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Earth Sciences
Marcel Danesi

EXAM NOTES LECTURE 4 - volcanic sunsets slide: lets focus on: the 2010 eruption at Eyjafjallajökull - unprecedented disruption of the European airspace -3 to 8 k m height eruptive column that lasted for more than one week - winds directed volcanic ash towards the heart of Europe, one of the denser air traffic areas worldwide. eurptions in Iceland was small but winds blew ash towards Europe and messed up ash clouds because of volcanic ash 1. Eyjafjallajökull erupts in 1821-1823 with felsic (trachydacite) magma ==Felsic=magma 2. In 2009 a new, deep source mafic (basaltic) magma is injected into plumbing system at Eyjafjallajökull; it erupts effusively at Fimmvörõuháls Mar 21 – Apr 7 2010 == new magma was injected in mafic and feslsic mix. Mafic and basalt came out in “fimmvorouhals’ and mafic came out 3. New phase Apr 14 2010, melt penetrates central crater beneath the glacier. Eyjafjallajökull begins to erupt explosively with intermediate (trachyandesite) magma (probably a mix of the pre-existing felsic magma with the newly injected mafic magma) - 3 2010 we had melt penetrate crater and erupt explosivly because of mixing of the 2 magma with made intermediate magma (which is explosive) Fimmvörõuháls, lava flow Mar 21 – Apr 7 2010 Incandescent SCORIA AND A STEAM CLOUD -- red clots are clots of lava shot out of a volcanoe because magma is to sticky to let gases out -some of the magma, comes out as clots called scoria -can tell diff btwn ash and steam which is white -massive lava clots at Massive Lava clots at Eyjafjallajökull Lightning caused by electrical discharge within the ash column - ash clouds cause alot of lightning Stratovolcano complex and ash plume with intensive lightning cone shapped and straddle volcanoes Ash column assumes the shape of a plinian eruption - plinian eruption is huge. Looks like a mushroom but not big enough to be philian consequences -With ash it is tough to breath -with flat roof ash can collapse it ***good questions is products of ifoca and the effects it has****** ME Eyjafjallajökull happened in Iceland spewing plume of ash that created lightning displays, coloured sunsets a fiery red across Europe  The volcano started to erupt on 21 March 2010, producing some spectacular lava fountains and a small amount of ash. As the pressure inside the volcano caused the magma (molten rock inside the volcano) to rise, the volcano heated up. This rise in temperature melted the glacier on the volcano and floodwaters reached the lowland at the base of the glacier.  When lava (the name for magma when it comes out of the volcano) comes into contact with cold water, or ice, it cools down very quickly. This causes the rock to contract fast and this in turn makes it shatter into tiny pieces. That’s the volcanic ash cloud that we started to see  The ash cloud was thick over South Iceland, forcing people to wear masks to filter out the harmful gases. The winds slowly started to spread the ash  The major problem with this volcano was volcanic ash and the ash plume that resulted from the eruption. This ash plume reached 11,000m into the air, high enough to reach into the Stratosphere and also to be distributed by high velocity jet streams between the Troposphere and the Stratosphere. The problem with the ash was that it was very fine grained LECTURE 5 Outline Metamorphic Processes – Protolith (source) – Degree of foliation – Polymorph minerals – Metamorphic facies – How do rocks respond to stress? – Compressive, tensile, shear stress – Elastic, brittle, ductile strain • Strain structures in rocks – Faults – Folds SEDIMENTARY ROCKS Source, process, product – Sedimentary environments: weathering & sediments – Clastic vs chemical – Fossils – Laws of stratigraphy\ Me: Types of stress •Compression – convergent plate boundaries –Crumpled, thickening vertically and shortening laterally –Creates folds, reverse and thrust faults –Himalayas, NW coast of N.A., Appalachians, western coast of S.A. •Tension – divergent plate boundaries –Extends crust, thins vertically and lengthens laterally –Creates basins, normal faults, grabens –Mid-Atlantic Ridge, East Pacific Rise (Gulf of California), Red Sea Rift •Shear – opposing forces along a plane –Forms parallel blocks, pull-apart basins, transform faults, folds and rotational structures –Gulf of California, San Andreas fault system, East Anatolian fault system, Enriquillo-Plantain Garden fault system (Caribbean and North America plates – Haiti) types of deformation •Elastic – returns to original state –Temporary, not permanent –Yield point – point of deformation beyond which change is permanent •Plastic – irreversible change in shape or volume that occurs without the rock breaking –Usually under conditions of high temp and press –Usually a slow process giving atoms time to shift in response to force applied •Brittle – irreversible change that penetrates mineral bonding –Usually under conditions of low temp and press –Force applied suddenly not allowing atoms time to shift or move in response to force Deformation factors •Heat – Allows “fluid” behavior, > heat = > plastic deformation •Time – Great amount of time allows plastic deformation to occur if force is applied continually. Little time doesn’t allow atoms to adjust so brittle failure is the result •Composition – hard vs soft minerals and rocks (e.g. qtz vs micas or granite vs shale) Strain 1 Folds •Monoclines – a single draped fold bending in only one direction (Fig. 10.18) •Synclines – Concave up, trough-like, youngest rocks at center (Fig. 10.9) •Anticlines – Convex up, arch-like, oldest rocks at center (Fig. 10.9) ie appalcjaian mountain- folds by reverse failting 2Faults: -•Normal – dip-slip, more vertical than horizontal, hanging wall moves down relative to footwall (tensional) (Fig. 10.21) •Reverse – dip-slip, hanging wall moves upward relative to footwall (compressional) (Fig. 10.23) •Strike-slip – Horizontal slip of adjacent blocks, right and left (Fig. 10.27) Thrust – special type of reverse, block moves at low angle (~45 degrees) (compressional PLATE TECTONICS AND ROCK FORMATIONS *******rock cycle question. Please relate rock cycle to plate tectonics ie what plate tectonic situation might you form igneous, metampriohic ect Where does metamorphism occur? - within mountain belts along CONVERGENT plate boundaries. - Different types of structures and metamorphic features form in different parts of a convergent system and reflect differences in the types of rocks involved, the metamorphic temperatures and pressures, the way the rocks deform, and the role of magma, if any - as rocks have increasing temperature and pressure they are metamorphosed - where temp and pressure is low do not metaphorophize OCEAN-CONTINENT CONVERGENT= METAP In ocean-continent convergent settings, an oceanic plate subducts beneath a continental plate, forming magma that invades the overriding continental plate. The type of metamorphism varies greatly between the hot environs near magma and the less hot conditions in shallow parts of the subduction zone. In most convergent boundaries, the overriding plate experiences compression, as described below. In some cases, not shown here, the overriding plate is not compressed, but instead experiences tension and normal faulting. CONTINENTAL COLLISION=METAMO Several steps and changes that happen in the solid state during metamorphism 1) RECRYSTALIZATION: existing crystals grow at the expense of others results in textures with interlocking grains- ex sandstone has round grains quartz has interlocking grains textbook: formation of cleavage and folation is aided by the recrystalization of existing minerals and the growth of new minerals. Adjacent minerals can grow with similar planar or linear orientation 2) (2) new minerals may form: ex, large garnet crystals often completely new mineral assemblage will form without changing overall numbers of atoms ex Basalt and gabbro. Basalt is extrusive forming different crystals than gabbro forming intrusively inside the earth New minerals not there before - ie garnet can form in minerals that was not there before - top right pic has tiney garnet - basalt, depending on how high temp it can have many results depending on temp - gabbro cools inside the earth but same as basalt which formed outside textbook: Remobolization: during metamorphism chemical constitents in a rock can be remobilized meaning they ca diffuse, dissolve or partiallu melt in one place and than form crystals in another. Such process help form light and dark colored bands in gniess 3) (3) change in texture especially foliation - schistosity - compositional banding (gneiss)  alot of metamor have a common texture called layering or FOLIATION. -it means that diff minerals line up by mineral type -squish it - ie gneiss. - reaction to pressure. Line up with like minerals textb: Pressure solution: formation of leavage involves a process called pressure solution. Material dissolves from highly stressed edges of grains and precipates elsewhere in the rock or is carried away by fluids. A rock can lose a significant volume during metamorphism ** she will ask us this - texture and composition tell us about pressure-temperature conditions (“metamorphic grade”) ex, fine-grained clay-rich sedimentary rock as protolith SHALE Increasing metamorphic grade: 1 starts off as shale (very crumbly and easy to erode which is a protolith) -when shale is metamorphized with pressure and temperature it can develop cleveage and becomes SLATE (not shiny and dark) 2 LOW GRADE- add more heat and pressure and you get PHYLITE 3 INTERMEDIATE GRADE- at higher grades crystals of mica become large enough to see. The resulting rock has a schisrosicty and is a shist (has lots of mica) more is SCHIST. Diff than shale (made from clay crumbly sedim) but more squishing clay broke down and became mica. Clay turns into new minerals called mica. Very shinny 4) more heating and squishing becomes GNIESS (fewer mica minerals) At even higher grade chemicals are mobalized and light and dark colered minerals separate forming gniess 5) high grade: More is MIGMATITE which is as close as you can get to almost melting because so squshed and heated. -point: on left LOW GRADE because low heating and squishing HIGH GRADE like mountains. Low heated and squished to high heated and squished HOW DO ROCKS RESPOND TO STRESS? SKETCH SIMPLE FOLDS AND FAULTS AND KNOW STRESS AND STRAINS Stress: is appled to the rock. the applied force (The pushing and pulling on the rock layers). Types of stress are 1) COMPRESSION 2) TENSION 3) SHEAR  Stress is a force acting on a rock per unit area. It has the same units as pressure, but also has a direction (i.e., it is a vector, just like a force). There are three types of stress: compression, tension, and shear. Stress can cause strain, if it is sufficient to overcome the strength of the object that is under stress.  Strain is a change in shape or size resulting from applied forces (deformation). Rocks only strain when placed under stress. Any rock can be strained. Strain can be elastic, brittle, or ductile. ** how a rock responds to stress types of strain Strain - Rock Deformation in Response to Stress Rock responds to stress differently depending on the pressure and temperature (depth in Earth) and mineralogic composition of the rock. ***deformation of a rock cylinder depends on confining (surrounding) pressure and temperature elastic deformation: Temporary inet: For small differential stresses, less than the yield strength, rock deforms like a spring. It changes shape by a very small amount in response to the stress, but the deformation is not permanent. If the stress could be reversed the rock would return to its original shape. brittle deformation: permenant, breaks occurs at cool shallow levels of the crust (low pressure low temp) inet:Near the Earth's surface rock behaves in its familiar brittle fashion. If a differential stress is applied that is greater than the rock's yield strength, the rock fractures. It breaks. Note: the part of the rock that didn't break springs back to its original shape. This elastic rebound is what causes earthquakes. Ductile: flowing, bending occurs at deep levels where temp ad pressures are high inet- Deeper than 10-20 km the enormous lithostatic stress makes it nearly impossible to produce a fracture (crack - with space between masses of rock) but the high temperature makes rock softer, less brittle, more malleable. Rock undergoes plastic deformation when a differential stress is applied that is stronger than its yield strength. It flows. This occurs in the lower continental crust and in the mantle strain also depends on time scale ex: sillyputt 3 strain structures in hand samples and outcrops: extensional stress - broke the layer into chunks (“boudinage” = sausages) 1) compressional stress 2) shear stress COMPRESSIONAL Compressional stress pushes matter (rock layers) together IE CONGLOMERATE   lecture: started as sedimentary called protalif which is conglomerate. its made of gravel and bits of other rocks. Other conglomerates made up of other rocks - affected by heat and pressure and boulders can be pulled or squished and change shape - if we talk about compression which direction would it come from? when compress get long access perpendicular to stress - bottom left to top right because stress perpend to long axis SHEAR STRESS is rotational.the stress is parallel to a face of the material lecture: feldspar when under shear stress and rotated and causing it too appear to have wings. TENSIONAL STRESS- pulls matter apart HOW DO ROCKS FRACTURE? 1) joints 2) faults BRITTLE DEFORMATION OF ROCKS A) JOINTS –Simple crack representing where rock was pulled by small amounts – no movemement just permanent breajs – sometimes cracks are filled ie eith quartz -joints: breaks in rocks and rocks break off at these points B) FAULTS -Faults is a fracture where rocks slip past one another. Can slip up/down or sideways NORMAL FAULT- hanging wall moves DOWN and footwall UP. Forms when rock units are pulled apart by tension. REVERSE FAULTS- hanging wall moves UP and footwall DOWN. Forms as a result of horizontal compression and shortens the rock units in a horizontal direction THRUST (type of reverse)- reverse fault has a gentle dip called thrust fault. Sheet of of rock above the fault is called a thrust sheet and is pushed up and over footwall rocks. We depict thrust faults with teeth on the thrust sheet, as shown here. STRIKE SLIP FAULT (aka transform) - When rocks along a fault move with a side-to-side motion, parallel to the strike of the fault surface, the fault is a strike-slip fault. Relative motion is horizontal, offsetting the blocks laterally in one direction or the other LEFT LATERAL SLIP FAULT - standing on one side and it moves left of you - the opposite side is displaced to the left across the fault RIGHT LATERAL SLIP FAULT fault is offset to the right, the strike-slip fault is a right-lateral fault. EXTENSION CAUSES NORMAL FAULTS COMPRESSION CAUSES REVERSE FAULTS OR THRUST SHEAR STRESS CAUSES STRIKE SLIP FAULTS (aka transform) Extension causes normal - Compression causes reverse or thrust *thrust fault build mountains - not surprising because come together and stress is opressional so faults are reve -1 everything flat 2 compression pushes in so older crust is on top of new crust strata would be old old new new.land is shorter bc thrusted 3more thrust taller mountains shear stress causes strike slip faults HOW TO TELL WHICH ONE IS WHICH??? RIGHT IS ALWAYS HANGING WALL LEFT IS FOOT WALL - FOLDS: DUCTILE ROCK FORMATION THESE OCCUR BECAUSE OF COMPRESSION DEFORMATION CAN FOLD ROCK LAYERS, both at depth and at the surface. The folded layers may be bent in gentle arcs or squeezed tightly into sharp angles. We classify folds based on their shape and orientation. Knowing the names of different types of folds gives us a convenient way to describe what we observe in landscapes and outcrops. 1Before folding, most rock layers are horizontal because most sedimentary and volcanic layers form with a more or less horizontal orientation. 2. Compressive stress causes shortening, often accom-modated by folding of the layers. When you scrunch up a rug, the folds (creases) are perpendicular to the direction of shortening, as shown here for rocks (▶). Compression can form folds, faults, or both. FOLDS 1) ANTICLINE 2) SYNCLINE 1) ANTICLINE n - oldest rock at the core in the centre If the rock layers warp up, in the shape of an A, the fold is generally called an anticline. In an anticline, the oldest rocks are in the center of the fold 2) SYNCLINE U -If rocks fold down in the shape of a V or U, the fold is generally called a syncline. In a syncline, the youngest rocks are in the center of the fold. This fold is a syncline oldest rocks start at botom but like a U youngest at bottom and oldest rock is at the top - started as sedimentary called protalif which is conglomerate. its made of gravel and bits of other rocks. Other conglomerates made up of other rocks - affected by heat and pressure and boulders can be pulled or squished and change shape - if we talk about compression which direction would it come from? when compress get long access perpendicular to stress - bottom left to top right because stress perpend to long axis SEDIMENTARY ROCKS CHAPTER 7 SEDIMENTARY depositional enviroment=where were the rocks made? Enviroments Land -Mountain environments • Streams & rivers • Sand dunes • Wetlands • Lakes Ocean -Beach • Coastal dunes • Tidal flat • Delta • Submarine delta • Lagoon • Barrier islands • Reef • Continental shelf & slope • Deep seafloor Physical & Chemical Weathering Physical weathering is the physical breaking apart of rocks that are exposed to the environment. There are four major causes of physical weathering. Physical Near surface fracturing — Many processes on or near the surface break rock into smaller pieces. These include fracturing caused by rocks pulling away from a steep cliff. Fractures also result when rocks expand as they are uplifted toward the surface and are progressively exposed to less pressure Frost & mineral wedging Rocks can be broken as water freezes and expands in fractures. When the ice melts, the fractured pieces may become dislodged from the bedrock. Crystals of salt and other minerals that grow in thin fractures can also cause rocks to break apart Thermal expansion  Rocks are heated by wildfires and by the sun during the day. As rocks heat up, they expand, often irregularly, and may crack. This process probably plays a relatively minor role in weathering, and geologists currently are debating its importance. Biological activity Roots can grow downward into fractures and pry rocks apart as the root diameter increases. Burrowing animals can transport rock and soil from depth and move it to the surface where it is exposed to the elements, weathered, and eroded. Chemical Dissolution — Some minerals are soluble in water, especially the weakly acidic waters that are common in nature. These minerals, along with the rocks, sediment, and soil that contain them, can dissolve. The dissolved material may be carried away in rivers, streams, or groundwater, or be used locally by plants. Oxidation Some minerals, especially those containing iron, are unstable when exposed to Earth‘s atmosphere. These minerals can combine with oxygen to form oxide minerals, such as iron oxides, which compose the reddish and yellowish material that forms when metal rusts Hydrolysis When silicate minerals are exposed to water, especially water that is somewhat acidic, the water reacts chemically with the minerals. This process commonly converts the original materials to clay minerals, and produces leftover dissolved material that is carried away by the water. Hydrolysis is responsible for the formation of many clay-rich soils. Biological reactions  Decaying plants produce acids that can attack rocks, and some bacteria consume certain parts of rocks. These biological processes cause minerals to break down into their constituent elements. 15.1 Physical weathering -weathering breaks rocks apart ==Physical weathering breaks rocks into smaller fragments without causing any change in their chemical makeup. These smaller fragments can then be attacked by chemical reactions, the process of chemical weathering, or they can be moved from the original site by the process of erosion. JOINTS AND WEATHERING A) role of joints -Joints are fractures, or very fine cracks, in rocks that show no significant offset. Joints help break rocks into smaller pieces and permit water and roots to penetrate into the rock, thereby promoting weathering. - form in rocks at depth and uplifted to the surface. Closely spaced jointing promotes rapid weathering. -Some joints form as a result of expansion due to cooling or to a release of pres sure as rocks are uplifted to the surface. These expansion joints can be difficult to distinguish from preexisting joints that formed by other processes -As Earth is sculpted by erosion, the topography influences stresses that build up when the weight of overlying rocks is unloaded. During unloading, expansion joints can form that mimic topography, peeling off thin sheets of rock, a process called exfoliation. B) How are joints expressed in the landscape - less jointed areas are more resistant to weathering. Spacing of joits along with rck type determine how fast a rock will weather and which parts will be most easily eroded. Other process that loosen rocks-When water in a fracture freezes, it expands 8% and exerts a strong outward-directed force on the walls of the fracture. This process of frost wedging C) How Fracturing a rock effects weathering -surface of a cube: if fractures the surface area of 2 by 2 cube is 24. Fracturing of a cube into many pieces 1 by 1 and 1 by 6 ect total area 48. Therefore fracturing has s doubled the exposed surface area, providing more surfaces where weathering can operate. The rock will therefore weather faster. HOW DOES CHEMICAL PROCESS‘ AFFECT ROCKS -CHEMICAL WEATHERING alters and decomposes rocks and minerals, principally through chemical reactions involving water. When chemical and physical weathering processes combine to break down and alter rocks, they produce minerals that are more stable in surface conditions than the original minerals. They transform rocks into clay, sand, and other materials. A) changing a rocks enviroment promotes weathering - Minerals that crystallize in high-temperature magmas are generally unstable when subjected to the low-temperature conditions that characterize Earth‘s surface. Most magma temperatures are above 700°C, whereas surface temperatures range from minus 40°C to plus 45°C (minus 40°F to plus 122°F). -Liquid water is more abundant on and near Earth‘s surface than at depth. Water, especially when it is slightly acidic, is a chemically active substance that can break the bonds in many minerals. It increases the rate of chemical weathering. -During metamorphism, some minerals crystallize beneath the surface in dry, high-pressure and high-temperature environments. Once such rocks reach Earth‘s low-pressure and low-temperature surface, they can change to different minerals that are stable at the new, wetter, low- pressure and low-temperature conditions. -Oxygen (O2) is abundant in the atmosphere and as a dissolved component in rain and most surface water. This oxygen chemically reacts with rocks, causing some minerals to oxidize (rust). B) DISSOLUTION - The main agents for chemical weathering are water and weak acids formed in water, such as carbonic acid (H2CO3). These agents dissolve some rocks, loosen mineral grains, form clay minerals, and widen fractures. - pit depends, widens as fractures widen flow and dissolve material from wales - Limestone (below) and other rocks rich in calcium carbonate or magnesium carbonate are soluble in water and in acids. They dissolve and form pits and cavities. C) OXIDIZATION - oxygen is common near Earth‘s surface and reacts with some minerals to change the oxidation state of an ion. This is common in iron-bearing minerals because iron (Fe) has several oxidation states. -Many mafic igneous rocks contain dark, iron-bearing minerals, such as pyroxene. Iron in pyroxene can become oxidized, producing iron oxide minerals. -If iron-bearing rocks become oxidized, they generally take on a red color from the iron oxide mineral hematite. Reddish rocks can lose their reddish color if they interact with fluids that have less oxygen D) Hydrolysis - When some minerals react with water they undergo a chemical reaction where the mineral combines with water to form a new mineral. This reaction, called hydrolysis, converts some minerals to clay. - One kind of feldspar, containing potassium (K), is called K-feldspar. When this mineral reacts with acids (waters that have free H+ ions), it can be converted into clay minerals by hydrolysis - If exposed to wet conditions, many rocks convert into clay minerals. The gray limestone shown here contained impurities that weathered into clay minerals and reddish hematite that accumulated between the blocks. 15.4 WHAT FACTORS INFLUENCE WEATHERING A) How does the character of a rock influence weathering? -Composition — Weathering of a rock is influenced by the types of minerals it contains. Most sandstone, like the one in this cliff, consists largely of quartz, a mineral that is very stable on Earth‘s surface; it mostly weathers by physical processes. In contrast, the recesses below the cliff contain fine-grained sedimentary rocks that are more easily weathered and eroded. - Variation in Composition — Some outcrops have different parts with large contrasts in susceptibility to weathering. The more susceptible parts will weather faster than the more resistant parts. Such differential weathering can form alternating ledges and slopes, as shown here, or rocks with holes where less resistant material has been removed. - Discontinuities — Fractures, bedding planes, and other discontinuities provide path-ways for the entry of water into a rock body. A rock with lots of these features will weather more rapidly than a massive rock containing few such discontinuities. For example, highly fractured parts of a cliff weather faster than less fractured parts. Rocks with thin layers generally break apart and weather more readily than rocks with thick layers. - Surface Area — Rock that is already broken into small pieces, such as these loose pieces, provides more surface area on which chemical weathering can act. Solid, unfractured bedrock provides less surface area and weathers more slowly. WHAT IS THE DEPISITIONAL ENVIROMENT FOR CLASTS? CARBONATE? 1) Sedimentary Environments of Deposition Following is a brief guide to the properties of sedimentary rocks deposited within various sedimentary environments. For photographs and sketches, refer to your text book or the web. Continental Environments- predominantly siliciclastic sediments (conglomerate, sandstone, siltstone, etc.) characterized by scarce fossils and no marine fossils. Fluvial (rivers) Alluvial Fans - deposits that form at the base of mountains where rapidly flowing streams suddenly emerge from a narrow valley, spread our, slow down, and dump the larger particles in their sediment load. They are poorly sorted and clasts are frequently angular. The composition of the fragments is similar to the rocks exposed in the nearby mountains. Sedimentary structures are not well developed and fossils are very rare. Braided Rivers - characterized by many channels separated by bars or small islands. Braiding results from rapid, large fluctuations in the volume of river water, and an abundance of coarse sediment. There are two main types of braided river facies: 1) rippled, cross-stratified gravels and coarse sandstones (bars) and 2) horizontally stratified, fine to coarse sands (channels). In a vertical section through an ancient braided river these will tend to alternate. Meandering Rivers - confined to one, highly sinuous channel, and contain finer sediment load than braided rivers. Meandering rivers also form bars, but they are formed on the inside bend of meander loops. As a result these bars build outward, the streams become more and more sinuous and migrate across the river basin. There are two main types of meandering river facies: 1) rippled, cross-bedded, fining-upward sequences of gravel and sand (bars) and 2) fine-grained sediments, such as silt and clay, containing burrows and plant debris (overbank or flood deposits). In a vertical section through an ancient meandering system, these will tend to alternate. A. Lacustrine (lakes) - difficult to characterize. They may contain numerous sedimentary structures, including cross-bedding, ripples, graded beds, footprints, mudcracks, and raindrop impressions. Fossils may be common. Plant fossils and freshwater bivalves and gastropods are particularly abundant. B. Paludal (swamps and marshes) - organic-rich shale and sandstone or coal deposits with thin stringers of silstone and shale. Plant fossils are common in all stages of preservation. C. Eolian (deserts and near beaches) - recognized by dune deposits, although the dominant sedimentary layering that is preserved is horizontal. D. Glacial - range in size from small bodies deposited by valley glaciers (alpine glaciers) to large sheets dumped from continental glaciers. Characterized by a variety of facies, but the most unique is diamictites, or pebbly mudstones Transitional to Shallow Marine Environments Deltas - form where rivers enter a standing body of water, slow down, and deposit more sediment than can be removed by waves and currents. Although deltas also from in lakes, the largest deltas occur in the oceans. Deltas are composed of several sub-environments, from the fluvial delta-top to the submarine base of the delta. Accordingly there are numerous types of fossils and sedimentary structures possible. Ancient delta deposits are most easily recognized by the larger package. Because of their formation process, there is a lateral gradation in particle size (and sedimentary rock type) along the delta, from sand near the river outlet to submarine clay deposits at the edges. As more sediment is added, the delta builds out into the standing body of water, with coarser sediments migrating across the clays that used to be at the delta edges. This results in a coarsening upward (regressive) sequence. Beaches and Barrier Islands - long, narrow accumulations of sand parallel to the shoreline. Barrier islands are separated from land by a shallow lagoon or marsh. Beach facies are composed primarily of fine- to medium-grained, well-sorted sand that displays subhorizontal parallel laminations and low-angle, seaward-, landward- and alongshore-dipping crossbeds. The variously dipping crossbeds are a result of the back-and-forth action of tides and longshore currents. Burrows are common in sediments of the transition zone between the beach and open shelf. Clastic shelf - bounded by coastal environments on the landward side and by the continental slope on the seaward side. Sediments consist mainly of sand and mud, and nearshore sands commonly grade seaward through a transition zone of mixed sand and mud to deeper-water muds. Cross bedding is common in the sands and bioturbation is common in the muds. Carbonate shelves and platforms - located primarily at low latitudes in clear, shallow, tropical seas where little continental, clastic sediment is introduced. 2) Phys/chemical weathering 3) 7.4 WHAT ARE THE CHARACTERISTICS OF CLASTIC SEDIMENTS SEDIMENT CONSISTS OF LOOSE FRAGMENTS of rocks and minerals, or clasts . When clastic sediment becomes sedimentary rock, the name assigned to the rock depends on the size and shape of the clasts. Other characteristics of the clasts, such as sorting of clasts, can be used to further describe the resulting rock. A. How classified: **SIZE of clasts: Boulders, cobbles, pebbles, sand, silt, clay (clay plus silt is mud) Shapes: Rounded (smooth travel far), angular shape with edges, angular (sharp corners/edges) Sphercity: spherical(circle) to tabular (rectangle) Size of particle: coarse( bigger) to fine (small interior) Sorting of particle: well sorted to poorly sorted B. What controls the size, shape, sorting class Once they are eroded from bedrock CLASTIC: sediments are moved and deposited by WATER, WIND AND GLACIER. - Steepness of Slope — Steep slopes, such as the one shown here, commonly have clasts that are larger, more angular, and more poorly sorted than the clasts observed on gentle (less steep) slopes - Strength of Current — Strong, turbulent river currents and ocean waves can move large clasts, such as these meter-wide boulders, but slow, less turbulent currents move only fine-grained sediment - Sediment Supply — A river, beach, or other agent of transport can only move the sediment that is available. Bedrock on this beach provides large boulders that must be worn down into smaller clasts. - Agents of Transport — Wind can carry only sand and finer particles, but rivers, glaciers, mudflows, and other agents of transport can pick up and carry large clasts. These dunes consist of nothing but well- sorted sand because wind cannot bring larger clasts to the area, and smaller material is blown away 7.5 What type of rocks do clastic form - clastic sediments named by size clay silt sand pebbles cobbles boulders - clastic sedimentary rocks are also named by grainsize: mudstone/shale sandstone conglomerate gravel sized clast: conglomerate, breccia. Sand sized: better defined layers, sandsone has quartz, graywacks. Mud sized: siltsone has silt sized particles and shale loose sediments -- show structures (ex. ripples ==> how/where sediment was deposited) -- need to be lithified (=made into rock) by weight of overlying sediments and cementation 7.5 How do clastic sediments become clastic sedimentary rocks 1. compaction: As sediment is buried beneath more sediment or other materials, increasing pressure pushes clasts together, a process called compaction. Compaction forces out excess water and causes sediments to lose as much as 40% of their volume, sometimes more. Originally loose sediment becomes more dense and more compact. 2. Cementation: Even after sediment is compacted, adjacent clasts do not fit together perfectly, and some openings remain. These pore spaces are commonly filled with water containing dissolved materials. The dissolved materials can precipitate to form minerals that act as a natural cement that holds the pieces of sediment together.  When sand grains and other sediment are deposited, and even after they are compacted, abundant pore spaces exist between the grains. These spaces are typically interconnected, which allows water to flow slowly through the sediment, carrying chemical components into or out of the sediment  As the sediment is buried, minerals can precipitate from water moving through the pore spaces, coating the surfaces of the grains, sticking them together. Miner-als that form in pore spaces, cements, decrease the amount of pore space, bind the grains together, and turn the sediment into hard sedimentary rock. 7.7 texture of clastic rocks - under microscope: ex sandstone shows rounded grains with cement in between ** know these =clastic sedimentary rocks conglomerate: gravel sized clasts has rounded pebbles, cobbles, or boul-ders with sand and other fine sediment between the large clasts. This conglomerate has well-rounded cobbles in a matrix of mostly quartz sand. What are the characteristics of coglomerate and where does it form? Clast size: Some have large clasts- characteristically pebbles, cobbles, or even boulders. The large clasts rest in a matrix of sand and mud; they are well rounded in some conglomerates and only partially rounded in others, like the one shown here. Some have finer grains- having few clasts larger than a centimeter or two. Such conglomerate represents less turbulent conditions, a source region that lacked large clasts, extreme abrasion of clasts during long transport, or some combination of these factors. Sorting: is mostly clasts with relatively little matrix. In the conglomerate in this photograph, many clasts rest directly on other clasts, instead of being completely separated by the sandy matrix. Less well sorted- containing scattered large clasts in a fine-grained matrix. The cobbles and pebbles shown here are surrounded by a matrix of mostly sand Environments of Formation- river or stream: form from sediment deposited near river/stream. clasts c
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