Geology EXAM 2 Study Guide
Geology EXAM 2 Study Guide 80176 - GEOL 1010 - 001
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80176 - GEOL 1010 - 001
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This 13 page Study Guide was uploaded by Ryan Jakszta on Sunday February 21, 2016. The Study Guide belongs to 80176 - GEOL 1010 - 001 at Clemson University taught by Alan B Coulson in Fall 2015. Since its upload, it has received 189 views. For similar materials see Physical Geology in Environmental Science at Clemson University.
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Date Created: 02/21/16
GEOL 1010 Dr. Coulson TEST 2 STUDY GUIDE Highlight= Important Principle Highligh= Key Term Lecture 5: S edimentary Rocks and Processes Forming Sedimentary Rocks sedimentary rocks are the most common on on earth’s surface used in construction, in energy resources, where fossils are found Parent roc original rock/preexisting rock Formation 1. Weatherin breaking down rock a. physical weatheri physically breaking down rock i. ex: plant roots breaking up rock ii. frost wedgi water between cracks of rocks freezes in low temps and breaks apart rocks potholes can be a result of this b. chemical weatheri chemical reaction breaks down the rock i. more common in nature ii. ex: Feldspar + O + HCO₃ ➡Kaolinite + dissolved ions iii. ex: Saprolite formation 2. Erosio carrying of sediments (transport process) a. requires energy b. 4 ways of transportation i. water (very common) ii. gravity (rocks rolling down a hill) iii. wind (sand blowing at a beach) iv. glacier ice (less obvious, but still common) 3. Depositio depositing sediments in new place a. basi any place you can deposit sediment b. accommodation space volume of space for sediment to be deposited c. subsidenc sinking of land into a basin d. Layers (strata, beds) 4. Lithificatio getting sediments and compacting them into one rock a. cementation solidifying fusion of sediments by compacting the rocks together i. water gets pushed out and deposits wet minerals, which act as the cement to bind the rocks and minerals together Classification 3 main categories of sedimentary rocks 1. Detrital (aka clastic) sediment mainly physical weathering a. ‘how big are the sediments?’ b. sorting ‘how uniform is the sediment size’ (wellsorted, moderate, poorlysorted?) i. improves as time progresses c. rounding roundness of minerals within rock i. improves as time progresses 2. Chemical Sediment form via chemical reactions a. dissolution and reprecipitation b. saltwater evaporation c. usually comprised of one major mineral type i. ex: halite = rock salt, quartz=chert d. economically viable 3. Biogenic Sediments used to be parts of plants/animals a. ex: shells (large or microscopic), coral, etc b. ex: chalk, limestone, coal Mass Wasting (Landslides) important due to danger of occurrence angle of repose max angle where a slope is stable typically 35°, but always check! slope destabilization lack of moisture (only dry sediment leads to difficult in compactness) too much moisture lack of vegetation plant roots are good at holding things in place, so lack of them leads to lack of holding things in place excessive vegetation roots can also form natural pathways for water to run down, and plants are heavy and could fall/slide types of mass wasting (based on material, type of movement, and speed) ex: Rockslide rocks sliding down at a moderate speed creep slope is unstable, and rocks are sliding very slowly *NOTE: unstable slope does not automatically mean landslide* Causes of Mass wasting lightning, earthquakes, deforestation, etc. are all causes Risk Assessment Map assessment of an area that shows dangerous spots adjustments are constantly made: landslide patterns change constantly Prevention: Drainage Control decrease slope grades building codes retaining walls rock bolts COST: although all of these prevention measures could be costly, the amount of money in damage would cost much more Case Study: Thistle, UT 1983 slide cost $200 million in damage deemed preventable if $0.5 million had been spent on drainage system Lecture 6: Metamorphism and Structural Geology Why do we care? many minerals used for technology metamorphic rocks help discover history of an area very slow process (could take a million years to start) Temperature increase is needed for process Geothermal gradient how hot it gets and how fast beneath the earth at different depths average geo. gradient = 30°C/km typical range = 2060°C/km can still be higher or lower in special cases high gradient = hotter temp per km Metamorphism vs. Heat contact metamorphism rock coming into contact with hot magma ex: Plutons projectile driven by temp localized/small scale Pressure vs. Heat 1 bar = 1 atm (atmospheric pressure) Pressure gradient is about 300 bar/km confining pressure pressure on all sides of object, even distribution ex: swimming under water directed pressure (differentia) pressure coming from mostly one direction most metamorphic rocks form at 1030 km (midlower crust) = 6.25 18.75 miles How metamorphic rocks get to surface as layers get pushed up through plate movements/faults, they soon get weathered/ eroded and make it to the surface regional metamorphism opposite of contact metamorphism at convergent plate boundaries pressure driven large scale fault metamorphism faults occur and form metamorphic rocks small scale, pressure driven Metamorphism vs. Fluid metasomatism hot groundwater interacts with rock water carries things in it and could deposit some things into rocks forms ores seafloor metamorphism close to MidOcean Ridge like metasomatism, but in specific area (MOR) Metamorphic Rocks and Environments Parent rock is the key to figuring out which metamorphic rock forms Metamorphic grade how much did the rock change lowgrade = low change, high grade= high change not very specific; there is a lot of variation in each field index minerals gives range of temps/pressures for rocks smaller range the better metamorphic facies group of index minerals that form under similar conditions ex: blueschist facies include minerals epidote, lawsonite, and glaucophane major facies : a. zeolite lowest temp/pressure b. Hornfels high temp increase but low pressure increase c. Blueschist high pressure but low temp increase (subduction zones) low temp due to coldness of oceanic plate submerging d. Eclogite very high pressure e. Granulite starting to melt again *NOTE: diogenesis = before facies start (NOT metamorphic rock)* Length of Metamorphism large range Prograde portion of history when rock had increase in temp/pressure retrograde temp/pressure of rock began decreasing changes within minerals Types of Metamorphic rocks 1. Foliated Metamorphic rocks sheets/layered appearance a. ex: slate, schist, gneiss (gneiss has felsic/mafic separation) i. not obvious: can come from different parent rocks, crystals can cover up sheets, etc. 2. NonFoliated Rocks opposite of Foliated a. difference from foliated is from type of pressure (confining is nonfoliated, directed is foliated) i. ex: Hornfels, Quartzite, Marble **know examples of Hornfels, blueschist, nonfoliated, and foliated** **Geology in the News: ‘Sudden’ volcanic eruptions found to trigger from gas bubbles in magma Structural Geology/Tectonic Forces Structural geology study of how rocks are deformed after they are formed Topographic features on surface of earth (on maps); landscape Tectonic forces (how rocks are formed) 1. Tensional stretching object (pulling in different directions) a. ex: divergent boundaries 2. Compressional squeezing in form multiple sides a. ex: convergent boundaries 3. Shearing sliding in 2 different directions a. ex: transform boundaries Responses: 1. Brittle strong/ resistant rocks shatter into random pieces 2. Ductile rock can bend and is malleable Responses vary based on: rock type temp/pressure speed of deformation quicker applying of deformation means more likely to have brittle reaction, while slower = ductile Types of Structures 1. Folds ductile response to compressional force happens on low/high scales typically happens in groups limb sections of fold with pretty straight portions hinge where rocks pivot/turn into curvy edges in a fold classifying folds (3) 1. shape crosssectional view (aka ‘roadcut’, ‘cliffface’) a. antiform rainbow shape b. synform ushape c. overturned : i. overturned antiform ii. overturned synform iii. overturned overturned antiform overturned overturned synform 2. Age of layers relative to each other acticline oldest layers is in between layers (center) syncline oldest layer on outside part of fold *NOTE : sometimes tectonic forces can cause an entire stack of layers to be turned upside down 3. Geometry how force was applied must be seen from above and second crosssectional views horizontal force applied from two sides above view horizontal stripes side view folds/layers plunging force applied from two sides and force applied to cause tipping up or down more common in world visible in above view, NOT in crosssectional 2. Joints brittle response and no other forces lots of cracks (called ‘joints’) most common geological structure 3. Faults brittle response with movement along cracks motion is relative varies in sizes (1 inch to 1000s of miles) classified by slip direction 1. DipSlip faults vertical motion inclined fault plane: one side clearly moves upward foot wall plane that has acute angle hanging wall plane that has obtuse angle Normal dipslip hanging moved down and foot moved up reverse dipslip hanging moved up and foot moved down Thrust fault handing goes up and foot goes down only difference between thrust and reverse: thrust is almost horizontal important in subduction zones **STUDY TIP: Don’t just memorize the pictures! You MUST identify hanging vs. foot walls to determine if it is normal or reverse 2. StrikeSlip fault horizontal movement no hanging/foot faults leftlater relative to each other, each block has moved to the left rightlatera relative to each other, each block has moved to the right **make sure that you know the orientation (birdseye view, crosssectional, etc)** **notice that different fault types form based on forces applied* Lecture 7: Earthquakes **Geology in the News: 6.4 magnitude earthquake in Taiwan caused the cancellation of Chinese New Year Why do we care? Can cause a lot of damage and loss of lives we can try to prevent What is an earthquake? when two plates move past each other, energy builds up Time 1: Stress<Friction Plates Stationary Time 2: Stress~Friction Elastic Deformation Time 3: Stress>Friction Plates move energy builds and process repeats itself small quakes are very common 1 million magnitude 2 quakes per year category 9 energy = annual energy used in USA Point of Movement focus where movement originates (many are 220 km deep) epicenter point directly above the focus on the surface Movements before and after foreshocks small movements prior to the earthquake in an attempt to relieve energy aftershocks small but bigger than foreshocks not all energy has been released in main quake Seismic Waves waves moving away from focus (3 types) 1. P (Primary) compressional motion through earth’s surface a. alternating compression/expansion b. 20 times faster than speed of sound c. can move through solid/liquid 2. S (Shear) a. added vertical range of motion b. cannot move through liquids c. half the speed of Pwaves d. forms shadow zone through earth 3. L (Long, Surface) move along the surface a. slowest b. moves in vertical/horizontal range Measurement and Detection seismometer aka seismograph (outdated) Myths: 1. You only need one machine a. you need 3: one for each axis 2. Old fashioned a. data is almost all digital today 3. Swinging needles for amplitude a. needle is on a pendulum and machine shakes (outdated) data xaxis travel time in minutes yaxis amplitude for all axes of movements p waves come first, then s, then a long period of L key to finding focus is different that different waves travel at different speeds distance = difference between p and s times draw circles with radius of this distance to triangulate focus How big was the earthquake? 1. Mercalli Index lower Roman numerals/little damage a. based on damage to environment b. not commonly used with scientists c. for the same quake, the index will be different per location 2. Richter Scale measures amount of shaking at various seismometer stations a. designed by Charles Richter in 1935 b. logarithmic scale i. ex: a magnitude 3 is 10x a magnitude 2 c. moving between numbers is a big deal 3. Movement magnitude measures amount of slip on the fault a. easiest to calculate from field measurements/seismometer data b. scientists prefer Earthquake Locations much deeper foci occur along subduction zones Blueschist facies has very brittle behavior, creating huge earthquakes in these zones Risk assessment maps made to indicate change of quakes Predicting quakes is nearly impossible Damage control land use policies ex: California Law (1972) ‘do not build on faults’ building codes Not building skyscrapers near fault zones myth: Earth cracks open and swallows things These are actually the best locations to build Site selection: building on strong foundation like bedrock is the best Gravels, sands and muds are worst choices liquificatio liquid inside unstable foundations lead to sinking and tipping buildings Lecture 8: Geologic Time **Geology in the News: Tin cans collapsed between walls from Taiwan earthquake Why do we care? we want to know when certain things occurred 2 approaches 1. Relative sequence of events; qualitative a. not hard numbers; more like ‘this before this but after this’ 2. Absolute not comparative; gives exact numbers a. can be very expensive to pay for Research, while relative is nearly free b. can need highly qualified researchers/lab equipment c. not always necessary Relative Dating Fossils any evidence of past life on earth (skeleton, shells, footprints, etc) only really found in sedimentary rocks led tostratigraphy study of strata people wanted to know about fossils and the rocks they were found in unconformities strata is rarely in continuous line (gaps/breaks in strata timeline) why are there gaps? 1. run out of sediments 2. run out of accommodation space (basin) 3. start eroding sediment faster than deposition types of unconformities: classified by strata above/below gap 1. disconformity different kinds on top and bottom (both sedimentary 2. nonconformity sedimentary on one side and not sedimentary on other 3. angular rocks below are tilted at angle while on top is horizontal a. complicated formation problems with unconformities identification can be difficult to classify duration how much time was lost? Stratigraphic Principles 1. principle of original horizontally strata is originally horizontal 2. principle of superposition oldest layer on bottom, youngest on top 3. principle of crosscutting two things intersect/cut through each other a. whatever did the cutting is the youngest formation 4. principle of faunal succession fossils found in specific order a. older fossils are on bottom, younger on top b. correlation comparing strata in two areas by age i. not all fossils are good for correlation ii. want to identify short spans of time iii. index fossils aka guide fossils good for correlation 1. very numerous 2. widespread 3. went extinct quickly 4. easy to identify iv. other correlation tools 1. lithostratigraphy correlate layers by rock type a. good for generalizing, but has a lot of exceptions and errors 2. sequence stratigraphy correlation based on patterns of unconformities a. works well in coastal areas 3. chemostratigraphy correlation based on chemical properties a. ex: Iridium anomaly at CretaceousTertiary 4. magnetostratigraphy looks at magnetic current Geologic time scale originally built via stratigraphy fossils were key to defining boundaries eons largest units on scale (only 34 recognized) 1. Hadean when earth formed a. 4.54 Ga b. almost no material left on earth to study this 2. Archean 42.5 Ga a. when different parts of continent formed b. atmosphere had no oxygen 3. Proterozoic oxygen begins forming a. 2 Ga 4. Phanerozoic most fossils found here a. 3 eras i. Paleozoic (550 Ma 200 Ma) vertebrates 1. Cambrian Explosion large diversity change (much more) ii. Mesozoic reptiles 1. 200 Ma 65 Ma iii. Cenozoic mammals 1. 65 Ma now **Geology in the News: new info on why earthquakes occur deep in subduction zones water released from a mineral called lawsonite enables to fault to move despite high pressure Absolute Ages Quantitative Approach 1. NonRadiometric Approach a. varves sediment deposit alternating dark/light layers in lakes i. need top layer to freeze to become a varve ii. each band represents different seasons dark colors = winter light colors = spring/summer 1 light band + 1 dark band = 1 year iii. used to find/measure times and to discover climates iv. only gives climate data for specific location v. can’t have mixing layers (caused by living organisms) b. dendrochronology counting rings in a tree i. used on local scale ii. can only go so far back in time with one tree iii. can use overlapping to get further back in time iv. must know what kind of tree some trees don’t form annual rings v. rings may not show due to climate issues 2. Radiometric use of radiometric data for dating specimens isotopes atoms of same element but with different numbers of neutrons labeled by atomic weight (protons+neutrons) some isotopes are unstable Radioactive Decay emitting particles of energy to become stable Radiation the given off energy parent atom starting atom daughter atom atom given off decay series/chain multiple radioactive daughters decay series ends with a stable daughter atom how to measure radioactive decay: misconception watching atoms ‘pop’ no way to know when an atom will decay ex: bag of popcorn popping halflif time it takes half of parent atom to decay decay/halflife is NOT linear; it is exponential (hence ‘exponential decay’) daughter and parent atoms are equal, and add up to original amount of parent atoms every radioactive isotope has its own halflife wide range don’t change with any environmental factor Requirements for Radiometric dating : 1. radioactive isotopes must be present in specimen 2. measureable amounts of parent and daughter atoms a. no parent = we don’t know how long it’s been b. no daughter = we don’t know how long it will be 3. can only go so far back in time a. why? parent eventually runs out i. about 5 halflives is about as far as you can go 4. Closed system specimen is not changing with environment a. open system problems: i. add/lose daughter = looks like very little time has passed ii. add/lose parent = looks like a lot of time has passed Case Study: Carbon 14 carbon has 3 isotopes, only one is radioactive 14 14 C⟶ N + particle + energy halflife: 5.730 years can track through 10 halflives forming carbon 14: why haven’t we run out? more Carbon 14 is constantly produced in atmosphere global distribution can find everywhere on earth steady state amount created is balanced with amount decayed how do we know it works? start by testing what you already know the age of ex: mummies in Egypt what can we date with carbon 14? rocks are terrible for dating with carbon 14 fossils and organic material is very good Calculating age N f ln( N o) Age = −0.693 * (half − life) N f N o = % carbon 14 in sample relative to amount found in living tissue ex: Mammoth tusk has 17% Carbon 14 still present answer: 21,987 years Assumptions: 1. System remains closed after death a. not good assumption 2. amount of Carbon 14 in living tissue doesn’t vary through time first problem: Carbon 14 produced varies over time variations are small and on short timescales people don’t understand that Carbon 14 is constant (mostly) second problem: fossil fuel burning has changed the relative amount of the carbon isotopes in the atmospheres Limit of Carbon 14 dating: some organisms don’t get Carbon 14 from food chain ex: the Zombie Clams
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