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WOU ES 105 - Geologic Time

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Earth Science, 11ed.American Geologic ExplorationLeaves of HistoryHistorical notes Historical notes Modern geology Modern geology Relative dating Principles of Relative DatingNicolaus Steno 1636-1686Principle of Original Horizontality Lateral ContinuityPrinciple of SuperpositionStratigraphic SuperpositionSuperposition is well illustrated by the strata in the Grand CanyonJames Hutton 1726-1797Principle of Cross-cutting RelationshipsCross-cutting relationshipsFolding occurred after depositionInclusionsHow inclusions formFormation of InclusionsThe fragments are included with the deposition of rock on top of the weathered surfaceTwo different modes of inclusionUnconformitiesAngular Unconformity Formation of an angular unconformitySimple angular unconformityFolding, erosion, deposition, foldingNonconformityNonconformityDisconformitySeveral unconformities are present in the Grand CanyonPrinciples of Relative DatingRelative Dating Exercise1Earth Science, 11ed.Edward J. Tarbuck & Frederick K. Lutgens Geologic TimeChapter 11American Geologic Exploration• John Wesley Powell• Colorado River Expedition—1869• Grand Canyon is Earth’s “Book of Revelations”Leaves of History Historical notes Catastrophism• Landscape developed by catastrophes • James Ussher, mid-1600s, concluded Earth was only a few thousand years old Historical notes Modern geology James Hutton • Theory of the Earth• Published in the late 1700s • “…we find no vestige of a beginning—no prospect of an end.”Modern geology• Uniformitarianism• Fundamental principle of geology "The present is the key to the past“2Modern geologyMost of geology represents uniformitarianismHowever, catastrophism has its place in our understanding.• Tsunamis• Krakatau• Meteor impactsRelative dating Placing rocks and events in proper sequence of formationDeciphering Earth’s history from clues in the rocksPrinciples of Relative Dating• Principle of original horizontality• Principle of lateral continuity• Principle of superposition• Principle of cross-cutting relationships• Principle of inclusionNicolaus Steno 1636-16861669 work relates to deposition of sediment• Principle of original horizontality• Principle of lateral continuity• Principle of superpositionhttp://www.ucmp.berkeley.edu/history/steno.htmlPrinciple of Original Horizontality • Sediment is deposited horizontally http://faculty.icc.edu/easc111lab/labs/labf/orig_horizontality.jpgLateral Continuityhttp://cse.cosm.sc.edu/hses/RelatDat/pages/lateral.htm3Principle of Superposition• Nicklaus Steno, 1669 • Oldest rocks are on the bottom Stratigraphic Superposition• Oldest rock A• Younger rocks above• E is the youngesthttp://cse.cosm.sc.edu/hses/RelatDat/pages/superpos.htmSuperposition is well illustrated by the strata in the Grand CanyonJames Hutton 1726-17971785 lectures Concerning the system of the Earth, its duration, and stability to the Royal Society of Edinburgh• Principle of crosscutting relationships• Principle of inclusionshttp://www-history.mcs.st-andrews.ac.uk/Mathematicians/Hutton_James.htmlPrinciple of Cross-cutting Relationships• Younger feature cuts through an older feature – Something must exist first to be cut by another thing• The ‘things’ cutting may be ‘things’, such as igneous intrusions• Or they may be events, like fault breaks, folding, or erosion periodsCross-cutting relationships4Folding occurred after depositionhttp://rst.gsfc.nasa.gov/Sect2/Sect2_6.htmlInclusions• One rock contained within another • Rock containing the inclusions is younger than the one the inclusions are derived fromHow inclusions form Formation of InclusionsThe fragments are includedwith the deposition of rock on top of the weathered surfaceTwo different modes of inclusionInclusions of granite in sedimentary deposit—formed later than granitehttp://www-rohan.sdsu.edu/~rhmiller/geologictime/GeologicTime.htmInclusions of sediment in granite—granite formed later than sediment5Unconformities• A break in the rock record • Three types of unconformities • Angular unconformity –• Disconformity – strata on either side are parallel • NonconformityAngular Unconformity• Tilted rocks are overlain by flat-lying rocks• Remember the principle of original horizontality?Formation of an angular unconformitySimple angular unconformityhttp://www.grisda.org/colorado/index.htmFolding, erosion, deposition, foldinghttp://rst.gsfc.nasa.gov/Sect2/Sect2_6.htmlNonconformity• Metamorphic or igneous rocks below • Younger sedimentary rocks above6NonconformityDisconformity• Gap in sedimentation that may have erosion also• Represents an interval in geologic time without rock deposited• Most difficult of the three unconformities to detect• Strata on either side are parallelSeveral unconformities are present in the Grand CanyonPrinciples of Relative Dating• Superposition• Original Horizontality and Lateral Continuity• Inclusions• Crosscutting Relationships• UnconformitiesRelative Dating


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WOU ES 105 - Geologic Time

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