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6: Weathering, Erosion, and Sedimentary Rocks

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    Learning Objectives

    • Describe how water is an integral part of all sedimentary rock formation
    • Explain how chemical and mechanical weathering turn bedrock into sediment
    • Differentiate the two main categories of sedimentary rocks : clastic rock formed from pieces of weathered bedrock; and chemical rock that precipitates out of solution by organic or inorganic means
    • Explain the importance of sedimentary structures and analysis of depositional environments, and how they provide insight into the Earth’s history

    Sedimentary rock and the processes that create it, which include weathering, erosion, and lithification, are an integral part of understanding Earth Science. This is because the majority of the Earth’s surface is made up of sedimentary rocks and their common predecessor, sediments. Even though sedimentary rocks can form in drastically different ways, their origin and creation have one thing in common, water.

    • 6.1: The Unique Properties of Water
      Water plays a role in the formation of most sedimentary rocks. It is one of the main agents involved in creating the minerals in chemical sedimentary rock. It also is a weathering and erosion agent, producing the grains that become detrital sedimentary rock. Several special properties make water an especially unique substance, and integral to the production of sediments and sedimentary rock.
    • 6.2: Weathering and Erosion
      Bedrock refers to the solid crystalline rock that makes up the Earth’s outer crust. Weathering is a process that turns bedrock into smaller particles, called sediment or soil. Mechanical weathering includes pressure expansion, frost wedging, root wedging, and salt expansion. Chemical weathering includes carbonic acid and hydrolysis, dissolution, and oxidation.
    • 6.3: Sedimentary Rocks
      Sedimentary rock is classified into two main categories: clastic and chemical. Clastic or detrital sedimentary rocks are made from pieces of bedrock, sediment, derived primarily by mechanical weathering. Clastic rocks may also include chemically weathered sediment. They are classified by grain shape, grain size, and sorting. Chemical sedimentary rocks are precipitated from water saturated with dissolved minerals. Chemical rocks are classified mainly by the composition of minerals in the rock.
    • 6.4: Sedimentary Structures
      Sedimentary structures are visible textures or arrangements of sediments within a rock. Geologists use these structures to interpret the processes that made the rock and the environment in which it formed. They use uniformitarianism to usually compare sedimentary structures formed in modern environments to lithified counterparts in ancient rocks. Below is a summary discussion of common sedimentary structures that are useful for interpretations in the rock record.
    • 6.5: Depositional Environments
      The ultimate goal of many stratigraphy studies is to understand the original depositional environment. Knowing where and how a particular sedimentary rock was formed can help geologists paint a picture of past environments—such as a mountain glacier, gentle floodplain, dry desert, or deep-sea ocean floor. The study of depositional environments is a complex endeavor.
    • 6.S: Weathering, Erosion, and Sedimentary Rocks (Summary)

    Thumbnail: Sandstone, The Wave, Arizona. (CC-BY-2.5; Lobineau).

    6: Weathering, Erosion, and Sedimentary Rocks is shared under a CC BY-NC-SA license and was authored, remixed, and/or curated by Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & Cam Mosher.

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