Sedimentology & Stratigraphy GL-3053 Quiz

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Questions and Answers

What are the three classes of sedimentary rocks, according to the presented classification?

  • Terrigenous clastic, chemical, and an unnamed third type. (correct)
  • Clastic, chemical, and organic.
  • Igneous, metamorphic, and sedimentary.
  • Detrital, biogenic, and volcanic.

Which of the following describes terrigenous clastic sediments?

  • Sediments formed by volcanic activity
  • Sediments that have precipitated directly from a solution.
  • Sediments transported as solid particles. (correct)
  • Sediments formed from the remains of organic matter.

What is a key characteristic of chemical sediments?

  • They were once dissolved in a solution. (correct)
  • They are generally found in deep ocean trenches.
  • They are formed by intense heat and pressure.
  • They are composed of large, angular fragments.

According to the course content, which topic directly follows 'SEDIMENTARY ROCKS CLASSIFICATION'?

<p>TEXTURES OF SEDIMENTARY ROCKS (A)</p> Signup and view all the answers

What distinguishes a claystone from a siltstone?

<p>Claystone is mostly composed of clay-sized particles, while siltstone is dominated by silt-sized particles (C)</p> Signup and view all the answers

What is the general term used for sedimentary rocks composed of silt and/or clay?

<p>Mudrock (A)</p> Signup and view all the answers

What characteristic is used to differentiate silt from clay by touch?

<p>Clay feels smooth, while silt feels gritty (D)</p> Signup and view all the answers

If a sedimentary rock is made with more than one-third of both clay and silt, how is it classified?

<p>Mudstone (B)</p> Signup and view all the answers

Which of the following is NOT a terrigenous clastic sedimentary rock?

<p>Limestone (B)</p> Signup and view all the answers

What is the approximate size range (diameter) of silt particles according to the content?

<p>4 - 62 micrometers (A)</p> Signup and view all the answers

Which of the following is an example of a specific type of sandstone, as mentioned in the content?

<p>Batupasir (B)</p> Signup and view all the answers

What differentiates terrigenous clastic rocks from carbonate clastic rocks?

<p>Their fundamental composition. (B)</p> Signup and view all the answers

Which of the following is NOT a chief constituent of detrital/terrigenous clastic rocks?

<p>Calcite crystals (B)</p> Signup and view all the answers

What is the primary criterion used to differentiate the various types of detrital rocks?

<p>Grain size. (A)</p> Signup and view all the answers

What is the Wentworth Scale?

<p>A scale used by sedimentologists for grain size. (A)</p> Signup and view all the answers

How does the phi scale relate to the grain diameter?

<p>It scales it logarithmically, using base 2. (A)</p> Signup and view all the answers

Why is a negative sign used in the phi scale formula?

<p>To represent the decreasing sizes of grains from right to left on a graph. (C)</p> Signup and view all the answers

What is the primary difference between sediments and sedimentary rocks?

<p>Sediments are loose material, rocks are lithified. (D)</p> Signup and view all the answers

Which of the following represents the correct relationship between breccia and conglomerate?

<p>Conglomerate has rounded grains, breccia has angular grains. (D)</p> Signup and view all the answers

What is the primary composition of limestone?

<p>Calcite (A)</p> Signup and view all the answers

Which type of chert is known for its banded form?

<p>Agate (B)</p> Signup and view all the answers

What triggers the deposition of evaporites such as rock salt and gypsum?

<p>Evaporation (A)</p> Signup and view all the answers

Which of the following processes does NOT contribute to the formation of limestone?

<p>Glacial sediments (B)</p> Signup and view all the answers

Which organisms are thought to contribute to the biological origin of chert?

<p>Diatoms and radiolarians (A)</p> Signup and view all the answers

What is the term for the broken shell limestone composed chiefly of shell fragments?

<p>Coquina (D)</p> Signup and view all the answers

What is the key mineral component of chert?

<p>Microcrystalline quartz (C)</p> Signup and view all the answers

What category of sedimentary rocks does travertine belong to?

<p>Chemical sedimentary rock (C)</p> Signup and view all the answers

What is the largest size of clastic sedimentary particles defined as clay according to the information provided?

<p>4 microns (A)</p> Signup and view all the answers

Which of the following best describes the mineral composition of clay minerals?

<p>They are primarily composed of aluminosilicates. (D)</p> Signup and view all the answers

Which technique is NOT mentioned as a method to distinguish and observe clay minerals?

<p>Atomic Force Microscopy (AFM) (A)</p> Signup and view all the answers

What characteristic structure do clay minerals exhibit?

<p>Layered crystal structure (B)</p> Signup and view all the answers

Which ions are primarily involved in linking the silica layers in clay mineral structures?

<p>Aluminium and magnesium (A)</p> Signup and view all the answers

What are the main constituents of clay-sized particles?

<p>Clay minerals (C)</p> Signup and view all the answers

The crystal layers in clay minerals principally consist of what?

<p>Silica with aluminium and magnesium ions (D)</p> Signup and view all the answers

What type of rock is categorized as terrigenous clastic sedimentary rock alongside claystone?

<p>Siltstone (D)</p> Signup and view all the answers

What technique is utilized to obtain a detailed image of minerals at a micron level?

<p>Scanning Electron Microscopy (D)</p> Signup and view all the answers

Which of the following statements regarding X-ray diffraction analysis (XRD) is correct?

<p>It identifies minerals based on the angles of diffracted X-rays. (A)</p> Signup and view all the answers

What distinguishes claystone from siltstone in terms of particle size composition?

<p>Claystone is made up of clay-sized particles accounting for over 2/3 of its composition. (D)</p> Signup and view all the answers

What term is most appropriate for mudrocks that show fissility and break parallel to the bedding plane?

<p>Shale (C)</p> Signup and view all the answers

How is the term 'mudrock' defined in geology?

<p>Any detrital sediment composed of silt and/or clay. (B)</p> Signup and view all the answers

What is the primary component of shale?

<p>Clay minerals and silt-sized particles (C)</p> Signup and view all the answers

Which composition would classify a rock as a mudstone?

<p>More than one-third of each component of silt and clay (C)</p> Signup and view all the answers

What characterizes the diffraction pattern observed in X-ray diffraction analysis?

<p>It is unique to each specific mineral present in the sample. (A)</p> Signup and view all the answers

Flashcards

Terrigenous Clastic Rocks

Rocks formed from solid particles transported and deposited by various processes.

Chemical Sedimentary Rocks

Rocks formed when minerals dissolved in water precipitate out and solidify.

Biogenic Sedimentary Rocks

Rocks formed by the accumulation of organic materials, such as plant or animal remains.

Detrital / Terrigenous Clastic Rocks

Rocks formed by the accumulation and lithification of fragments derived from pre-existing rocks, like sandstone or shale.

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Wentworth Scale

A classification system that classifies sedimentary rocks based on the size of the particles that make up the rock.

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Phi Scale

A numerical representation of the Wentworth Scale, which uses the logarithm base two to express grain size.

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Breccia

A type of clastic sedimentary rock characterized by angular fragments, often found near their source area.

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Conglomerate

A type of clastic sedimentary rock composed of rounded fragments, often found further from the source.

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Lithification

The process of transforming loose sediment into solid rock.

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Mixed (Descriptive and Genetic) Classification

A unique classification scheme that considers both the descriptive and genetic aspects of sedimentary rocks.

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Sandstone

Clastic sedimentary rock composed of sand-sized grains.

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Siltstone

A fine-grained sedimentary rock composed of silt-sized particles.

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Claystone

A fine-grained sedimentary rock composed of clay-sized particles.

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Mudrock

A general term for sedimentary rocks formed by the accumulation of silt and clay.

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Mudstone

A mixture of silt and clay, where more than one-third of the particles are clay-sized.

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What is the size of clay particles?

Clay is the finest grade of clastic sedimentary particles, defined as those less than 4 microns in diameter.

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What are clay minerals composed of?

Clay minerals are primarily made up of phyllosilicate minerals, which have a layered crystal structure.

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How are clay minerals formed?

Clay minerals form from the breakdown of feldspars and other silicate minerals.

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What are mudrocks?

Mudrocks are a category of sedimentary rocks that are composed of fine-grained sediments, including silt and clay.

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What are siltstone and claystone?

Siltstone and claystone are two types of mudrocks, named based on the dominant grain size of the rock.

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Describe claystone.

Claystones are mudrocks primarily composed of clay minerals. They are known for being very fine-grained and often exhibit fissility (the tendency to break along parallel planes).

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How can we distinguish clay minerals?

Scanning Electron Microscopy (SEM) is a technique used to observe and distinguish clay minerals. In SEM, a fine electron beam scans the sample's surface, generating secondary electrons used to create an image.

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What is the composition of clay mineral layers?

The crystal layers of clay minerals are primarily made of silica, combined with aluminium and magnesium ions. These ions are linked by oxygen atoms.

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X-ray Diffraction (XRD) Pattern Analysis

A technique that uses X-rays to identify minerals in claystone by analyzing the diffraction patterns produced when X-rays interact with the crystal structure of the minerals.

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Scanning Electron Microscopy (SEM)

A type of microscopy that uses a focused beam of electrons to scan the surface of a sample, producing high-resolution images of the surface morphology and composition.

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Shale

A term commonly used for mudrocks exhibiting a fissility, meaning they break easily along parallel planes.

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Slate

Fine-grained metamorphic rock derived from shale, exhibiting a distinct cleavage that breaks along parallel planes.

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What is chert?

A chemical sedimentary rock composed of microcrystalline quartz, formed from the precipitation of silica in water.

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What are some varieties of chert?

Various types of chert, including flint and jasper.

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What is agate?

A banded form of chert, with alternating layers of different colors.

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What are evaporates?

Chemical sedimentary rocks formed by the evaporation of water, leaving behind minerals like halite (rock salt) and gypsum.

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What is limestone?

A chemical sedimentary rock, most commonly formed from the accumulation of calcium carbonate (CaCO3) shells and skeletons of marine organisms. It's the most abundant chemical sedimentary rock.

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What is travertine?

A type of limestone formed by the deposition of calcium carbonate from hot springs or other freshwater sources.

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What is oolitic limestone?

A type of limestone formed by the accumulation of small, spherical grains of calcium carbonate called ooliths.

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What is chalk?

A type of limestone formed by the accumulation of microscopic marine organisms, mainly plankton.

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Study Notes

Sedimentary Rock Classification

  • Sedimentary rocks are formed from the accumulation and lithification of sediments.
  • Classification schemes categorise sedimentary rocks based on origin, composition and texture.
  • Different classifications exist, including genetic and mixed (descriptive and genetic) methods.

Genetic Classification

  • Terrigenous Clastic Sedimentary Rocks:
    • Loose materials formed from transported solid particles.
    • Key components include lithics, quartz, feldspar, micas, clay minerals and biogenic particles.
    • Grain size is a crucial factor in classifying these rocks.
    • Wentworth Scale uses phi scale representation of grain diameter in mm
  • Chemical Sedimentary Rocks:
    • Formed by precipitation from solution (e.g., evaporation).
    • Major components include inorganic processes (e.g. chert, evaporites) and organic processes that have a biochemical origin.
    • Chert is microcrystalline quartz; Evaporites include rock salt and gypsum. Limestone (travertine, oolitic limestone, coquina, chalk) is also a chemical sedimentary rock.
  • Biogenic Sedimentary Rocks:
    • Predominantly composed of plant and animal remains.
    • Includes corals, molluscs, diatoms, radiolarians, and limestones. Coal is a biogenic rock comprised from plant material..

Volcaniclastic Sedimentary Rocks

  • Formed from volcanic eruptions or the breakdown of volcanic rocks.
  • Different types of volcaniclastic deposits occur:
    • Autoclastic: non-explosive fragmentation
    • Pyroclastic: explosive eruptions (fallout, flow, surge)
    • Resedimented syn-eruptive volcaniclastic: rapid resedimentation of texturally unmodified pyroclastic or autoclastic particles.
    • Volcanogenic sedimentary: aggregates containing reworked preexisting materials.

Carbonate Rocks

  • Carbonate rocks contain more than 50% carbonate minerals.
  • Classification can be based on biogenic, clastic or chemical origins.
  • Includes various types such as limestone, dolostone, and chalk.

Dunham Classification of Carbonate Sedimentary Rocks

  • This classification scheme uses three main criteria to categorize carbonate rocks:
    • Presence/absence of mud/micrite
    • Supporting fabric (indicating original sediment characteristics)
    • Evidence for presence/absence of organic binding during deposition

Limestone Components

  • Limestone consists of grains, mud, and cements.
  • Grains include non-skeletal grains (e.g., peloids, ooids, pisolites, composite grains, intraclasts, oncoids, lithoclasts, micritized grains) and skeletal grains (e.g., sponges, foraminifera, echinoderms, molluscs, bryozoans, brachiopods, trilobites, ostracodes, stromatoporoids, corals).

Mudrocks (Siltstone & Claystone)

  • Composed of silt or clay-sized particles.
  • Can include siltstone (mostly silt) or claystone (mostly clay)
  • Classification based on grain size.

Terminology

  • Clastic: Composed of pieces of pre-existing rocks.
  • Fissility: Tendency of a rock to split along thin, parallel layers.
  • Matrix-supported: clasts are surrounded by a finer-grained matrix.
  • Clast-supported: clasts are in contact with each other, with no matrix present.
  • Organic: Formed by living organisms.
  • Grain size: Size of the particles within the sedimentary rock (Wentworth Scale, Phi Scale).
  • Texture: refers to the arrangement of the grains within the rocks..
  • Composition: The different types of materials within the sedimentary rock.

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