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