* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
SES 4UI - Mr. J. Snyder Learning Goals Student will be able to: 1) Explain the formation of all 3 types of sedimentary rocks 2) Identify common types of sedimentary rocks. Success Criteria Student will show their understanding by: 1) Understanding term used in Sedimentary rock formation and identification 2) Explaining the geological environment in which different sedimentary rocks form. 3) State the uses or importance of common sedimentary rocks Before We Start Rock Identification Lab Key Concepts Immediately following this Some of these slides provide presentation, Students should study the Rock Identification Trays that include sedimentary rocks. Samples 10 - 18 are sedimentary rocks and include clastic, chemical and organic sedimentary rocks. background information that helps you to understand key concepts. In order to allow you to focus on key concepts: 1) Black font is used for key concepts 2) Red font is used for background information Remember once again - Looking Deeper geologists do not learn to identify rocks just for the sake of classification! A rock will tell the Geologist the conditions in which the rock formed! This is a key to understanding conditions in the past. For example when a geologist sees this limestone road cut and its fossils, it tells the geologist that this region was once a shallow, warm sea teeming with ancient marine creatures. The geologist can also determine the economic value of the rocks in that region. Sedimentary Rocks Rocks composed of particles derived from pre-existing rocks or by the crystallization of minerals that were held in solutions. A general characteristic of this group is the layering or stratification. The Weathering Process Terms: weathering erosion transport deposition lithification cementation Weathering causes rock to be eroded at the earth’s crust. Erosion is both a physical and chemical process. Chemicals dissolved in water tend to break down the less resistant minerals (mafic minerals, micas, etc.) and leave resistant minerals (such as quartz and feldspar) behind. Fragments of rock eroded from an outcrop are called clasts. The Weathering Process Terms: weathering erosion transport deposition lithification cementation Clasts are transported by rivers, streams, wind and ocean currents Eroded sediments are transported and deposited by water wind and ice. Deposition often occurs far from the source of the rock. Major rivers can carry continental sediments and deposit them in oceans thousands of kilometers downstream. Erosion Wind Erosion Size of clasts and sequence of deposition Glacial Erosion Weathering Notice in the figure to the right that rate that minerals weather (break down chemically) is in the exact opposite order to Bowen’s Reaction series. Basically more silica-poor minerals erode more slowly. Note: erosion tends to be a physical process while weathering is a chemical process. Deposition and Cementation As water slows down, the largest sediments are deposited first followed by smaller and smaller particles. As a result, sedimentary rocks are often sorted into layers of different sized particles. As sediments are deposited in ever thicker layers, pressure and temperature causes lithification. During lithification, water is squeezed out of the sediments, the grains are compacted together and then cemented into sedimentary rock. The cement between the grains is often quartz and calcite. Sedimentology and Stratigraphy These two sciences come together when : 1) Sedimentologists (sedimentary Geologists) identify rock types in each layer and perhaps their identifying fossil assemblages 2) Stratigraphers try to trace these layers over (often by looking at the sequence of layers or again by using fossil assemblages. 3) Using these sciences together, geologists can date or find fossils, locate petroleum bearing rocks (and areas where petroleum is trapped) Sedimentology and Stratigraphy The Morrison Formation is famous because it hosts some of the best Dinosaur fossils in the world. Classifying Sedimentary Rocks There are three groups of sedimentary rocks: Clastic Chemical Organic (Biochemical) Clastic Sedimentary Rocks Clastic sedimentary rocks are those composed of rock fragments that have been cemented together. They are classified according to the predominant grain size present. Using this scheme, they can be classified as: Sediment Particle Size Rock Name conglomerate (rounded) or breccia (angular grains) >256 mm boulder 64-256 mm cobble 2-64 mm pebble 0.0625 – 2 mm sand sandstone 0.0039 – 0.0625 mm <0.0039 mm silt siltstone mud shale Clastic Sedimentary Rocks Conglomerate Sandstone Siltstone (not included in the rock sets) Breccia Shale Further Classification (Not in this course) In this course we will stick to the terms above, but recognize that professional sedimentary geologists require more precise terms. Prefixes can also be added to indicate the dominant mineralogy. For example, a quartz-rich sandstone is a quartzose sandstone, a feldspar-rich sandstone is an arkose, a mica-rich sandstone is a micaceous sandstone, and a lithic-rich sandstone or shale is a greywacke. Quartz-rich sandstones are generally older because they have undergone more erosion and chemical weathering Clastic Sedimentary Rock Types change as you move downstream The clasts become smaller as they are transported downstream – this is due to the fact that the river or stream becomes slower and loses more energy The clasts change shape from more angular to more rounded as they are transported downstream (due to abrasion (erosion) The clasts become more sorted (the clasts have a more uniform size) as you move downstream. 1) Clastic Sediment Rocks Talus slopes Mtn. Streams Beaches Alluvial Fans Rivers (plains) Oceans Delta Note that as a river moves downstream, its slope decreases and water velocity decreases. The net effects] is that clasts are more rounded downstream and are better sorted by size and Mineralogy 2) Chemical Sedimentary Rocks a) Precipitation of Minerals The most common is Limestone, where CaCO3 (calcite) is precipitated in shallow ocean environments. Limestone is very common – it is forming on continental shelves around the globe. Most of southern Ontario is underlain by thick deposits of limestone, indicating that Ontario was at the bottom of a shallow sea millions of years ago. Fossils are common in Limestone and Dolomite. Various limestone samples Limestone Limestone has value as a building material (slabs for buildings & patios), source of cement , chalk and as crushed stone for roadways and construction Limestone quarry for cement Limestone quarry for slabs Chalk White Chalk Cliffs of Dover Limestone building Limestone gravel quarry 2) Chemical Sedimentary Rocks a) Precipitation of Minerals Dolomite (CaMg(CO3)2) forms (precipitates) in warm, near shore marine sediments. It looks very similar to limestone but tends to be harder. Chert (SiO2) forms in deep marine areas where silica precipitates out. Chert is hard to identify by small samples because it does not show layering. dolomite chert Dolomite and Chert Dolomite is named after dolomite Chert Dolomite Mountains in Italy Flint = black chert Jasper = red chert the Dolomite mountains of Italy. Dolomite can usually be distinguished from Limestone due to a weaker acid reaction and a harder, crystalline appearance. Chert is very hard (7), since it is made entirely of silica (SiO2) like quartz Chert has conchoidal fracture like glass and quartz. Chert comes in other famous varieties such as flint (used by Stone Age humans to make the first tools) and Jasper. 2) Chemical Sedimentary Rocks b) Evaporites These rocks form when seas dry up or lakes dry up in arid drainage basins. The minerals calcite, halite (NaCl), gypsum (CaSO4∙2H2O) and potash (mostly KCl) can precipitate out in layers. Halite (NaCl), Gypsum (CaSO4∙2H2O) and potash (mostly KCl) can form in very thick layers and are mined for road salt, wallboard and fertilizer respectively. Halite Gypsum Potash Salt Mines in Goderich, Ontario A vast shallow inland sea covered central N. America 400 million years ago. During periodic drying periods, the sea would evaporate and vast salt deposits would be produced. Most salt is used for roadways in winter. A chunk of unrefined salt from Goderich Inside the Sifto mine in Goderich A vast pile of salt from a mine located below Cleveland, Ohio Gypsum Mines in Ontario The evaporation of seas also produces vast quantities of Gypsum which is used to make Drywall. Underground Gypsum mine in Hagersville, Ont. Open Pit Gypsum mine in Ontario The largest natural mineral crystals (10 meters long) ever discovered were these Gypsum crystals in a cavern found in a mine in Mexico Potash Mining in Saskatchewan Canada is the world’s leading producer of Potash. Almost all of it is mined near Esterhazy, Sask. Potash forms from the extreme evaporation of sea water (Potash is precipitated after Halite). Potash is mostly composed of KCl (Sylvite) , but also includes K2CO3 and K2SO4. Underground and solution mining is used. Solution mining (also used for salt and sulfur) is done by injecting hot water to dissolve the salt, pumping it to the surface and evaporating out the solid. Potash is used as fertilizer, providing K which is an essential nutrient in plant growth - it stimulates early growth, increases protein production, improves the efficiency of water use, hardiness and disease resistance. Potash Mining in Saskatchewan The USA Potash (KCl) looks like red Halite (NaCl) but has a bitter taste. Solution Potash Mining Underground Potash Mining and Israel have vast evaporation ponds for production of Potash (see below) 3) Organic Sedimentary Rocks These rocks form from organic processes or are the remains of living skeletons. 1) Coal - The remains of organic materials die in anoxic (low O2 environments) such as bogs or marshes where the plants cannot be decomposed. These marshy areas are buried and compacted. Millions of years of burial, compaction and pressure required to turn “peat” into coal. 2) Limestone - the skeletons of marine organisms form vast limestone deposits or former coral reefs are converted into limestone formations. Coal Formation Coal Mining Note the size of these massive open-pit operations. North America, especially the USA, has massive deposits - enough to fuel electricity consumption for centuries - but at the cost of high air pollution and acid rain (SO2) and massive CO2 emissions. China’s modern industrial advance (and terrible airpollution problems) are fueled mostly by their vast coal deposits. Historical Coal Mining Coal fueled the Industrial Revolution of the 1800’s. Many operations were underground mines (Great Britain, Nova Scotia). Today, openpit and mountain-top removal operations produce the most coal. Notice that the thickness of the coal seam does not allow the miners to stand up. Imagine your back after a day of work. Small Pit Ponies were bred to haul coal carts. Notice the supports used to prevent cave-ins (an ever-present danger ). In Nova Scotia, the coal seams ran out underneath the ocean. Modern Coal Mining In the USA (Appalachia), coal layers are exposed for mining by removing entire mountain tops. Environmental damage is substantial as waste rock is dumped into valleys. Organic Limestone Many invertebrate organisms form CaCO3 shells (corals, clams, snails, etc). However the most important group are the microscopic diatoms (more commonly known to us as phytoplankton). When diatoms die, there skeletons sink to the bottom of the ocean (usually shallow continental shelves). Over millions of years these diatoms form thick layered deposits of limestone. Diatoms are responsible for most limestone deposits. Since chalk is a pure form of limestone, your teacher is basically smearing the skeletons of dead marine organisms on the blackboard. Limestone Reefs Limestone reefs are made almost entirely of fossil corals which can be seen on close inspection. These reefs often host petroleum deposits.