Interpreting Earth’s Rocks to Determine Its Past History

Determining Geologic History: Geologists are like CSI detectives wanting to know Where?, When?, Why?, How? Sometimes very little “evidence” remains (exposure, erosion) Evidence has been moved or tampered with! Rocks have been moved (faults, folds) Usually no witnesses!

Geologic Time Relative dating - sequence of geologic events in a region (order of past events) (not dating your cousin )

Principle of Superposition Oldest layer on bottom (if tectonically undisturbed) Younger Older http://www.angelfire.com/az3/mohgameil/Layering4.jpg

Principle 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.

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

Principle of Original Horizontality Rock are originally deposited horizontal Folding happened AFTER rocks were deposited

folded rock layers = compression by tectonic activity

Cross-Cutting Relationships 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

practice

Law of Inclusions

Index fossils Fossils that lived for a short time can be used to date layers Found world wide Examples?

James Hutton: The father of modern geology (1726-1797) Uniformitarianism: “The present is the key to the past.” ?????????

Examples of uniformitarianism Petoskey stones Striations Rock formation Paleoclimates Earthquake location What else?

Order the layers 1-7

Unconformities = “Missing Time” Result of erosion

Angular Unconformities Folded layers on bottom, flat layers on top rock layers are eroded new horizontal layers are deposited angular unconformity (rock layers have been eroded away)

Angular Unconformity F E D C B A

Nonconformity – igneous rocks on bottom; overlain by sedimentary rocks sedimentary rock layers Cambrian Precambrian Granite

Nonconformity

Disconformity DISCONFORMITY:Missing rock layers (sedimentary) Very hard to see

Disconformities

Let’s Play…. Name the UNCONFORMITY!

Siccar Point, Scotland

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

granite shale sandstone limestone http://www.env.duke.edu/eos/geo41/st013.gif

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

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

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