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