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퇴적물, 퇴적암 퇴적암 구성 비율 Sedimentary rocks cover about 75% of the world's land area 퇴적암으로부터의 정보 • • • • • • • • • • • • • Paleoclimate Conditions Paleoenvironment – Arid and Tropical Belts (presence of seas, deltas, beaches, rivers, lakes, glaciers, coral reefs, swamps, mountains, deserts, etc.) Source Material History of Transport and Deposition Relief Latitude – Climate Belts Climate / Temperature Sea Level Changes in Atmospheric Chemistry Plate Movements Tectonic Setting – Evolution of Earth Fossils – Evolution of Organisms Relative and Absolute Age Dating 암석의 순환 • Sedimentary Rocks are formed from sediments. 퇴적암은? • Composed of sediment = loose particulate material – Chemical and Physical weathering – clay, silt, sand, gravel, etc. • Sediment derivation by weathering – Chemical (decomposition) – Physical (disintegration) • Sediment becomes sedimentary rock through diagenesis(속성작용), which involves: – Lithification (암석화작용) • Compaction (다짐작용) • Cementation (교결작용) – Recrystallization (재결정작용) (of carbonate sediment) 퇴적물에서 퇴적암으로 (Turning Sediment into Rock) • Diagenesis (속성작용) – all of the chemical, physical, and biological changes that take place after sediments are deposited. • Occurs within the upper few kilometers of Earth’s crust at temperatures generally less than 150 to 200 ºC (metamorphism occurs beyond this threshold). Turning Sediment into Rock • Diagenesis Includes: • Recrystallization – development of more stable minerals from less stable ones. Example = CaCO3 to CaMg(CO3)2 • Lithification – unconsolidated sediments are transformed into solid sedimentary rock by compaction and cementation. Turning Sediment into Rock • Diagenesis Includes • Compaction: 입자와 입자 사이 공극이 줄면서 공극을 채우고 있던 물이 짜여져 나옴 – Sediment accumulates. – Weight of overlying material compresses deeper sediments. – Deeper sediment is further buried becoming more compacted and firm. – Grains are pressed increasingly closer reducing pore space by as much as 40% (clays). – Most significant lithification process in fine-grained sedimentary rock (shales). 속성작용(Diagenesis): Lithification Sediment Rock Turning Sediment into Rock • Diagenesis Includes • 교결작용(Cementation): 공극수에 용해된 물질이 입자 사이의 공간에 침전하여 입자들을 엉겨 붙게 하는 작용 – Most important process by which sediments are transformed to sedimentary rocks. – Chemical diagenesis that involved the precipitation of minerals carried in solution into the open pore spaces between individual grains. – Natural Cements include calcite, silica, and iron oxide. Cementation Typical Cements: • Calcite • Quartz • Iron Oxide 퇴적암의 분류 • Rock types are based on the source of the material. • 쇄설성암(Detrital Rocks) – Derived from both the chemical and mechanical weathering of pre-existing rock forming detritus that is then transported and deposited in another location. • 탄산염암(Carbonate Rocks) – Sediment that was once in solution and precipitated by organic or inorganic processes. 퇴적암 분류 기준 • Sedimentary rocks are classified based on their texture (grain size and shape) and composition (mineral content). • Detrital rocks are subdivided primarily based on particle size and composition. – The chief constituents of detrital rocks include: – – – – Clay minerals Feldspars Quartz Micas • Chemical rocks are subdivided primarily based on composition. – The chief constituents of chemical rocks include: – Calcite – Microcrystalline Quartz – Gypsum, Halite, and Sylvite Classification of Sedimentary Rocks • Two major textures are used in the classification of sedimentary rocks. • Clastic – Discrete fragments and particles. – All detrital rocks have a clastic texture. – Some chemical rocks – coquina and oolitic limestone – also posses clastic textures. • Nonclastic (or Crystalline) – Pattern of interlocking crystals. – May resemble an igneous rock. Types of Sedimentary Rocks • Detrital Sedimentary Rocks – – – – Conglomerate or Breccia Sandstone Siltstone Shale or Claystone • Chemical/Biochemical Sedimentary Rocks – Evaporites – Carbonate sedimentary rocks (limestones and dolostone) – Siliceous sedimentary rocks (chert, diatomite) – Organic sedimentary rocks (Coals – peat, lignite, bituminous, and anthracite) Identification of Sedimentary Rocks STOP 쇄설성 퇴적암의 특성 Detrital Sedimentary Rocks • Detrial rocks have a clastic (broken or fragmental) texture that may consist of: – Clasts – larger pieces, such as sand or gravel. – Matrix – mud or fine-grained sediment surrounding the clasts. – Cement – the chemical “glue” that holds it all together. • Types of Cement: – Calcite – Iron Oxide – Silica 역지지 역암 (Clast -Supported Conglomerate) (River Deposits) 기질지지 역암(Matrix-Supported Conglomerate) (Glacial/Landslide Deposits) 2.2 Gyr Conglomerate “Modern” Glacial Sediments 입도에 따른 쇄설성 퇴적암의 분류 Particle size is used to distinguish among the various types of detrital rocks. • Gravel(자갈): Grain size greater than 2 mm. – If rounded clasts = Conglomerate (역암) – If angular clasts = Breccia (각력암) • Sand(모래): Grain size 1/16 to 2 mm – Sandstone • Silt(실트): Grain size 1/256 to 1/16 mm (gritty) – Siltstone • Clay(점토): Grain size less than 1/256 mm (smooth) – Shale (if fissile) – Mudstone (if massive) Grain Size • Gravel ≥ 2 mm • Sand – 2 mm to 1/16 mm • Silt – 1/16 mm to 1/256 mm • Clay ≤ 1/256 mm Detrital Sedimentary Rocks are Classified by Grain Size Grain Size Rock Name Gravel Conglomerate = Rounded Clasts Breccia = Angular Clasts Sand Sandstone Silt Siltstone Clay Shale = Fissile Mudstone = Massive Detrital Sedimentary Rocks Shale Conglomerate Sandstone Breccia 입도(입자 크기)의 의미 • The energy of the environment and media of deposition. • Currents of water or air sort the particles by size – the stronger the current, the larger the particle size carried. Grain Size Interpretation • Gravel • High Energy • Sand • Silt • Clay STOP • Low Energy • River, Beach • River, Beach, Desert • Delta, Shallow Ocean • Deep Ocean, Lake, Swamp 분급(Sorting) • Sorting refers to the distribution of grain sizes in a rock. – Well Sorted – All the grains are approximately equal in size. – Poorly Sorted – Particles of variable size are mixed together. Degrees of Sorting 분급의 의미 • The energy of the environment and media of deposition. Interpretation: Transport Agent Poorly Sorted Gravity and Glaciers (and Rivers) Well Sorted Water and Wind What Does the Degree of Sorting Tell Us? • 퇴적환경 별 에너지 수준 반영: • Windblown sands are typically better sorted than wave-washed sediments. • Particles washed by waves are commonly better sorted than materials deposited by streams. 분급도의 의미 • 기원지로부터의 운반 거리와 퇴적률 반영: • Poor sorting indicates sediments were transported a short distance and deposited rapidly. – Examples: Alluvial Fans (선상충적지) and Glacial Tillite (표석점토암) deposits • Well-sorted sediments indicate the sediments were transported a longer distance and deposited more gradually. – Examples: Deep-ocean deposits 입자의 모양(Grain Shape) • Grain shape is described in terms of rounding (원마도) of grain edges and sphericity(구형도) (equal dimensions, or how close it is to a sphere). • When currents transport sedimentary particles, the particles collide together breaking off sharp edges. 원마도와 구형도(Rounding & Sphericity) Spherical Oblong Degree of rounding is expressed using the following scale: highly angular –> angular –> subangular –> subrounded –> rounded –> highly rounded (A) An angular particle (all edges sharp). (B) A rounded grain that has little sphericity. (C) A well-rounded, highly spherical grain. Gravel Sized Detrital Rocks (Subdivided Based on Grain Roundness) Conglomerate Breccia Grain Shape • Degree of rounding also indicates distance from source and/or transport time: • Very well rounded sand grains suggest that a sand has traveled a great distance from the source over a long time period. • They also may have been recycled from older sandstones. STOP Short Interpretation: Distance of Transport Far 화학적 풍화 • Transport time also affects the mineral composition of a sedimentary deposit: – Substantial weathering and long transport leads to the gradual destruction of weaker and less stable minerals such as feldspars and ferromagnesian minerals (Bowen’s Reaction Series). – Quartz – the most stable mineral at the Earth’s surface survives. 퇴적암의 색 • Black and dark gray coloration in sedimentary rocks generally indicates the presence of organic carbon and/or iron. • Organic carbon in sedimentary requires anoxic environmental conditions. Color of Sedimentary Rocks • Red coloration in sedimentary rocks indicates the presence of iron oxides (Ferric Iron – Fe+3) . • Red beds typically indicate deposition in well-oxygenated continental sedimentary environments. • May also be transitional or marine. Red siltstone w/ tracks Hematite-cemented Sandstone (Clinton Fm.) Color of Sedimentary Rocks • Green and gray coloration in sedimentary rocks indicates the presence of iron, but in a reduced (rather than an oxidized) state. • Ferrous iron (Fe+2) generally occurs in oxygen-deficient environments. STOP 쇄설성 퇴적암 유형별 특성 Detrital Sedimentary Rocks • Common Detrital Sedimentary Rocks (in order of increasing particle size) • Shale – A very fine-grained rock composed of clay-sized particles. – Most common sedimentary rock. – Particles deposited in thin layers commonly referred to as laminae. – Shale is fissile – splits readily into thin, flat layers. Detrital Sedimentary Rocks • 이암(Mudstone) • Composed of mud – a mixture of silt and clay. • May exhibit fissility. • Breaks into chunks or blocks. Detrital Sedimentary Rocks • Siltstone – Composed of largely of siltsized particles with lesser claysized particles. – Lacks fissility. – Breaks into chunks or blocks. Formation of Shales to Siltstones • Due to their Fine Grain Size: – Clay and silt-sized particles tends to remain suspended in the water column. – Deposition occurs as the result of gradual settling from relatively quiet, non-turbulent currents. – Lithified predominantly via compaction. – Clays and shales typically indicate low energy environments, sheltered from waves and currents. – Such environments include lakes (lacustrine), river floodplains, lagoons, and portions of deep ocean basins. – Composition and color can further indicate the environment of deposition (e.g., coaly shales). Detrital Sedimentary Rocks • 사암(Sandstone) – Composed of sand-sized particles. – Lithified predominantly via cementation. – Forms in a variety of environments. – Sorting, shape, and composition of the grains can be used to interpret the rock’s origin and history. – Compositional components include: • Quartz – predominant mineral • Feldspar • Rock Fragments 사암의 종류 • • • • Quartz Sandstone – Dominated by quartz; mature Arkose(장석질사암) – 25% or more feldspar; immature Graywacke(잡사암) – About 30% dark fine-grained matrix; immature Lithic Sandstone – Quartz, muscovite, chert, and rock fragments. Less than 15% matrix. Immature Four categories of sandstone as seen in thin section under the microscope. Diameter of field is about 4 mm. 석영사암(Quartz Sandstone) Composed of well-sorted, rounded quartz grains suggests long-distance transport, highly weathered, and moderate deposition and burial rates. Arkose (장석질사암) • Composed of quartz, feldspars, and micas indicates granitic source rocks. Typically poorly sorted, angular particles with minimal chemical weathering (indicated by the presence of feldspar) suggests short-distance transport, minimal chemical weathering in an arid climate, and rapid deposition and burial. Sandstone Close-Ups • Quartz Sandstone (left) • Arkose (Sandstone with >10% feldspar) Detrital Sedimentary Rocks • 역암과 각력암(Conglomerate and Breccia) – Both are composed of particles greater than 2mm in diameter (gravel) with sand, silt, and clay particles between. – Particles are large enough to identify distinctive rock types and therefore source rocks. – Gravels accumulate in a variety of environments and typically indicate steep slopes and/or very turbulent currents. – Examples: energetic mountain streams, strong wave activity along rapidly eroding coastline, and glacial and landslide environments. Detrital Sedimentary Rocks • Conglomerate and Breccia – Conglomerate consists largely of rounded gravels. – Breccia is composed mainly of large angular particles. 역암 노두 Composition of variable materials, poorly sorted, and rounded particles suggests relatively short-distance transport (but long enough to have high degree of abrasion), some mechanical and minimal chemical weathering, and rapid deposition and burial. Interbedded Sandstone and Conglomerate 사암과 역암의 교호층 Suggests distinctive periods of alternating depositional environments of high and low energy. Breccia Composition of variable materials, poorly sorted, and angular particles suggests short-distance transport, minimal mechanical and chemical weathering, and rapid deposition and burial. 화학적/생화학적 퇴적암 화학적 퇴적암 • Consist of precipitated material that was once in solution. • Precipitation of material occurs in two ways: • Inorganic Processes: – Evaporation – Hydrothermal – Chemical Activity • Organic Processes: – Biochemical Origin from water dwelling organisms 화학적, 생화학적 퇴적암의 분류 1. 탄산염암(Carbonate Rocks) – Form by chemical processes and biochemical processes (secreting shells). 2. 규질암(Siliceous Rocks) – Form from chemical processes (silica replacing limestone) or biochemical processes (silica-secreting organisms). 3. 증발암(Evaporites) – Form from the evaporation of seawater. Carbonate Rocks 1. 석회암(Limestones) – – – Most abundant chemical rock. Composed of predominantly of calcite (CaCO3) and secondarily aragonite (CaCO3). Marine biochemical limestones form from preexisting organisms: • • • – Inorganic limestones form by inorganic processes (evaporation, chemical activity): • • 2. Reef Limestone(생물초석회암) – 생물초(reef)에 사는 생물들의 탄산염 골격이 교결되어 생성 Coquina(패각암 또는 코퀴나) – 부서진 조개껍질 조각들의 입자 Chalk(백악 또는 초크) – 미세한 부유성 바다미생물의 탄산염 껍질 Oolitic Limestone (어란상석회암) Travertine (온천석회암) Dolostones(백운암) (or Dolomites) – Composed of Dolomite (CaMg (CO3)2) 해양성 탄산염암의 생성환경 • Some carbonate rocks form in lakes, caves, and hot springs. • Most carbonate rocks form in the shallow marine environments: – – – – – – Marine Warm Water Shallow Water (less than 200 m deep) Tropical Climate (30 ° N - 30 ° S of equator) Clear Water (low to no terrigenous input) Sunlight Required for photosynthesis by algae 유기화학적 퇴적암 • 백악(Chalk) – Chalk is a soft, porous rock composed of almost entirely of the hard parts of microscopic calcareous marine organisms. 유기화학적 퇴적암 • Coquina – Coquina is a coarse-grained rock composed of poorly-cemented shells and shell fragments. 무기화학적 퇴적암 • Oolitic Limestone – Oolitic limestone is composed of small spherical grains of CaCO3 called ooids. Origin of Ooids in Oolitic Limestones • Ooids are tiny spheres composed of concentrically laminated calcium carbonate. • Ooids form in shallow marine waters and begin as tiny “seed” particles (commonly shell fragments) are constantly agitated by currents. • As the seeds are rolled around in the CaCO3 supersaturated warm waters, layers of CaCO3 are concentrically precipitated around the seed. 무기화학적 퇴적암 • Travertine – Travertine forms in caves (stalagtites, stalagmites, curtains, etc.) when groundwater encounters air, CO2 comes out of solution and causing CaCO3 to precipitate. – Also forms from precipitation of calcite around hot springs. Carbonates: Dolomite • Composed of dolomite CaMg(CaCO3)2 – a calciummagnesium carbonate mineral. • Dolomite (Dolostone) can form by the direct precipitation of seawater in a few areas of the world where intense evaporation of seawater concentrates the magnesium. • Typically formed secondarily from limestone. • Magnesium that has been concentrated in sea water replaces some of the calcium in the CaCO3 structure (diagenesis). 규질 퇴적암 • Chert – – – – Made of microcrystalline quartz (silica). Massive and hard. Often replaces limestone. Varieties include the following: • Flint – dark in color due to organic matter • Jasper – red in color due to iron oxide • Agate – banded form or chert Siliceous Sedimentary Rocks • Chert – Chert has various modes of origin: • Inorganic – Precipitated from groundwater as nodules. • Inorganic – Precipitated from groundwater associated with the decomposition of lava flows and layers of volcanic ash (silica-rich). • Organic – Biochemical Sediment – Siliceous ooze (gel) derived from silica skeletons of marine organisms (diatoms and radiolarians). 규질 퇴적암 • Diatomite (규조토) – Made of microscopic planktonic organisms called diatoms. – Resembles chalk, but does not fizz in acid. 증발암(Evaporites) • • • • Evaporation triggers deposition of chemical precipitates. Formed from dried basin areas that were submerged by shallow arms of sea with little or no connection to open ocean. When seawater evaporates, minerals precipitate in sequence according to their solubility forming salt flats. Gypsum precipitates before halite, which precipitates before sylvite(칼리암염): 1. 2. 3. Rock Gypsum – Composed of gypsum (CaSO4 . 2H2O) Rock Salt – Composed of halite (NaCl) Sylvite – Composed of potassium chloride (KCl) Rock Salt (Halite) Bonneville Salt Flats, Utah Layered Rock Gypsum(석고) 유기적 퇴적암– Coal • Composed of organic matter such as trees, bark, wood, leaves, etc. buried for millions of years. • Stages in coal formation (in order) as a function of increasing depth of burial (increase in temperature and pressure): • Plant Material • Peat (토탄) • Lignite (갈탄) • Bituminous Coal (역청탄) • Anthracite Coal (무연탄) 석탄의 생성단계 유기적 퇴적암– 석탄 • Stages of Coal Formation 1. Plant Material – Accumulations of large amounts of plant remains in a stagnant, oxygen-deficient environment (늪지), where oxidation and thus complete decomposition of the plant remains is not possible. Anaerobic bacteria (혐기성 박테리아) partially decompose plant remains releasing oxygen and hydrogen, thereby increasing the carbon percentage and creating a layer of peat. Organic Sedimentary Rocks – Coal • Stages of Coal Formation 2. Peat – A soft brown material in which plant structures are still easily recognizable 3. Lignite – With shallow burial, peat slowly changes to lignite – a soft brown coal • • Increase temperature and pressure squeezes out the volatiles (water and organic gases) increasing the proportion of fixed carbon The greater the carbon content, the greater the coal’s energy ranking 석탄의 생성단계 (Successive Stages in Coal Formation) Organic Sedimentary Rocks – Coal • Stages of Coal Formation 4. Bituminous – Deeper burial transforms lignite to bituminous coal – a soft black coal. 5. Anthracite – Forms during regional metamorphism under increased temperature and pressure. • Anthracite is a very hard, black, shiny, metamorphic rock. Successive Stages in Coal Formation STOP