Section Assessment 6.1, 6.2, 6.3 Flashcards
How are clastic sediments formed, and how do scientists classify them?
Clastic sediments are formed fro the abundant deposits of loose sediments found on Earth’s surface. Scientists classify them based on their particle size.
Why do sediment deposits tend to form layers?
Sediment deposits tend to form layers because of deposition. During deposition, sediments are deposited when transport stops and the particles will settle out forming layers of sediment. Largest particles at the bottom (as water slows down particles settle first) and smallest particles at the top.
As sediments are buried, what two factors increase with depth. How do these factors cause lithification?
The two factors that increase with depth as sediments are buried are temperature and pressure. These factors cause lithification because lithification begins with compaction as the overlying sediments a force the grains closer together which causes the physical change into sedimentary rock.
Compare and contrast graded bedding and cross-bedding.
Graded bedding- bedding in which the particle sizes become progressively heavier and coarser towards the bottom layers.
Cross-bedding- is formed as inclined layers of sediment move foreward across a horizontal surface
Graded bedding layers ar do served in marine sedimentary rock which were created by underwater landslides.
Cross-bedding examples are sandy beaches and sand bars in streams (small scale) and migrating sand dunes (large scale).
Compare and contrast them ain’t yes of clastic sedimentary rocks.
Course-grained clastics- consist of gravel sized rock and mineral fragments. Two rock types are conglomerates which have rounded fragments and Breccias which contain angular fragments.
Medium-grained clastics- sedimentary rocks that contain sand-sized rock and mineral fragments. Sandstone is formed when these medium-sized sediments are buried and lithified.
Fine-grained clastics- these sedimentary rocks consist of silt and mud and are called siltstone and mudstone (shale). Siltstone is composed of silt-sized grains, while shale is composed of silt and clay sized particles. Shale breaks along thing layers and has low porosity which forms barriers that hinder the movement of groundwater and oil.
Why do chemical sedimentary rocks form primarily in areas that have high rates of evaporation?
Chemical sedimentary rocks form in areas of high rates of evaporation because when the concentration of dissolved minerals in a body of water reaches saturation, crystal grains precipitate out of the solution and settle at the bottom. Layers of the sedimentary rocks that form as a result are called evaporites. As more minerals are carried in evaporation continues to remove freshwater and maintain high mineral concentrations.
Why is coal an organic sedimentary rock?
Coal is an organic sedimentary rock because it formed from the remains of plant material.
The original concentration of dissolved minerals in a restricted ocean basic was enough to form only a thin evaporate layer. How, then, is it possible that thick evaporate layers formed there?
It is possible that thick evaporate layers formed there because as more dissolved minerals are carried into the basins,e vapor action continues tour emote freshwater and maintain high mineral concentrations which will, over time, lead to thick layers of evaporate minerals.
Compare and contrast the formation of the three types of sedimentary rock.
Rock type:
Clastic- course, medium or fine grained
Chemical- calcite, halite, and gypsum
Organic- calcium carbonate (shells), plant matter
Rock name:
Clastic- conglomerate or breccia, sandstone, shale
Chemical- limestone, rock salt, rock gypsum
Organic- limestone, coal
Method of Formation:
Clastic- formed from the abundant deposits f loose sediments (lithification of clastic sediments).
Chemical- When the concentration of dissolved minerals reaches saturation, crystal grains precipitate out of the solution and settle at the bottom. (Precipitation of dissolved minerals from water).
Organic- formed from the remains of once living things (accumulation and lithification of remains of living things).
How can the chemical composition of a rock be changed during metamorphism?
The chemical composition of a rock can be changed during metamorphism when temperature or pressure becomes high enough and the rocks convert to magma. If the rocks do not reach the melting point and when high temperature and pressure combine to alter the texture, mineralogy, or chemical composition, a metamorphic rock forms.
What are the three main types of metamorphism? Compare and contrast the factors that cause each type.
1) Regional metamorphism- when high temperatures and pressure affect large regions of Earth’s crust. Can be low grade, intermediate grade, or high grade which will reflect the intensity of temperature and pressure.
2) Contact Metamorphism- when molten rocks come in contact with solid rocks. High temperatures and moderate-to-low pressure form the mineral assemblage, that are characteristic of contact metamorphism.
3) Hydrothermal metamorphism- when very hot water reacts with rock and laters its chemistry. Hydrothermal mineral scan dissolve some minerals, break down others, and deposit new ones.
How does quartzite differ from schist?
Schist- foliated (wavy layers and bands of minerals).
Quartzite- non foliated (lack mineral grains with long axes in one direction).
How are the three types of rocks classified (metamorphism)?
They are classified according to how they form.
What causes foliated metamorphic textures?
Result from high pressure during metamorphism which causes minerals to be flat and needlelike.
What parts of the rock cycle occur deep in Earth’s crust?
The parts of the rock cycle that occur deep within the Earth’s crust are magma crystallizing, sediments being cemented, and deeply burried rocks metamorphosing.
