Sedimentary RocksSedimentary RocksChapter 4 Section 4

Sedimentary RocksSedimentary RocksSediments are loose materials like rock

fragments, mineral grains, and bits of shell.Sediments come from already-existing rocks

that are weathered and eroded.Sedimentary rocks form when sediments are

pressed and cemented together, or when minerals form from solutions.

Sedimentary rocks form as layers. The oldest layers are at the bottom because they were deposited first.-Sometimes the forces within the Earth overturn layers of rock, and the oldest are no longer on the bottom.

Sedimentary RocksSedimentary Rocksover 75% of the surface are

sedimentary rocks!

Classifying Sedimentary Classifying Sedimentary Rocks.Rocks.Sedimentary rocks are classified

by their composition and the manner in which they are formed.

Sedimentary rocks are classified as detrital (clastic), chemical, or organic (nonclastic).

Detrital Sedimentary Detrital Sedimentary RocksRocksDetrital, or clastic sedimentary rocks

are made from the broken fragments of other rocks. These loose sediments are compacted and cemented together to form solid rock.

The process that breaks rocks into smaller pieces is called weathering,.-Rocks are weathered by things such as air water and ice.-Sediments are classified by size. Clay is the smallest sediment, followed by silt, then sand, and then gravel, the largest sediment.

Detrital Sedimentary Detrital Sedimentary RocksRocksErosion moves sediments to a new location

where they are deposited. Pressure from the upper layers pushes down on the lower layers of sediment.

If the sediments are small, they can stick together to form a solid rock. The process is called compaction.

If the sediments are large, pressure can’t make them stick together. Cementation occurs when minerals like quartz and calcite, are deposited by water between pieces of sediment. The minerals act like glue and form a detrital sedimentary rock.

Conglomerate, sandstone, siltstone, and shale are all detrital sedimentary rocks named for the shapes and sizes of sediments that formed them.

Examples of Detrital Examples of Detrital Sedimentary RocksSedimentary Rocks

Compaction and Compaction and CementationCementation

Chemical Sedimentary Chemical Sedimentary RocksRocksChemical sedimentary rocks form

when dissolved minerals come out of solution.

Minerals collect when seas or lakes evaporate. The deposits of minerals that come out of solution form sediments and rock.

Gypsum and rock salt form when water that is rich in dissolved salts evaporates. Halite forms rock salt.

Chemical Sedimentary Chemical Sedimentary RocksRocksCalcium carbonate is carried in

solution in ocean water. When calcium carbonate comes out of solution it forms calcite. Limestone is a chemical sedimentary rock that is formed as crystals of calcite grow together.

Large areas of the United States have limestone bedrock because seas covered much of the country throughout geologic history.

Chemical Sedimentary Rock Chemical Sedimentary Rock ExampleExample

Organic Sedimentary Organic Sedimentary RocksRocksOrganic sedimentary rocks are made

of the remains of once living things.Fossil-rich limestone is made from the

remains of once living organisms.-If a rock is made completely out of shell fragments that you can see it is called coquina.-Chalk is another organic sedimentary rock made of microscope shells.

Organic Sedimentary Organic Sedimentary RocksRocksCoal is an organic sedimentary rock

that is formed when pieces of dead plants are buried under other sediments in swamps. The sediments are compacted over millions of years to form coal.

Chemical and organic sedimentary rocks are also called nonclastic sedimentary rocks, because they are not made up of broken fragments of other rocks.

Organic Sedimentary Rock Organic Sedimentary Rock ExampleExample