Lecture 11.docx - GEO 1111 Geologic time (geochronology) 1)...

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GEO 1111Geologic time (geochronology)1)Relative datingcompare2 or more entities to determine which isoldera.Principle of uniformitarism:present is key to pasti.Same processesact throughout time, but possibly atdifferent ratesii.More influentialthan catastrophes大 灾 难 –hurricanes, floods,impactsiii.For general cases: OKrivers flow downhill; volcanoes erupt lavaiv.Specific cases: ?there have not always been rivers; volcanoes notalways erupt same composition lave; ancient Earth spun morerapidly than it does nowv.But still useful determine how rocks are ‘positioned’b.Law of superpositioni.Most sediments settle fromwater/windii.Youngrock material (sediment) is deposited ontopofearlier, olderdepositsc.Principle of horizontalityi.Layers of sediment and lava are generally deposited in a~horizontalpositionii.When/if tilted, how to identify upper or top surface?d.Principle of cross-cutting relationshipsi.Intrusive(igneous) formation must beyoungerthan rock it cutsacross; also used forfaultsii.Matching of rocks of similar ages in different regions is known ascorrelation1.Lithostratigraphic – matching upcontinuous rock sequences2.Chronostratigraphic – matching uprocks of thesame age;usually done withfossilsusing biostratigraphy3.Often relies uponfossils4.Sedimentary stratain widely separated area could beidentified and correlated by theirdistinctive fossil content5.Fossils: remains ofancient organisms

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Term
Fall
Professor
DUMAS

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