Formation of Sedimentary Rocks
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Essential Questions • How are sedimentary rocks formed? • What is the process of lithification? • What are the main features of sedimentary rocks? Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Vocabulary Review New • • • • • • • texture Copyright © McGraw-Hill Education sediment lithification cementation bedding graded bedding cross-bedding Formation of Sedimentary Rocks Weathering and Erosion • Sediments are small pieces of rock that are moved and deposited by water, wind, glaciers, and gravity. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Weathering • Chemical weathering occurs when the minerals in a rock are dissolved or otherwise chemically changed. • During physical weathering, minerals remain chemically unchanged. Rock fragments break off of the solid rock along fractures or grain boundaries. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Weathering • When exposed to both chemical and physical weathering, granite eventually breaks apart and might look like this decomposed granite. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Erosion • The removal and transport of sediment is called erosion. • The four main agents of erosion are wind, moving water, gravity, and glaciers. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Erosion • After rock fragments and sediments have been weathered out of the rock, they often are transported to new locations through erosion. Eroded material is almost always carried downhill. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Deposition • Deposition occurs when transported sediments are deposited on the ground or sink to the bottom of a body of water, forming layers with the largest grains of sediment at the bottom. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Energy of transporting agents • As moving water slows down, some sediment deposits are sorted into layers of different-sized particles. The largest particles settle out first, then the next largest, and so on. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Weathering and Erosion Energy of transporting agents • Wind can move only small grains, so sediment deposits made by wind are usually fine and well-sorted. • Some sediment deposits contain particles of all sizes because they are dumped in unsorted piles when, for example, a glacier melts or there is a landslide. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Lithification • As more sediment is deposited in an area, the bottom layers are subjected to increasing pressure and temperature. These conditions cause lithification, the physical and chemical processes that transform sediments into sedimentary rocks. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Lithification Compaction • Lithification begins with compaction. The weight of overlying sediments forces the sediment grains closer together, causing physical changes. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Lithification Cementation • Cementation occurs when dissolved minerals precipitate out of groundwater and their growth glues sediment grains together into solid rock. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Sedimentary Features Bedding • The primary feature of sedimentary rock is horizontal layering called bedding, which results from the way sediment settles out of water or wind. • Bedding in which the particle sizes become progressively heavier and coarser toward the bottom layers is called graded bedding. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Sedimentary Features Bedding • Cross-bedding is formed as inclined layers of sediment are deposited across a horizontal surface. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Sedimentary Features Ripple marks • When sediment is moved into small ridges by wind or wave action or by a river current, ripple marks form. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Visualizing Cross-Bedding and Ripple Marks • Moving water and loose sediment result in the formation of sedimentary structures such as cross-bedding and ripple marks. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Sedimentary Features Angular vs. rounded • As sediment is transported, pieces that began with an angular shape knock into each other and become rounded as their edges are broken off. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Sedimentary Features Evidence of past life • Fossils are the preserved remains, impressions, or any other evidence of once-living organisms. • During lithification, parts of an organism can be replaced by minerals and turned into rock, such as shells that have been mineralized. Copyright © McGraw-Hill Education Formation of Sedimentary Rocks Review Essential Questions • How are sedimentary rocks formed? • What is the process of lithification? • What are the main features of sedimentary rocks? Vocabulary • sediment • lithification • cementation Copyright © McGraw-Hill Education • bedding • graded bedding • cross-bedding Formation of Sedimentary Rocks
