Ch07 sedimentary rocks

193
Sedimentary Rocks Sedimentary Rocks and Environments and Environments Chapters 4 and 5 Chapters 4 and 5

description

 

Transcript of Ch07 sedimentary rocks

Page 1: Ch07 sedimentary rocks

Sedimentary Rocks Sedimentary Rocks and Environmentsand Environments

Chapters 4 and 5Chapters 4 and 5

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Proportions ofProportions ofRock Types on the EarthRock Types on the Earth

Sedimentary rocks cover about 75% of the world's land areaSedimentary rocks cover about 75% of the world's land area

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What Can Sedimentary Rocks Tell Us?What Can Sedimentary Rocks Tell Us?• Paleoclimate ConditionsPaleoclimate Conditions• Paleoenvironment – Arid and Tropical Belts (presence of Paleoenvironment – Arid and Tropical Belts (presence of

seas, deltas, beaches, rivers, lakes, glaciers, coral reefs, seas, deltas, beaches, rivers, lakes, glaciers, coral reefs, swamps, mountains, deserts, etc.)swamps, mountains, deserts, etc.)

• Source MaterialSource Material• History of Transport and Deposition History of Transport and Deposition • ReliefRelief• Latitude – Climate BeltsLatitude – Climate Belts• Climate / TemperatureClimate / Temperature• Sea LevelSea Level• Changes in Atmospheric ChemistryChanges in Atmospheric Chemistry• Plate MovementsPlate Movements• Tectonic Setting – Evolution of EarthTectonic Setting – Evolution of Earth• Fossils – Evolution of OrganismsFossils – Evolution of Organisms• Relative and Absolute Age DatingRelative and Absolute Age Dating

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The Rock CycleThe Rock Cycle

• Sedimentary Sedimentary Rocks are Rocks are formed from formed from sediments.sediments.

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Sedimentary RocksSedimentary Rocks • Composed of Composed of sedimentsediment = loose particulate = loose particulate

material – material – ChemicalChemical and and PhysicalPhysical– clayclay,, silt silt,, sand sand,, gravel gravel, etc., etc.

• Sediment derivation by weatheringSediment derivation by weathering– Chemical Chemical ((decompositiondecomposition))– Physical Physical ((disintegrationdisintegration))

• Sediment becomes sedimentary rock Sediment becomes sedimentary rock through through diagenesisdiagenesis, which involves: , which involves: – LithificationLithification

• Compaction Compaction • Cementation Cementation

– RecrystallizationRecrystallization (of carbonate sediment) (of carbonate sediment)

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Turning Sediment into RockTurning Sediment into Rock

• Diagenesis Diagenesis – all of the chemical, – all of the chemical, physical, and biological changes that physical, and biological changes that take place after sediments are take place after sediments are deposited.deposited.

• Occurs within the upper few Occurs within the upper few kilometers of Earth’s crust at kilometers of Earth’s crust at temperatures generally less than 150 temperatures generally less than 150 to to 200 ºC200 ºC (metamorphism occurs (metamorphism occurs beyond this threshold).beyond this threshold).

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Turning Sediment into RockTurning Sediment into Rock

• Diagenesis Includes:Diagenesis Includes:• RecrystallizationRecrystallization – development of more – development of more

stable minerals from less stable ones. stable minerals from less stable ones. Example = CaCOExample = CaCO33 to CaMg(CO to CaMg(CO33))22

• LithificationLithification – unconsolidated sediments – unconsolidated sediments are transformed into solid sedimentary are transformed into solid sedimentary rock by rock by compactioncompaction and and cementationcementation..

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Turning Sediment into RockTurning Sediment into Rock• Diagenesis IncludesDiagenesis Includes

• CompactionCompaction::– Sediment accumulates. Sediment accumulates. – Weight of overlying material compresses Weight of overlying material compresses

deeper sediments.deeper sediments.– Deeper sediment is further buried Deeper sediment is further buried

becoming more compacted and firm.becoming more compacted and firm.– Grains are pressed increasingly closer Grains are pressed increasingly closer

reducing pore space by as much as 40% reducing pore space by as much as 40% (clays).(clays).

– Most significant lithification process in Most significant lithification process in fine-grained sedimentary rock (shales).fine-grained sedimentary rock (shales).

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Diagenesis: LithificationDiagenesis: Lithification

SedimentSediment

RockRock

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Compaction and LithificationCompaction and Lithification

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Turning Sediment into RockTurning Sediment into Rock

• Diagenesis IncludesDiagenesis Includes• CementationCementation: :

– Most important process by which Most important process by which sediments are transformed to sediments are transformed to sedimentary rocks.sedimentary rocks.

– Chemical diagenesis that involved the Chemical diagenesis that involved the precipitation of minerals carried in precipitation of minerals carried in solution into the open pore spaces solution into the open pore spaces between individual grains.between individual grains.

– Natural CementsNatural Cements include include calcitecalcite, , silicasilica, , and and iron oxideiron oxide..

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Diagenesis: LithificationDiagenesis: Lithification

SedimentSediment

RockRock

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CementationCementation

Typical CementsTypical Cements::• CalciteCalcite• QuartzQuartz• Iron OxideIron Oxide

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Types of Sedimentary RocksTypes of Sedimentary Rocks

• Rock types are based on the Rock types are based on the sourcesource of of the material.the material.

• Detrital RocksDetrital Rocks – Derived from both the – Derived from both the chemical and mechanical weathering of chemical and mechanical weathering of pre-existing rock forming detritus that is pre-existing rock forming detritus that is then transported and deposited in another then transported and deposited in another location.location.

• Chemical RocksChemical Rocks – Sediment that was – Sediment that was once in solution and precipitated by once in solution and precipitated by organic or inorganic processes.organic or inorganic processes.

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Classification of Sedimentary RocksClassification of Sedimentary Rocks• Sedimentary rocks are classified based on Sedimentary rocks are classified based on

their their texturetexture ( (grain size and shapegrain size and shape) and ) and composition composition ((mineral contentmineral content).).

• Detrital Detrital rocks are subdivided primarily based onrocks are subdivided primarily based on particle size and compositionparticle size and composition..– The chief constituents of detrital rocks include:The chief constituents of detrital rocks include:

– Clay mineralsClay minerals– FeldsparsFeldspars– QuartzQuartz– MicasMicas

• Chemical Chemical rocks are subdivided primarily based rocks are subdivided primarily based onon compositioncomposition..– The chief constituents of chemical rocks include:The chief constituents of chemical rocks include:

– CalciteCalcite– Microcrystalline QuartzMicrocrystalline Quartz– Gypsum, Halite, and SylviteGypsum, Halite, and Sylvite

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• Two major Two major textures textures are used in the are used in the classification of sedimentary rocks.classification of sedimentary rocks.

• ClasticClastic– Discrete fragments and particles.Discrete fragments and particles.– All detrital rocks have a clastic texture.All detrital rocks have a clastic texture.– Some chemical rocks – coquina and Some chemical rocks – coquina and

oolitic limestone – also posses clastic oolitic limestone – also posses clastic textures. textures.

• Nonclastic (or Crystalline)Nonclastic (or Crystalline)– Pattern of interlocking crystals.Pattern of interlocking crystals.– May resemble an igneous rock.May resemble an igneous rock.

Classification of Sedimentary RocksClassification of Sedimentary Rocks

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Types of Sedimentary RocksTypes of Sedimentary Rocks • DetritalDetrital Sedimentary Rocks Sedimentary Rocks

– Conglomerate or Breccia Conglomerate or Breccia – Sandstone Sandstone – Siltstone Siltstone – Shale or ClaystoneShale or Claystone

• ChemicalChemical//Biochemical Biochemical Sedimentary RocksSedimentary Rocks– Evaporites Evaporites – Carbonate sedimentary rocks (limestones and Carbonate sedimentary rocks (limestones and

dolostone) dolostone) – Siliceous sedimentary rocks (chert, diatomite) Siliceous sedimentary rocks (chert, diatomite) – Organic sedimentary rocks (Coals – peat, lignite, Organic sedimentary rocks (Coals – peat, lignite,

bituminous, and anthracite) bituminous, and anthracite)

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Identification of Sedimentary RocksIdentification of Sedimentary Rocks

STOP

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Characteristics of Detrital Characteristics of Detrital Sedimentary RocksSedimentary Rocks

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Detrital Sedimentary RocksDetrital Sedimentary Rocks

• Detrial rocks have a Detrial rocks have a clasticclastic (broken or (broken or fragmental) texture that may consist of:fragmental) texture that may consist of: – ClastsClasts – larger pieces, such as sand or gravel. – larger pieces, such as sand or gravel.– Matrix Matrix – mud or fine-grained sediment – mud or fine-grained sediment

surrounding the clasts.surrounding the clasts.

– CementCement – the chemical – the chemical “glue” that holds it all “glue” that holds it all together.together.• Types of Cement: Types of Cement:

– Calcite Calcite – Iron Oxide Iron Oxide – SilicaSilica

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Clast SupportedClast SupportedConglomerateConglomerate

(River Deposits)(River Deposits)

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Matrix Supported Conglomerate Matrix Supported Conglomerate (Glacial/Landslide Deposits)(Glacial/Landslide Deposits)

““Modern”Modern”Glacial SedimentsGlacial Sediments

2.2 Gyr Conglomerate2.2 Gyr Conglomerate

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Detrital Sedimentary Rocks Detrital Sedimentary Rocks are Classified by Grain Sizeare Classified by Grain Size

Particle size is used to distinguish among Particle size is used to distinguish among the various types of detrital rocks.the various types of detrital rocks.

• GravelGravel: Grain size greater than : Grain size greater than 2 mm2 mm. . – If rounded clasts = If rounded clasts = ConglomerateConglomerate – If angular clasts = If angular clasts = BrecciaBreccia

• SandSand: Grain size : Grain size 1/16 to 2 mm1/16 to 2 mm – – SandstoneSandstone• SiltSilt: Grain size : Grain size 1/256 to 1/16 mm1/256 to 1/16 mm (gritty) – (gritty) –

Siltstone Siltstone • ClayClay: Grain size : Grain size less than 1/256 mmless than 1/256 mm (smooth) (smooth)

– ShaleShale (if fissile) (if fissile) – MudstoneMudstone (if massive) (if massive)

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Grain SizeGrain Size• Gravel ≥ 2 mmGravel ≥ 2 mm• Sand – 2 mm to 1/16 mmSand – 2 mm to 1/16 mm• Silt – 1/16 mm to 1/256 mmSilt – 1/16 mm to 1/256 mm• Clay ≤ 1/256 mmClay ≤ 1/256 mm

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Detrital Sedimentary Rocks Detrital Sedimentary Rocks are Classified by Grain Sizeare Classified by Grain Size

Grain Size Rock Name

Gravel Conglomerate = Rounded Clasts Breccia = Angular Clasts

Sand Sandstone

Silt Siltstone

Clay Shale = Fissile

Mudstone = Massive

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Detrital Sedimentary RocksDetrital Sedimentary Rocks

ShaleShale SandstoneSandstone

ConglomerateConglomerate BrecciaBreccia

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What Does Grain Size Tell Us?What Does Grain Size Tell Us?

• The energy of the environment and The energy of the environment and media of deposition.media of deposition.

• Currents of water or air sort the Currents of water or air sort the particles by sizeparticles by size – the stronger the – the stronger the current, the larger the particle size current, the larger the particle size carried.carried.

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Grain Size InterpretationGrain Size Interpretation

• GravelGravel

• SandSand

• SiltSilt

• ClayClay

• River, BeachRiver, Beach

• River, Beach, River, Beach, DesertDesert

• Delta, Shallow Delta, Shallow OceanOcean

• Deep Ocean, Deep Ocean, Lake, SwampLake, Swamp

• High EnergyHigh Energy

• Low EnergyLow Energy

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SortingSorting• SortingSorting refers to the distribution of refers to the distribution of

grain sizes in a rock. grain sizes in a rock. – Well SortedWell Sorted – All the grains are approximately – All the grains are approximately

equal in size.equal in size.– Poorly SortedPoorly Sorted – Particles of variable size are – Particles of variable size are

mixed together.mixed together.

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Degrees of SortingDegrees of Sorting

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What Does the Degree of Sorting Tell Us?What Does the Degree of Sorting Tell Us?• The energy of the environment and media of The energy of the environment and media of

depositiondeposition..

Interpretation:Interpretation:Poorly SortedPoorly SortedWell SortedWell Sorted

Transport AgentTransport AgentGravity and Glaciers (and Rivers)Gravity and Glaciers (and Rivers)Water and WindWater and Wind

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What Does the What Does the Degree of Sorting Tell Us?Degree of Sorting Tell Us?

• The energy of the environment and The energy of the environment and media of depositionmedia of deposition::

• WindblownWindblown sands are typically better sands are typically better sorted than sorted than wave-washed wave-washed sediments.sediments.

• Particles washed by Particles washed by waveswaves are are commonly better sorted than materials commonly better sorted than materials deposited by deposited by streamsstreams..

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• Degree of sorting also indicates Degree of sorting also indicates distance from the sourcedistance from the source and and deposition ratedeposition rate::

• Poor sortingPoor sorting indicates sediments were indicates sediments were transported a transported a short distanceshort distance and and deposited rapidlydeposited rapidly. .

– Examples: Alluvial Fans and Glacial Tillite Examples: Alluvial Fans and Glacial Tillite deposits deposits

• Well-sortedWell-sorted sediments indicate the sediments indicate the sediments were transported a sediments were transported a longer longer distancedistance and and deposited more graduallydeposited more gradually..

– Examples: Deep-ocean depositsExamples: Deep-ocean depositsSTOP

What Does the What Does the Degree of Sorting Tell Us?Degree of Sorting Tell Us?

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Grain ShapeGrain Shape• Grain shapeGrain shape is described in terms of is described in terms of rounding rounding of of

grain edges and grain edges and sphericity sphericity (equal dimensions, (equal dimensions, or how close it is to a sphere). or how close it is to a sphere).

• When currents transport sedimentary particles, When currents transport sedimentary particles, the particles collide together breaking off sharp the particles collide together breaking off sharp edges.edges.

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Rounding & SphericityRounding & Sphericity

SphericalSpherical

OblongOblong

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Figure 3-13 (p. 72)Figure 3-13 (p. 72)Degree of rounding is expressed using the following scale: Degree of rounding is expressed using the following scale: highly angular –> angular –> subangular –> subrounded –> rounded highly angular –> angular –> subangular –> subrounded –> rounded –> highly rounded–> highly rounded((AA) An angular particle (all edges sharp). ) An angular particle (all edges sharp). ((BB) A rounded grain that has little sphericity. ) A rounded grain that has little sphericity. ((CC) A well-rounded, highly spherical grain. ) A well-rounded, highly spherical grain.

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Gravel Sized Detrital RocksGravel Sized Detrital Rocks(Subdivided Based on Grain Roundness)(Subdivided Based on Grain Roundness)

BrecciaBreccia

ConglomerateConglomerate

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Grain ShapeGrain Shape• Degree of roundingDegree of rounding also indicates also indicates

distance from sourcedistance from source and/or and/or transport transport timetime::

• Very well rounded sand Very well rounded sand grainsgrains suggest that a suggest that a sand has sand has traveled a great traveled a great distance from the source distance from the source over a long time periodover a long time period. .

• They also may have They also may have been been recycled from older recycled from older sandstonessandstones.. STOP

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Interpretation:Interpretation:Distance of TransportDistance of Transport

ShortShort FarFar STOP

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Chemical WeatheringChemical Weathering• Transport timeTransport time also affects the also affects the

mineral compositionmineral composition of a of a sedimentary deposit:sedimentary deposit:– Substantial weathering and long Substantial weathering and long

transporttransport leads to the leads to the – Gradual destruction of weaker and less Gradual destruction of weaker and less

stable minerals such as feldspars and stable minerals such as feldspars and ferromagnesian minerals (Bowen’s ferromagnesian minerals (Bowen’s Reaction Series).Reaction Series).

– QuartzQuartz – the most stable mineral at the – the most stable mineral at the Earth’s surface survives.Earth’s surface survives.

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Color of Sedimentary RocksColor of Sedimentary Rocks

• BlackBlack and and dark graydark gray coloration in coloration in sedimentary rocks generally indicates sedimentary rocks generally indicates the presence of the presence of organic carbonorganic carbon and/or and/or ironiron. .

• Organic carbon in sedimentary requires Organic carbon in sedimentary requires anoxic environmental conditionsanoxic environmental conditions. .

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Color of Sedimentary RocksColor of Sedimentary Rocks

• RedRed coloration in coloration in sedimentary rocks sedimentary rocks indicates the presence of indicates the presence of iron oxides iron oxides (Ferric Iron – (Ferric Iron – FeFe+3+3) . ) .

• Red beds typically Red beds typically indicate deposition in indicate deposition in well-oxygenated well-oxygenated continental sedimentary continental sedimentary environmentsenvironments. .

• May also be transitional May also be transitional or marine. or marine.

Red siltstone w/ tracksRed siltstone w/ tracks

Hematite-cementedHematite-cementedSandstone (Clinton Fm.)Sandstone (Clinton Fm.)

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Color of Sedimentary RocksColor of Sedimentary Rocks

• GreenGreen and and graygray coloration in coloration in sedimentary rocks indicates the sedimentary rocks indicates the presence of presence of ironiron, but in a , but in a reducedreduced (rather than an oxidized) state. (rather than an oxidized) state.

• Ferrous ironFerrous iron (Fe (Fe+2+2) generally occurs in ) generally occurs in oxygen-deficient environmentsoxygen-deficient environments. .

STOP

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Overview of Detrital Overview of Detrital Sedimentary Rock TypesSedimentary Rock Types

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Detrital Sedimentary RocksDetrital Sedimentary Rocks• Common Detrital Sedimentary Rocks Common Detrital Sedimentary Rocks

((in order of increasing particle sizein order of increasing particle size))• ShaleShale

– A very fine-grained rock A very fine-grained rock composed ofcomposed of clay-sized clay-sized particlesparticles. .

– Most common sedimentary Most common sedimentary rock.rock.

– Particles deposited in thin Particles deposited in thin layers commonly referred to layers commonly referred to as as laminaelaminae..

– Shale is Shale is fissilefissile – – splits readily splits readily into thin, flat layersinto thin, flat layers. .

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Detrital Sedimentary RocksDetrital Sedimentary Rocks

• MudstoneMudstone• Composed of Composed of mudmud – a mixture of silt and clay. – a mixture of silt and clay. • May exhibit fissility.May exhibit fissility.• Breaks into chunks or blocks.Breaks into chunks or blocks.

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Detrital Sedimentary RocksDetrital Sedimentary Rocks

• SiltstoneSiltstone– Composed of Composed of

largely of largely of siltsilt--sized particles sized particles with lesser clay-with lesser clay-sized particles.sized particles.

– Lacks fissilityLacks fissility..– Breaks into Breaks into

chunks or blocks.chunks or blocks.

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Formation of Shales to SiltstonesFormation of Shales to Siltstones

• Due to their Fine Grain Size:Due to their Fine Grain Size:– Clay and silt-sized particles tends to remain Clay and silt-sized particles tends to remain

suspended in the water columnsuspended in the water column. . – Deposition occurs as the result of Deposition occurs as the result of gradual settlinggradual settling

from relatively from relatively quietquiet,, non-turbulent currentsnon-turbulent currents..– Lithified predominantly via Lithified predominantly via compactioncompaction.. – Clays and shales typically indicate Clays and shales typically indicate low energy low energy

environmentsenvironments, , sheltered from waves and currentssheltered from waves and currents. . – Such environments include Such environments include lakes (lacustrine), lakes (lacustrine),

river floodplains, lagoons, and portions of deep river floodplains, lagoons, and portions of deep ocean basinsocean basins..

– Composition and colorComposition and color can further indicate the can further indicate the environment of deposition (e.g., coaly shales).environment of deposition (e.g., coaly shales).

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Detrital Sedimentary RocksDetrital Sedimentary Rocks• SandstoneSandstone

– Composed of sand-sized particles.Composed of sand-sized particles.– Lithified predominantly via Lithified predominantly via cementationcementation. . – Forms in a Forms in a variety of environmentsvariety of environments..– SortingSorting, , shapeshape, and , and compositioncomposition of the of the

grains can be used to interpret the rock’s grains can be used to interpret the rock’s origin and history.origin and history.

– Compositional components include:Compositional components include:• QuartzQuartz – predominant mineral – predominant mineral• FeldsparFeldspar• Rock FragmentsRock Fragments

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Major Types of SandstoneMajor Types of Sandstone • Quartz SandstoneQuartz Sandstone – Dominated by quartz; mature – Dominated by quartz; mature • ArkoseArkose – 25% or more feldspar; immature – 25% or more feldspar; immature• GraywackeGraywacke – About 30% dark fine-grained matrix; – About 30% dark fine-grained matrix;

immature immature • Lithic SandstoneLithic Sandstone – Quartz, muscovite, chert, and – Quartz, muscovite, chert, and

rock fragments. Less than 15% matrix. Immaturerock fragments. Less than 15% matrix. Immature

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Figure 5-24 (p. 95)Figure 5-24 (p. 95)Four categories of sandstone as seen in thin section Four categories of sandstone as seen in thin section under the microscope.under the microscope. Diameter of field is about 4 mm. Diameter of field is about 4 mm.

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Quartz SandstoneQuartz Sandstone

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Composed of Composed of well-sortedwell-sorted, , roundedrounded quartz quartz grains suggests grains suggests long-distance transportlong-distance transport, , highly weatheredhighly weathered, and , and moderate deposition moderate deposition and burial ratesand burial rates..

Quartz SandstoneQuartz Sandstone

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ArkoseArkose

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ArkoseArkose

• Composed of quartz, feldspars, and micas indicates granitic source rocks. Typically poorly sorted, angular particles with minimal chemical weathering (indicated by the presence of feldspar) suggests short-distance transport, minimal chemical weathering in an arid climate, and rapid deposition and burial.

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Sandstone Close-UpsSandstone Close-Ups

• Quartz Sandstone (left)Quartz Sandstone (left)• Arkose (Sandstone with >10% feldspar)Arkose (Sandstone with >10% feldspar)

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Detrital Sedimentary RocksDetrital Sedimentary Rocks

• Conglomerate and BrecciaConglomerate and Breccia– Both are composed of Both are composed of particles greater than particles greater than

2mm in diameter2mm in diameter (gravel) with sand, silt, and (gravel) with sand, silt, and clay particles between.clay particles between.

– Particles are large enough to identify distinctive Particles are large enough to identify distinctive rock types and therefore rock types and therefore source rockssource rocks..

– Gravels accumulate in a variety of environments Gravels accumulate in a variety of environments and typically indicate and typically indicate steep slopes and/or very steep slopes and/or very turbulent currentsturbulent currents..

– Examples: Examples: energetic mountain streams, strong energetic mountain streams, strong wave activity along rapidly eroding coastline, wave activity along rapidly eroding coastline, and glacial and landslide environments. and glacial and landslide environments.

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Detrital Sedimentary RocksDetrital Sedimentary Rocks• Conglomerate and BrecciaConglomerate and Breccia

– Conglomerate consists largely of Conglomerate consists largely of rounded rounded gravels.gravels.– Breccia is composed mainly of large Breccia is composed mainly of large angularangular

particles.particles.

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Conglomerate Deposits along Conglomerate Deposits along the Coast of Washingtonthe Coast of Washington

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Outcrop of ConglomerateOutcrop of Conglomerate

Composition of variable materials, Composition of variable materials, poorly sortedpoorly sorted, and , and roundedrounded particles suggests relatively particles suggests relatively short-distance short-distance transporttransport (but long enough to have high degree of (but long enough to have high degree of abrasion), abrasion), some mechanical and minimal chemical some mechanical and minimal chemical weatheringweathering, and , and rapid deposition and burialrapid deposition and burial..

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Interbedded Sandstone and Interbedded Sandstone and ConglomerateConglomerate

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Interbedded Interbedded Sandstone and Sandstone and ConglomerateConglomerate

Suggests distinctive Suggests distinctive periods of alternating periods of alternating

depositional environments depositional environments of high and low energy.of high and low energy.

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BrecciaBreccia

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BrecciaBreccia

Composition of variable materials, Composition of variable materials, poorly sortedpoorly sorted, , and and angularangular particles suggests particles suggests short-distance short-distance transporttransport, , minimal mechanical and chemical minimal mechanical and chemical weatheringweathering, and , and rapid deposition and burialrapid deposition and burial..

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Chemical/Biochemical Chemical/Biochemical Sedimentary RocksSedimentary Rocks

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Chemical Sedimentary RocksChemical Sedimentary Rocks

• Consist of precipitated material that Consist of precipitated material that was once in solution.was once in solution.

• Precipitation of material occurs in two Precipitation of material occurs in two ways:ways:

• Inorganic Processes: Inorganic Processes: – EvaporationEvaporation– HydrothermalHydrothermal– Chemical ActivityChemical Activity

• Organic Processes:Organic Processes: – Biochemical OriginBiochemical Origin from water dwelling from water dwelling

organismsorganisms

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Types of Chemical/Biochemical Types of Chemical/Biochemical Sedimentary RocksSedimentary Rocks

1.1. Carbonate RocksCarbonate Rocks – Form by chemical – Form by chemical processes and biochemical processes and biochemical processes (secreting shells). processes (secreting shells).

2.2. Siliceous RocksSiliceous Rocks – Form from – Form from chemical processes (silica replacing chemical processes (silica replacing limestone) or biochemical processes limestone) or biochemical processes (silica-secreting organisms).(silica-secreting organisms).

3.3. EvaporitesEvaporites – Form from the – Form from the evaporation of seawater.evaporation of seawater.

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Carbonate RocksCarbonate Rocks 1.1. LimestonesLimestones

– Most abundant chemical rock.Most abundant chemical rock.– Composed of predominantly of Composed of predominantly of calcitecalcite (CaCO (CaCO33) )

and secondarily and secondarily aragonitearagonite (CaCO (CaCO33).).– Marine Marine biochemical limestonesbiochemical limestones form from pre- form from pre-

existing organisms:existing organisms:• Fossiliferous LimestoneFossiliferous Limestone – coral reefs, shell fragments – coral reefs, shell fragments• CoquinaCoquina – shell fragments – shell fragments • Chalk Chalk – microscopic organisms – microscopic organisms • MicriteMicrite (Microcrystalline Limestone) – microscopic organisms (Microcrystalline Limestone) – microscopic organisms

– Inorganic limestones form by inorganic Inorganic limestones form by inorganic processes (evaporation, chemical activity):processes (evaporation, chemical activity):

• Oolitic LimestoneOolitic Limestone• TravertineTravertine• Crystalline Limestone Crystalline Limestone • MicriteMicrite (Microcrystalline Limestone) (Microcrystalline Limestone)

2.2. DolostonesDolostones (or (or DolomitesDolomites))– Composed of Dolomite (CaMg (COComposed of Dolomite (CaMg (CO33))22))

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Formation of LimestonesFormation of Limestones• Most limestones are the Most limestones are the direct or indirect direct or indirect

result of biologic activityresult of biologic activity..– Organic:Organic:

• May contain shells or the remains of other marine May contain shells or the remains of other marine organisms (microscopic or macroscopic).organisms (microscopic or macroscopic).

Microscopic Microscopic Foraminifera (chalk)Foraminifera (chalk)

Shell Fragments Shell Fragments (coquina)(coquina)

Fossiliferous LimestoneFossiliferous Limestone

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Formation of LimestonesFormation of Limestones• Most limestones are the Most limestones are the direct or indirect direct or indirect

result of biologic activityresult of biologic activity..– Inorganic:Inorganic:

• Inorganic limestones precipitate from CaCOInorganic limestones precipitate from CaCO33-bearing -bearing

solutions. solutions. • Form in Form in cavescaves and and hotspringshotsprings when when groundwater groundwater

encounters air and COencounters air and CO22 comes out of solution causing comes out of solution causing

CaCOCaCO33 to precipitate. to precipitate.

• Precipitate from seawaterPrecipitate from seawater as a result of biologic activity as a result of biologic activity such as photosynthesis by microscopic marine plants such as photosynthesis by microscopic marine plants and algae removes COand algae removes CO22 from seawater leading to from seawater leading to

calcium carbonate precipitation.calcium carbonate precipitation.• Precipitation occurs due to changes in water chemistry, Precipitation occurs due to changes in water chemistry,

pressure, and/or temperature conditions.pressure, and/or temperature conditions.

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Characteristics of the Environment Characteristics of the Environment of Marine Carbonate Formationof Marine Carbonate Formation

• Some carbonate rocks form in Some carbonate rocks form in lakeslakes, , cavescaves, , and and hot springshot springs..

• Most carbonate rocks form in the shallow Most carbonate rocks form in the shallow marine environmentsmarine environments::– MarineMarine– Warm WaterWarm Water – Shallow WaterShallow Water (less than 200 m deep) (less than 200 m deep)– Tropical ClimateTropical Climate (30 ° N - 30 ° S of equator) (30 ° N - 30 ° S of equator) – Clear WaterClear Water (low to no terrigenous input) (low to no terrigenous input) – Sunlight RequiredSunlight Required for photosynthesis by algae for photosynthesis by algae

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Organic Chemical Sedimentary RocksOrganic Chemical Sedimentary Rocks

• Fossiliferous LimestonesFossiliferous Limestones– Limestones containing various sized shells and/or Limestones containing various sized shells and/or

other fossil fragments cemented typically with other fossil fragments cemented typically with calcitecalcite..– Coral ReefsCoral Reefs and and shell bedsshell beds create marine fossiliferous create marine fossiliferous

limestones from the invertabrate animal’s secretion of limestones from the invertabrate animal’s secretion of their their external calcarenous skeletonsexternal calcarenous skeletons..

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Modern Modern Coral Coral

Reef at Reef at Bora Bora

Bora in Bora in French French

PolynesiaPolynesia

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El Capitan El Capitan Peak in Peak in

Guadalupe Guadalupe National National

Park, Texas - Park, Texas - Exposed Exposed Permian-Permian-

aged aged Massive Massive

Coral Reef Coral Reef ComplexComplex

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• Micritic LimestonesMicritic Limestones• Microcrystalline limestones Microcrystalline limestones composed of clay-composed of clay-

sized calcite particles (sized calcite particles (lime mudslime muds) of biological ) of biological (organic) microscopic skeletons of(organic) microscopic skeletons of calcareouscalcareous algaealgae. Deposited in generally . Deposited in generally quiet watersquiet waters..

• Can also have chemical (inorganic) origin by the Can also have chemical (inorganic) origin by the precipitation of calcite from seawater.precipitation of calcite from seawater.

Organic Chemical Sedimentary RocksOrganic Chemical Sedimentary Rocks

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• ChalkChalk– Chalk Chalk is a soft, porous rock is a soft, porous rock

composed of almost entirely of the composed of almost entirely of the hard parts of hard parts of microscopic microscopic calcareous marine organismscalcareous marine organisms..

Organic Chemical Sedimentary RocksOrganic Chemical Sedimentary Rocks

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CoccolithophoridCoccolithophorid. Shells are composed . Shells are composed of calcium carbonate. Image magnified of calcium carbonate. Image magnified 7,000 times.7,000 times.

LimancinaLimancina, a tiny swimming marine snail, , a tiny swimming marine snail, or pterapod.or pterapod.The foot is modified into a pair of winglike fins, The foot is modified into a pair of winglike fins, shown at left. At the right are two empty shellsshown at left. At the right are two empty shells

Types of Sea Floor SedimentsTypes of Sea Floor Sediments• Biogenous (or Organic) SedimentBiogenous (or Organic) Sediment

– Calcareous OozesCalcareous Oozes – Form chalk in waters less than – Form chalk in waters less than about 4,000-5,000 m – foraminifera, pteropods, and about 4,000-5,000 m – foraminifera, pteropods, and coccolithophores.coccolithophores.

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Origin of Carbonate Sediments Origin of Carbonate Sediments and Rocksand Rocks

Much Much lime mudlime mud forms from the forms from the disintegration of disintegration of calcareous algaecalcareous algae (such as (such as HalimedaHalimeda andand Penicillus Penicillus). ). When the When the calcareous algae calcareous algae die, their skeletons die, their skeletons break down and break down and disintegrate disintegrate producing producing aragonite aragonite needle mudsneedle muds. . These These lime muds lithify to lime muds lithify to form fine-grained form fine-grained limestone. limestone.

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Microscopic Microscopic Hard Parts Hard Parts

(Skeletons) of (Skeletons) of Radiolarians Radiolarians

and and ForaminiferaForaminifera

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• CoquinaCoquina– Coquina Coquina is a coarse-grained rock is a coarse-grained rock

composed of poorly-cemented composed of poorly-cemented shells and shell fragments.shells and shell fragments.

Organic Chemical Sedimentary RocksOrganic Chemical Sedimentary Rocks

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• Crystalline LimestoneCrystalline Limestone– Crystalline limestone usually forms when the Crystalline limestone usually forms when the

mineral calcite (CaCO3) precipitates from mineral calcite (CaCO3) precipitates from seawater. seawater.

– Diagenesis recrystallizes calcite into Diagenesis recrystallizes calcite into intergranular network of crystals.intergranular network of crystals.

Inorganic Chemical Sedimentary RocksInorganic Chemical Sedimentary Rocks

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• Oolitic LimestoneOolitic Limestone– Oolitic limestone Oolitic limestone is composed of small is composed of small

spherical grains of CaCO3 calledspherical grains of CaCO3 called ooids. ooids.

Inorganic Chemical Sedimentary RocksInorganic Chemical Sedimentary Rocks

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Origin of Ooids in Origin of Ooids in Oolitic LimestonesOolitic Limestones

• OoidsOoids are tiny spheres are tiny spheres composed of concentrically composed of concentrically laminated calcium carbonate.laminated calcium carbonate.

• Ooids form in shallow marine Ooids form in shallow marine waters and begin as tiny waters and begin as tiny ““seedseed” particles (commonly ” particles (commonly shell fragments) are shell fragments) are constantly agitated by constantly agitated by currentscurrents..

• As the seeds are rolled As the seeds are rolled around in the CaCO3 around in the CaCO3 supersaturated warm waters, supersaturated warm waters, layers of CaCO3 are layers of CaCO3 are concentrically precipitatedconcentrically precipitated around the seed.around the seed.

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• TravertineTravertine– Travertine Travertine forms in forms in cavescaves (stalagtites, stalagmites, (stalagtites, stalagmites,

curtains, etc.) curtains, etc.) when groundwater encounters air, when groundwater encounters air, COCO22 comes out of solution and causing CaCO comes out of solution and causing CaCO33 to to

precipitate.precipitate.– Also forms from precipitation of calcite around Also forms from precipitation of calcite around hot hot

springssprings. .

Inorganic Chemical Sedimentary RocksInorganic Chemical Sedimentary Rocks

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Carbonates: DolomiteCarbonates: Dolomite • Composed of dolomiteComposed of dolomite

CaMg(CaCOCaMg(CaCO33))22 – a– a calcium-calcium-magnesium carbonatemagnesium carbonate mineral. mineral.

• Dolomite (Dolostone) can form Dolomite (Dolostone) can form by the direct precipitation of by the direct precipitation of seawater in a few areas of the seawater in a few areas of the world where world where intense intense evaporation of seawater evaporation of seawater concentrates the magnesiumconcentrates the magnesium. .

• Typically formed secondarily Typically formed secondarily from limestone. from limestone.

• Magnesium that has been Magnesium that has been concentrated in sea water concentrated in sea water replacesreplaces some of the calcium in some of the calcium in the CaCOthe CaCO33 structure structure ((diagenesisdiagenesis).).

STOP

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Siliceous Sedimentary RocksSiliceous Sedimentary Rocks • ChertChert

– Made of microcrystalline quartz (silica). Made of microcrystalline quartz (silica). – Massive and hard.Massive and hard.– Often replaces limestone.Often replaces limestone.– Varieties include the following:Varieties include the following:

• FlintFlint – dark in color due to organic matter – dark in color due to organic matter• JasperJasper – red in color due to iron oxide – red in color due to iron oxide • AgateAgate – banded form or chert– banded form or chert

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• ChertChert– Chert Chert has various modes of origin:has various modes of origin:

• InorganicInorganic – Precipitated from groundwater – Precipitated from groundwater as nodules. as nodules.

• InorganicInorganic – Precipitated from groundwater – Precipitated from groundwater associated with the decomposition of lava associated with the decomposition of lava flows and layers of volcanic ash (silica-rich).flows and layers of volcanic ash (silica-rich).

• OrganicOrganic – – Biochemical SedimentBiochemical Sediment – Siliceous – Siliceous ooze (gel) derived from silica skeletons of ooze (gel) derived from silica skeletons of marine organisms (diatoms and marine organisms (diatoms and radiolarians).radiolarians).

Siliceous Sedimentary RocksSiliceous Sedimentary Rocks

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Modern Marine DiatomsModern Marine DiatomsDiatom shells are composed of silica Diatom shells are composed of silica and have two perforated structures and have two perforated structures that overlap like the two parts of a that overlap like the two parts of a shallow round box for pills.shallow round box for pills.

RadiolariaRadiolariaThese protistans build their skeletons of silica. These protistans build their skeletons of silica. The structures tend to be modifications of either a The structures tend to be modifications of either a spherical (A) or helmet (B) shape. Image spherical (A) or helmet (B) shape. Image magnified 100 times.magnified 100 times.

Types of Sea Floor SedimentsTypes of Sea Floor Sediments• Biogenous (or Organic) Biogenous (or Organic)

SedimentSediment– Siliceous OozesSiliceous Oozes – –

Radiolarians and Diatoms Radiolarians and Diatoms

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Siliceous Sedimentary RocksSiliceous Sedimentary Rocks • DiatomiteDiatomite

– Made of microscopic Made of microscopic planktonic organisms calledplanktonic organisms called diatomsdiatoms. .

– Resembles chalk, but does Resembles chalk, but does not fizz in acid.not fizz in acid.

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EvaporitesEvaporites • EvaporationEvaporation triggers deposition of chemical triggers deposition of chemical

precipitates.precipitates.• Formed from Formed from dried basin areasdried basin areas that were that were

submerged by shallow arms of sea with submerged by shallow arms of sea with little little or no connection to open oceanor no connection to open ocean. .

• When seawater evaporates, minerals When seawater evaporates, minerals precipitate in sequence according to their precipitate in sequence according to their solubility formingsolubility forming salt flatssalt flats..

• GypsumGypsum precipitates beforeprecipitates before halitehalite, which , which precipitates beforeprecipitates before sylvitesylvite::

1.1. Rock GypsumRock Gypsum – Composed of gypsum (CaSO – Composed of gypsum (CaSO44 . 2H . 2H22O) O)

2.2. Rock SaltRock Salt – Composed of halite (NaCl) – Composed of halite (NaCl)3.3. Sylvite Sylvite – Composed of potassium chloride (KCl)– Composed of potassium chloride (KCl)

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Rock Salt (Halite) Rock Salt (Halite)

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Bonneville Salt Flats, UtahBonneville Salt Flats, Utah

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Layered Rock GypsumLayered Rock Gypsum

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Organic Sedimentary Rocks – CoalOrganic Sedimentary Rocks – Coal

• Composed of Composed of organic matterorganic matter such as trees, such as trees, bark, wood, leaves, etc. buried for millions bark, wood, leaves, etc. buried for millions of years.of years.

• Stages in coal formation (in order) as a Stages in coal formation (in order) as a function of increasing depth of burial function of increasing depth of burial ((increase in temperature and pressureincrease in temperature and pressure): ):

• Plant MaterialPlant Material• Peat Peat • Lignite Lignite • Bituminous Coal Bituminous Coal • Anthracite Coal Anthracite Coal

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Successive Successive Stages in Stages in

Coal Coal FormationFormation

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• Stages of Coal FormationStages of Coal Formation1.1. Plant MaterialPlant Material – Accumulations of large – Accumulations of large

amounts of plant remains in aamounts of plant remains in a stagnantstagnant, , oxygen-deficient environmentoxygen-deficient environment ( (swampswamp), ), where oxidation and thus complete where oxidation and thus complete decomposition of the plant remains is not decomposition of the plant remains is not possible.possible.

Anaerobic bacteriaAnaerobic bacteria partially decompose plant partially decompose plant remains releasing oxygen and hydrogen, remains releasing oxygen and hydrogen, thereby increasing the carbon percentage thereby increasing the carbon percentage and creating a layer of and creating a layer of peat.peat.

Organic Sedimentary Rocks – CoalOrganic Sedimentary Rocks – Coal

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• Stages of Coal FormationStages of Coal Formation2.2. PeatPeat – A soft brown material in which – A soft brown material in which

plant structures are still easily plant structures are still easily recognizablerecognizable

3.3. LigniteLignite – With shallow burial, peat – With shallow burial, peat slowly changes toslowly changes to lignite lignite – a soft – a soft brown coalbrown coal

• Increase temperature and pressure Increase temperature and pressure squeezes out the volatiles (water and squeezes out the volatiles (water and organic gases) increasing the proportion organic gases) increasing the proportion of fixed carbonof fixed carbon

• The greater the carbon content, the The greater the carbon content, the greater the coal’s energy rankinggreater the coal’s energy ranking

Organic Sedimentary Rocks – CoalOrganic Sedimentary Rocks – Coal

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Successive Stages in Coal FormationSuccessive Stages in Coal Formation

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• Stages of Coal FormationStages of Coal Formation

4. 4. BituminousBituminous – Deeper burial – Deeper burial transforms lignite to bituminous transforms lignite to bituminous coal – a soft black coal. coal – a soft black coal.

5.5. AnthraciteAnthracite – Forms during – Forms during regional metamorphism under regional metamorphism under increased temperature and increased temperature and pressure. pressure. • Anthracite Anthracite is a very hard, black, is a very hard, black,

shiny,shiny, metamorphic rock. metamorphic rock.

Organic Sedimentary Rocks – CoalOrganic Sedimentary Rocks – Coal

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Successive Stages in Coal FormationSuccessive Stages in Coal Formation

STOP

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Sedimentary Environments Sedimentary Environments

of Depositionof Deposition

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Sedimentary EnvironmentsSedimentary Environments

• A geographic setting where sediment is A geographic setting where sediment is accumulating.accumulating.

• Includes all of the physical, chemical, Includes all of the physical, chemical, biological and geographic biological and geographic conditionsconditions under under which sediments are deposited. which sediments are deposited.

• By By comparing comparing modern sedimentary deposits modern sedimentary deposits with ancient sedimentary rocks, the with ancient sedimentary rocks, the depositional conditions can be interpreted.depositional conditions can be interpreted.

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Sedimentary EnvironmentsSedimentary Environments

• Use characteristics such as Use characteristics such as grain sizegrain size, , grain shapegrain shape, , compositioncomposition, etc. to , etc. to determine:determine:– OriginOrigin– HistoryHistory– Method and Length of TransportMethod and Length of Transport– Nature and Environment of DepositionNature and Environment of Deposition– Reconstruct Ancient Environments and Reconstruct Ancient Environments and

Geographical RelationshipsGeographical Relationships

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The Characteristics of a Sedimentary The Characteristics of a Sedimentary Environment Depend on:Environment Depend on:

1.1. Tectonic Setting Tectonic Setting 2.2. Rocks in the Source Area from which the Rocks in the Source Area from which the

Sediment is Derived Sediment is Derived 3.3. Climate (and its effect on weathering) Climate (and its effect on weathering) 4.4. Method of Sediment Transport Method of Sediment Transport 5.5. Location of Deposition/Formation Location of Deposition/Formation 6.6. Physical, Chemical, and Biological Processes Physical, Chemical, and Biological Processes

in the Depositional Environment in the Depositional Environment 7.7. Post-Depositional Processes of Lithification Post-Depositional Processes of Lithification

(Cementation, Compaction, Recrystallization) (Cementation, Compaction, Recrystallization) 8.8. Time Time

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Depositional EnvironmentsDepositional EnvironmentsThere are three broad categories of There are three broad categories of

Depositional Environments:Depositional Environments: • Marine EnvironmentsMarine Environments – Ocean – Ocean • Transitional EnvironmentsTransitional Environments – Along contact between ocean and land – Along contact between ocean and land

• Continental EnvironmentsContinental Environments – On land – On land

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Marine Depositional Marine Depositional EnvironmentsEnvironments

• Shallow (up to about 200 meters depth)Shallow (up to about 200 meters depth)– Land-derived sediments deposited on the Land-derived sediments deposited on the

continental shelf (coarser-grained – sands, silts, continental shelf (coarser-grained – sands, silts, and clays).and clays).

– Coral reefsCoral reefs

• Deep (seaward of continental shelves)Deep (seaward of continental shelves)– Deep-sea sediments – fine-grained sediments Deep-sea sediments – fine-grained sediments

(silts and clays) that have remained entrained in (silts and clays) that have remained entrained in water column for long periods of time and water column for long periods of time and transported great distances. Originate at transported great distances. Originate at continental shelf as the result of turbidity continental shelf as the result of turbidity currents (deep-sea fans).currents (deep-sea fans).

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Marine Marine Depositional Depositional

EnvironmentsEnvironments

1.1. Continental Continental ShelfShelf

2.2. Continental Continental Slope Slope

3.3. Continental Continental Rise Rise

4.4. Abyssal PlainAbyssal Plain

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Types of Sea Floor SedimentsTypes of Sea Floor Sediments

• Terrigenous SedimentTerrigenous Sediment– Mineral grains from weathered continental Mineral grains from weathered continental

rocks.rocks.– Fine-grained sediment (clay, mud).Fine-grained sediment (clay, mud).– Accumulates slowly (5,000 to 50,000 years to Accumulates slowly (5,000 to 50,000 years to

deposit 1 cm).deposit 1 cm).– Color may be black, Color may be black, redred, or , or brownbrown..

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Marine Depositional EnvironmentsMarine Depositional Environments Location Water Depth Slope Width Features Sediments Sedimentary Rocks

Continental Shelf

● Flooded edge of Continent.

● Flooding occurred when the glaciers melted about 10,000 years ago.

Shallow water (less than 200 m deep)

Relatively flat

(slope < 0.1º)

Up to 300 km wide

(averages 80 km wide)

● Exposed to waves, tides, and currents.

● Locally cut by submarine canyons (eroded by rivers during Ice Age low sea level stand).

● Covered by land derived detrital sediments pebbles, sand, silt, and clay.

● Larger sedimentary grains are deposited closer to shore.

● Coral reefs and carbonate sediments in tropical areas.

● Pebble Conglomerates, Sandstones, Siltstones, Mudstones, and Shales

● Organic Limestones – Fossiliferous Limestones, Oolitic Limestones, Coral Reef Limestones, and Coquina

● Evaporites in enclosed seas

Continental Slope

Seaward of continental shelf.

Steeper slope at edge of continent.

Deeper water More steeply inclined.

(slope 3 – 6º)

~20 km wide

● Boundary between continental and oceanic crust.

● Rapid sediment transport from continental shelf down slope by dense, muddy turbidity currents.

● Sediments pass seaward to the continental rise and abyssal plain.

● Turbidites – Fining-upward sequence with a base of pebble conglomerates in a sandy matrix that grade up through coarse to medium sandstones, followed by silty sandstones, and finally siltstones and shales. This vertical succession of changing lithology is representative of strong to waning flow regime currents and their corresponding sedimentation.

Continental Rise

Base of the continental slope.

1,400 to 3,200 m

More gradual slope

Up to 100s of km wide

● Submarine fans form off submarine canyons.

● Turbidity currents form submarine fans off submarine canyons.

● Sediments pass seaward into the abyssal plain.

Abyssal Plain

Deep ocean floor 3 to 5 km+

(2 - 3 miles+)

Nearly flat NA ● Covered by very fine-grained detrital sediments and shells of microscopic organisms that have remained entrained in water column for long periods of time and transported great distances.

● Originate at continental shelf as the result of turbidity currents (deep-sea fans).

● Siltstones, Mudstones, and Shales

● Fine-grained Inorganic Limestones (Micritic and Crystalline)

● Fine-grained Organic Limestones – Foraminifera forming Chalk or Micritic Limestones

● Fine-grained Inorganic Siliceous Rocks – Diatoms forming Diatomite

● Chert (Radiolarians and Volcanic Ash)

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Transitional Depositional Transitional Depositional EnvironmentsEnvironments

• Environments at or near the transition Environments at or near the transition between the land and the sea.between the land and the sea.

• Consist of land-derived sediments Consist of land-derived sediments deposited on the continental shelf (coarser-deposited on the continental shelf (coarser-grained – sands, silts, and clays).grained – sands, silts, and clays).

• Forming pebble conglomerates, Forming pebble conglomerates, sandstones, siltstones, mudstones, and sandstones, siltstones, mudstones, and shales.shales.

• CarbonatesCarbonates

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Transitional Transitional Depositional Depositional

EnvironmentsEnvironments

1.1. Deltas Deltas 2.2. BeachesBeaches3.3. Barrier IslandsBarrier Islands4.4. Lagoons Lagoons 5.5. Tidal Flats Tidal Flats 6.6. Estuaries Estuaries

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Transitional Depositional EnvironmentsTransitional Depositional Environments Description Location Features Sediments Sedimentary Rocks

Deltas ● Fan-shaped accumulations of sediment.

● Forms where a river flows into a standing body of water, such as a lake or the sea.

● The delta builds seaward (or progrades) as sediment is deposited at the river mouth.

● Coarser sediment is deposited near the mouth of the river.

● Finer sediment is carried seaward and deposited in deeper water.

● Pebble Conglomerates, Sandstones, Siltstones, Mudstones, and Shales

Beaches and Barrier Islands

● A long, relatively narrow island running parallel to the mainland.

● Served to protect the coast from erosion by surf and tidal surges.

● Barrier Islands are separated from the mainland by a lagoon (or salt marsh)

● Exposed to wave energy

● Marine fauna

● Dominated by sand

● Associated with lagoon (or salt marsh) deposits

● Associated with tidal flat deposits

● Beaches – Quartz Sandstones, other sandstones, Conglomerates

● Barrier Islands – Quartz Sandstones

● Lagoons and Tidal Flats – Siltstones, Mudstones, and Shales

Lagoons ● Shallow bodies of water.

● Landward side of barrier islands.

● Also present behind reefs, or in the center of atolls.

● Protected from the pounding of the ocean waves by barrier islands.

● Contain finer sediment than the beaches and barrier islands (usually silt and clay)

● Siltstones, Mudstones, and Shales

Tidal Flats ● Nearly flat, low relief areas.

● Border lagoons, shorelines, and estuaries

● Periodically flooded and exposed by tides (usually twice each day)

● May be marshy, muddy, sandy or mixed sediment types (terrigenous or carbonate)

● Sandy Siltstones, Mudstones, and Shales

● Carbonates

● Laminations and ripples are common.

● Sediments are intensely burrowed.

● Stromatolites may be present (if conditions are appropriate)

Estuaries ● Mouth of a river drowned by the sea.

● Many estuaries formed due to sea level rise as glaciers melted at end of last Ice Age.

● Some formed due to tectonic subsidence.

● Forms where a river flows into a standing body of water, such as a lake or the sea.

● Brackish water (mixture of fresh and salt)

● May trap large volumes of sediment.

● Sand, silt, and clay may be deposited depending on energy level

● Sandstones, Siltstones, Mudstones, and Shales

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Fan Delta Bird-Foot Delta

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• Subenvironments of a Barrier Island ComplexSubenvironments of a Barrier Island Complex

Barrier Island ComplexBarrier Island Complex

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The The Outer Outer

Banks – Banks – Barrier Barrier Island Island

ComplexComplex

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Tidal FlatsTidal Flats

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EstuariesEstuaries

North Carolina's Neuse River EstuaryNorth Carolina's Neuse River Estuary

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Continental Depositional Continental Depositional EnvironmentsEnvironments

• Continental environments are those Continental environments are those environments which are present on the environments which are present on the continents (as opposed to in the oceans).continents (as opposed to in the oceans).

• Consist of land-derived sediments deposited in Consist of land-derived sediments deposited in various sedimentary environments (boulders, various sedimentary environments (boulders, pebbles, sands, silts, and clays).pebbles, sands, silts, and clays).

• Detrital sedimentary rocks – conglomerates, Detrital sedimentary rocks – conglomerates, brecias, sandstones, siltstones, mudstones, and brecias, sandstones, siltstones, mudstones, and shales. shales.

• Inorganic Carbonates – hotspring and cave Inorganic Carbonates – hotspring and cave formationsformations

• Evaporites in desert climatesEvaporites in desert climates

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Continental Continental Depositional Depositional

EnvironmentsEnvironments

1.1. Rivers or Fluvial Rivers or Fluvial Environments Environments

2.2. Lacustrine (or Lacustrine (or Lake) Lake) EnvironmentsEnvironments

3.3. Glacial Glacial Environments Environments

4.4. Aeolian Aeolian Environments Environments

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Continental Depositional Continental Depositional EnvironmentsEnvironments

• Fluvial – dominated by erosion and Fluvial – dominated by erosion and deposition associated with streams.deposition associated with streams. – Stream channel deposits, floodplains, terrace Stream channel deposits, floodplains, terrace

deposits, bars, alluvial fans, landslides/mass deposits, bars, alluvial fans, landslides/mass movement, swamps, meander movement, swamps, meander scars, lakesscars, lakes

Land-derived sediments variable grain sizes – gravel, sands, silts, and claysLand-derived sediments variable grain sizes – gravel, sands, silts, and clays

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Lacustrine Environments (Lakes)Lacustrine Environments (Lakes)• May be large or small. May be large or small. • May be shallow or deep. May be shallow or deep. • Filled with Filled with terrigenous, carbonate, or terrigenous, carbonate, or

evaporitic sedimentsevaporitic sediments. . • Sediments are typically Sediments are typically fine-grainedfine-grained but but

may be coarse near the edges. may be coarse near the edges. • Fine sediment and organic matter settling Fine sediment and organic matter settling

in some lakes produced laminated oil in some lakes produced laminated oil shales. shales.

• Playa lakesPlaya lakes are shallow, temporary lakes are shallow, temporary lakes that form in arid regions. They periodically that form in arid regions. They periodically dry up as a result of evaporation.dry up as a result of evaporation.

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Continental Depositional Continental Depositional EnvironmentsEnvironments

• Glacial – dominated by erosion and Glacial – dominated by erosion and deposition associated with glaciers.deposition associated with glaciers.

– Terminal, lateral, medial, ground, Terminal, lateral, medial, ground, recessional, and end moraines; recessional, and end moraines; outwash plains; drumlins; eskersoutwash plains; drumlins; eskers

Land-derived sediments variable grain sizes – gravel, sands, silts, and claysLand-derived sediments variable grain sizes – gravel, sands, silts, and clays

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Continental Depositional Continental Depositional EnvironmentsEnvironments

• Eolian – dominated by erosion and Eolian – dominated by erosion and deposition associated with winddeposition associated with wind..– Sand dunes, playa lakesSand dunes, playa lakes

Land-derived sediments finer-grained – Land-derived sediments finer-grained – sands and siltssands and silts

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Sedimentary StructuresSedimentary Structures

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• Sedimentary Structures: Sedimentary Structures: – Features visible at the Features visible at the scale of an outcropscale of an outcrop. . – Formed at the time of deposition or shortly Formed at the time of deposition or shortly

thereafter, but before lithification.thereafter, but before lithification.– Manifestations of the Manifestations of the physical and biological physical and biological

processesprocesses that operated in depositional that operated in depositional environments.environments.

– May be May be created during depositioncreated during deposition by the water or by the water or wind which moves the sediment.wind which moves the sediment.

– May May form after depositionform after deposition – such as footprints, – such as footprints, worm trails, or mudcracks.worm trails, or mudcracks.

– Provide information about the Provide information about the environmental environmental conditionsconditions under which the sediment was deposited. under which the sediment was deposited.

– Some structures form in Some structures form in quiet waterquiet water under under low low energyenergy conditions, whereas others form in conditions, whereas others form in moving moving waterwater or or high energyhigh energy conditions. conditions.

Sedimentary StructuresSedimentary Structures

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Sedimentary StructuresSedimentary Structures

• Stratification:Stratification:– Layering or BeddingLayering or Bedding – The most obvious feature of sedimentary The most obvious feature of sedimentary

rocks.rocks.– The layers (or beds or strata) are visible The layers (or beds or strata) are visible

because of differences in the color, because of differences in the color, texture, or composition of adjacent beds.texture, or composition of adjacent beds.

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• Sedimentary rocks generally have Sedimentary rocks generally have bedding bedding or or stratificationstratification

BeddingBedding

– Individual layers less than 1 cm thick are laminations

• common in mudrocks

– Beds are thicker than 1 cm

• common in rocks with coarser grains

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• Some beds show an upward gradual decrease Some beds show an upward gradual decrease in grain size, known as in grain size, known as graded beddinggraded bedding

Graded BeddingGraded Bedding

• Graded bedding Graded bedding is common in is common in turbidity currentturbidity current depositsdeposits– which form which form

when sediment-when sediment-water mixtures water mixtures flow along the flow along the seafloorseafloor

– As they slow, As they slow, – the largest the largest

particles settle particles settle out out

– then smaller then smaller onesones

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Graded BeddingGraded Bedding

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Interbedded Interbedded Sandstone and Sandstone and Conglomerate Conglomerate

(Sandstone (Sandstone exhibits graded exhibits graded

bedding)bedding)

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• Cross-bedding forms when layers come to Cross-bedding forms when layers come to rest rest – at an angle to the surface at an angle to the surface – upon which they accumulateupon which they accumulate– as on the downwind side of a sand duneas on the downwind side of a sand dune

• Cross-beds result from transport Cross-beds result from transport – by either water or windby either water or wind

• The beds are The beds are inclinedinclined or dip downward or dip downward – in the direction of the prevailing currentin the direction of the prevailing current

• They indicate ancient current directions, They indicate ancient current directions, – or or paleocurrentspaleocurrents

• They are useful for relative dating They are useful for relative dating – of deformed sedimentary rocksof deformed sedimentary rocks

Cross-Bedding or Cross-Bedding or Cross-StratificationCross-Stratification

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Cross-Bedding or Cross-Bedding or Cross-StratificationCross-Stratification

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Cross-BeddingInsert Animation #17 – Cross BeddingInsert Animation #17 – Cross Bedding

Cross-Bedding or Cross-Bedding or Cross-StratificationCross-Stratification

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• Tabular cross-Tabular cross-beddingbedding forms forms by deposition on by deposition on sand wavessand waves

Tabular Cross-BeddingTabular Cross-Bedding

• Tabular cross-Tabular cross-beddingbedding in the Upper in the Upper Cretaceous Two Cretaceous Two Medicine Formation Medicine Formation in Montanain Montana

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Tabular Cross-BeddingTabular Cross-Bedding

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Trough Cross-Trough Cross-BeddingBedding

• Trough cross-Trough cross-beddingbedding formed by formed by migrating dunesmigrating dunes

• Trough cross-Trough cross-bedsbeds in the in the Pliocene Six Mile Pliocene Six Mile Creek Formation, Creek Formation, MontanaMontana

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• Small-scale alternating ridges and troughsSmall-scale alternating ridges and troughs – known as known as ripple marksripple marks are common are common – on bedding planes, especially in sandstoneon bedding planes, especially in sandstone

• Current Ripple MarksCurrent Ripple Marks – form in response to water or wind currents form in response to water or wind currents – flowing in one directionflowing in one direction– and have and have asymmetric asymmetric profiles allowing geologists profiles allowing geologists – to determine to determine paleocurrent directionspaleocurrent directions

• Wave-Formed Ripple MarksWave-Formed Ripple Marks – result from the result from the to-and-fro motion of wavesto-and-fro motion of waves– tend to be tend to be symmetricalsymmetrical

• Useful for relative dating of deformed Useful for relative dating of deformed sedimentary rocks.sedimentary rocks.

Ripple MarksRipple Marks

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• Ripples with an Ripples with an asymmetrical asymmetrical shapeshape

• In the close-up of In the close-up of one ripple, one ripple, – the internal the internal

structure structure – shows small-scale shows small-scale

cross-beddingcross-bedding• The photo shows The photo shows

current ripples current ripples – that formed in a that formed in a

small stream small stream channel channel

– with flow from right with flow from right to leftto left

Current Ripple MarksCurrent Ripple Marks

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Current Ripple MarksCurrent Ripple Marks

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• As the waves As the waves wash back wash back and forth,and forth, – symmetrical symmetrical

ripples formripples form

• The photo The photo shows wave-shows wave-formed ripple formed ripple marksmarks – in shallow in shallow

seawaterseawater

Wave-Formed RipplesWave-Formed Ripples

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• When clay-rich sediments dry, they shrinkWhen clay-rich sediments dry, they shrink – and crack into polygonal patterns and crack into polygonal patterns – bounded by fractures called bounded by fractures called mud cracksmud cracks

• Mud cracks require Mud cracks require wetting and dryingwetting and drying to form, to form,

Mud CracksMud Cracks

– as along a as along a lakeshorelakeshore

– or a or a river flood river flood plainplain

– or where mud is or where mud is exposed at exposed at low low tide along a tide along a seashoreseashore

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• Mud cracks Mud cracks typically fill intypically fill in– with sediment with sediment – when they are when they are

preservedpreserved– as seen hereas seen here

Ancient Mud CracksAncient Mud Cracks• Mud cracks in ancient rocksMud cracks in ancient rocks

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Mud CracksMud Cracks A polygonal pattern of cracks produced A polygonal pattern of cracks produced

on the surface of mud as it drieson the surface of mud as it dries

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• Biogenic Sedimentary StructuresBiogenic Sedimentary Structures include: include:– TracksTracks– BurrowsBurrows– TrailsTrails

• Called Called Trace FossilsTrace Fossils

• Extensive burrowing by organisms Extensive burrowing by organisms – is called is called bioturbationbioturbation

• It may alter sediments so thoroughly It may alter sediments so thoroughly – that other structures are disrupted or that other structures are disrupted or

destroyed.destroyed.

Biogenic Sedimentary StructuresBiogenic Sedimentary Structures

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• U-shaped BurrowsU-shaped Burrows

BioturbationBioturbation

• Vertical BurrowsVertical Burrows

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BioturbationBioturbation

• Vertical, dark-colored areas in this rock are Vertical, dark-colored areas in this rock are sediment-filled burrowssediment-filled burrows– Could you use burrows such as these to relatively Could you use burrows such as these to relatively

date layers in deformed sedimentary rocks?date layers in deformed sedimentary rocks?

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Determining “Up Direction"Determining “Up Direction"• Because the rocks can be overturned by tectonic forces, Because the rocks can be overturned by tectonic forces,

what initially appears to be younger because it is on top, what initially appears to be younger because it is on top, may in fact turn out to be at the bottom of the section!may in fact turn out to be at the bottom of the section!

• Sedimentary structures can be used to determine "Sedimentary structures can be used to determine "up up directiondirection" " – Graded Beds Graded Beds – Cross Beds Cross Beds – Mudcracks Mudcracks – Flute Marks Flute Marks – Symmetrical (but not Asymmetrical) Ripples Symmetrical (but not Asymmetrical) Ripples – Scour Marks (Sole Marks)Scour Marks (Sole Marks)– Stromatolites Stromatolites – Burrows Burrows – Tracks Tracks

• Features which can be used to determine "up direction" Features which can be used to determine "up direction" are called are called geopetal structuresgeopetal structures

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Figure 5-23 (p. 94)Figure 5-23 (p. 94)Various kinds of geopetal indicatorsVarious kinds of geopetal indicators

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Fossils: Evidence of Past LifeFossils: Evidence of Past Life• By definition, fossils are the traces or By definition, fossils are the traces or

remains of remains of prehistoric lifeprehistoric life now now preserved in rock.preserved in rock.

• Fossils are generally found in sediment Fossils are generally found in sediment or or sedimentary rocksedimentary rock..– rarely in metamorphic – rarely in metamorphic –

destroyeddestroyed– almost never in igneous almost never in igneous

rock – exception trace rock – exception trace fossils of trees in fossils of trees in basaltic lava flowsbasaltic lava flows

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• Geologically fossils are important for Geologically fossils are important for many reasons:many reasons:

Fossils: Evidence of Past LifeFossils: Evidence of Past Life

– Aid in interpretation of Aid in interpretation of the geologic past.the geologic past.

– Serve as important time Serve as important time indicators.indicators.

– Serve as important Serve as important indicators of past indicators of past environmental environmental conditions.conditions.

– Allow for correlation of Allow for correlation of rocks from different rocks from different places.places.

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Sedimentary FaciesSedimentary Facies

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• A A sedimentary faciessedimentary facies is a body of is a body of sedimentsediment – with with distinctivedistinctive – physical, chemical, and biological attributesphysical, chemical, and biological attributes – deposited side-by-sidedeposited side-by-side – with other sediments with other sediments – in in different environmentsdifferent environments– can be used to can be used to interpret the depositional interpret the depositional

environmentenvironment

• Every depositional environment puts a Every depositional environment puts a distinctive imprint on the sediment, distinctive imprint on the sediment, making a particular facies. making a particular facies.

Sedimentary FaciesSedimentary Facies

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Figure 5-33 (p. 101)Figure 5-33 (p. 101)Sedimentary facies (lithofacies) developed in the sea Sedimentary facies (lithofacies) developed in the sea adjacent to a land area.adjacent to a land area. The upper surface of the diagram The upper surface of the diagram shows present-day facies, whereas the front face shows shows present-day facies, whereas the front face shows the shifting of facies through time. Notice that bottom-the shifting of facies through time. Notice that bottom-dwelling organisms also differ in environments having dwelling organisms also differ in environments having different bottom sediment and water depth.different bottom sediment and water depth.

Each depositional environment grades laterally Each depositional environment grades laterally into other depositional environments.into other depositional environments.

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Virtually all lithostratigraphic units are "Virtually all lithostratigraphic units are "timetime transgressivetransgressive" or " or diachronousdiachronous ( (they, or they, or their contacts, their contacts, cut across time linescut across time lines).).

Red Lines G and O are Time LinesRed Lines G and O are Time Lines

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Facies and Sea Level ChangesFacies and Sea Level Changes • A A marine transgressionmarine transgression occurs when sea occurs when sea

level rises with respect to the land.level rises with respect to the land.• During a marine transgression, During a marine transgression,

– the the shoreline migrates landwardshoreline migrates landward – and the and the environments paralleling the shoreline environments paralleling the shoreline

migrate landwardmigrate landward as the sea progressively covers as the sea progressively covers more and more of a continent.more and more of a continent.

• Each laterally adjacent depositional Each laterally adjacent depositional environment produces a sedimentary facies.environment produces a sedimentary facies.

• During a transgression, the During a transgression, the facies forming facies forming offshore become superposed upon facies offshore become superposed upon facies deposited in nearshore environmentsdeposited in nearshore environments..

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Facies and Sea Level ChangesFacies and Sea Level Changes

• A transgression produces a A transgression produces a fining-fining-upwardupward ( (deepening-upwarddeepening-upward) sequence ) sequence of facies.of facies.

• Finer-grained (deeper water) facies Finer-grained (deeper water) facies overlie coarser-grained (shallower overlie coarser-grained (shallower water) facies.water) facies.

• Sometimes called an Sometimes called an onlap sequenceonlap sequence..

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• The rocks of each facies become The rocks of each facies become youngeryounger – in a landward directionin a landward direction during a marine transgression during a marine transgression

• One body of rock with the same attributes One body of rock with the same attributes – (a facies) was deposited gradually at different times (a facies) was deposited gradually at different times – in different places so it is in different places so it is time transgressivetime transgressive– meaning the ages vary from place to placemeaning the ages vary from place to place

Marine TransgressionMarine Transgression

Older Older ShaleShale

Younger Younger ShaleShale

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Sedimentation During a Transgression Sedimentation During a Transgression Produces an Onlap SequenceProduces an Onlap Sequence

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• Three Three formations formations deposited deposited – in a in a

widespread widespread marine marine transgression transgression

– exposed in the exposed in the walls of the walls of the Grand Canyon, Grand Canyon, ArizonaArizona

A Marine Transgression in A Marine Transgression in the Grand Canyonthe Grand Canyon

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Causes of TransgressionsCauses of Transgressions

1.1. MeltingMelting of polar ice caps. of polar ice caps.

2.2. DisplacementDisplacement of ocean water by of ocean water by undersea volcanism.undersea volcanism.

3.3. Localized sinking or Localized sinking or subsidencesubsidence of the land in coastal areas.of the land in coastal areas.

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RegressionsRegressions• A A marine regressionmarine regression occurs when sea level occurs when sea level

rises with respect to the land.rises with respect to the land.• During a marine regression, During a marine regression,

– the the shoreline migrates seawardshoreline migrates seaward– and the and the environments paralleling the shoreline environments paralleling the shoreline

migrate seaward migrate seaward as the sea progressively as the sea progressively migrates off the continentmigrates off the continent

• A regression produces a A regression produces a coarsening upwardcoarsening upward ((shallowing-upwardshallowing-upward) sequence of facies. ) sequence of facies.

• Coarser-grained (shallower water) facies Coarser-grained (shallower water) facies overlie finer-grained (deeper water) facies.overlie finer-grained (deeper water) facies.

• This is sometimes called an This is sometimes called an offlap sequenceofflap sequence..

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• A marine A marine regression regression – is the opposite of a is the opposite of a

marine marine transgressiontransgression

• It yields a vertical It yields a vertical sequence sequence – with nearshore with nearshore

facies overlying facies overlying offshore faciesoffshore facies

– and rock units and rock units become become younger in younger in the seaward the seaward directiondirection

Marine RegressionMarine Regression

Younger ShaleYounger Shale

Older Older ShaleShale

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Sedimentation During a Regression Sedimentation During a Regression Produces an Offlap SequenceProduces an Offlap Sequence

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Causes of RegressionsCauses of Regressions

1.1. Buildup of ice in the Buildup of ice in the polar ice capspolar ice caps..

2.2. Formation of Formation of glaciersglaciers..

3.3. Localized Localized upliftuplift of the land in of the land in coastal areas.coastal areas.

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Sea Level ChangesSea Level Changes • Worldwide sea level change is known as Worldwide sea level change is known as eustaticeustatic sea levelsea level

change. change. • Fluctuations in sea level are caused by things such as: Fluctuations in sea level are caused by things such as: • Changes in the size of the polar ice caps, due to climatic Changes in the size of the polar ice caps, due to climatic

changes.changes. – Melting of ice caps leads to sea level rise (transgression).Melting of ice caps leads to sea level rise (transgression).– Growth of ice caps and glacier formation leads to drop in sea level Growth of ice caps and glacier formation leads to drop in sea level

(regression).(regression).

• Rate of sea floor spreadingRate of sea floor spreading – during times of rapid sea floor – during times of rapid sea floor spreading and submarine volcanism, the ocean ridge spreading and submarine volcanism, the ocean ridge system is enlarged by the addition of lava, displacing water system is enlarged by the addition of lava, displacing water onto the edges of the continents (transgression). onto the edges of the continents (transgression).

• Localized subsidence or uplift of the landLocalized subsidence or uplift of the land – In the 8000 – – In the 8000 – 10,000 years since the melting of the last glacial ice sheet 10,000 years since the melting of the last glacial ice sheet over North America, parts of Canada have risen due to over North America, parts of Canada have risen due to isostaticisostatic uplift by up to 300 meters. uplift by up to 300 meters.

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Isostatic ReboundIsostatic Rebound

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The Vail sea-level The Vail sea-level curve of major curve of major cycles of sea-level cycles of sea-level changes.changes. The letters The letters EE, , MM, , and and LL refer to Early, refer to Early, Middle, and Late.Middle, and Late.((After Vail, P. R., et al., 1977. After Vail, P. R., et al., 1977. American Association American Association of Petroleum Geologists of Petroleum Geologists Memoir 26Memoir 26.).)

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Figure 5-37 (p. 103)Figure 5-37 (p. 103)A rise in sea level will affect a far greater area A rise in sea level will affect a far greater area along low-lying coastlines than along along low-lying coastlines than along coastlines composed of highlands that rise coastlines composed of highlands that rise steeply adjacent to the sea.steeply adjacent to the sea.

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The Continental The Continental Shelf and Shelf and

Coastal Plain Coastal Plain Areas will be Areas will be Most Affected Most Affected by Sea Level by Sea Level Rise and FallRise and Fall

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What if the ice on Earth melted?What if the ice on Earth melted?

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Recent Sea Level CurveRecent Sea Level Curve

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Rock UnitsRock Units

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Lithostratigraphic UnitLithostratigraphic Unit • A body of sedimentary, extrusive igneous, A body of sedimentary, extrusive igneous,

metasedimentary, or metavolcanic rock metasedimentary, or metavolcanic rock distinguished on the basis of lithologic distinguished on the basis of lithologic characteristics (texture, color, composition, characteristics (texture, color, composition, etc.) and stratigraphic position.etc.) and stratigraphic position.

• GroupGroup – composed of 2 or more formations – composed of 2 or more formations• Formation Formation – composed of 2 or more members– composed of 2 or more members• Member Member – composed of 2 or more beds– composed of 2 or more beds• BedBed – smallest lithostratigraphic rock unit – smallest lithostratigraphic rock unit

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Lithostratigraphic UnitsLithostratigraphic Units • GroupGroup – composed – composed

of 2 or more related of 2 or more related formationsformations

• Formation Formation – – composed of 2 or composed of 2 or more membersmore members

• Member Member – – subdivisions within subdivisions within formations formations composed of 2 or composed of 2 or more bedsmore beds

• BedBed – smallest – smallest lithostratigraphic lithostratigraphic rock unitrock unit

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• Lithologically homogeneousLithologically homogeneous – all beds are – all beds are the same rock type or a distinctive set of the same rock type or a distinctive set of interbedded rock types.interbedded rock types.

• Distinct and different from adjacent rock Distinct and different from adjacent rock unitsunits above and below. above and below.

• Traceable from exposure to exposure Traceable from exposure to exposure ((correlationcorrelation)), and of , and of sufficient thickness to sufficient thickness to be mappablebe mappable..

• Named for a geographic localityNamed for a geographic locality where where particularly well exposed (This locality is particularly well exposed (This locality is referred to as the type section.) If the beds referred to as the type section.) If the beds are dominated by a single rock type, this are dominated by a single rock type, this may appear in the name. may appear in the name.

Lithostratigraphic UnitsLithostratigraphic Units

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CorrelationCorrelation• Correlation of rock units from one area Correlation of rock units from one area

to another is known as to another is known as stratigraphystratigraphy..– Lithostratigraphic CorrelationLithostratigraphic Correlation – Matching – Matching

up rock units on the basis of lithology and up rock units on the basis of lithology and stratigraphic position. stratigraphic position.

– Biostratigraphic CorrelationBiostratigraphic Correlation – Matching up – Matching up rock units on the basis of fossils they rock units on the basis of fossils they contain.contain.

– Chronostratigraphic CorrelationChronostratigraphic Correlation – – Matching up rock units on the basis of age Matching up rock units on the basis of age equivalence, as determined by radioactive equivalence, as determined by radioactive dating methods or fossils. dating methods or fossils.

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Figure 5-44 (p. 108)Figure 5-44 (p. 108) Correlation of lower Correlation of lower Cambrian rock units in Cambrian rock units in western Montana.western Montana.

The letters The letters CC, , BB, , GG, and , and AA indicate the occurrences of indicate the occurrences of trilobite index fossils trilobite index fossils CedariaCedaria, , BathyuriscusBathyuriscus, , GlossopleuraGlossopleura, and , and AlbertellaAlbertella. .

((Modified from Schmidt et al. 1994. U.S. Modified from Schmidt et al. 1994. U.S. Geological Survey Bulletin 2045Geological Survey Bulletin 2045.).)

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Figure 5-38 (p. 105)Figure 5-38 (p. 105)If the lithology of a rock is not sufficiently distinctive to permit its If the lithology of a rock is not sufficiently distinctive to permit its lithostratigraphic correlationlithostratigraphic correlation from one locality to another, its position from one locality to another, its position in relation to distinctive rock units above and below may aid in in relation to distinctive rock units above and below may aid in correlation.correlation. In the sample shown here, the limestone unit at locality In the sample shown here, the limestone unit at locality AA can can be correlated with the lowest of the four limestone units at locality be correlated with the lowest of the four limestone units at locality BB because of its position between the gray shale and the sandstone units.because of its position between the gray shale and the sandstone units.

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Geologic MapsGeologic Maps

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Depicting the PastDepicting the Past

Various ways in which the distribution of Various ways in which the distribution of rocks can be depicted:rocks can be depicted:

• Geologic columns Geologic columns • Stratigraphic cross-sections Stratigraphic cross-sections • Structural cross-sections Structural cross-sections • Geologic maps Geologic maps • Paleogeographic maps Paleogeographic maps • Isopach maps Isopach maps • Lithofacies mapsLithofacies maps

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Geologic ColumnsGeologic Columns

• Geologic ColumnsGeologic Columns show the vertical show the vertical succession of rock succession of rock units at a given units at a given location. They are location. They are used in correlation used in correlation and in the and in the construction of cross-construction of cross-sectionssections

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Generalized Generalized Geologic Geologic Column for Column for Grand Canyon Grand Canyon National ParkNational Park. .

((From McKee, E. D. From McKee, E. D. 1982. The Supai Group 1982. The Supai Group of the Grand Canyon, of the Grand Canyon, U.S. Geological Survey U.S. Geological Survey Professional Paper Professional Paper 11731173.).)

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Stratigraphic Cross-SectionsStratigraphic Cross-Sections

• Stratigraphic Stratigraphic Cross-SectionsCross-Sections correlate correlate geologic geologic columns from columns from different different locations to locations to show how rock show how rock units change in units change in thickness, thickness, lithology, and lithology, and fossil content fossil content in a given area in a given area

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Structural Cross-SectionsStructural Cross-Sections• Structural Cross-SectionsStructural Cross-Sections show a slice through the show a slice through the

Earth's crust, and may be drawn to emphasize the Earth's crust, and may be drawn to emphasize the lithologic equivalence of the strata.lithologic equivalence of the strata.

• They illustrate the They illustrate the timing of tiltingtiming of tilting, , foldingfolding, and , and faultingfaulting of rock units. Tops and bottoms of rock units of rock units. Tops and bottoms of rock units are plotted by elevation. Folds and faults are depicted are plotted by elevation. Folds and faults are depicted clearly.clearly.

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Geologic Geologic MapsMaps

• Geologic MapsGeologic Maps show show the distribution of the distribution of various layers and various layers and types of rocks in an types of rocks in an area. area.

• Geologic maps are Geologic maps are prepared by geologists prepared by geologists who locate the who locate the positions of contacts positions of contacts between formations in between formations in the field, and plot them the field, and plot them on a map. on a map.

• Map symbols indicate Map symbols indicate structural features structural features (folds, faults, etc.) and (folds, faults, etc.) and formation names. formation names.

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Figure 5-46 (p. 109)Figure 5-46 (p. 109)Steps in the preparation of a geologic map.Steps in the preparation of a geologic map. ((AA) A suitable base map is selected. ) A suitable base map is selected. ((BB) The locations of rock exposures of the ) The locations of rock exposures of the various formations are then plotted on the base various formations are then plotted on the base map. Special attention is given to exposures map. Special attention is given to exposures that include contacts between formations; that include contacts between formations; where they can be followed horizontally, they where they can be followed horizontally, they are traced onto the base map also. Strike (the are traced onto the base map also. Strike (the compass direction of a line formed by the compass direction of a line formed by the intersection of the surface of a bed and a intersection of the surface of a bed and a horizontal plane) and dip (the angle an inclined horizontal plane) and dip (the angle an inclined stratum makes with the horizontal) are stratum makes with the horizontal) are measured wherever possible and added to the measured wherever possible and added to the data on the base map. After careful field study data on the base map. After careful field study and synthesis of all the available information, and synthesis of all the available information, formation boundaries are drawn to best fit the formation boundaries are drawn to best fit the data. data. ((CC) On the completed map, color patterns are ) On the completed map, color patterns are used to show the areal pattern of rocks used to show the areal pattern of rocks beneath the cover of soil. beneath the cover of soil. ((DD) A cross-section is shown along line A-A9. ) A cross-section is shown along line A-A9. ((EE) A block diagram illustrates strike and dip.) A block diagram illustrates strike and dip.

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Paleogeographic MapsPaleogeographic Maps

• Paleogeographic Paleogeographic MapsMaps are are interpretive maps interpretive maps which depict the which depict the geography of an geography of an area at some time area at some time in the past, for in the past, for example, maps example, maps showing the showing the distribution of distribution of land and sea in land and sea in the past. the past.

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Paleogeographic Paleogeographic MapsMaps

• Figure 5-48 (p. 110)• Constructing a Paleogeographic Map:(1) For the selected area, collect all

available data that show the occurrence of the selected time-rock unit. Plot every point where rocks appear for that time period.

(2) Plot the rock types observed on that time-rock unit. Determine whether the strata originated on land or in the sea.

(3) Draw the paleogeographic map.

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Isopach MapsIsopach Maps• Isopach MapsIsopach Maps show the thickness of show the thickness of

formations or other units in an area. formations or other units in an area.

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Figure 5-49 (p.111) Figure 5-49 (p.111)

Isopach map of Isopach map of Upper Ordovician Upper Ordovician formations in formations in Pennsylvania and Pennsylvania and

adjoining states.adjoining states.

((After Kay, M. 1951. After Kay, M. 1951. Geological Society of Geological Society of America Memoir No. America Memoir No. 4848.).)

Isopach Isopach MapsMaps

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Lithofacies MapsLithofacies Maps• Lithofacies MapsLithofacies Maps show the distribution of lithofacies show the distribution of lithofacies

that existed at a given time over an area, or show the that existed at a given time over an area, or show the percentage of some lithologic component (such as percentage of some lithologic component (such as clay), or show the ratio of one rock type to another clay), or show the ratio of one rock type to another within the unit. within the unit.

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Figure 5-52 (p. 112)Figure 5-52 (p. 112)Lithofacies map of Lower Silurian rocks in the eastern Lithofacies map of Lower Silurian rocks in the eastern

United States.United States. ((After Amsden, T. W. 1955. Bull Am Assoc Petrol Geol 39:60–74After Amsden, T. W. 1955. Bull Am Assoc Petrol Geol 39:60–74.).)