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Questions and Answers
Which sediment is classified as mud according to grain size?
Which sediment is classified as mud according to grain size?
What is the primary factor used to classify terrigenous clastic rocks?
What is the primary factor used to classify terrigenous clastic rocks?
What is indicated by a rock having more than 25% feldspar according to the classification scheme?
What is indicated by a rock having more than 25% feldspar according to the classification scheme?
In Dott’s classification scheme, what characterizes a rock that is 95% quartz?
In Dott’s classification scheme, what characterizes a rock that is 95% quartz?
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What defines wackes in the Pettijohn classification?
What defines wackes in the Pettijohn classification?
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What does the maturity of sediment mainly reflect?
What does the maturity of sediment mainly reflect?
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What term is used to refer to sediment that has gone through the rock cycle multiple times?
What term is used to refer to sediment that has gone through the rock cycle multiple times?
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Which adjective would best describe a poorly sorted, dark-colored rock?
Which adjective would best describe a poorly sorted, dark-colored rock?
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What characteristic is most indicative of arkose sandstone?
What characteristic is most indicative of arkose sandstone?
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Which climate is most likely to produce immature sandstones?
Which climate is most likely to produce immature sandstones?
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What does increased textural maturity in sediment indicate?
What does increased textural maturity in sediment indicate?
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Which type of sandstone is commonly associated with deltaic coastal plains?
Which type of sandstone is commonly associated with deltaic coastal plains?
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What is the main feature of graywacke sandstone?
What is the main feature of graywacke sandstone?
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Which type of sandstone often indicates an association with coal?
Which type of sandstone often indicates an association with coal?
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Compositional maturity is defined by the presence of which types of grains?
Compositional maturity is defined by the presence of which types of grains?
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What does chemical weathering in a humid climate typically remove from sediments?
What does chemical weathering in a humid climate typically remove from sediments?
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Which type of sandstone is considered to be the most mature?
Which type of sandstone is considered to be the most mature?
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Which statement best describes provenance in relation to sediment?
Which statement best describes provenance in relation to sediment?
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What is a primary implication of finding quartz sandstone?
What is a primary implication of finding quartz sandstone?
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What type of sandstone would be associated with a volcanic source rock?
What type of sandstone would be associated with a volcanic source rock?
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In the context of sedimentary petrology, what is a common implication of greywacke's grading?
In the context of sedimentary petrology, what is a common implication of greywacke's grading?
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In a tectonic setting that includes granitic rocks, which sandstone type is likely to be predominant?
In a tectonic setting that includes granitic rocks, which sandstone type is likely to be predominant?
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For studies aimed at determining ancient depositional environments, what aspect of sandstones is primarily considered?
For studies aimed at determining ancient depositional environments, what aspect of sandstones is primarily considered?
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Which characteristic is NOT commonly associated with quartz arenite?
Which characteristic is NOT commonly associated with quartz arenite?
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Study Notes
Classification of Clastic Sedimentary Rocks
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A fundamental categorization of sedimentary rocks is based on the type of deposited material and the deposition methods.
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A straightforward classification of clastic rocks and sediment is based on the dominant grain size of the material.
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Gravel, sand, and mud are the three main categories of sedimentary rocks based on grain size. Gravel is further categorized into cobbles and pebbles. Sand can be characterized as coarse, medium, or fine. The term "mudstone" signifies the presence of silt or clay-sized particles.
Sandstones Classification
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Most classifications of sandstones focus on the rock's composition.
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Dott's classification scheme is widely used and based on the relative proportion of quartz, feldspar, and lithic fragments.
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The scheme categorizes sandstones into quartz arenite (95% quartz), arkose (25% feldspar), and lithic arenite (more than 25% feldspar).
Pettijohn Classification
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This classification scheme is focused on the percentage of matrix.
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Classifies sandstones into two groups – matrix-poor (15%) and matrix-rich (wackes or greywackes).
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Wackes are typically dark-colored and poorly sorted.
Clastic Sedimentary Rocks: Maturity
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Clastic sedimentary rocks can be formed from "multicycled particles," meaning they have been through the rock cycle multiple times.
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Sedimentary rocks become more mature with each cycle.
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Textural maturity is reflected in changes in grain size, shape, sorting, rounding, and sphericity.
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Sandstone names often indicate the maturity of the rock:
- Quartz arenite is more mature than quartz graywacke.
Compositional Maturity
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Compositional maturity is determined by the relative proportion of soft and unstable grains.
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More mature sediments contain fewer soft or unstable grains.
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100% quartz grains represent the most mature sediment.
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The average igneous and metamorphic rocks contain 60% feldspar compared to the average sandstone with 12% feldspar, suggesting the recycling of materials through the rock cycle.
Provenance of a Sediment
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Provenance refers to the origin of a sediment.
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The provenance of a sediment can be inferred from its composition, reflecting the source rock and the tectonic and climatic characteristics of the source area.
Tectonic Setting
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The source rock of a sediment and the tectonic setting are closely related.
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Arkosic sandstone indicates a source area rich in granites, often found along convergent margins like the Andes.
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Abundant volcanic and low-grade metamorphic rock fragments in sandstone suggest an island-arc setting.
Climate
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Climate significantly influences weathering in the source area, impacting the composition of the produced sediment.
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Physical weathering, primarily in cold arid climates, produces abundant detrital grains, leading to immature sandstone.
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Chemical weathering in warm humid climates removes unstable minerals, resulting in more mature sediments.
Geologic Settings
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Different types of sandstone indicate various depositional environments:
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Quartz sandstone is often found in stable, shallow-water environments.
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Arkose is linked to rapid erosion and arid climates, typically deposited in fault troughs or near granitic mountains.
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Graywacke suggests rapid erosion and a tectonically active source area, often found alongside volcanic rocks.
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Lithic sandstone is often associated with coastal plains and nearshore marine environments.
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Classifying Sandstones
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The choice of classification method depends on the research objectives.
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Grain-size analysis is suitable for studies focusing on ancient depositional environments.
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Detailed compositional analysis is required for studies on ancient tectonic settings.
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Compositional classification is necessary for understanding the mechanical properties of sandstone, relevant for studies like excavation costs.
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Description
This quiz covers the classification of clastic sedimentary rocks based on grain size and composition. Learn about the different categories including gravel, sand, and mud, as well as the Dott's classification for sandstones. Test your knowledge on sedimentary rock types and their characteristics.
