Earth Science Notes SEDIMENTARY 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 Rocks Conglomerate 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 (CaCO 3 ) – 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