Chapter 5 – Sediment and Sedimentary Rocks Sedimentary rocks are composed of sediment. Sediment...

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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.

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

Oregon CaveOregon Cave

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.

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.

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

Liquid WaterLiquid Water

Cold and Dry WeatheringCold and Dry Weathering

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)

Sedimentary Environments - ShaleSedimentary Environments - 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

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

Chapter 5 – Sediment and Sedimentary Rocks Sedimentary rocks are composed of sediment. Sediment...

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