geology section 2
What do mud cracks and ripple marks indicate about the geologic past?
Mud cracks indicate that the sediment was deposited in an area that was alternately wet and dry, whereas ripple marks indicate that the sediment was deposited by directional currents in water or air.
How are chemical sedimentary rocks primarily identified, and how does this differ from how clastic sedimentary rocks are primarily identified?
Chemical sedimentary rocks are identified based on their compositions, whereas clastic sedimentary rocks are identified based on their particle sizes.
What type of chemical sedimentary rock is found in petrified wood?
Chert
What are the textures of clastic and nonclastic sedimentary rock?
Clastic rock consists of different discrete fragments cemented together. Nonclastic rock consists of patterns of interlocking crystals.
Which of the following minerals listed below, found also on page 144, is represented by the green crystals in the igneous rock below?
Olivine
________ are tiny "seed" particles created when small sediments or shell fragments are rolled by waves in water supersaturated with calcium carbonate.
Ooids
How does the volume of sedimentary rocks in Earth's crust compare with the volume of igneous and metamorphic rocks?
Sedimentary rocks represent 5 to 10 percent of the crust, whereas igneous rocks and metamorphic rocks combined represent 90 to 95 percent of Earth's crust.
________ are fragments of preexisting materials that have been broken down through the processes of weathering.
Sediments
A ________ marks the end of one episode of sedimentation and the beginning of another.
bedding plane
Can you identify the minerals that comprise igneous rocks? Drag the appropriate labels to their respective targets. The specific colors of the referenced mineral crystals within the rocks have been supplied to assist you. Labels will only be used once, and not all labels will be used.
biotite (dark brown crystals) potassium feldspar (pastel crystals) quartz (white crystals)
gneous rocks are mainly composed of _______ minerals.
silicate
Which of the characteristics below would you use to differentiate between basalt and gabbro?
Gabbro has larger crystals than basalt.
In this activity, choose from statements that describe how grain size and current velocity are connected, and how that helps us understand graded beds. Read the following sentences and select which is true.
Graded beds are evidence of a decrease in current velocity during deposition whereby coarse sediments settle out first, followed by finer sediments as the velocity decreases over time.
_______ form when molten rock cools and crystalizes.
Igneous rocks
In this activity, choose from statements about turbidity currents and graded-bed formation as exemplified in the Gigapan image. Read the following statements and select which are true. Specifically, focus on the relationships between grain size and velocities in turbidity currents.
In the Gigapan image, the sedimentary layers can be described as turbidites that were formed by repeated deposition of sediments from turbidity currents in a marine setting. Turbidity currents have high concentrations of sediments, making them heavy enough to travel down slopes coherently, even in marine environments.
________ processes, such as evaporation or precipitation, can precipitate chemical sediments.
Inorganic
Match the various grades of coal in order from lowest grade to highest grade. (Note: First refers to lowest grade and Fourth refers to highest grade.) Drag the terms on the left to the appropriate blanks on the right.
Lignite - Second Anthracite coal - Fourth (highest grade) Peat - First (lowest grade) Bituminous coal - Third
Which answer correctly distinguishes among limestone, dolostone, and chert?
Limestone, which is composed of calcium carbonate, forms by both chemical and biochemical means; dolostone, which is composed of calcium-magnesium carbonate, forms strictly by chemical means; chert, which is composed of microcrystalline quartz, forms most often chemically and to a lesser extent biochemically.
_______ describes how heat, intense pressure, and/or chemical changes can make a new rock.
Metamorphism
Match the sediment size with the appropriate rock. Drag the terms on the left to the appropriate blanks on the right. (Terms can be used more than once.)
Breccia −− Gravel Arkose −− Sand Quartz sandstone −− Sand Siltstone −− Silt Claystone −− Clay
Which of the characteristics below would you use to differentiate between diorite and porphyritic andesite?
A porphyritic andesite has two noticeably different crystal sizes within the same rock, whereas a typical diorite only has one crystal size within the same rock.
Differentiate between the formation of biochemical rocks and the formation of inorganic chemical rocks.
Biochemical rocks form from organisms that were once alive, such as limestone from marine shells, whereas inorganic chemical rocks form from non-biological processes, such as salt that is left behind when a lake evaporates.
How are breccia, conglomerate, sandstone, and shale different?
Conglomerate and breccia are both composed of gravel-sized grains. Grains are rounded in conglomerate and angular in breccia. Sandstone is composed of sand-sized rounded grains. Shale consists of grains not identifiable without a great magnification.
Which of the following textural terms describes when minerals form a pattern of interlocking crystals in a nonclastic chemical sedimentary rock
Crystalline
Match the textural descriptions with the appropriate sedimentary composition. Drag the terms on the left to the appropriate blanks on the right.
Detrital −− Subangular clasts, poor sorting. Organic −− Black, fibrous material. Some layering. Chemical −− Crystalline appearance.
Which of the following characteristics below would you use to differentiate between granite and diorite?
Diorite is made of equal parts of light and dark crystals, whereas granite has more light crystals and fewer dark crystals.
________ is the process where calcium ions in limestone are replaced with magnesium or small amounts of iron.
Dolomitization
Graded bedding will display particles that are fine near the bottom of the layer and get progressively coarser toward the top.
False
The picture below shows the correct solution to the previous question, which asked you to sort minerals into the categories felsic and mafic based on their chemical compositions. Based on this picture, please determine which of the sentences below is true.
Felsic minerals are generally lighter in color than mafic minerals
Which of the following characteristics below would you use to differentiate between granite and pegmatitic granite?
Pegmatitic granite has crystals larger than one centimeter, whereas granite has crystals smaller than one centimeter.
What is the raw material for coal, and how does it accumulate?
Plants are the raw material for coal; to form coal plants must accumulate in oxygen deficient swamp water.
Which of the below characteristics that you would use to differentiate between scoria and pumice?
Pumice is more felsic, and thus lighter in color, than scoria. A pumice weighs significantly less than a scoria of the same size.
Which of the characteristics below would you use to differentiate between rhyolite and andesite?
Rhyolite is more felsic, and thus is lighter in color, than andesite
What sedimentary structure(s) can you identify in the above image?
Ripplemarks
Match the rock with the appropriate category of sedimentary rock. Drag the terms on the left to the appropriate blanks on the right. (Terms can be used more than once.)
Sandstone −− Detrital Chert −− Chemical Shale −− Detrital Bituminous coal −− Organic Rock salt −− Chemical Coquina −− Chemical
Sort the following everyday examples of sedimentary processes into the bins labeled with the sedimentary processes they most closely represent. Drag the appropriate items into their respective bins.
Sediment Erosion/transport -The dirt going down the drain after you give your dog a bath and drain the tub Dirt being blown off a patio Deposition of sediment -Dust collecting on furniture Weathering of rock -Tree roots extending into a rock layer and breaking it down -Ice expanding in a crack in the road creating a pothole Compaction/lithification -A dump truck dumps a load of gravel on your lawn. The dirt below it becomes more consolidated
By what process do sediments become well sorted, and by what process do sediments become poorly sorted?
Sediments that are transported for a long, sustained time tend to become well sorted, whereas sediments that are transported over a rather short period of time tend to be poorly sorted.
Compaction will be the most significant lithification process for which of the following rocks?
Shale
Which of the following rocks composed of silt- and clay- sized particles displays fissility?
Shale
_______ is the shape, size, and arrangement of grains that make up a rock.
Texture
Which of the examples below shows how carbon moves from the geosphere directly to the atmosphere?
The burning of fossil fuels (e.g., coal) releases carbon dioxide directly into the atmosphere.
What is diagenesis?
The changes that convert sediments to sedimentary rocks after deposition
Which of the processes listed below would transform an exposure of granite in the mountains into sedimentary rocks?
The granite would mechanically weather into small particles, which would travel down the slope of the mountain via mass wasting, be deposited, and undergo diagenesis when the sediments are buried under younger layers of rock.
What does the presence of mudcracks indicate about the paleoenvironment?
There was a wet environment that is drying up.
Study the two igneous rocks in the image. Using what you know about igneous rock identification, determine how these two rocks are related.
They both have a mafic composition
What are the reasons that this rock possesses neither a glassy texture nor a vesicular texture?
This rock does not have a glassy luster. This rock does not contain any visible holes. This rock does not possess a conchoidal fracture.
Approximately 75 percent of the planet's landmasses are covered by sedimentary and sedimentary rocks.
True
Due to their size, stream gravels need a swift current to be transported, whereas sands need a current with less energy.
True
Volcanic activity in the early history of the Earth is believed to be responsible for much of the CO2 found in the atmosphere.
True.
What level of sorting is visible in the above image?
Well sorted
How do chemical weathering and the formation of biochemical sediment remove carbon from the atmosphere and store it in the geosphere?
When carbon dioxide in the atmosphere combines with water, it creates carbonic acid, which precipitates and chemically weathers the rocks on Earth. The result of this weathering is bicarbonate, which ultimately ends up in the oceans and is used by marine organisms to make their shells. When these organisms die, their skeletons settle to the ocean floor and eventually become a rock layer containing the carbon dioxide.
Which of the following methods of transportation will result in the best degree of sorting?
Wind
Which of the choices below lists the successive stages in coal formation from first step to last?
accumulation of plant remains, peat formation, lignite formation, bituminous coal formation, anthracite coal formation
Can you identify the minerals that comprise igneous rocks? Drag the appropriate labels to their respective targets. The specific colors of the referenced mineral crystals within the rocks have been supplied to assist you. Labels will only be used once, and not all labels will be used.
black crystals hornblende white crystals plagioclase feldspar
Which of the choices below correctly describes three common cements in sedimentary rocks and the ways of identifying them?
calcite (which effervesces in dilute acid), silica (which produces the hardest sedimentary rocks), and iron oxides (which give rocks a reddish color)
A soft, porous rock made up almost entirely of the hard parts of microscopic marine organisms is ________.
chalk
Which of the following environments would produce igneous rocks?
divergent boundaries convergent boundaries hot spot
Evaporites, such as _____.
gypsum and halite, form when minerals that were previously dissolved in water are deposited as the water evaporates
What is the single most common and characteristic feature of sedimentary rocks?
horizontal strata or beds
What are the three broad categories of sedimentary environments with an example of each?
marine environments, such as deep ocean floors; continental environments, such as deserts; transitional environments, such as tidal flats
Which igneous composition contains mostly olivine crystals with minor amounts of pyroxene?
ultramafic