Sedimentary Rocks!
Formation of Sedimentary Rocks It’s all part of the Rock Cycle, baby!
So, how are these things made anyway? Weathering Erosion Deposition Lithification
Weathering Can result in particles as big as boulders or so small they require a microscope to see them! Chemical Weathering: Minerals are dissolved or otherwise chemically changed. Physical Weathering: Minerals remain chemically unchanged
Physical Weathering Hydraulic Action Frost weathering Pressure Release Rocks are broken down, but not changed. Heat, water, ice, or pressure may cause physical weathering. Heat and cooling may cause rock to expand and contract. Ice may cause frost weathering. Pressure can cause underlying rocks to expand and break the rocks above them. Water can enter rock very quickly and cause it to expand and break.
Chemical Weathering Chemical weathering changes the composition of rocks. Water is often involved, interacting with minerals to cause chemical reactions. This process is gradual and ongoing.
Erosion Erosion is the removal and transport of sediment. There are four main agents of erosion: wind, moving water, gravity, and glaciers. You can see erosion all around you!
Wind Erosion Wind erosion occurs almost always in deserts. Sand dunes are formed by wind erosion.
Water Erosion The energy of water waves, along with the chemical content of the water, erodes the coastline. Erosion of sand is easy for water waves to do. River erosion is what caused the Grand Canyon to form!
Gravity Erosion This is the movement of sediment down a slope. Also called “mass wasting.” Some types are creep, slides, flows, topples, and falls.
Glacial Erosion More powerful than erosion caused by moving water, but not as common. A glaciers can break off pieces of rocks and carry them with it as it moves (plucking), or scoop rock up like a bulldozer and carry it along (abrasion).
So, weathering and erosion are the same thing, right? WRONG!!! Weathering loosens particles, erosion transports them. IN OTHER WORDS… when something is weathered it is broken down into smaller pieces, when it is eroded it moves away. SO….. Weathering decomposes rocks, but as soon as it is transported, we call it erosion!
So, what happens after that? Deposition… when the transported sediments are deposited on the ground or sink to the bottom of a body of water.
…Okay, but how does all of that sediment become a ROCK? Lithification! Occurs in 2 main steps: compaction and cementation.
Compaction and Cementation Volume and spaces between sediment are decreased Because of the weight of sediments above Cementation – Sediments are glued together by minerals deposited from water
Types of Sedimentary Rock Sedimentary rock can be classified by HOW it forms Chemical Organic Clastic
Chemical Sedimentary Rock Formed from minerals that were once dissolved in water One reason this happens… evaporation Ex – halite Bonneville Salt Flats, Utah
Organic Sedimentary Rock Formed from the remains of living things Remains are compacted and cemented to form sedimentary rock Also called bioclastic
Organic Sedimentary Rock Coal – plant remains Limestone – shell remains of marine animals
Clastic Sedimentary Rock Formed from fragments of preexisting rocks 1. Large fragments cemented together by fine particles Ex – conglomerate Ex – breccia
Clastic Sedimentary Rock 2. Sand-sized grains cemented together Ex – sandstone
Clastic Sedimentary Rock 3. Clay-sized particles cemented together Ex - shale
Clastic Characteristics Sorting Tendency for air or water to separate sediments by size Well Sorted Poorly Sorted
Clastic Characteristics Angularity Particles that first break from a source are angular Particles that have moved long distances are round & smooth
Sedimentary Features Stratification Layering of sedimentary rock Layers are called beds Cross-beds Slanting layers that form within beds
Sedimentary Features Ripple Marks Caused by the action of wind or water on sand Mud Cracks Occur when a flooded area, like a lake bed, dries and the mud shrinks Fossils Traces of ancient plants and animals