Various types of geological unconformities. - UBC EOAS

Disconformity: exists where the layers above and below an erosional boundary have the same orientation · Nonconformity: develops where sediments are deposited on ... Varioustypesofgeologicalunconformities. Readthispage.Thereisaninteractivetableofexamplesatthebottomforyoutopracticerecognizingthevarioustypesofgeologicalfeatures.Thisisthelastoffour"interactive"pages. f.UnconformitiesUnconformitiesrepresentperiodsofnon-depositionofsedimentoractiveerosionofstrata.TheyhelpusappreciatethatthegeologicalrecordinanyonelocationisNOTcompletebutcontainsgaps.UnconformitiesmayrepresentimportantperiodsofactivityinEarthhistorysuchasmountainbuildingeventswherestrataarebeingactivelyupliftedanderoded.Figure1.22Schematicofselectedtypesofunconformity.Severaltypesofunconformityarerecognized(refertofigureabove):Disconformity:existswherethelayersaboveandbelowanerosionalboundaryhavethesameorientationNonconformity:developswheresedimentsaredepositedontopofanerodedsurfaceofigneousormetamorphicrocksParaconformity:strataoneithersideoftheunconformityareparallel,thereislittleapparenterosionAngularunconformity:strataisdepositedontiltedanderodedlayers(suchasatSiccarPoint)Thesesixphotosareexamplesofdifferenttypesofunconformitiesfromaroundtheworld.Usedropdownboxestolabelthesecorrectlyandclickthe"Check"buttontoseeifyouarecorrect.Rememberthediscussionboardforexchangingquestions,ideasandanswerswithfellowstudentsoraTA.Toseefullsizeimagesright-click(alt-click)andpick"viewimage".YousawthisviewofSiccarpointearlier.Figure1.26AbandofigneousrockwithinsedimentaryrocksatthebaseoftheGrandCanyon,Arizona.Thediagonalbandisroughly1-2metresthick.Figure1.27fromGuatemala,photoattheGeologyandGeophysicsScienceCentre,USGeologicalSurvey.AngularunconformityDikeorIntrusionDisconformityFaultNonconformityAngularunconformityDikeorIntrusionDisconformityFaultNonconformityAngularunconformityDikeorIntrusionDisconformityFaultNonconformityThisPrecambrian-Cambrianinterfaceindicatesa1Gagapinthegeologicalrecord.ImagefromWikipedia,annotationsbyS.Sutherland.ThisinterfaceisbetweenfoldedMiddleJurassicandoverlyingLateJurassicstrata,inUtah.Thebiggertreesareprobablyabout2mhigh.Imagecopyright©byThomasMcGuire,madeavailableviatheEarthScienceWorldImageBank.From