Sedimentary rocks

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Sedimentary Rocks Deposited on or Near Surface of Earth by Mechanical or Chemical Processes What Rocks Tell Us Rock Type Igneous Sedimentary Metamorphic How Classified Composition Texture What it Tells Us Tectonic Setting Cooling History Chemical Composition Surface Environment Grain Size Energy of Environment Composition Original Rock Type Mineral Makeup Temperature, Pressure Texture Degree of Change Types of Sedimentary Rock • Clastic (terrigenous or detrital) – – – – Conglomerate or Breccia Sandstone Siltstone Shale • Chemical/biochemical – Evaporites – Carbonate sedimentary rocks (limestones and dolostone) – Siliceous sedimentary rocks • Organic (coals) – Other - ironstones Sedimentary Rocks are the Principal Repository for Information About the Earth’s Past Environment Depositional environments in ancient sediments are recognized using a combination of sedimentary facies, sedimentary structures and fossils Environmental Clues in Sedimentary Rocks • Grain Size - Power of Transport Medium • Grading - Often Due to Floods • Rounding • Sorting } • Cross-bedding - Wind,Transport, Reworking Wave or Current Action Environmental Clues in Sedimentary Rocks • Fossils – Salt Water - Corals, Echinoderms – Fresh Water - Insects, Amphibians – Terrestrial - Leaves, Land Animals • Color And Chemistry – Red Beds - Often Terrestrial – Black Shale - Oxygen Poor, Often Deep Water – Evaporites – Arid Climates Sedimentary Rocks Clastic Rocks • Made of Fragmentary Material • Deposited by – Water (Most Common) – Wind – Glacial Action – Gravity Biochemical Sedimentary Rocks • Evaporation • Precipitation • Biogenic Sediments Clasts (larger pieces, such as sand or gravel) • Clasts and matrix (labelled), and iron oxide cement (reddish brown color) Terrigenous (also called detrital or clastic) • Terrigenous sedimentary rocks are classified according to their texture (grain size): Gravel: Grain size greater than mm If rounded clasts = conglomerate If angular clasts = breccia Coal Seams, Utah • Delta, continental environments • Carbonized Woody Material • Often fossilized trees, leaves present Coal Formation Plant Fragments Are Often Visible in Coal Characteristics and names of some common clastic sedimentary rocks Particle Size Rock Name Rock Characteristics mud (see below) Shale smooth feel, layered appearance mud (mud sized particles: < 0.063 mm) Mudstone smooth feel, massive to layer silt (silt sized particles: 0.063 - 0.004 mm) Siltstone slightly gritty feel, may have layered appearance sand (sand-sized particles: 0.0625-2.0 mm) Sandstone granules, pebbles, cobbles, boulders (granule to boulder sized particles: mm - > 256 mm) Conglomerate large rounded fragments composed of older rock materials granules, pebbles, cobbles, boulders (granule to boulder sized particles: mm - > 256 mm) Breccia large angular fragments composed of older rock materials rough gritty feel, constituent grains clearly visible, including quartz, feldspar, other minerals, and rock fragments Characteristics of common non-clastic sedimentary rocks that will not react with dilute HCl Grain size very fine grained: can't see constituent particles with naked eye variable grain size Rock Name Rock Characteristics Chert hard, scratches glass, typically white, green, or red; tends to have conchoidal fracture Rock Gypsum soft, can be scratched with fingernail; may be translucent or opaque Characteristics of common non-clastic sedimentary rocks that will react with dilute HCl Grain Size Rock Name Rock Characteristics very fine grained, can't make out particles with naked eye Chalk Pure white, powdery, light-weight, will write on sidewalks or walls variable in grain size Limestone dense and soft, with a crystalline or dull (earthy) luster medium grained, particles commonly visible with naked eye Coquina fragments of fossils, usually shells of invertebrates Fossil Limestone dense and soft, may be crystalline or dull, with visible fossils, such as snail or clam shells or other taxa variable in grain size Sedimentary Rock Review Of Sedimentary Processes This chart is a review of the various steps involved in the formation of sedimentary rocks that have been discussed above Landforms Associated with Sedimentary Rocks Mesa • Flat-topped hill capped with hard rock Cuesta • Gently-tilted layer of hard rock: Door Peninsula • The gentle upper slope, on top of the layer is called the dip slope Hogback • A sharp ridge of hard rock, edge of a steeplydipping layer Mesas, Utah Grandfather Bluff, Wisconsin Cuestas, Wyoming A Hogback, Wyoming Flatirons, Boulder, Colorado Garden of the Gods, Colorado [...]... Clay less than 0.001 mm Siltstone Silt 001-0.1 mm Sandstone Sand 01-1 mm Conglomerate Gravel 1mm + Sedimentary rocks made of silt- and clay-sized particles are collectively called mudrocks, and are the most abundant sedimentary rocks Bedding or Stratification • • • • • Almost Always Present in Sedimentary Rocks Originally Horizontal Tilting by Earth Forces Later Variations in Conditions of Deposition... become rocks such as siltstone, sandstone and conglomerate Compaction Clastic particles smaller than silt, such as mud are deposited on the sea floor As they are buried, the weight of overlying sediments presses downward on the mud particles and compacts them, resulting in the formation of rocks such as claystone,mudstone or shale TYPES OF SEDIMENTARY ROCKS Clastic rocks • • • • Chemical & Organic rocks. .. •Breccia Angular fragments CLASTIC ROCKS • Formed from broken rock fragments weathered and eroded by river, glacier, wind and sea waves These clastic sediments are found deposited on floodplains, beaches, in desert and on the sea floors solidify (mudstone) Clastic rocks • Clastic rocks are classified on the basis of the grain size: conglomerate, sandstone, shale etc Clastic Rocks Classified by: • Grain... shale TYPES OF SEDIMENTARY ROCKS Clastic rocks • • • • Chemical & Organic rocks Sandstones Conglomerates Breccia Shale/mudstones Evaporites rocks These rocks are formed due to evaporation of saline water (sea water) eg Gypsum, Halit (rock salt) Carbonate rocks Organic rocks Form basically from CaCO3 – both by chemical leaching and by organic source (biochemical) eg Limestone; dolomite Form due to decomposition... non-clastic sedimentary rocks that will not react with dilute HCl Grain size very fine grained: can't see constituent particles with naked eye variable grain size Rock Name Rock Characteristics Chert hard, scratches glass, typically white, green, or red; tends to have conchoidal fracture Rock Gypsum soft, can be scratched with fingernail; may be translucent or opaque Characteristics of common non-clastic sedimentary. .. materials Biogenic Sediments –Chalk: which is made up of foraminefera is very fine grained Non-Clastic Sedimentary Particles I Broken fragments of calcite, mostly from algae Shallow sub tidal sediments from the Yucatan, Holocene Chalk Largest fragments are about 1 mm in length Biogenic Sediments Non-Clastic Sedimentary Particles Broken shell fragments of calcite frombivalve molluscs These shell fragments... continental environments • Carbonized Woody Material • Often fossilized trees, leaves present Coal Formation Plant Fragments Are Often Visible in Coal Characteristics and names of some common clastic sedimentary rocks Particle Size Rock Name Rock Characteristics mud (see below) Shale smooth feel, layered appearance mud (mud sized particles: < 0.063 mm) Mudstone smooth feel, massive to layer silt (silt sized... SO4 (Sol'n) = CaSO4 • Gypsum • Limestone • Iron Formations Alteration After Deposition • Dolomite Biogenic Sediments • Limestone - Shells, Reefs, Etc Organic Remains • Coal • Petroleum EVAPORITIC ROCKS These rocks are formed within the a depositional basin from chemical substances dissolved in the seawater or lake water Gypsum CaSO4.2H20 Halite (NaCl) Economic importance of Evaporites • SALT: other then... These shell fragments accumulated on a beach and are cemented together This rock is almost 100 percent shell fragments, and is therefore called a coquina Largest fragments about 2 cm in length CARBONATE ROCKS • Limestone: It is a non-clastic rock formed either chemically or due to precipitation of calcite (CaCO3) from organisms usually (shell) These remains will result in formation of a limestone •Limestones... the type of organism responsible for the formation –Fossiliferous Limestone: which medium to coarse grained, as it is formed out of cementation of Shells COALS: Organic Remains Coals are carbon-rich rocks that are composed of the altered remains of woody plant debris The two principal types of coals are: •lignite (brown coal): composed •of loosely bound (friable) organic •detritus, including some
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