Samantha_Hernandez_Chapter-5

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Geology

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Dec 6, 2023

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Chapter 5 Weathering, Erosion, and Sedimentary Rocks Assignment 1. What are the two basic categories of weathering and how do the products of each category differ? - mechanical weathering: physical forces breaks into smaller pieces - chemical weathering: chemical transformation into new or more compounds 2. When a rock is mechanically weathered, how does its surface area change? How does this influence chemical weathering? - It is broken into smaller and smaller pieces, each retaining the characteristics of the original material - By breaking rocks into smaller pieces, mechanical weathering increases the amount of surface area available for chemical weathering 3. How do joints promote weathering? - joints allow water to penetrate to depth and start the process of weathering long before the rock is exposed 4. How is carbonic acid formed in nature, and what occurs when carbonic acid reacts with limestone or marble? - When gaseous carbon dioxide is dissolved in water, its hydrophobic nature carves out a cylindrical cavity, setting the stage for the proton transfer reactions that produce carbonic acid. 5. List the five basic controls of soil formation and which factor is most influential in soil formation? - parent material, - climate, - topography, - organisms, - time. The most influential factor in soil formation is climate. 6. Outline the steps that would transform an exposure of granite in the mountains into various sedimentary rocks. The steps that would transform an exposure of granite in the mountains into various sedimentary rocks are weathering, erosion, transportation, deposition, compaction, and cementation. First, weathering breaks down the granite into smaller pieces through physical or chemical processes. Then, the smaller pieces are eroded and transported by wind, water, or ice. The eroded material is deposited in a new location, where it undergoes compaction and cementation. Compaction occurs when the weight of the overlying material presses down on the sediment, reducing the pore space between the grains. Cementation occurs when minerals precipitate out of solution and fill the pore space, binding the sediment grains together. Over time, these processes can produce various sedimentary rocks, such as sandstone, shale, and limestone 7. List and briefly distinguish among the three basic sedimentary rock categories. The three basic sedimentary rock categories are clastic, chemical, and organic rocks.
- Clastic rocks are made up of fragments of preexisting rocks that have been transported and deposited. The fragments are typically cemented together by minerals such as quartz, calcite, or clay. Examples of clastic rocks include sandstone, shale, and conglomerate. - Chemical rocks form when minerals precipitate out of solution, often as a result of evaporation. Examples of chemical rocks include limestone, dolomite, and rock salt. - Organic rocks are made up of the remains of once-living organisms, such as shells, bones, or plant material. Examples of organic rocks include coal, chalk, and fossiliferous limestone. 8. Describe how sediments become sorted and rounded. Sediments become sorted and rounded through the process of transportation. When sediments are transported by wind, water, or ice, they are subjected to abrasion, which wears away rough edges and corners, producing a more rounded shape. As the sediments are transported, they are also sorted by size and weight. Smaller, lighter sediments are carried further than larger, heavier ones, resulting in a sorting of sediment sizes. The degree of sorting and rounding depends on the distance the sediments are transported and the nature of the transporting medium. 9. What are the two categories of chemical sedimentary rock? Give an example of a rock that belongs to each category and explain why. - The two categories of chemical sedimentary rock are evaporites and biochemical rocks. Evaporites form when water evaporates and leaves behind dissolved minerals, such as halite (rock salt) or gypsum. An example of an evaporite is rock salt, which forms when seawater evaporates and leaves behind salt crystals. - Biochemical rocks form from the remains of once-living organisms, such as shells or plant material. An example of a biochemical rock is fossiliferous limestone, which is made up of the shells of ancient marine organisms. They are made of calcium carbonate, which precipitates out of seawater when the organisms die and settle to the bottom. The type of chemical sedimentary rock that forms is dependant on the composition of the water and the organisms present in the environment . 10. How might sedimentary structures be useful clues about the geologic past? Pick a sedimentary environment and explain the type of sediment, sediment size, sedimentary rock type, and sedimentary structures that would be typical of that sedimentary environment. Sedimentary structures can provide clues about the geologic past by revealing information about the conditions in which the sediments were deposited. For example, cross-bedding in sandstone can indicate that the sediment was deposited by wind or water currents, while ripple marks in sandstone or mudstone can indicate the direction of flow. By studying these structures, geologists can infer the depositional environment, such as whether the sediment was deposited in a river, a lake, or a marine environment, and what the climate was like at the time. One example of a sedimentary environment is a river. The sediment in a river is usually composed of sand, silt, and clay, with varying sizes of particles depending on the velocity of the water. The sedimentary rock type that would be typical of a river environment is sandstone or mudstone. Sedimentary structures in this environment include cross- bedding, which forms when sand is deposited by the current in a series of inclined layers, and ripple marks, which form when the current creates small waves in the sediment. The orientation of the cross- beds and ripple marks can indicate the direction of flow in the river.
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