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100 ES Midterm 2 Study Guide. Dr. Sherilyn Williams-Stroud 15 November, 2004 Attached are the quizzes on chapters 9-12, and an answer key. Make sure you understand the concepts represented in the quiz multiple choice questions. To prepare for the material in chapter 13, review the graded quiz you took on line for that chapter. Make sure you also understand how to apply relative dating to a deformed structure using bedding, faulting and cross-cutting relationships. Understand the different types of mass wasting the difference between slides and flows, and the speeds at which the different types of mass movements travel downhill Understand the relationships between the ages of beds in the middle of an anticline or syncline with the ages of the beds on the flanks of each of those structures. Be able to draw a cross section of an anticline or syncline. Read and understand the textbook section in chapter 13 dedicated to the Ogallala Aquifer. Understand what causes groundwater tables to drop and not recover, what is porosity and permeability, and what is recharge. If you want even more to study, I have also attached my lecture notes (the ones I typed I don't have type-up lecture notes for chapter 12) for chapters 9-13. Name: __________________________ Date: _____________ 1. A) B) C) D) Marble is a metamorphic rock that forms from __________? granite limestone sandstone shale 2. A) B) C) D) What is metasomatism? a change in the bulk composition of a rock during metamorphism metamorphism caused by circulation fluids heated by nearby magmatic intrusions metamorphism caused by tectonic movements along faults the parallel alignment of minerals in a metamorphic rock 3. What type of metamorphism is caused by high temperature and high pressure imposed over a large volume of crust? A) burial B) contact C) regional D) shock 4. A) B) C) D) What type of metamorphism is caused by igneous intrusions? burial metamorphism contact metamorphism regional metamorphism shock metamorphism 5. A) B) C) D) Which of the following statements regarding radiometric dating is true? After two half-lives, no radioactive atoms remain. Carbon-14 cannot be used to date material more than 100,000 years old. Sedimentary rocks can be dated more easily than igneous rocks. The radioactive decay product is called the parent atom. 6. A) B) C) D) Radiometric dating is least useful for dating __________ rocks. basaltic granitic metamorphic sedimentary 7. A) B) C) D) Radiometric dating is possible if a rock contains a measurable amount of ___________. daughter atoms parent atoms both daughter and parent atoms either daughter or parent atoms 8. A) B) C) D) The parallel alignment of mica in a metamorphic rock is an example of ______. bedding foliation metasomatism porphyroblasts 9. Which of the following sequences describes the metamorphic changes in a shale with increasing metamorphic grade? A) schist gneiss slate B) gneiss slate schist C) slate schist gneiss D) gneiss schist slate 10. Light-colored rocks with coarse bands of segregated light and dark minerals are called ______. A) gneisses B) quartzites C) schists D) slates 11. A) B) C) D) Which of the following metamorphic rocks is always foliated? hornfels marbles quartzites schists 12. A) B) C) D) What is a porphyroblast? a common type of copper ore deposit an igneous rock with two distinct crystal sizes a relatively large metamorphic mineral a strongly foliated metamorphic rock 13. A) B) C) D) The principle of superposition states that __________. a fault is younger than the rocks it cuts sediments are deposited as essentially horizontal layers the present is the key to the past undisturbed sedimentary layers get progressively younger from bottom to top 14. A) B) C) D) Who proposed the theory of evolution? Leonardo da Vinci Charles Darwin William Smith Alfred Wegener The following questions refer to the geologic cross section below. Units A, B, C, D, E, and F are sedimentary rocks. Unit G is a granite. 15. A) B) C) D) The horizontal line labeled X-X' is a(n) ______. angular unconformity contour cross bed fault 16. A) B) C) D) Which of the following units is the youngest? unit A unit B unit C unit F 17. A) B) C) D) Which of the following statements is true? Deposition of unit A occurred before deposition of unit B. Erosion took place prior to deposition of unit B. Unit C is younger than unit A. The granite is older than unit F. 18. Which of the following is used by geologists to determine the relative ages in a rock sequence? A) cross-cutting relations B) fossils C) stratigraphy D) all of the above 19. Which of the following is an erosion surface that separates two sets of sedimentary layers with non-parallel bedding planes? A) angular unconformity B) cross bed C) disconformity D) nonconformity 20. A) B) C) D) Which of the following materials might be dated using carbon-14? granite iron ore sandstone wood 21. A) B) C) D) Which of the following is the best statement of the principle of original horizontality? Igneous intrusions form horizontal layers. Metamorphic isograds are horizontal before deformation. Sediments are deposited as horizontal layers. Most igneous, metamorphic, and sedimentary rocks in the Earth's crust form horizontal layers. Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. B B C B B D C B C A D C D B A A B D A D C Name: __________________________ Date: _____________ 1. A) B) C) D) The dip of a unit represents the ___________. angle at which the bed inclines from the horizontal direction of intersection of the rock layer and a horizontal surface part of the unit that has been eroded tilt of the rock unit before deformation 2. Which of the following types of tectonic forces tends to squeeze and shorten a rock body? A) compressive forces B) shearing forces C) tensional forces D) all of the above 3. A) B) C) D) What type of forces dominate at convergent plate margins? compressive forces shearing forces tensional forces torsional forces 4. A) B) C) D) What type of fault is depicted in the cross section above? left-lateral strike-slip fault normal fault reverse fault right-lateral strike-slip fault 5. A) B) C) D) The San Andreas Fault is a result of what type of forces? compressive forces shearing forces tensional forces all of the above 6. What is the scientific term for a crack along which no appreciable movement has occurred? A) axis B) fault C) fold D) joint 7. What type of fault is characterized by the rocks above the fault plane moving downward, relative to the rocks below the fault plane? A) a normal fault B) a reverse fault C) a strike-slip fault D) all of the above 8. A) B) C) D) Which of the following types of tectonic forces causes faulting? compressive forces shear forces tensional forces all of the above 9. A) B) C) D) An overturned fold is characterized by two limbs _________. at right angles to one another dipping in the same direction, with one limb tilted beyond vertical dipping steeply in opposite directions dipping gently in opposite directions 10. A) B) C) D) What is a thrust fault? a low-angle normal fault a low-angle oblique fault a low-angle reverse fault a low-angle strike-slip fault 11. If sedimentary rocks on a geologic map form a zigzag pattern, the underlying structure probably consists of __________. A) domes and basins B) horizontal anticlines and synclines C) intersecting joint sets D) plunging anticlines and synclines 12. A) B) C) D) Which of the following forces is the dominant cause of mass movement? gravity seismic energy tidal force wind 13. A) B) C) D) Which of the following is not an important factor in causing mass movements? amount of water in materials nature of slope materials steepness and instability of slopes temperature of slope materials 14. A) B) C) D) Which of the following statements is true? Fine sand forms steeper slopes than coarse sand. Angular pebbles form steeper slopes than coarse sand. Water-saturated sand forms steeper slopes than dry sand. Dry debris forms steeper slopes than damp debris. 15. A) B) C) D) The angle of repose does not depend upon which of the following? particle composition particle shape particle size water content 16. A) B) C) D) Which of the following situations is most likely to undergo mass wasting? a dry, moderate slope of unconsolidated material a wet, moderate slope of unconsolidated material a dry, steep slope of unconsolidated material a wet, steep slope of unconsolidated material 17. A) B) C) D) Surface tension is greatest when sand is __________. dry damp, but not saturated with water saturated with water oversaturated with water ? 18. The illustration above depicts a cross section through a pile of quartz sand. The angle depicted in the diagram is called the __________. A) angle of repose B) bedding angle C) cleavage angle D) dip 19. A) B) C) D) Which of the following has the steepest angle of repose? angular quartz pebbles coarse quartz sand fine quartz sand All of the above have the same angle of repose. 20. A) B) C) D) Which of the following would be most likely to undergo liquefaction? granite talus slope unconsolidated soil water-saturated sand Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. A A A B B D A D B C D A D B A D B A A D Rock Deformation Most common forms: Folding and Faulting Folds and faults are the "structures" that structural geologists use to interpret deformation history of the rocks Slide 2 We can see pieces of these structures in outcrops. An outcrop is an exposure of rock that is not covered by soil or rock rubble Often, an entire structure is not visibleIt could be eroded, and/or most of it is below the surface. Geologists can see a piece of a structure at the surface, and figure out what the entire structure must look like by measuring the orientations of the beds that form the folds. If the entire fold is not visible, for instance, then you can measure the orientation of dipping beds that are part of the fold. Slide 3 The orientation of a dipping bed is given by two measurements: Strike Dip Strike is the direction of a line in the plane that is horizontal Dip is _|_ to that line, and is in the direction of maximum dip. The magnitude of the dip is angle that the plane makes with a horizontal plane, measured down from horizontal Slide 4 You can think of strike as the roof line of a house, And dip is the slope of the sides of the roof. If water runs down the roof, it makes a line parallel to the dip. The two measurements are always 90 degrees apart. Slide 5 Nice example an of outcrop where you can see only a part of the structure, a fold. Dip and strike of the beds are readily apparent. The kids are walking parallel to the strike. The dip of the beds is to the left of the picture (their right side) Slide 6 When rocks deform, they can be ductile or brittle If they are ductile they bend (or stretch) into a different shape Folds are formed by ductile rock behavoir Slide 7 If they are brittle they break. When rocks break, they can form joints or faults. Slide 8 Joints are breaks in the rock where rocks on either side of the break have not moved relative to each other. (Remember joints from the hoodoo assignment) These joints are much closer together than the joints in the hoodoos, and the rock type is different Slide 9 A fault forms when the rock on either side of the break moves relative to the other side, parallel to the fault surface. Since the fault is usually a planar surface, you can also measure the strike and dip of a fault plane. Slide 10 The type of fault is given by the sense of movement of the beds along the fault plane When the rocks above the fault plane move down w.r.t. the rocks below the fault plane, it's a normal fault Slide 11 Younger beds move DOWN relative to older beds. Slide 12 This is also called a dip-slip type of fault, because the slip on the fault plane in is the same direction as the dip of the fault plane Slide 13 The tectonic stresses that cause these kinds of faults are extensional So this type of fault would be common in a divergent plate boundary setting an example is the Red Sea rift between the African and Arabian plates. Slide 14 Satellite picture of the real thing Slide 15 When rocks above the fault plane move up w.r.t. the rocks below the fault plane, it's a reverse fault. Slide 16 Younger beds move UP relative to older beds. The tectonic stresses that cause these kinds of faults are compressive Slide 17 If the fault plane dips less than 45 degrees, it's called a thrust fault Where would these types of faults be common? Slide 18 Thrust and reverse faults are common in convergent plate boundaries. Sometimes the slip on the faults is 10s of kilometers, putting younger rocks on top of older rocks over a relatively large area. - Keystone thrust sheet in Southern Nevada. Slide 20 If the slip on the fault is horizontal, it's called a strike-slip fault If you are standing on one side of the fault, and the beds move to your left relative to your side, it's a left lateral fault. Slide 21 If you are standing on one side of the fault, and the beds move to your right relative to your side, it's a right lateral fault. Slide 22 What kind of plate boundary is the location for these kinds of faults? Strike slip faults are caused by tectonic shear stresses. Shear stress is common at transform plate boundaries San Andreas Fault river is offset across the fault Slide 23 A more general case is where the faults have a component of dip slip AND strike slip movement. This is called oblique slip. Slide 24 We characterize folds by identifying different parts of a fold: Fold limbs Fold axial plane Fold axis If the fold axis is not horizontal, the fold is plunging Slide 25 If the axial planes of folds are vertical, then they are symmetrical folds Slide 26 If the axial planes are not vertical, then they are asymmetrical folds Slide 27 Outcrop of asymmetrical folds Slide 28 and slide 29 If both limbs of the fold are dipping the same way, the folds are overturned Slide 29 and 30 Why would we call these folds overturned? - the dip of one of the limbs has gone past vertical in the deformation, - and one of the limbs has younger beds below older beds. Slide 31 When the limbs dip down from the axis, the fold is called an anticline When the limbs dip up from the axis, the fold is called a syncline How folds are expressed in outcrop depends on the way that they weather. What features do the resistant types of rock form? Valleys will form where the more easily eroded layers are. Slide 32 The Appalachian Mountains form distinctive valleys and ridges. These are old mountains that have under gone a lot of erosion Slide 33 You see different rocks in the middle of synclines and anticlines that form the valleys and ridges Younger rocks are in the middle of the synclines Older rocks are in the middle of the anticlines Slide 34 Air photo - You can see the places where the folds plunge. Slide 35 You can draw a cross section using those age relationships, which shows where the older and younger rocks are. Youngest rocks here are Carboniferous (aged >300 ma) Slide 36 If the fold plunges in all directions, it's a dome. Domes can form when some kind of ductile buoyant rock pushes up the layers from below (like a magma, or a salt) draw it Or Domes can form when a fold forms from one compression even, and then is deformed from another compression event at right angles to the first. Draw it Slide 37 Air photo of a dome in Wyoming If the beds are dipping down toward the middle, it's a basin Where would the youngest beds be? Slide 38 Folds can be really bigWavelength of these folds is 1 km (northwest Canada) Slide 39 What are the relative ages of these structures? 1. folded bed 2. thrust fault 3. erosional surface 4. lava 5. normal faults Slide 40 Block diagrams showing development of structures. A geologist would look at the last one and piece together the history of what happened. ____________________________________________________ Hydrology the study of water. Like Geology the study of the earth SLIDE 2 When reading the chapter, you found out that by far, most of the water on the earth is the salt water of the oceans, about 96%. After that, the majority of the total volume fresh water is not usable, because it's locked up in glaciers and polar ice (about 3% of the total water on the earth) Of the water that we can use, most of it comes from groundwater (only 1% of the total). All that water that we see as rain water, and in rivers and lakes only comprises 0.001% of the total. SLIDE 3 All the water on earth moves from one reservoir to another (the ocean, the atmosphere, the land), which defines the hydrologic cycle. The processes are: evaporation, precipitation, runoff. SLIDE 4 Climate locally influences the hydrologic cycle. In warm climates, the air can hold more water, and so has a higher relative humidity. If there is a mountain range near where warm moist air is blown onshore, it rises over the mountains, gets cool, and then the water droplets condense, and rain falls. This precipitation leaves less moisture in the air as it passes over the mountain range, so arid climates are developed on the other side of the mountain from the ocean. This is the rainshadow effect. SLIDE 5 One of the processes (again) in the hydrologic cycle is runoff. Runoff occurs when the ground is saturated, and water cannot percolate into it. On these maps, high precipitation correlates with high runoff. SLIDE 6 So the runoff can change seasonally, or year to year. Streams discharge a lot of water during wet periods, and wetlands and swamps are full of water. During wet periods, the ground and the rock can be saturated with water SLIDE 7 The useable freshwater that is found in the ground is found in rocks that have a high porosity. Porosity is the volume of the pore space between the grains in a rock. Sedimentary rocks can have a high porosity if they are coarse grained and well sorted. Poorly sorted rocks have lower porosity because the pore spaces are filled up with little grains. Cementation lowers porosity because cement fills the pores. Fine-grained rocks have very small holes. Why might crystalline rocks, like granite, have a low porosity? SLIDE 8 Another property of rock related to the pore spaces and the grain size and sorting is the permeability. Permeability is a measure of how easily a fluid can flow through the pore spaces in a rock. There's usually a relationship between porosity and permeability, but permeability can be low even if porosity is high this is the case when the pore spaces are not connected to each other. Vesicular basalt is one example where this is the case. SLIDE 9 A large rock body with good porosity and permeability is an aquifer. 2 types of aquifers: unconfined and confined. Unconfined has a saturated zone and an unsaturated zone with a groundwater table between. The level of that table is free to fluctuate up and down during dry and wet periods. SLIDE 10 A confined aquifer has impermeable rocks above and below. Because confined aquifers can't be recharged by percolation straight down into the ground from precipitation, they usually have some upland recharge area. SLIDE 11 There is no groundwater table associated with a confined aquifer, but it has a pressure surface. That is the average height of what would be the water table in the recharge area. If you drill a well into a confined aquifer, the water level will rise to the pressure zone, even if it is lower than that at the place where the well is drilled. If the top of the well is below the pressure surface, it flows freely, and is called an artesian well. SLIDE 12 An artesian spring would occur at a place below the pressure surface where water comes out of rocks. In this case, there is a perched water table, because saturated rocks sit on top of a non-permeable rock that we call an aquiclude. The perched water table is above the main water table. SLIDE 13 In and unconfined aquifer, if the water is pumped out, the water table develops a depression around the pumping well it forms because the groundwater water flow rate is not fast enough to fill the pore spaces back up when the water is extracted from the well. If you keep it up, you could eventually deplete the aquifer. SLIDE 14 This is happening in the Ogallala Aquifer in Texas and NM. The water table level has dropped by 30 feet (since?), mostly from pumping for agricultural irrigation. Even without pumping, because this area gets low rainfall, it would take several thousand years for the groundwater table to rise back up to its original position. SLIDE 15 Caves are a geologic feature caused by erosion of rocks by groundwater. They usually occur in limestones, and near the surface (carbon-dioxide rich water needs to infiltrate. Why? Carbon dioxide and water molecules combine to form carbonic acid, and limestone is soluble in acid.) The distinctive topography that forms above caves is called karst topography. SLIDE 16 Carlsbad Caverns. (who's been in a cave?) The formation from the ceiling are stalagtites, from the floor are stalagmites. Drip from above, drip to below... ... View Full Document

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