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Chapter 5 – Sediment and Chapter 5 – Sediment and Sedimentary RocksSedimentary Rocks
Sedimentary rocks are composed of sediment.
Sediment forms at or near earth’s surface through the processes of weathering, transportation, deposition, and lithification.
Importance of sedimentary rocks include:Energy resources
PetroleumUraniumCoal
Sedimentary ResourcesSedimentary Resources
Importance of sedimentary rocks include:Mineral resources
Limestone: cementRock salt: saltRock gypsum: plaster
Importance of sedimentary rocks include:Environment of deposition
Oceans and seasLakes and swampsRiver valleys and flood plainsDeltasSand dunes
Every Rock Tells a StoryEvery Rock Tells a Story
Because sedimentary rocks form at earth’s surface, they tell the geologist what was happening on the surface when that rock was deposited. The rocks tell the story of Earth.
For example . . .
Limestone generally only grows in sea water.If a geologist finds limestone in Kansas,
the geologist concludes that Kansas was once underwater.
Sedimentary RocksSedimentary Rocks
Sedimentary rocks are composed of sediment.
Sediment can be either clastic (pieces) or chemical.
Clastic sediment is pieces of pre- existing rock like gravel, sand, silt and clay.
Chemical sediment is chemicals dissolved in water.
SedimentSediment
Sediment comes in two varieties.
Sediment can be either clastic (pieces) or chemical.
Clastic sediment is pieces of pre- existing rock like gravel, sand, silt and clay.
Chemical sediment is chemicals dissolved in water.
Clastic SedimentClastic Sediment
Clastic sediment forms from the mechanical, physical and chemical breakdown of rock.
The process of breaking rock down into smaller pieces aids further breakdown by chemical weathering.
Chemical SedimentChemical Sediment
Chemical sediment forms by the chemical dissolution and alteration of rocks at or near earth’s surface.
Chemical sediment is transported by stream waters to lakes and the oceans.
Weathering Chapter 15Weathering Chapter 15
Mechanical WeatheringMechanical Weathering
Frost wedgingAlternate freezing and thawing
Temperate mountainous climates
9% expansion as water freezes
Up to 80,000 pounds per square inch pressure
Talus SlopeTalus Slope
Generally form a large pile of rock at the base of mountains called talus slope.
UnloadingUnloading
As the weight of overlying rock is weathered and eroded away the rock expands and produces fractures (or joints) parallel to the topography. Exfoliation.
JointsJoints
Vertical joints (cracks without displacement) form by expansion and contraction.
Joints from Top with StriationsJoints from Top with Striations
Columnar joints with glacial striations. Devils Postpile National Monument.
Thermal Expansion JointsThermal Expansion Joints
Results from the daily cycle of temperature changes producing daily expans-ion and contraction. Most prominent in hot deserts.
Biological ActivityBiological Activity
Plants and burrowing animals cause much joint expansion.
Biological ActivityBiological Activity
The greatest mechanical weathering is now produced by catepillars.
Biological ActivityBiological Activity
The greatest mechanical weathering is now produced by catepillars.
Mechanical Weathering Enhances Mechanical Weathering Enhances Chemical WeatheringChemical Weathering
As mechanical weathering progresses, it enhances chemical weathering by increasing the surface area to volume ratio.
Comparison of Surface Area to Volume Comparison of Surface Area to Volume RatioRatio
The volume of a cube 2 cm on a side is:
2 x 2 x 2 = 8 cm3
The surface area of one side is 2 x 2 = 4 cm
There are six sides, so the total surface area is
4 cm x 6 = 24 cm2
Comparison of Surface Area to Volume Comparison of Surface Area to Volume RatioRatio
If the 2 cm cube is bisected by 3 joints how does this affect the surface area?
Each face of the 1 cm cube has a surface area of 1 cm x 1 cm = 1 cm2. There are six sides to each cube so the surface area would be 6 x 1 cm2 = 6 cm2. But there are a total of 8 little cubes so the total surface area is now
6 cm2 x 8 = 48 cm2
Compare this to the previous surface area of 24 cm2. The surface area has doubled!
Chemical WeatheringChemical Weathering
The most important chemical causing chemical weathering is H2O-the universal solvent.
However H2O in contact with CO2 gas in the atmosphere reacts to form carbonic acid.
H2O + CO2 = H2CO3 with a pH of about 5.7; a weak acid.
Dissolution WeatheringDissolution Weathering
When water precipitates (rains) on halite it will dissolve. NaCl + H2O = Na+ + Cl- + H2O
Cave Formation (Karst Topography)Cave Formation (Karst Topography)
When carbonic acid infiltrates into limestone or marble rock joints it begins to dissolve the calcite. CaCO3 + H2CO3 = Ca+ + HCO3
- + CO2
Solid rock dissolves into calcium ions, bicarbonate ions and carbon dioxide gas. All dissolved in water which carries these products away leaving a cave.
Cave roofs collapse to form cenotes or sinkholes.
CaveCave
When.
Oregon CaveOregon Cave
When.
Hydrolysis of Granite 1Hydrolysis of Granite 1
The most abundant rock in earth’s crust is granite. The most abundant mineral in granite is feldspar. Feldspar hydrolyses to kaolinite clay + bicarbonate + soluble silica.
Hydrolysis of Granite 2Hydrolysis of Granite 2
Feldspar + Carbonic acid = Kaolinite clay + Potassium + Sodium + Calcium + Soluble Silica (SiO2)
Soluble silica is important because it becomes the silica cement that makes sand into a sandstone.
White SandstoneWhite Sandstone
sandstone.
Hydrolysis of Granite 3Hydrolysis of Granite 3
This weathering of feldspar in granite then releases the quartz grains to form sand that will become sandstone. The kaolinite clay becomes the clay mineral that makes shale.
Shale is the most abundant sedimentary rock.
Oxidation of BiotiteOxidation of Biotite
Biotite mica in granite reacts with carbonic acid to make kaolinite clay and releases iron that can become the hematite cement that binds sand grains together to form sandstone.
Red SandstoneRed Sandstone
sandstone.
Factors that influence WeatheringFactors that influence Weathering
Minerals presentBowen’s Reaction Series
Available liquid waterWater is the most
important weathering agentTropicsAntarctica
TemperatureAs temperature rises rate
of chemical reactions increases.
Bowen’s Reaction SeriesBowen’s Reaction Series
Minerals presentBowen’s Reaction Series
Available liquid waterWater is the most
important weathering agentTropicsAntarctica
TemperatureAs temperature rises rate
of chemical reactions increases.
Liquid WaterLiquid Water
Minerals presentBowen’s Reaction Series
Available liquid waterWater is the most
important weathering agentTropicsAntarctica
TemperatureAs temperature rises rate
of chemical reactions increases.
Cold and Dry WeatheringCold and Dry Weathering
Minerals presentBowen’s Reaction Series
Available liquid waterWater is the most
important weathering agentTropicsAntarctica
TemperatureAs temperature rises rate
of chemical reactions increases.
Sedimentary Rock PicturesSedimentary Rock Pictures
Gravel clasts.Chemical
sedimentary rock.
Clastic Sedimentary RocksClastic Sedimentary Rocks
Clastic sediment, composed of rock and/or mineral fragments from pre-existing rocks.
A convenient method to classify clastic material is by its clast (particle) size.
Clastic Sedimentary Rock Clastic Sedimentary Rock ClassificationClassification
Size Range (mm) Particle Name Rock Name
> 256 mm Boulder Conglomerate
64-256 mm Cobble (rounded clasts)
4-64 mm Pebble Breccia
2-4 mm Granule (angular clasts)
Quartz Sandstone
1/16 – 2 mm Sand Arkose Sandstone
Graywacke Sandstone
1/256 – 1/16 mm Silt Siltstone
< 1/256 mm Clay Claystone
A rock that is about 1/3 silt and 2/3 clay and is fissile (laminated)
Shale
Sedimentary Environments - ShaleSedimentary Environments - Shale
Shale
Most abundant sedimentary rockDeposition in quiet, non-
turbulent water.Particles tend to form in thin
lamellae.Deep sea environment or far
away from high energy.Offshore and away from high-
energy surf zone.
Shale PicturesShale Pictures
Shale ImportanceShale Importance
The dark colors of shale usually are caused by the deposition of small amounts of incompletely decayed organic material.
Oil shaleMethane shale
Sedimentary Environments – Quartz Sedimentary Environments – Quartz SandstoneSandstone
Quartz Sandstone: Quartz is highly resistant to weathering so it is what is left over when all the other common minerals have weathered away. Mature.
Traveled the farthest.Sand dunes.Beach sand.
Sedimentary Environments – Arkose Sedimentary Environments – Arkose SandstoneSandstone
Arkose Sandstone: Contains roughly equal amounts of quartz and feldspar. Less mature than quartz sandstone and the presence of feldspar indicates deposition closer to source area (mountains).
Much of the sand size material in the upper portions of the Santa Ana River near the the San Gabriel and San Bernardino Mountains is akose.
Arkose Sandstone PictureArkose Sandstone Picture
Sedimentary Environments – Sedimentary Environments – Graywacke SandstoneGraywacke Sandstone
Graywacke Sandstone: Usually dark colored rock composed of quartz, feldspar, rock fragments, mafic minerals and a matrix of fine clays and silts. Very immature.
Common as turbidity currents fromed from submarine landslides associated with the edge of the continental shelf or trenches.
Graywacke Sandstone PictureGraywacke Sandstone Picture
Sandstone texturesSandstone textures
Two important textures in sandstones.
Rounding: the degree of rounding determines the transportation distance with more rounding indicating a longer transport distance.
Sandstone Textures continuedSandstone Textures continued
Sorting: the range of clast sizes. Usually determined by the means of transportation.
Well sorted = most clasts are the same size.
Poorly sorted = wide range of particle sizes.
Sandstone Textures continued againSandstone Textures continued again
Three transporting agents.
Wind: very fine sorting. All sand grains nearly the same size.
Water: intermediate sorting.
Ice: very poor sorting. Clay size to boulders transported together.
Sedimentary Environments – Sedimentary Environments – ConglomerateConglomerate
Conglomerates form in high energy environments.
By floodsNear mountainsSteep terrains
Usually poorly sorted.Nine foot boulder in
back yard.
Angular clasts indicate deposition very near source. Breccia.
Sedimentary Environments – Sedimentary Environments – Conglomerate continuedConglomerate continued
Rock fragments (clasts) may be used to determine the source area.
Polka-Dot Granite of Joshua Tree National Park
Conglomerate PictureConglomerate Picture
Lithifying AgentsLithifying Agents
Conglomerates and sandstones are lithified by cementation. Natural cements dissolved in groundwater precipitate minerals that end up transforming sediment into rock.
Three cements.QuartzHematiteCalcite
How could you distinguish these?
Chemical Sedimentary RocksChemical Sedimentary Rocks
Cemical sedimentary rocks form from the precipitation of chemicals from water.
Salt encrusted iguana. Ready for serving?
Oceans SaltsOceans Salts
Ocean Ions (Salts) AbundanceChlorine (Cl-)Sodium (Na+)Sulfate (SO4
2-)Magnesium (Mg2+)Bicarbonate (HCO3
-)Calcium (Ca2+)Potassium (K+)
Precipitation of these salts governed by chemical laws. Calcium carbonate is closest to the solubility limit despite low abundance.
Ocean Salt Precipitation OrderOcean Salt Precipitation Order
Calcite (CaCO3) - 50% water
evaporatedGypsum (CaSO4 2H2O) - 80% water evaporated
Halite (NaCl) - 90% water evaporated
What would be the order of salt precipitation as the Mediterranean Sea evaporated?
LimestonesLimestones
Little sea organisms have evolved protective armor against predators.
What to make shells out of?calcium carbonate (calcite or
aragonite-a polymorph)
Many limestones are composed of the shells of sea organisms.
Limestone ReefLimestone Reef
Reef Limestone RequirementsReef Limestone Requirements
Little sea organisms. What do they require?
Warm water (>18° C 22-28 ° C optimum) - solubility
Shallow water (bottom of food chain are plants that require sunlight) - <~200 ft water depth; 1% light left
Little clastic sediment - covers plants
Warm Water LocationsWarm Water Locations
.
Great Barrier ReefGreat Barrier Reef
.
Great Barrier ReefGreat Barrier Reef
.
Limestone Types - Fossiliferous Limestone Types - Fossiliferous LimestoneLimestone
A limestone that contains fossils.
.
Limestone Types - CoquinaLimestone Types - Coquina
A limestone that is composed of broken shell fragments. Anastasia Formation, Florida. Beach environment.
.
Limestone Types - Oolitic LimestoneLimestone Types - Oolitic Limestone
Composed of limestone and clay spheres. Typical of lagoons inbetween barrier island and mainland.
.
Limestone Types - ChalkLimestone Types - Chalk
White Cliffs of Dover.
.
Limestone Types - ChalkLimestone Types - Chalk
Single cell coccolith shell.
.
Limestone Types - ChalkboardLimestone Types - Chalkboard
Chalkboard slate. And you think you have it tough.
.
Limestone Types - Travertine Fly Limestone Types - Travertine Fly GeyserGeyser
As calcium carbonate water cools at the surface calcite precipitates as layered travertine.
.
Limestone Types - Travertine - Limestone Types - Travertine - HavasupaiHavasupai
Grand Canyon, Arizona.
.
Limestone Types - Travertine - Limestone Types - Travertine - PamukkalePamukkale
Turkey.
.
Limestone Types - DolomiteLimestone Types - Dolomite
Limestone rock reacts with magnesium in warm ocean waters.
CaCO3 + Mg2+ = (Ca,Mg)CO3 + Ca2+
Since the magnesium ion is smaller than the calcium it replaces, the volume is decreases during dolomitization which increases porosity. A good reservoir for petroleum. Kuwait.
.
Limestone Types - Dolomite QatarLimestone Types - Dolomite Qatar
.
Other Biochemical SedimentOther Biochemical Sediment
Chert - a rock composed of single cell shells of radiolaria. Typically deep sea sediement.
.
Other Biochemical SedimentOther Biochemical Sediment
Ribbon chert in central California.
.
Other Biochemical Sediment - Other Biochemical Sediment - DiatomiteDiatomite
A rock formed of diatoms.
.
Other Biochemical Sediment - Other Biochemical Sediment - DiatomiteDiatomite
UsesFuller’s Earth: Removing sheep
wool greaseSwimming pool filterAdded to toothpaste and baby
foodDynamite: nitroglycerine stabilizerInsecticide
Evaporites - Rock SaltEvaporites - Rock Salt
UsesFood
Need some salt in our diet
Preservative - jerkyRoad salt (bad - sort of)Water softener (bad)Mined out areas for storage
Evaporites - Camp Verde Salt MineEvaporites - Camp Verde Salt Mine
.
Evaporites - Rock GypsumEvaporites - Rock Gypsum
UsesWallboardPlasterStuccoSoil Amendment
Breaks up Adobe soils
Enviornment of DepositionEnviornment of Deposition
Grand CanyonMuav LimestoneBright Angel ShaleTapeats Sandstone
Using the Principle of Superposition, the Sandstone was deposited first (its at the bottom.)
.
Tapeats SandstoneTapeats Sandstone
Depositional environment was a beach
.
Bright Angel ShaleBright Angel Shale
Depositional environment was offshore of the beach in quiet water.
.
Muav LimestoneMuav Limestone
Depositional environment was offshore away from shale deposition.
.
Rising Sea LevelRising Sea Level
.
Rising Sea Level - Glaciation?Rising Sea Level - Glaciation?
What can cause a rise in sea level?
Glaciation - If we take water out of the oceans and place it on land as ice sea level can change by about 600 feet. At the peak of the last glacial cycle sea level was ~450 feet lower than today. If all the glaciers and ice caps melt, sea level would rise by ~150 feet. These cycles can take place in cycles of tens of thousands of years.
Pleistocene GlaciationPleistocene Glaciation
.
Rising Sea Level - Plate Tectonics?Rising Sea Level - Plate Tectonics?
What can cause a rise in sea level?
When the rate of plate tectonics increases, the width of the mid-ocean ridges increases, displacing ocean water onto continental surfaces.
Plate TectonicsPlate Tectonics
.
Plate TectonicsPlate Tectonics
.