Ch 6 Sedimentary and Metamorphic Rocks. End of Section Reviews

Transcription

1 Ch 6 Sedimentary and Metamorphic Rocks End of Section Reviews

2 Section 6.1 Formation of Sedimentary Rocks Pg #1-6

3 1. Describe how sediments are produced by weathering and erosion. Weathering is the physical or chemical process where rocks are broken down to form sediments. Physical weathering does not change the rock s composition. Chemical weathering does change the rock s composition Erosion is the process where forces such as water, wind, ice, or gravity transport sediments to some remote location.

4 2. Use a flowchart to show why sediments deposits tend to form layers Weathering (the break down of rock); leads to Erosion (the transport of sediments by water, wind, ice, or gravity); leads to Deposition (as the erosional force loses energy); leads to Periodic repetition of events form layers (due to seasons or weather); leads to Compaction (as layers bury and apply pressure to lower layers); leads to Cementation (as ground water deposits minerals to bind grains together) Lithification (the combination of cementation and compaction that results in the formation of sedimentary rock.)

5 3. Illustrate the formation of graded bedding.

6 4. Compare temperature and pressure conditions at Earth s surface and below Earth s surface, and relate them to the process of lithification. As depth increases, both temperature and pressure increase. Increasing pressure results in compaction, pushing sediments together, part of the lithification process. Increasing temperatures result in chemical reactions the result in deposition of minerals from ground water, effectively binding sediment together. This is cementation and is the second part of the lithification process.

7 5. Evaluate this statement: It is possible for a layer of rock to show both cross-bedding and graded bedding. It is a true statement. Graded bedding can form as large particles settle first during the formation of cross bedding. This may be seen in sand dunes or river sediments.

8 6. Determine whether you are walking upstream or downstream along a dry mountain stream if you notice that the shape of sediment is getting more angular as you continue walking. Explain. You are walking up stream since sediments are rounded as sharp edges are broken off during the erosion process. The farther the sediment is from its source the rounder and smoother it will be.

9 Section 6.2 Types of Sedimentary Rocks Pg #1-7

10 1. State the type of sedimentary rock that is formed from the weathering and erosion of rocks and sediment. Clastic Sedimentary Rock

11 2. Explain why coal is a biochemical sedimentary rock. Coal forms from the remains of once-living plant materials. Therefore it is organic.

12 3. Calculate the factor by which grain-size increases with each texture category. 32X --- 1/16 1/8 ¼ ½ X --- 1/256 1/128 1/64 1/32 1/16 The factor is a multiple of 2, 4, 8, or 16. Characterized by doubling.

13 4. Analyze the environmental conditions to explain why most chemical sedimentary rocks form mainly in areas that have high rates of evaporation. Areas with warm temperatures and arid conditions would result in high rates of evaporation and evaporite formation. These conditions exist in deserts.

14 5. Propose a scenario to explain how it is possible to form additional layers of evaporites in a body of seawater when the original amount of dissolved minerals in the water was enough to form only a thin evaporite. Water flowing into a shallow area would deposit a thin layer of evaporates. Periodic instances of new water flowing in would bring in new dissolved minerals to thicken the layers. Example 1: Fresh water flowing into the Great Salt Lake Example 2: Salt water flowing into a secluded tide pool during high tide and leaving minerals behind as the water evaporated.

15 6. Examine the layers of shale in Figure 6.11 and explain why shale contains no cross-bedding or ripple marks. Shale is composed of the Very Fine sediment particles with sizes ranging from 1/256 th to 1/16 th of one millimeter. In order to deposit, water must be stationary so that the particles settle out. If the water is not moving there can not be any ripple marks or crossbedding since these are only found as a result of moving water.

16 7. Assume that the volume of a layer of mud will decrease by 35 percent during deposition and compaction. If the original sediment layer is 30 cm thick, what will be the thickness of the shale layer after compaction? If the mud layer loses 35% of its thickness during compaction, the final thickness will be 65% of 30cm. 30cm X.65 = 19.5cm

17 Section 6.3 Metamorphic Rocks Pg #1-7

18 1. Summarize how temperature increases can cause metamorphism. Increases in temperature cause reorganization of atoms in the elements that make up the minerals. This results in the formation of new minerals or causes minerals to grow larger.

19 2. Summarize what causes foliated metamorphic textures to form. High pressure and temperature causes minerals with flat of linear crystals to grow with a preferred or unidirectional orientation. Increased pressure and temperature acting on rocks that have mixtures of light and dark minerals causing them to flatten and form layers.

20 3. Apply the concept of the rock cycle to explain how the three main types of rocks are classified. The three types of rock are classified by the processes by which they were formed. Igneous Rocks Form from molten material Sedimentary Rocks Form from the lithification (compaction and cementation) of sediments Metamorphic Rocks Form from the application of high heat and pressure (Not enough to melt) to pre-existing rocks.

21 4. Compare and contrast the factors that cause the three main types of metamorphism Contact Changes due to contact with an igneous intrusion Regional Changes due to pressure changes over a large region colliding tectonic plates -- mountains Hydrothermal Changes due to the action of heated water.

22 5. Infer which steps of the rock cycle are skipped when Granite metamorphoses to Gneiss. It goes from Igneous directly to Metamorphic. It skips the sedimentary / above ground parts of the rock cycle.

23 Area of Study: 6. Predict the location of an igneous intrusion based on the following mineral data. Muscovite and chlorite were collected in the northern portion of the area of study; garnet and staurolite were collected in the southern portion of the area. Chlorite Muscovite Staurolite Garnet Due to the increasing grade of metamorphism the igneous intrusion is south of the area of study. Low Grade Metamorphism Intermediate Grade Metamorphism High Grade Metamorphism Igneous Intrusion

24 7. Gemstones often form as porphyroblasts. Gemstones are described in terms of carat weight. A carat is equal to 0.2g or 200mg. A large garnet discovered in New York in 1885 weighs(has a mass of) 4.4kg and is 15cm in diameter. What is the carat weight of this gemstone? Useful givens and assumptions: 1 carat = 0.2 g or 200mg Garnet = 4.4 kg 1000g = 1kg 4.4kg X (1000g/1kg) = 4400g 4400g X (1carat/0.2g) = 22000carats