Sedimentary Rocks Bits and Pieces
Sedimentary rocks form as sediment is: lDeposited lBuried lCompacted lCemented
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=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
Yucca Mountain • Nuclear waste depository http://www.youtube.com/watch?v=tbq9a2oyMAo http://www.youtube.com/watch?v=Q41vzLjwZqM
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.
Nature’s Palette Antelope Canyon
Clastic Sedimentary Rocks • Breccia – angular • Conglomerate - rounded
Clastic Sedimentary Rocks • Sandstone – can be various size grains.
Clastic Sedimentary Rocks • Siltstone
Clastic Sedimentary Rocks • Shale – breaks along bedded planes.
Bioclastic Sedimentary Rocks • Bituminous coal – plant remains = carbon
Bioclastic Sedimentary Rocks • Limestone – cemented shell fragments or precipitates of biologic origin = calcite
Chemical Sedimentary Rocks • Rock salt - Crystalline texture composed of halite.
Chemical Sedimentary Rocks • Dolostone – Crystalline texture composed of dolomite. Fossil
Chemical Sedimentary Rocks • Rock Gypsum – Crystalline texture composed of gypsum.