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Chapter 6.1
Formation of Sedimentary Rocks
Vocabulary• Texture- the size, shape, and crystal size • Sediment- Pieces of solid material that have
been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation.
• Lithification- physical and chemical process that transform sediments into sedimentary rocks.
Vocabulary Cont.• Cementation-when mineral growth cements
sediment grains together into rock.• Cross-bedding- bedding in which the particle
sizes become progressively heavier and coarser towards the bottom layers.
• Graded bedding- bedding formed when inclined layers of sediment move forward across horizontal surface.
• Bedding- horizontal layering of sedimentary rocks.
Weathering Weathering
Produces clastic sediment
Physical Processes
Minerals in rock are
chemically unchanged.
Rock fragments break off.
Occurs when Earth’s crust is exposed
Chemical Processes
Minerals in rocks are
chemically changed.
Occurs through
Erosion and Transport
Wind Moving Water
Gravity Glaciers
Process of Lithification
• Lithification begins when the weight of overlaying sediments forces sediment grains closer together. Water in pressed out. The grains are then compacted together. Sediments that are buried will experience high temperatures and will have cementation.
Complete page 56 in SNB on your own
Section 6.2 Vocab
Clastic: sediments having particles ranging in size from boulders to microscopic particles, which often have worn surfaces and rounded corners.Clastic Sedimentary Rock: sedimentary rocks formed from deposits of loose sedimentsPorosity: the percentage of open spaces between grains in a rockEvaporite: chemical sedimentary rocks that form as a result of crystal grains precipitating out of a supersaturated body of waterReservoir: a subsurface area of rock that has enough porosity to allow for the accumulation of oil, natural gas, or water
Clastic sedimentary rocks
Coarse-grainedType of fragments: gravel sizeTypes of rock formed: conglomerate, brecciaFormed by: high-energy flows of water
Medium GrainedType of fragments: sandType of rock formed: sandstoneFormed by: stream and river channels, beaches, deserts
Fine-grainedType of fragments: silt and mudType of Rock formed: siltstone, shale
Medium-grained clasticsPorosities as high as 30-40%-When pore spaces connected it allows for water to move through sandstoneCan hold reservoirs of oil, natural gas, and groundwater
Fine-grained clasticsVery low porosityForm barrier to the movement of groundwater and oil
Chemical Sedimentary Rocks
Chemical Sedimentary Rocks
Sequence
___ Thick layers of evaporites can accumulate as evaporation removes freshwater.___ Water evaporates and leaves behind dissolved minerals.___ Minerals are dissolved and carried into lakes and oceans by chemical weathering.___ Layers of chemical sedimentary rocks called evaporites form.___ The concentration of minerals reaches the saturation point.___ Crystal grains precipitate out of the solution and settle on the bottom.
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Biochemical Sedimentary RocksWhat forms themThe remains of the once-living animals and plants
Where they formShallow-water environments Swamps and coastal areas
How limestone formsOrganisms use calcium carbonate in seawater to make their shells. Calcium carbonate precipitates out of the water and crystallizes between the grains of calcium sediment during lithification.
How Coal formsThick layers of vegetation accumulate. The layers are buried and compressed and are lithified into coal.
Importance of Sedimentary Rocks
Provide Information
about
SedimentaryRocks
ProvideResources
PastAnimals and
plantsBedrock
AncientRivers, lakes,
And shorelines
Uranium PhosphateAnd iron
Oil, naturalGas, and coal
Buildingmaterials
Real-World ConnectionA company want to drill a new oil well. They know that a layer of oil containing shale is located beneath a thick layer of siltstone. Describe challenges the company might face.
The siltstone has low porosity, so the oil will not flow though it. The company would have to drill though the siltstone to reach the oil-containing shale. If the layer of siltstone is too thick, the company might not be able to drill deep enough to reach the oil.
6.3 Metamorphic Rocks
Intrusive- Igneous rocks that cool slowly beneath Earth’s surface
Regional Metamorphism- Belts of metamorphic rock covering large areasContact Metamorphism- Metamorphism that occurs when molten rocks come in contact with solid rocks.Hydrothermal Metamorphism- Metamorphism caused when very hot water reacts with rocks and alters its chemistry and mineralogy.Foliated- Metamorphic rocks containing wavy layers and bands of minerals.Nonfoliated- Metamorphic rocks composed of minerals with blocky shapes.Rock Cycle- The continuous cycle of changing and remaking rocks.
Causes of Metamorphism
Conditions necessary for metamorphism
High Pressure
1. Materials being buried alive 2. Igneous intrusion
Low Pressure
Can be caused by
1. Weight of the rocks above
2. Compressive forces during mountain building
Types of Metamorphism
I. Regional Metamorphism A. Occurs when high temperatures and pressure affect large regions of Earth’s crust. B. Geologists can divide metamorphic rock belts into zones based on the mineral groups found in the rocks.II. Contact Metamorphism A. Occurs when magma comes in contact with solid rock. B. Can result in zones of different mineral surrounding an intrusion.III. Hydrothermal Metamorphism A. Occurs when very hot water reacts with rock and changes its chemistry and mineralogy. B. Can result in dissolved minerals, break down of minerals, and deposits of new minerals.
Metamorphic TextureTexture Shape of
crystalsHow formed Examples
Foliated Flat, needlelike
High pressure during metamorphism
Schist, gneiss
Nonfoliated blocky No pressure during metamorphism
Quartzite, marble
Porphyroblast Very large Reorganization of atoms during metamorphism
garnet
Mineral Changes
Like in fractional crystallization. Minerals in solid rock are stable at certain temperatures and pressures. During metamorphism. The minerals in rock change into new minerals. The new minerals are stable under the new temperatures and pressure conditions. These kinds of changes are called solid- state alterations.
Compare mineral changes in metamorphism to changes in fractional crystallization. Name the process of mineral change in metamorphism.
Composition Changes Hot fluid movie in and out of rock during metamorphism. This can change the original composition of the rock. Chemical changes often happen during contact metamorphism near igneous intrusions. Hydrothermal fluids move into the surrounding rocks and change their mineralogy, texture and chemistry.
Synthesize
Rocks are constantly changing from one type through internal and external processes. A rock’s age tells when it took its present form.
A geologist says that a certain rock us 500 million years old. Tell if this can be true, and why or why not.
Other Metamorphic is Latin of “Changed form” James Hutton proposed the rock cycle in the
1700’s