Earth Science Notes SEDIMENTARY ROCKS. Objectives I can… Explain what Sedimentary Rocks are Explain the processes that create sediments and sedimentary.

Earth Science NotesSEDIMENTARY ROCKS

Objectives

I can…• Explain what Sedimentary Rocks are• Explain the processes that create sediments

and sedimentary rocks• Classify Sedimentary Rocks. • Tell the geological history of an area based on

the bedding patterns

Sedimentary Rocks

• Rocks formed from sediments• Sedimentary rocks often form as layers on the

bottom of a body of water.

Sedimentary Rock Formation

• Sediments are loose materials like small rocks, minerals, and organic debris.

• Weathering and erosion produce sediments– Weathering – the breaking down of rocks into bits via

chemical and mechanical means.

– Erosion – the moving of these small bits of rock to a new location where they are deposited.

Sedimentary Rock Formation

• Weathering and Erosion

Sedimentary Rock Formation

• Sedimentary rocks form from other rocks• These rocks are compacted and cemented

together.– Compaction – sediments stick together due to pressure

– Cementation – minerals are deposited between pieces of sediment – holding it together.

• Lithification the process by which sediments can undergo chemical and physical processes to become sedimentary rocks.

Sedimentary Rock Formation• Compaction and Cementation

Sedimentary Rock Formation

• Sedimentary rocks display certain characteristics that allows draw conclusions about the history of landforms and rock formations.

• One such feature bedding. This is the result of sediment settling out in large flat areas.

Sedimentary Rock Formation

• STRATIFICATION refers to the way sediment layers are stacked over each other, and can occur on the scale of hundreds of meters. It is a fundamental feature of sedimentary rocks.

Sedimentary Rock Features

Types of Bedding• Graded Bedding – size of the

sediments become large the farther down you go in a rock layer– form when a steep pile of

sediment on the sea floor (or lake floor) suddenly slumps into a canyon or off a steep edge.

Sedimentary Rock Features

Types of Bedding• Cross-Bedding – forms when sand is transported as

sand-dune like bodies, in which sediment is moved up and eroded along a gentle up-current slope, and redeposited (avalanching) on the downcurrent slope.

Sedimentary Rock Features

• RIPPLE MARKS are produced by flowing water or wave action.

Ancient ripples on a sandstone surface. Ripples are symmetrical and show "tuning-fork" branches. This indicates to a geologist that the sandstones were deposited in an environment with wave action (nearshore).

Sedimentary Rock Features

• Sedimentary rocks may contain “signs” of life.

Classification of Sedimentary Rocks

Clastic (Detrital) Sedimentary Rocks: sedimentary rocks made from broken bits of other rocks

• Ex: Conglomerate – large sediments, rounded rocks• These types of rocks have rounded sediments because

they were near wind and water

• EX: Breccia – large sediments, sediments have sharp angles

• These types of rocks have jagged sediments because they were not near wind and water

Detrital Sedimentary RocksConglomerate Breccia

Classification of Sedimentary Rocks

Chemical Sedimentary Rocks: sedimentary rocks that form when dissolved minerals come out of solution.

• Often founds along seas or lakeshores. • This type of rock is the only form of sedimentary

rock that did not form from preexisting rocks.– Ex: Limestone (CaCO3) – forms when calcium carbonate comes out of

a solution.• Limestone is deposited on bottom of lakes and seas.

– Ex: Rock salt – forms when the evaporation of water occurs, leaving behind the salt

Chemical Sedimentary Rocks

Classification of Sedimentary Rocks

Organic (Biochemical) Sedimentary Rocks: sedimentary rocks made of once living things

• This type of rock will form when clams, corals, snails, and mussels die and let their shells accumulate on the ocean floor.– Ex: Chalk – made from the shells of organisms.– Ex: Coal – formed from the decay and compaction of plant

materials.

Organic Sedimentary Rocks

Sedimentary Rocks

Summary• What makes a rock

Sedimentary?• Formation of Sedimentary

Rocks• Classification of Sedimentary

Rocks– Detrital / Chemical / Organics