Sedimentary Rocks

deposition

Origin of Sedimentary Rocks

• Most common rocks on the earth are igneous.

• 2nd common sedimentary

Sedimentary Rock

• Rocks formed from sediments– 1. Sediments cemented

together (detrital)

– 2. Fall out of solution as a precipitate (chemical)

– 3. plant material pressed together (organic)

Sediments are:

• Pieces of minerals

• Pieces of rock

• Pieces of organic matter

• Minerals dissolved in water – in solution

Detrital Sedimentary Rocks

• Also known as clastic sedimentary rocks

• From Greek klastos, broken;

• Detrital or clastic sedimentary rocks are rocks made from broken pieces of other rock that have been cemented together to form a new rock

Sizes of sediment designation kind of rock formed

(copy chart in notebook)

How sedimentary rocks are formed

Strata – layers of rock

• • Millions of years have gone by and

there are many layers of deposited sediment now.

• Some of the sediment granules have been cemented together by minerals that were dissolved in the water. 

• They have turned into layers of rock.

Compaction

• Pressure from the upper layers of sediments squeeze out water.

• Reduce the spaces between the particles

• They become packed together more tightly.

• New rock formed

Cementation • Water soaks through soil

• Dissolves minerals such as calcite, hematite and limonite (kinds of cement)

• Solution moves through open spaces between sediment and fills spaces

• Minerals fall out of solution (precipitate – solid left from solution)

• “cement” the sediment together.

• New rock formed

Calcite, hematite, limonite areKinds of cement.

Classification of Sedimentary Rocks

• `1. Detrital Sedimentary Rocks – Clastic

• Lt. Detritus – to wear away

• Made from broken fragments of other rocks. Compacted and cemented together.

• Clastic Gr.klastos – broken

conglomerate

• Rounded gravel sized sediments cemented together

Breccia

• Angular sediments that are cemented.

• Found at talus slopes

Talus slope

Sandstone

• Sand sized sediment cemented together

Shale

• Clay sized sediment held together by compaction.

Coquina

• Beach pebbles, shells and animal bodies cemented together

• Found along shores

Chemical Sedimentary Rocks

• 2. chemical sedimentary rocks

• Minerals precipitated out of a solution.– (falls out of solution

when water evaporates)

• Calcite in caves

• Halite – salt mines ancient salt seas

Limestone

• Calcium carbonate (CaCO3) carried in ocean water dissolved from animal shells.

• Deposited on sea or ocean floors

• Precipitates out of solution.

• Precipitate – any solid that comes out of solution

Rock salt

• Found in evaporated salt water lakes or seas.

• Precipitates out when water is evaporated

Fossiliferous limestone

• Limestone with fossils.

• Found in old salt water lakes, bays, seas

Chalk

• Smashed microscopic shell bodies of sea animals.

• compacted

Coal

• Decayed organic matter that had been compacted to form a rock.