Formation of Sedimentary Rocks

1. Formation of Sedimentary Rocks Chapter 6.1

2. 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.

3. 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

4. How do you get sediments? • 2. Erosion: Removal and transport of sediment • Four main agents of erosion • Wind • Water • Gravity • Glaciers

5. 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

7. 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

10. 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

12. 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