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Formation of Sedimentary RocksChapter 6.1
Sediments
• Small pieces of rocks that are moved and deposited by water, wind, glaciers, and gravity
• When sediments are glued together, they form sedimentary rock.
How do you get sediments?
• 1. Weathering: when rocks wear down. 2 types
• - chemical weathering: minerals in the rock are dissolved or chemically changed
• -physical weathering: minerals are NOT changed, rock fragments break off along fractures
How do you get sediments?
• 2. Erosion: Removal and transport of sediment• Four main agents of erosion– Wind– Water– Gravity– Glaciers
Lithification
• Physical and chemical processes that transform sediments into sedimentary rocks
• Compaction– Weight of overlying sediments forces the sediment
grains closer together• Causes physical changes
• Cementation– Mineral growth glues sediment together into solid
rock• Dissolved minerals precipitate out of ground water
Sedimentary Features
• Bedding– Horizontal layering of sedimentary rocks– Results from the way sediment settles out of water or
wind– Two types of bedding
• Graded bedding– Particle size becomes progressively heavier and coarser toward the
bottom layers
• Cross bedding– Formed as inclined layers of sediment are deposited across a
horizontal surface– Small scale on beaches
Ripple marks
• Occurs when sediment is moved into small ridges by wind or wave action, or by a river current– Back and forth motion
creates symmetrical ripples
– Movement in one direction creates asymmetrical ripples
Sorting and Rounding
• Jagged edges are smoothed by the constant knocking into other grains– Amount of rounding is
determined by how far the sediment has traveled
– Harder minerals have better chance of rounding