Chapter 5 – Sediment and Chapter 5 – Sediment and Sedimentary Rocks Sedimentary 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 Petroleum Uranium Coal
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Chapter 5 – Sediment and Sedimentary Rocks Sedimentary rocks are composed of sediment. Sediment forms at or near earth’s surface through the processes.
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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
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
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.
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
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.
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.
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.
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.
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.