Formation of Sedimentary Rocks Chapter 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