GEOL 101 1nd Edition Lecture 14 Outline of Last Lecture I. Slope FailureII. Land FailureOutline of Current LectureI. Sedimentary RocksII. Detrital Sedimentary RocksIII. Chemical Sedimentary RocksIV. EnvironmentsV. Energy ResourcesCurrent LectureSedimentary Rocks- Sedimentary rocks—products of mechanical and chemical weathering. They account for about 5 percent (by volume) of Earth’s upper crust. (Majority or rocks exposed at surface are sedimentary).-Sedimentary rocks make a thin veneer that “coats” the surface-They are essential to geologists because they contain evidence of past environments:- Provide information about transport- Contain fossil fuels- Contain petroleum, coal, and economic resources-Material that has been mechanically or chemically weathered may become a new rock througha process called digenesis.-Digenesis refers to all of the chemical, physical, and biological changes that occur to sediment after it has been deposited again.-The most common form of digenesis is Lithification. - Process by which loose unconsolidated sediment is transformed into solid rock.- This involves compaction and cementationo Compaction: As sediment accumulates, the weight of the overlying material compresses the sediment underneath.  Grains squeezed together and pore space between grains is reduced Most common in fine-grained rocks (silt and clay sized)o Cementation: Loose material is cemented together by materials that precipitate out of solutionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Cement forms in pore spaces and “glues” grains together Commonly, the cement is calcite, silica, or iron oxide- Most sedimentary rocks are lithified by a combination of these two processes-Remember how there are two types of weathering? Mechanical and chemical?- Since Sedimentary rocks form from weathered material, there will be two types of sedimentary rocks -Sedimentary rocks are based on the source of the material:- Detrital rocks—sediment as solid particles– These solid particles are typically the result of mechanical weathering, but they may be from chemical weathering too.- Chemical rocks—sediment that was once in solution– These rocks form as material precipitates out of solution (opposite of dissolving)Detrital Rocks-Detrital sedimentary rocks are made up of weathered solid particles-Most of these particles are:- Clay minerals- Quartz- Feldspar- Micas-Detrital rocks are classified based on their grain sizes-Detrital sedimentary rocks tell us a great deal about the environment where rocks formed.-Shale- Most common sedimentary rocks- Composed of mud-sized particles (clay and silt)o Very fine grainedo These fine particles are picked up by currents, therefore in order to settle out of the water, it must be calmo Common environments for shale to form include lakes, lagoons, and deep ocean basins As the silt and clay particles accumulated, they can form layers, or laminae- Shale is often black, which indicates high amount of organic mattero Black shales typically form in oxygen-poor environments (swamps)o Leaf fossils are fairly common in shaleso Because shale is composed of fine particles, it is easily weatheredo In an outcrop, it is a “slop former” whereas more resistant rock layers are “cliff formers”- Sandstone- Composed of sand-sized particles- Forms in a variety of environments:o Near shorelines (beach sand)o In deserts (sand dunes)o In deep water- Characteristics that can help interpret the sedimentary environment include:o Sortingo Shapeo Composition- Sorting: how close in size the grains are to each othero Well-sorted sandstone has grains that are all about the same sizeo Poorly-sorted sandstone has grains that are variable in size (within the sand-size range)- Shape: how angular or round the grains areo Angular grains are jaggedo Rounded grains are smooth, and spherical- Composition: mineral make-up of the sand grainso Commonly, Quartz is the dominant mineral in a sandstonequartzose sandstone Quartz is very resistant to weathering, and so it lasts long enough to be incorporated into a rock Other minerals are more easily weathered, and will dissolve, oxidize, or weather into clayso In some sandstones, Feldspar is the dominant mineralarkose sandstone  Feldspar will chemically weather into clay, so if it gets preserved in a sandstone, the sandstone must have formed very shortly after physical weatheringo If a sandstone has mud-sized combined with sand grains, it is called a greywacke Greywackes generally form in ocean basins as submarineo Conglomerate consists of large rounded bits of gravelo Breccia is composed of mainly large angular particlesChemical Rocks- Consist of material that has been precipitated out of solution- Precipitation of material occurs in two ways:o Inorganic processeso Organic processes (biochemical origin) -Limestone- Most abundant chemical rock- Composed of mostly calcite-Biochemical limestones form as:- coral reefs – abundant invertebrate animal lifefossils- coquina (broken shells)- chalk (microscopic organisms)-Inorganic limestones include:- Travertine- Oolitic limestone-Dolostone—formed secondarily from limestone-Chert—made of micro-crystalline quartz- Colorful varieties include:o Agate (banded form)o Flint (gray)o Jasper (red)o Onyx (black)-Evaporites—saturated water evaporates, the ions precipitate as minerals come out of solution, and form rocks.o Examples include rock salt and rock gypsum-Coal—remains of ancient plantso Different from other rocks because it is composed of organic material Often there are visible leaf and wood fragmentso Stages in coal formation (in order)1. Plant material2. Peat3. Lignite4. Bituminous Sedimentary Environments-Sedimentary rocks tell us a great deal about the environment in which they formed- A sedimentary environment is any geographic setting where you have sediment accumulating o Streams, beaches, swamps-Different environments produce different characteristics in the sediments- Grain size, grain shape, composition, sorting, etc.-Types of sedimentary environments:- Continental Environmentso Dominated by erosion and deposition associated with streamso Colder regions are glacier erosiono Wind takes on a great role in and out of coastal region- Marine Environmentso