Sedimentary Rocks Section 3.3

Formation of Sedimentary Rocks Sedimentary comes from the Latin word sedimentum, which means settling All sedimentary rocks begin to form when existing rocks are broken down into sediments There are several major processes that contribute to the formation of sedimentary rocks: Weathering, Erosion and Deposition Compaction and Cementation

Formation of Sedimentary Rocks Weathering is the breaking down of rock into sediments Erosion involves weathering and the transportation of sediments Deposition is the process when water, wind, ice or gravity loses energy causing sediments to drop Larger sediments are deposited first, smaller sediments are dropped later

Formation of Sedimentary Rocks Compaction is a process that squeezes, or compacts, sediments, pushing water out Compaction is caused by the weight of sediments Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments

Classification of Sedimentary Rocks Sedimentary Rocks can be classified into two main groups according to the way they form Clastic – rocks that are made of weathered bits of rocks and minerals Classified by particle size Chemical – forms when dissolved minerals precipitate from water solutions Biochemical sedimentary rocks contain shells and skeletal remains of organisms

Clastic Sedimentary Rocks Breccia Conglomerate Clastic Sedimentary Rocks Sandstone

Chemical Sedimentary Rocks Chert Rock Salt Flint Limestone

Biochemical Sedimentary Rocks

Features of some Sedimentary Rocks Sedimentary rocks give clues to how, when and where the rocks formed Layers of sedimentary rock records a period of sediment deposition. The oldest layers are found at the bottom Ripple marks may indicate that the rock was formed along a beach or stream bed Mud cracks are formed when wet mud or clay dried and shrank, leaving a record of a dry environment Fossils found in sedimentary rocks can help answer questions about the rock

Mud cracks Fossils Layers of sedimentary rock Ripple marks

Summary of Sedimentary Rocks Sedimentary rocks form as the result of five major process Weathering produces particles called sediments Wind, water, ice and gravity erode and deposit sediments Sediments are compacted and cemented to form sedimentary rocks Sedimentary rocks can be classified according to how they form, by using rock formation, texture and composition

(Table 2 on page 79)