Liam Murphy - GEOL200 - Lab Assignment 09 [MARKED]

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Liam Murphy 8 e ’.O 3540040 : o GEOL 200 - Introductory to Physlcal Geology ;* s g Lab Assignment #9 September 7™, 2021 S 1. Refer to the vertical cross sections in Geologic Cross Sections 3 and 4 on page 224 of the Laboratory Manual (Activity 8.2), and determine the relative ages of the rock bodies and other lettered features. Indicate the relative age relationships by placing the letters on the blanks below, from oldest (at the bottom) to youngest (at the top). Indicate the presence of unconformities in your sequences for,each cross section. For example, in Geologic Cross Section 3, an unconformity occurs after unit A and before unit E. (Hint: When interpreting geologic cross sections, always start with the question: What was there first? That is, the interpretation of cross sections is usually easier if you proceed from the oldest event to the youngest.) Note the types of unconformities (disconformity, nonconformity, etc.) and the age of the unconformity in relation to the rock strata. Geologic Cross Section 3 Strata Types and ages of unconformities Infill Erosional Surface, Non Conformity v Surface Erosional Surface, Non—Conformity,g/ Fault Line f" g - X¢ J4 Conformable Contacts [ Conformable Contacts Conformable Contacts Youngest Erosional Surface, Non-Conformity / Conformable Contacts i Conformable Contacts Igneous Dike, Intrusive lgnegus‘Contact 1y Conformable Contacts, » ' o 3 A Conformable Contacts . * Angular Unconformity |,/ ¢ Fault Line iyt Intrusive Igneous Body Country Rock TTTTTEETITTITIT Oldest Geologic Cross Section 4 Strata Types and ages of unconformities Youngest House Infill Infill Erosional Surface, Non-Conformity v _Z Surface Erosional Surface, Non-Conformity v ? Fault Line Intrusive Igheous Contact Conformable Contacts Conformable Contacts Erosional Surface, Non-Conformity / Liam Murphy Unit 11: Waves, Beaches, and Coasts GEOL 200 Lab Assignment #9 Athabasca University Page 1 of 4 September 7th, 2021 8 2t TITTTTTER

' Liam Murphy Intrusive Igneous Dike Conformable Contacts Conformable Contacts Erosional Surface, Non-Conformity v Infill Erosional Surface, Non-Conformity v Conformable Contacts Erosional Surface, Non-Conformity \/ Intrusive Igneous Dike Fault Line Conformable Contacts Conformable Contacts Conformable Contacts Erosional Surface, Non—Conformlty.,/ Fault Line Country Rock [TTTTTTTTT PRrER- Oldest Examine Figures 9.1 and 9.2 that you have just completed above, and identify all of the zones where you would expect to find contact metamorphism (distinguish the layer causing the metamorphism from the layer being metamorphosed). Keep in mind the mode of origin of the various rock types and the principles for determining relative ages. Remember that contact metamorphism only occurs at the contact where hot igneous rocks have intruded older rocks. A layer of rock deposited after an intrusion and an unconformity does not undergo contact metamorphism. For example, on Figure 8.8, unit D is not metamorphosed at its contact with unit B. Geologic Cross Section 3 e PandF A\so E @ X e RandM ; e HandM = . e AandM R R Geologic Cross Section 3 AandV Aand L Also 11dey AandF ] SandV . Sand O Sand M Sand X SandB E and X Answer Activity 8.4 questions A-C (page 226), and Activity 8.5 questions A (1-3) (page 227) and B (page 228) in the Laboratory Manual. Activity 8.4 b 14 ks * A. A solidified lava flow containing zircon mmeral crystals is present in a sequence of rock layers that are eXposed ina hillside. A mass spéctrometer analysis was used to count the atoms of uranium-235 and lead-207 lsotopes in zircon samples from the lava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer to Fig 8.14 to help you answer the following questions. e Unit 11: Waves, Beaches, and Coasts GEOL 200 ; Lab Assignment #9 Athabasca University . Page 2 of 4 September 7', 2021

1. About how many half-lives of the uranium-235 to lead-207 decay pair have elapsed in the zircon crystals? . s, = 70.7% , D= 29.3% 4 e n =% or0.500 / il " . M) 2. What is the numerical age of the lava flow based on its zircon crystals? Explain how you arrived at your answer. P = 70.7% D;= 29.3% n= ¥ or 0.500 tip = 7.038 x 108 yr 7.038 x 108 yr x 0.500 = 3.519 x 108 yr 3. What is the age of the rock layers above the lava flow? ’ : / The layers above the lava flow can be dated around the end of the Carboniferous Period (359 x 10°yr) to the o beginning of the Permian Period (299 x 108 yr). 2 eginning of the érmlan erio x 10°yr Sl&.’a\\ \10‘/“6'2/\‘-&” 3{(.4 MQ 4. What is the age of the rock layers beneath the lava flow? Z 2y They layers below the lava flow can be dated around the end of.the Devonian Periad to the beginning of the Carboniferous Period (359 x 108 yr). E&Y\ Coro@,( \@UW\X 3 ( ( 1 . I M ¢ - B. Astronomers think that the Earth probably formed at the same time as all of the other rocky materials in o&jl:,a solar system, including the oldest meteorites. The oldest meteorites ever found on Earth contain nearly equal amounts of both uranium-238 and lead-206. Based onFig. 8.14, what is Earths approximate age? Explain your reasoning. Parent Isotope: Uranium-238 Daughter lsotopé: Lead-206 5 Py = 50% D= 50% Age of Specimen = 1.000 x to2 typ = 4.468 x 10° yr 1.000 x (4.468 x 10° yr) = 4.468 x 10° yr “Approx Age of the Earth = 4.468 x 10%yr or 4.468 Billion Years 7./ SN s ; & o The calculated age of the earth is similar own an Fig 8.12 of 4.55 x 10° yr. . C. The radioactive isotope carbon-14 (C-14) is continuously replenished in organisms while they are alive. When an organism dies, it is no longer able to take new C-14, and so the amount of G-14 decreased as it decays to its stable daughter product: nitrogen-14 (N-14). 1. The carbon in a buried peat bed has about 6% of the C-14 of modern shells. When the plants that now form the buried peat were alive, they absorbed C-14 and probably had about the same amount of C-14 as modern shells, so about 94% of peats original C-14 has decayed. What is a reasonable initial estimate of the age of the peat bed? Explain. 5 Parent Isotope: Carbon-14 Daughter Isotope: Nitrogen-14 P = 6.2% Di= 93.8% Age of Specimen = 4.000 x t1/ 0.x 10% yr - l 4.000 x (5.730 x 10% yr) =22.92 x 103 yr Approx Age of the Earth = 22.92 x 10° yr 6r 22.92 Thousand Years a{ M V\(X,( . ik ’ ) 3 / a8 Al ; .t % ‘.“;‘; “~ P ‘ » , z}‘ !V Liam Murphy : Unit 11: Waves, Beaches, and Coasts GEOL 200 Ped A A Lab Assignment #9 Athabasca University Page 3 of 4 , ¥ by ff% 1 September 7th, 2021

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W\ 2. In sampling the peat bed, you must be careful to avoid any young plant roots or old limestone. Why? S Plant roots have a lower C14 content which could falsely indicate a that the peat is younger than it actuayy is, where as Limestone has a higher C14 content which could also falsely indicate the Peat Beds age but by indicating that it is older than it actually is. %V‘ S,\\ i Activity 8.5 A. Refer to Fig. A8.5.1, which shows an outcrop in a surface coal mine in northern New Mexico. Note the sill, sedimentary rocks, fault, and places where a fossil leaf was found and isotope data for zircon crystals in‘the sill. 1. What is the relative age of the sedimentary rocks in this rock exposure? Explain your reasoning. £d The sedimentary rock can be dated as approximately 23 Myr by the presence of a fossilised Fagopsis Tree within 5 the sedimentary rock and the underlying sandstone. The Fagopsis Tree leaf can be dated around 23 Mry within the Cenozoic Era and either the Neogene or Paleogene Period. ; PO ol Nt & ymnts NSV Tl P DY 2, %“Whatis the numerical age of the sill? Use the information in Fig. 8.14, and show how you calculated the answer. g Parent Isotope: Uranium-235 Daughter Isotope: Lead-207 P = 98.9% Di=1.10% . o . i ‘ Utz =038 %200yr 1R Y n=0Q18%h LR 5 0.016 x (7.038 x 108 yr) = 1.12608 x 1’07yr / Numerical Age of the Sill: 1.12608 x 107yr 3. Locate the fault. Approximately how much separation has occurred along this fault? 5 i+ Two Metres (2) m '/ What addgtjior;al i‘gtgr;mation would you like to have to make a better estimate of fault separation? 7 - B. Make a numbered list of the geologic events that contributed to the development of the geological features in this outcrop, starting with deposition of the sandstone (oldest event: 1) and ending with the time this picture was taken. Include the name(s) of relevant period(s) from the geologic time scale as well as the isotopic age of the sill in your writing. Your reasoning and number of events may differ from those of other students. Opcler oy Hlame Relevant Period o Isotopic Age 1. Sandstone Deposition Jurassic Period 201 Myr 2. Shale Deposition Cretaceous Period 66 Myr 3. Uncomfortity Paleogene Period 23 Myr - 4. Basalt Depostion Neogene Period 11.26 Myr 5. Reverse Fault occurred Neogene Period 10 Myr 6. Sill Erosion took place Quaternary Period 6 Myr 7 . | Vegetation Growth Present Period 1 Myr 8. Photograph taken = - Present Period Last Year Liam Murphy GEOL 200 Athabasca University [ O/g\ d SuReE Amotbm suf%M/f‘ Unit 11: Waves, Beaches, and Coasts Lab Assignment #9 Page 4 of 4 September 7th, 2021 1)