Interpreting Earths Rocks to Determine Its Past History

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/az 3/mohgameil/Layering 4. 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. youngest fault oldest These are younger than the surrounding rock

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 • Earthquake location • Striations • Rock formation • Paleoclimates • 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: //www 001. upp. so-net. ne. jp/fl-fg/06 -02. htm

limestone shale sandstone granite http: //www. env. duke. edu/eos/geo 41/st 013. gif

http: //www 001. upp. so-net. ne. jp/fl-fg/06 -02. htm

Resources • • http: //courses. geo. ucalgary. ca/glgy 209 L 03/docs/Lecture 15_GLGY 209_six. pdf http: //perth. uwlax. edu/faculty/stoelting/Intro/Guides/Images 2/law_of_superposition_b. jpg http: //www. science. sjsu. edu/scied/255/ppt/superposition/img 025. jpg http: //www. gpc. peachnet. edu/~jsummero/Cross-cutting-a. jpg • • http: //www. gc. maricopa. edu/appliedscience/gjc-nsf/images/CRH 0204. 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%20 Gallery/Big%20 Bend%20 Region, %20 Texas/Big% 20 Bend%20 National%20 Park%20 -%20 Syncline%20 -%20 Javalina%20 Creek%20%20 June%201995. jpg http: //geoimages. berkeley. edu/Geo. Images/Johnson/Images/Large/CD 3/028. jpg http: //www. vvdailypress. com/travel/rainbow/images/rock. jpg http: //academic. emporia. edu/aberjame/struc_geo/folds/fold 06. jpg http: //www. geology. pitt. edu/images/folds. jpg http: //faculty. evansville. edu/de 3/b 39902/PPoint/Geologic%20 Time/img 007. jpg http: //www. photo. net/photo/pcd 2882/grand-canyon-region-aerial-85. 3. jpg http: //www. cowanstark. com/horsehoe-bend. jpg http: //home. flash. net/~alanm 52/Cross_cutting. jpg http: //wwwclass. unl. edu/geol 101 i/images/igneous%20 images/Black%20 Canyon%20 Gunnison. 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/Us 67 -1/us 67 cut. jpg http: //maverick. gc. maricopa. edu/appliedscience/gjcweb/geomap/images/MW 8 -11. jpg http: //www 3. uakron. edu/geology/Foos/parks/rmgcan 2. html http: //www. ldeo. columbia. edu/dees/ies 2/slides/disconformity. gif http: //geology. lssu. edu/NS 102/images/figure%2009 -06. gif http: //www. crienterprises. com/C-Assets/J-Hanifa-Unconf-W-Birk. jpg http: //www. uoguelph. ca/~sadura/stgref/stg 32 b. gif http: //www. geo-outdoors. info/images/eye_protection. jpg • http: //enterprise. cc. uakron. edu/geology/natscigeo/Lectures/time/gtime 1. htm