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Interpreting Earth’s Rocks to Determine Its Past History

Interpreting Earth’s Rocks to Determine Its Past History. Geologic Time chapter 18. Relative Dating - sequence of geologic events in a region (order of past events) Not quantitative. Law of Superposition. Oldest layer on bottom (if undisturbed) Only works for SED rocks. Younger. Older.

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Interpreting Earth’s Rocks to Determine Its Past History

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  1. Interpreting Earth’s Rocks to Determine Its Past History

  2. Geologic Timechapter 18 • Relative Dating - sequence of geologic events in a region (order of past events) • Not quantitative

  3. Law of Superposition • Oldest layer on bottom (if undisturbed) • Only works for SED rocks Younger Older http://www.angelfire.com/az3/mohgameil/Layering4.jpg

  4. Law of Superposition In horizontal rock layers, the oldest and first formed is on the bottom. 5 is the youngest because it is on the top, closest to the surface.

  5. The Grand Canyon http://www.calstatela.edu/faculty/acolvil/sediment/superposition.jpg

  6. Principle of Original Horizontality • Sediments are originally deposited as horizontal (or near horizontal) beds (ONLY FOR SED ROCKS) Folding happened AFTER rocks were deposited

  7. folded rock layers = compression by tectonic activity

  8. Cross-Cutting Relationships(overlap law) • An igneous intrusion (or fault) is younger than the rock layers that it cuts across. These are younger than the surrounding rock youngest fault oldest

  9. Cross-Cutting Relationships 6 is younger than1, 2, or 3 because it cuts across them!

  10. 3 2 3 4 1 2 5 1

  11. Which came first? A B C D E Order the rock layers above from oldest to youngest.

  12. Which came first? A C B C D B D D E The first layer deposited and the oldest is D, followed by C, A, B, and E.

  13. Law of inclusions • The inclusion (xenolith) is older than the rock it is in • Snickers bar

  14. James Hutton: The father geology (1726-1797) Uniformitarianism: processes acting on earth today (volcanism, erosion, plate tectonics, glaciation, etc.) have done so in the past IN THE SAME WAY! “The present is the key to the past.”

  15. Unconformities = “Missing Time” • Represented by squiggly lines on cross sections

  16. Angular unconformity

  17. Angular Unconformities • Folded layers below horizontal layers. rock layers are eroded new horizontal layers are deposited angular unconformity (rock layers have been eroded away)

  18. Angular Unconformity sedimentary rocks above and below unconformity surface with rocks below tilted at an angle F E D C B A

  19. Nonconformity – younger sedimentary rocks rest on older igneous rocks sedimentary rock layers Cambrian Precambrian Granite

  20. Nonconformity

  21. Disconformity DISCONFORMITY:Missing rock layers (sedimentary) Very hard to pick out

  22. Disconformities

  23. Let’s Play….Name the UNCONFORMITY!

  24. Siccar Point, Scotland

  25. http://www001.upp.so-net.ne.jp/fl-fg/06-02.htm

  26. Resources • http://courses.geo.ucalgary.ca/glgy209L03/docs/Lecture15_GLGY209_six.pdf • http://perth.uwlax.edu/faculty/stoelting/Intro/Guides/Images2/law_of_superposition_b.jpg • http://www.science.sjsu.edu/scied/255/ppt/superposition/img025.jpg • http://www.gpc.peachnet.edu/~jsummero/Cross-cutting-a.jpg • http://www.gc.maricopa.edu/appliedscience/gjc-nsf/images/CRH0204.JPG • http://maverick.gc.maricopa.edu/appliedscience/gjcweb/geomap/images/ang.unconf.jpg • http://www.geog.ouc.bc.ca/physgeog/contents/images/hutton.jpg • http://www.bigbendpaleo.com/Photo%20Gallery/Big%20Bend%20Region,%20Texas/Big%20Bend%20National%20Park%20-%20Syncline%20-%20Javalina%20Creek%20-%2020%20June%201995.jpg • http://geoimages.berkeley.edu/GeoImages/Johnson/Images/Large/CD3/028.jpg • http://www.vvdailypress.com/travel/rainbow/images/rock.jpg • http://academic.emporia.edu/aberjame/struc_geo/folds/fold06.jpg • http://www.geology.pitt.edu/images/folds.jpg • http://faculty.evansville.edu/de3/b39902/PPoint/Geologic%20Time/img007.jpg • http://www.photo.net/photo/pcd2882/grand-canyon-region-aerial-85.3.jpg • http://www.cowanstark.com/horsehoe-bend.jpg • http://home.flash.net/~alanm52/Cross_cutting.jpg • http://www-class.unl.edu/geol101i/images/igneous%20images/Black%20Canyon%20Gunnison.jpg • http://freespace.virgin.net/craven.pendle/stratigraphy/unconformity.jpg

  27. http://comp.uark.edu/~sboss/siccar.jpg • http://www.pittstate.edu/services/scied/Teachers/Field/Camp/Us67-1/us67cut.jpg • http://maverick.gc.maricopa.edu/appliedscience/gjcweb/geomap/images/MW8-11.jpg • http://www3.uakron.edu/geology/Foos/parks/rmgcan2.html • http://www.ldeo.columbia.edu/edu/dees/ees/ies2/slides/disconformity.gif • http://geology.lssu.edu/NS102/images/figure%2009-06.gif • http://www.crienterprises.com/C-Assets/J-Hanifa-Unconf-W-Birk.jpg • http://www.uoguelph.ca/~sadura/stgref/stg32b.gif • http://www.geo-outdoors.info/images/eye_protection.jpg • http://enterprise.cc.uakron.edu/geology/natscigeo/Lectures/time/gtime1.htm

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