <—> H2CO3 (carbonic acid)
• Illite – From moderate weathering of granites
K (Al, Mg, Fe) (Al Si4) O10 (OH)2
Common Clays
• Montmorillonite – From moderate weathering of basalts
(Na, Ca) (Al, Mg)2 Si4O10 (OH)2 . nH2O
• Kaolinite – From intense weathering of igneous source
3 Al2 (Si2O5) (OH)4
GRANITE
* Quartz – SiO2
* Orthoclase (K-spar) – KAlSi3O8
Albite (Na plag) – NaAlSi3O8
Muscovite
Biotite
BASALT
* Pyroxene – Mg,Fe,Ca,Na,Al (Si2O6)
* Anorthite (Ca Plag) – CaAl2Si2O8
Olivene – Fe/Mg2SiO4
GRANITE
BASALT
* Quartz – SiO2
* Orthoclase (K-spar) – KAlSi3O8
Albite (Na plag) – NaAlSi3O8
Muscovite
Biotite
* Pyroxene – Mg,Fe,Ca,Na,Al (Si2O6)
* Anorthite (Ca plag) – CaAl2Si2O8
Olivene – Fe/Mg2SiO4
Hydrolysis
Quartz – SiO2
Illite – K Clay
(K loss)
Montmorillonite – Mg Clay
More weathering
(Mg loss)
Kaolinite
(Si loss)
More weathering
Bauxite – Al(OH)3
Silic Acid – H4SiO4
(Fe loss)
Hematite – Fe2O3
Bauxite (trace)
Carbonation Reactions
Carbonate + H20 +CO2 —> Ca++ + 2HCO3
Produce microkarst, karst
terranes, sink holes, and caves
Microkarst - Jamaica
Oxidation Reactions
Metal + O2 (+ H20) —> metal oxide
(e.g. Pyrite, FeS2)
—> (Hematite, Fe2O3 + SO4 + H)
(e.g. Pyroxene, ~FeSiO3) —> (Hematite, Fe2O3 + SiO2)
Red Beds
Additional Reactions
• Direct Solution
Soluble mineral + H2O <—> dissolved ions in solution
(e.g. Anydrite - CaSO4, Halite - NaCl) <—> Ca++ Na++ Cl-- SO4-• Hydration
Nonhydrated mineral + H2O —> hydrated mineral
(e.g. Hematite - Fe2O3)
—> (Goethite - 2Fe OOH)
with a change in volume
(e.g. Anhydrite - CaSO4)
—>
(Gypsum - CaSO4 . 2H2O)
Halmyrolysis - Weathering
of Ocean Crust
Black Smoker
II Mechanisms (cont.)
Chemical Weathering
• Biological
Organic Acids
CO2
Chelation
Fe, Al silicate + organic compound —> chelated cations in solution
(e.g. Lichen attacking rocks)
III Products of Weathering
• Resistates
**Quartz
• Secondary Minerals
**Clays
Oxides
Hydroxides
• Soils – weathered rock plus
organic material
• Dissolved Ions
HCO3 Ca H4SiO4
SO4 Cl Na Mg K
These become chemical sedimentary rocks – e.g. ……..
IV Temporal Patterns
• Cyclical changes driven by tectonics and climate
• Unidirectional changes driven by planetary and
biological evolution
- Atmospheric oxygen by 2.0Ga
- Appearance of land plants by ~ 400Ma
- Appearance of grasses by ~100Ma
Geology 3550
Sedimentation &
Stratigrphy
Erosion, Transport and
Deposition of Sediments
Ice and mass movements
are capable of moving large
particles, but are volumetrically
less significant than wind and
water
Erosion, Transport and Deposition of Sediments
I Controls On Erosion
II Mechanisms of Erosion and Transportation
III A Quick Look at Fluid Flow
IV Streams as Transport Agents
V Deposition of Sediments
I Controls On Erosion
•Source
Consolidated vs unconsolidated
Fractured vs not
Crystalline vs sedimentary
Weathered vs fresh
•Climate
High precipitation contributes to erosion
Plants reduce erosion
•Topography
Erosion rate positively correlated
with uplift rate
II Mechanisms of Erosion and Transportation
•Mass Movements
Dry
Rock Fall, Rock Slide
Fluid-Assisted
Grain Flows, Fluidized Sed Flows, Debris Flows,
Turbidity Currents
•Ice
Abrasion
Plucking
•Wind
Abrasion (Ventifacts)
Deflation (Desert Pavements?)
•Water (flowing water and waves)
Abrasion and Chipping
Dissolution
Hydraulic Lifting/Entrainment
II Mechanisms of Erosion and Transportation (cont.)
•Ice
-Erosion
Abrasion
Plucking
Oversteepened slopes
- Transport
Material carried on and in the ice
Tills characterized by poor sorting, little rounding
Outwash and wind blown deposits will show
better sorting
Extensive loess deposits
are associated with the
last glaciation
II Mechanisms of Erosion and Transportation (cont.)
•Wind
- Erosion by
Abrasion (Ventifacts)
Deflation (Desert Pavements?)
Favored by dry climate (few plants)
- Transport involves fine material (air may be viewed
as a very low viscosity fluid)
- Deposits tend to be very well sorted
III A Quick Look at Fluid Flow
•Fluids (air and water)
Fluid vs Plastic
Laminar vs Turbulent Flow
Shear Stress (tau τ)
Kinematic (nu ν) and Dynamic (mu μ) Viscosity
Reynolds (Re) and Froude (Fr) Numbers
•Entrainment
Bernoulli Effect
Drag Force
Fluid Force
Hjulstrom Diagram
Wave Orbital Velocity
Laminar vs Turbulent Flow
P&S p. 33
Increasing velocity, decreasing fluid viscosity, increasing
bed roughness, increasing depth, all contribute to turbulent flow
1 Dynamic Viscosity
τ
μ = _____
du/dy
shear stress
rate of deformation
(μ = 0.0131 @ 10o C, fresh water)
2 Kinematic Viscosity
μ
ν = _____
P
dynamic viscosity
density (mass/unit volume)
(P = 0.999gm/c @ 10o C, fresh water)
3 Reynolds Number
ULP
UL
Re = ______ = ______
μ
ν
where U = velocity
(cm/sec)
L = depth (or grain dia) cm
P = density
ratio of fluid inertial forces/fluid viscous forces
500 - 2000, critical threshold for transition from laminar to turbulent
4 Froude Number
U
Fr = _______
SQRT (g L)
where U = velocity (cm/sec)
where g = Gravitational
constant (981 cm/sec2)
ratio of fluid inertial forces/gravitational forces in flow
Fr <1 = tranquil flow
Fr > 1 = rapid flow
predicts sedimentary structures (dunes, antidunes)
Forces Acting on a Grain at Rest
•Gravity
•Friction
•Cohesion
•Fluid lift force (Bernoulli)
•Fluid drag force
•Net fluid force
P&S p.35
5 Drag Force
Τo
FD= _____
N
Τo =
boundary shear stress
number of exposed grains
γ
specific
gravity
Rh
hydraulic
radius
S
~U
slope velocity
Waves
Wave mechanics
•Energy from wind
- Velocity, duration, distance (fetch)
- Surface cohesion important (from
hydrogen bonds between water
molecules)
Waves (cont.)
•Water moves in circular orbits
- Orbital diameter decreases with
depth
- Orbit velocity a function of diameter
- Orbits “feel” bottom at depth ~ ½ λ
Orbits become more elliptical
Wave length decreases
Wave height increases
Breakers form
6 Wave Orbital Velocity
πH
Ut = _______________
T sin h (2 π h/L)
where L = wavelength (m)
T = wave period (sec)
H = wave height (m)
h = water depth (m)
π = pi
@ h =1/2 L, wave feels bottom
@ h = 1/20 L, orbits very elliptical
@ L = 150m, h = 15m, T = 10sec, H = 1m
Ut = 30cm/sec (capable of moving ~1mm grain)
IV Streams as Transport Agents
Terms
•Competency - maximum particle size
- largely determined by velocity
•Capacity - total load
- largely a function of discharge
(volume)
•Discharge - velocity x channel size
- input from tributaries and sheet wash
- Colorado R at Moab ~100 -700 cubic m/sec
- Mississippi R at mouth 173,600 cubic m/sec
- Amazon R at mouth 1,800,000 cubic m/sec
IV Streams as Transport Agents
Terms (cont.)
•Velocity - determined by discharge, gradient,
channel shape, bed roughness
- < 1 to > 30km/hr
•Load
Dissolved
Suspended
Saltation
Traction
IV Streams as Transport Agents
•Stream Profile
Downstream
Changes
•Channel shape
•Gradient
•Tributaries
•Discharge
•Velocity
•Load
V Deposition of Sediments
•Cause - Decrease in energy
Gravity overcomes turbulence and fluid
viscosity
- Settling Velocity/Stoke's Law
- Shape Effects/Zingg Shapes
- Maximum Projection Sphericity
•Environments of deposition
7 Stokes Law
U= C D2
where U = settling velocity (cm/sec)
D = sphere dia. (cm)
(Ps - Pf) g
C= ___________
18 μ
where Ps = density of grain
Pf = density of fluid
@ D= 0.05cm (1 phi), μ = 0.0131, Pf = 0.999,
Ps = 2.65 (quartz)
U = 17.2 cm/sec
Rg (Reynolds grain #) = 57.3
8 Maximum Projection Sphericity
MPS = Cube Root (Ds2/Di Dl)
where Ds = minimum axis
Di = intermediate axis
Dl = maximum axis
(all axes are orthogonal)
Dl
Ds
Di
multiply MPS by sieve diameter to get equivalent sphere size
V Deposition of Sediments
•Environments of deposition - examples………
Geology 3550
Sedimentation &
Stratigraphy
Inorganic Sedimentary
Structures
I Primary Structures
Depositional
• Bedding/Stratification
- Massive - featureless
- Stratified
Graded
Parallel
Cross-stratified
Trough
Hummocky
Tabular Herringbone
Climbing
• Bedding Surfaces
Lenticular
Ripples
Wavy
Dunes
Flaser
I Primary Structures (cont.)
Depositional
• Bedding/Stratification
- Stratified
Graded
Parallel
Cross-stratified
Trough
Hummocky
Tabular Herringbone
Climbing
I Primary Structures (cont.)
Depositional
• Bedding Surfaces
Lenticular
Wavy
Flaser
Ripples
Dunes
Antidunes
P&S p. 55
Lower plane bed
Flow velocity (and grain
size) controls the type
of sedimentary structure
generated
P&S p. 47
I Primary Structures
Erosional
• Scours/Flute Casts
•Tool Marks
• Channels
• Truncation
• Intraclasts
II Secondary Structures
•Dissolution/Precipitation
Vugs
Concretions
Salt Hoppers Geopetal Fills
Mineralized crusts
Dendrites
Birdseye
• Hydration/Dehydration
Mud Cracks
Syneresis Cracks
• Deformational
Slump
Boudinage
Flame
Shock
Teepee
Load Casts
II Secondary Structures (cont.)
• Hydration/Dehydration
Mud Cracks
Syneresis Cracks
• Deformational
Slump
Boudinage
Flame
Shock
Teepee
Load Casts
II Secondary Structures (cont.)
•
Deformational
Slump
Flame
Teepee
Boudinage
Shock
Ball and Pillow
Load Casts
Most are associated with high sedimentation rates……
Geology 3550
Sedimentation &
Stratigraphy
Biogenic Sedimentary
Structures
Biogenic Sedimentary Structures
I Bioturbation
II Bioerosion
III Biostratification
IV “Other” Structures
V Biogenic Structures and Diagenesis
VI Temporal Patterns
Biogenic Sedimentary Structures
I Bioturbation
• Activities
Dwelling
Resting
Locomotion
• Interpretation
- Behavior
- Ichnofacies
- Ichnofabric
- Sediment Parameters
Feeding
Escape
Biogenic Sedimentary Structures
I Bioturbation (cont.)
• Activities
Dwelling
Resting
Locomotion
• Interpretation
- Behavior
- Ichnofacies
- Ichnofabric
- Sediment Parameters
Feeding
Escape
Biogenic Sedimentary Structures
II Bioerosion
• Micro - Micritization
Blue-green algae
• Macro
Sponges, bivalves, sea urchins, parrot fish
• Interpretation
Sedimentation rate
Paleobathymetry (photic zone)
Biogenic Sedimentary Structures
II Bioerosion (cont.)
• Micro - Micritization
Blue-green algae
• Macro
Sponges, bivalves, sea urchins, parrot fish
• Interpretation
Sedimentation rate
Paleobathymetry (photic zone)
Biogenic Sedimentary Structures
III Biostratification
• Biograded Bedding
• Stromatolites
LLH
SH
• Other
Oncoids
Ooids
• Interpretation
Paleobathymetry
Salinity?
Biogenic Sedimentary Structures
III Biostratification (cont.)
• Biograded Bedding
• Stromatolites
LLH
SH
• Other
Oncoids
Ooids
• Interpretation
Paleobathymetry
Salinity?
Biogenic Sedimentary Structures
IV “Other” Structures
• Reef / Bioherm / Biostrome / Thrombolite
• Concretions
• Geopetal Fills
Biogenic Sedimentary Structures
V Biogenic Structures and Diagenesis
• Micritization
• Burrow Mottling
• Silicified Burrows
• Stromatolites and Dolomitization
Biogenic Sedimentary Structures
VI Temporal Patterns
• Little or no burrowing in Precambrian
(Requires metazoa, requires body cavity)
• Shallow burrowing (few cm) in Cambrian
(Implications for intraclasts)
• Increased grazing eliminated stromatolites from
normal, open marine settings after Camb.
• Burrowing depth increase in Devonian
(Problems for sessile benthos?)
• Major expansion in burrowing in Mesozoic
Geology 3550
Sedimentation &
Stratigraphy
Detrital/ Clastic/ Terrigenous/
Extrabasinal Rocks
Detrital/ Clastic/ Extrabasinal/ Terrigenous Rocks
I Classification
Texture
Composition
II Rock types
these categories
are based on
texture - size
Conglomerate/Breccia
Sandstone
Siltstone
Shale/Mudstone
III Diagenesis
Eogenesis
Mesogenesis
Telogenesis
Detrital/ Clastic/ Extrabasinal/ Terrigenous Rocks
I Classification
•Texture - Physical appearance
- Grain Size
- Grain Shape
- Sorting
- Grain/Matrix Relationships
•Composition - Chemistry and mineralogy
II Clastic Rock types
•Conglomerate/Breccia
Orthoconglomerate
(Oligomict, Petromict)
Paraconglomerate
(Diamictite, Tillite)
•Sandstone
Arkose
Litharenite
Quartzarenite/Orthoquartzite
Wackes
•Siltstone
•Shale/Mudstone
Kaolinite
Chlorite (Fe, Mg, SiO2)
Illite (K rich)
Glauconite (K, Fe, SiO2)Montmorillonite (Mg rich)
II Clastic Rock types (cont.)
•Conglomerate/Breccia
Orthoconglomerate
(Oligomict, Petromict)
Paraconglomerate
(Diamictite, Tillite)
•Sandstone
Arkose
Litharenite
Quartzarenite/Orthoquartzite
Wackes
•Siltstone
•Shale/Mudstone
Kaolinite Chlorite (Fe, Mg, SiO2)
Illite (K rich)
Glauconite (K, Fe, SiO2)Montmorillonite (Mg rich)
II Clastic Rock types (cont.)
•Conglomerate/Breccia
Orthoconglomerate
(Oligomict, Petromict)
Paraconglomerate
(Diamictite, Tillite)
•Sandstone
Mudrocks
Arkose
Litharenite
Quartzarenite/Orthoquartzite
Wackes
•Siltstone
•Shale/Mudstone
Kaolinite Chlorite (Fe, Mg, SiO2)
Illite (K rich)
Glauconite (K, Fe, SiO2)Montmorillonite (Mg rich)
III Diagenesis
•Environments
- Eogenesis - near surface
- Mesogenesis - deep burial
- Telogenesis - uplifted, exposed to
ground water
•Changes
- Compaction - porosity reduction
- Cementation - porosity reduction
- Dissolution - creation of secondary porosity
- Formation of new minerals - may increase or
decrease porosity
Geology 3550
Sedimentation &
Stratigraphy
Chemical Sedimentary
Rocks
Chemical/ Precipitates/ Intrabasinal Rocks
I Carbonates
II Siliceous Rocks
III Evaporites
IV Phosphates
V Sedimentary Ironstones
VI Carbon-rich Rocks
VI Standard Rock Symbols
Chemical/ Precipitates/ Intrabasinal Rocks
I Carbonates
•Limestone CaCO3
- Origins
- Dunham and Folk Classifications
- Allochems
•Dolostone CaMg(CO3)2
- Models for Dolomitization
•Carbonate Diagenesis
- Diagenetic Environments
- Diagenetic Changes
Limestone Origins
•Inorganic Precipitation?
- Travertine
Cave Flowstone
Tufa Spring Deposits
- Some marine cements?
•Organic Precipitation
Although most limestones are marine, some do occur in
freshwater lakes with high carbonate content (e.g. Bear
Lake, UT). Freshwater limestones may be
associated with interdune areas in arid regions (e.g.
Navajo Sandstone and related rocks in the western US).
Descriptive terms for limestones that you should not use
Encrinite
Oolite
Coquina
Marl
Chalk
Noncarbonate
Calcareous Shale
Shaley, Dolomitic
Limestone
50%
Shaley
Limestone
Dolostone
Limestone
Dolomite
50%
Calcareous Dolomite
Dolomitic Limestone
Calcite
Chemical/ Precipitates/ Intrabasinal Rocks
I Carbonates
•Limestone CaCO3
- Origins
- Dunham and Folk Classifications
- Allochems
•Dolostone CaMg(CO3)2
- Models for Dolomitization
•Carbonate Diagenesis
- Diagenetic Environments
- Diagenetic Changes
Dolomitization
•Calcite - CaCO3 - is transformed to CaMg(CO3)2
•Favored by high (>1) Mg/Ca ratios in seawater
•Most models increase Mg by removing Ca through formation
of gypsum and anhydrite
•Dorag/Schizohaline/Mixing model does not require high Mg/Ca
•Much dolomite forms secondarily during deep burial diagenesis
and migration of brines
•Stromatolites are often dolomitized as the cyanobacteria contain
Mg in photosynthetic pigments
Chemical/ Precipitates/ Intrabasinal Rocks
I Carbonates
•Carbonate Diagenesis
- Diagenetic Environments
Eogenesis
Mesogenesis
Telogenesis
- Diagenetic Changes
Early cementation - little compaction
Hardground formation
Neomorphism - crystal growth
Pressure solution - stylolitization
Dolomitization and void formation
II Siliceous Rocks - SiO2
•Cryptocrystalline/microcrystalline, not quartz
•Precipitated from solution
•Occurs in low concentrations in sea water
•Different stability field than CaCO3
•Possibly from alteration of volcanic ash
Bedded
•May come from deep sea siliceous oozes
Nodular
•Often found replacing burrows or body fossils
•E.g. Chert, flint, jasper, chalcedony, opal
III Evaporites
•Minerals
- Gypsum - CaSO4 . H2O
and Anhydrite - CaSO4
(76-93% humidity)
- Halite - NaCl (67-76% humidity)
- Potash ~ KCl (<67% humidity)
•Environments
- Restricted marine basins - e.g. Permian of Utah, S Texas
- Coastal salinas - e.g. S Texas
- Sabkahs - e.g. Persian Gulf
- Playa lakes - e.g. Great Salt Lake, UT
IV Phosphate Deposits ~ Ca(PO4)CO3(F,P,Cl)
•A nutrient (like silica) so rare in ocean surface waters requires upwelling
•Common at Proterozoic/Phanerozoic boundary breakup of Rodinia?
•May have influenced evolution of skeletonized life
•Also common in Permian rocks of western U. S. e.g. Phosphoria Fm. in UT, ID, WY
•Bone beds may also contain large quantities of phosphates
Sil. Oolitic Iron Ores
•Important in eastern iron industry (AL, NY)
•Due to reworking of heavily weathered soils
followed by marine transgression?
•Early replacement phenomenon?
Sil. Oolitic Iron Ores,
Birmingham, AL
VI Carbon-rich Rocks
•Coals
- Environments
- Maturation Sequence
•Oil and Natural Gas
- Environments
- Maturation Sequence
- Traps
•Oil Shales and Tar Sands
Coals Require
•High productivity
- Nutrients
- Moisture
- Warm
•Burial
Coal Maturation Sequence
•Vegetation
•Peat
•Lignite
•Bituminous
•Anthracite
Swamp, S LA
Carbon-rich Rocks - Oil and Natural Gas
Most are marine
Requires
•High Productivity
- Nutrients
•Burial and preservation
- Deltas ideal
Maturation stages
•Organic matter - mainly plankton - not dinosaurs!
•Kerogen
•Petroleum
•Natural gas
A Successful Petroleum Field Requires
•Source rock - fine grained, organic rich
•Maturation - time, temperature, pressure
•Reservoir rock - high permeability
- What reduces permeability?
- What increases permeability?
•Cap rock or seal - fine grained, non permeable
•Trap
- Structural
- Stratigraphic