Geology Exam Review 2012

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Queen's University
Geological Sciences and Geological Engineering
GEOL 104
Michael T.Mc Bride

Geology Exam Review 2012 Geologic TimeAbsolute Time is the age of a geologic feature or event in terms of years or millions of yearsRelative Time is the age of a geologic feature in terms of being older or younger than something elseFundamental Principles of Relative Time 1 Law of Original HorizontalitySedimentary units were originally deposited in horizontal layers parallel to the Earths surfaceFolded or tilted beds have been disturbed after deposition 2 Law of SuperpositionIn a sequence of sedimentary strata or extrusive igneous rocks that has not been overturned the oldest layer is at the bottomOlder beds above younger indicate the beds have been overturned 3 James Hutton 1785Uniformitarianismpresent is the key to the pastRecognized great gaps in the geologic record by examining cycles of erosion deposition erosion etc which required extensive timeWilliam Smithearly 1800created the first geologic map using fossils of England 4 Law of Faunal SuccessionFossil organisms only existed during certain periods in definite order giving the relative age of the rock bedIndex fossils are widespread geographically and are limited to a short span of time 5 Law of CrossCutting Relationshipsfaultsintrusions are assumed to be younger than the rock affected or disturbed 6 Law of Inclusionsfragments of one rock that are enclosed within another are older than the rock it is enclosed inInclusions if the fragment is one rock type contained within another rockXenolith if the inclusion is igneous within country rockRadiometric Dating allowed the actual ages in millions of years to be added to the geologic columnradioactive decay occurs at a known rate from parent atom to daughter atomsfresh rocks have no daughter present meaning they are newly formed ie just crystallized from magmaover time some daughter atoms become present and there is no loss or gain of parent or daughter atoms closed systemwhen ratio of daughter to parent is equal the half life is reachedGeologic Column suggests the age of Earth is between 4246 Ga billions of years Unconformities are surfaces that represent a gap in the geologic recordDisconformity layers above and below the unconformity are parallel and sedimentary however there is signs of erosion suggesting a gap in depositionAngular Unconformity sedimentary or extrusive igneous beds below and above the unconformity are not parallelNonconformity sedimentary rocks overlie OLDER crystallineigneous rocks Rock DeformationNormal Stress is compressive or tensile an acts PERPENDICULAR to the surface of a bodyShear Stress acts PARALLEL to the surfaceNormal Normal ShearCompressive Tensile parallel Axial Strain causes a change in length of a body while Shear Strain changes the shape or angle of a bodyJoints are often planar fractures that form without movement and allow access to groundwater the formation of mineral deposits gold and exposure to chemical weatheringa joint set consists of a number of parallel joinsjoint system if 2 joint sets occur and intersect
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