Sedimentary rocks form as sediment is: Deposited Buried Compacted Cemented
Sedimentary rocks fall into 3 groups: Clastic/inorganic Organic Chemical
Physical Weathering Clastic sediments are produced when rock physically weathers, which means it breaks apart. Big rocks break into smaller rocks. Weathering is an extremely slow process.
There are 6 sizes of clastic sediments. Boulders Cobbles Pebbles Sand Silt Clay
Particles are collected and transported by running water. http://www.youtube.com/ watch?v=fATA1SOLICowww.youtube.com/ watch?v=fATA1SOLICo
Abrasion Sediments become smoothed and rounded as they bounce along the bottom of the stream and hit against each other.
Deposition and Sorting A stream loses velocity when entering quiet waters so its ability to transport sediment decreases. Particles drop to the bottom. This is deposition. Large particles settle first. Other particles settle according to size. Smallest particles last. This is sorting.
Burial and Compaction As more sediments accumulate, the bottom ones are buried. This increased weight of the top sediments physically squeezes the lower sediments together which compacts them. Heavy Weight OUCH!
Cementation All the waters of the Earth contain dissolved minerals. These dissolved minerals and sometimes clay fill up spaces between the rock fragments and bind them together. This is cementation.
Stratification Sedimentary rocks often form in horizontal layers called strata.
Fossils These layers or strata often contain fossils. Only sedimentary rocks contain fossils.
Fossil Structures Mud cracks and ripple marks give evidence of environment at formation.
Organic(Bioclastic)Sediments The remains of plants and animals. The two most common are shells and plant material.
Chemical Sediments Chemical sediments form when water evaporates and the materials dissolved in the water precipitate (settle).
Bonneville Salt Flats Home of the land speed record. Thrust SSC – 763 mph http://www.youtube.com/watch?v=LKQ-xj5C2m8
Characteristics of Sedimentary Rocks Sedimentary rocks are the most common type of rocks on Earth’s surface. Sedimentary rocks usually form underwater. Sedimentary rocks may contain fossils. Sedimentary rocks often form in layers or strata. Sedimentary rocks are our keys to the past.