Earth Science Chapter 3 Section 3 Sedimentary Rocks Earth Science Chapter 3 Section 3

Introduction Most of the earth’s surface is covered by sedimentary rock. Sedimentary rock provides geologists with a lot of information about the history of the earth.

Formation of Sedimentary Rock Weathering, Erosion, and Deposition Weathering: break down of rock Chemical: change in composition of structure Mechanical: physical break down or rock Erosion: movement of sediment water, wind, ice, and gravity Water is the most powerful agent Deposition: erosion stops and sediments are laid down Larger sediments are deposited first The larger the sediment size the more energy required to carry it

Compaction and Cementation Lithification: combining of sediment into rock Compaction: packing of sediment Cementation or lithification takes place when dissolved minerals are bound together. This normally occurs in areas where there was once water.

Classification of Sedimentary Rocks Clastic Sedimentary Rocks Sediments from preexisting rocks Most common minerals are feldspars and quartz Conglomerate and breccia: larger visible sediments Conglomerate: rounded Breccia: angular Sandstone: sand sized grains Shale: small fine sediments

Chemical Sedimentary Rocks Dissolved sediments that precipitate from water Form when water evaporates Rock salt forms from halite Limestone forms from calcite

Organic Sedimentary Rocks Biochemical rocks that form from biological processes Form when an organism dies and their body is broken down into sediment Organic limestone made from shells Coal forms from the remains of swamp plants

Sedimentary Rock Features Strata: layering of sedimentary rock Each layer represents a period of deposition Layers closer to the surface are younger than the deeper layers (law of superposition) Determining which layer is younger or older is called relative dating Fossils: remains or trace of ancient life Fossils can only be found in sedimentary rock Fossils form when organisms are quickly buried

Ripple marks: rock has formed in the presence of moving water Mud cracks: rock has formed as sediments are drying.

Stratification of Sedimentary Rock Ripple Marks Mud Cracks