Lab9_Maps and relative age_Winter 2019_JH (1)

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Glendale Community College *

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111

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Electrical Engineering

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Jan 9, 2024

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Geo 111 Lab Lab 9 Student name: _________________ Lab 9: Mastering skills on maps and relative age I. Relative age determination on a cross-section Lab Objectives  Recall and use the basic principles of relative geologic time to place events in a relative chronologic order.  Combine concepts of relative geologic time and numerical dating to reconstruct the history of geologic events in a particular area. In the previous lab you were introduce to basic relative age and numerical age concepts. Below are the laws for relative age determination. a) Law of Original Horizontality: Strata consisting of sedimentary layers and lava flows were originally deposited in a horizontal orientation. b) Law of Lateral Continuity: Strata and lava flows extend laterally (tabular) in all directions until they thing out to nothing or reach the edge of their depositional basin. c) Law of Superposition: In an undisturbed sequence of strata or lava flows, the oldest layer is at the bottom and the youngest is at the top of the sequence. d) Law of Inclusions: Any piece of rock that has become included in another rock or body of sediment must be older than that of the rock or sediment into which it has been incorporated. e) Law of baked contacts: The principle of baked contacts states that an igneous intrusion “bakes” (metamorphoses) surrounding rocks, so the rock that has been baked must be older than the intrusion. f) Law of Cross-Cutting: Any feature that cuts across a rock or body of sediment must be younger than the rock or sediment that it cuts across. g) Law of Unconformities: An unconformity represents gaps in the geologic record that formed wherever layers were not deposited for a time or layers were removed by erosion. The three types of unconformities include:  -Disconformity- An unconformity between parallel strata or lava flows.  -Nonconformity- An unconformity between younger sediment rocks and igneous/metamorphic rocks.  -Angular Unconformity- An unconformity between two sets of strata that are not parallel to one another.  QUESTION 1: Below is a geologic cross-section of the Grand Canyon. Use principles of cross-cutting relationships to get relative age of each marked rock formation or unconformity. Specify which law from the list above applies to each age determination. When dealing with an unconformity, determine the type it is. Youngest will be on top of the table. order Rock or event label Rock type Laws for relative age determination applied 1 G Muav limestone Mississippian deposition 2 H Bright Angel shale Devonian deposition 3 I Tapeats sandstone Silurian deposition 4 R Unconformity 5 A Nankoweap group Mississippian deposition 6 B Chuar shales Pennsylvanian deposition 7 C Dox sandstone Permian intrusion 8 D Shinumo quartzite Pennsylvanian-Permian unconformity 9 L Hakatal shale Cambrian intrusion

Geo 111 Lab Lab 9 10 F igneous sill Pennsylvanian deposition 11 E Bass dolomite Permian deposition 12 M gravel layer Cambrian unconformity 13 S Unconformity 14 J Zoroaster granite Ordovician deposition 15 K Vishnu schist Cambrian deposition II. Mastering topo and geologic map skills QUESTION 2: Topo map exercise. For horizontal scale, note that the long side of the map represents 0.5 miles. a) Hand contour the map below using C.I. = 20 ft. Note that the elevation of the lowest contour will be 320 ft.

Geo 111 Lab Lab 9 b) Calculate the gradient of hill slope between points A and B shown in the cross-section below. A= 360 B =420 Gradient = 420-360 = 60/1.5 =30FT  The gradient of hill slop is about 30ft. c) Calculate the gradient of hill slope between points C and D shown in the cross-section below. a. C = 415 b. D = 380 Graditent = 415-380 = 35/2.7 = ~12ft d) Compare and contrast the results for b and c in terms of spacing between contour lines on map in the two areas. The gradient between points A and B is significantly steeper (40 ft per unit) compared to the gradient between points C and D (approximately 13 ft per unit). This indicates a more rapid elevation change between points A and B.

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Geo 111 Lab Lab 9 e) Calculate the distance of travel from C to D. Hint: use the Pythagorean theorem equation a 2 =b 2 +c 2 f) Draw a vertical dike running through point E with strike of N20W. g) Assume that the line connecting A to D is representation of a granitic dike. Measure its strike. Write down the result here.