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LAB3:RELATIVEGEOLOGICTIMEANDSTRATIGRAPHICINTERPRETATIONSPARTI:RELATIVETIMEANDSTRATIGRAPHYINTRODUCTION EXERCISE3.1.IdentifyingUnconformitiesInFigure3.2,anunconformitysurfacehasbeenmarkedwithadarkwigglyline.Thespecifictypeofunconformityisdifferentdependingonwherealongthewigglylineyoulook.FindexamplesofthethreetypesofunconformitiesinFigure3.2anddrawtheminthelabeledboxes.Includetherocktextures(patterns)astheyappearinthegeologicalcross-section.
Figure3.2:Geologicalcross-section.
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EXERCISE3.2.ReconstructingRelativeGeologicalTime
Figure3.3isageologiccross-sectionwhereeachrockunitisassignedaletterasalabel.UsethelabelsinFigure3.3andthestratigraphicprinciplestoanswerthequestionsthatfollow.
Allrocksaresedimentaryexceptforthefollowing:
• H:metamorphic• PandS:intrusiveigneousrocks
Figure3.3:Geologicalcross-section.Thespacebelowisprovidedforyoutomakenotes.
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1. Whichistheoldestgeologicevent?____________________________________________________
2. WhichgeologiceventsaredefinitelyolderthantheintrusionS?____________________________
3. WhatstratigraphicprincipleisusedtodateFaultBontherightsideofthefigure?
_________________________________________________________________________________
4. Whichpairsofrocklayersdefineunconformities?________________________________________Tohelpyouwithquestion6,itmaybeusefultomarkthelocationofeachoftheseonyourdrawingbymakingthesecontactsthicker,orbyusingacolouredpenciltohighlighttheirlocations.
5. Whichisthemostrecent(youngest)geologicaleventinthecrosssectionabove?________________________________________________________________________________
6. Placetherockunitsandthefaults(usingthelettersAandB)inorderrangingfromtheoldesttothe
youngestbyplacingthecorrespondinglettersintothespacesbelow.
(Oldest)____,____,____,____,____,____,____,____,____,____,____,____,_____,_____(Youngest)
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PARTII:INTERPRETINGSTRATIGRAPHYINASTRATIGRAPHICLOGEXERCISE3.3–InterpretingStratigraphicLogsTables3.2and3.3summarizestratigraphiclogsfromtwodifferentlocations.Usethefollowinginstructionstointerpretandcompleteeachlog.Note:TheonlineLabManualincludesanexampleofwhatacompletedlogmightlooklike.
1. IdentifythedepositionalenvironmentbyinterpretingthewrittenfaciesdescriptionanddrawnstratigraphiccolumnusingtheinformationfromLab2.Writethenameoftheenvironmentnexttothelogsketch.
2. Startingatthebottomofthelog,decidewhetherthetransitionfromonefaciestothefaciesaboveitrepresentsachangetoadeeperwaterfacies(transgression)orashallowerwaterfacies(regression).Writethecorrespondingchange(TorR)intheboxonthehorizontallineseparatingthetwofacies.
3. Intheright-handcolumn,plotthefaciesaccordingitslocationbyshadingthecorrectdot.Forexample,ifanenvironmentisabeach,shadethedotunder"Beach."Therearealsodotsforintermediateenvironments.Ifanenvironmenthasdeeperwaterthan"Beach,"butshallowerthan"Shelf,"youwouldshadethedotbetweenthosetwoenvironments.Rememberthattheprogressionfromfinefar-offshoresedimentstocoarsecoastalsedimentsmaynotbesmooth.Onceyou'veshadedthecorrectdots,connectthedotsusingstraightlinestocreateasealevelcurveliketheoneshowninFigure3.9.
4. Indicateperiodsoftransgressionorregressionbyplacingarrowsonthestraightlinespointingleft(transgression)orright(regression).(SeeFigure3.10intheonlineLabManual.)
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Table3.2:Siliclasticdominatedsystem.FaciesDescription
Strat.Log
Environment RelativeSeaLevelHighLow(Transgressions) (Regressions)OceanTerrestrialBasinShelfBeachDistalProximal
Hummockysequences;silt;lowanglecrossbedsandripples;abundantmarinefossils
¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ Shadethecorrectdotforeachenvironment,thenconnecttheshadeddotstodrawthesea-levelcurve. ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢
Gravelsdowncuttinglaminatedsilts,overlainbysands,thensilts,plantfragments
Darkorganicsilt,mud,stormwashsandlayers,Cruziana
Quartzsst.;abundantripples,Skolithos
Hummockysequences;sandandsiltwithalayerofgravelnearthebase
Qtzsst.;gentlydippingparallellaminations,shells,wooddebris.
¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢
*Startingfromthebottomofthestratigraphiccolumn,markintheboxnexttoeachboundarylinebetweenfacieswhetherthefacieschange,movingupwardsinthecolumn,representsthatsealevelistransgressing(T)orregressing(R).
Trans.orRegress.T/R*
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Table3.3:Carbonatedominatedsystem.FaciesDescription
Strat.Log
Environment RelativeSeaLevelHighLowTransgressionsRegressionsOceanTerrestrialBasinShelfBeachDistalProximal
Light-grey,unbeddedbiolithite;debrisflowsandslumps
Shadethecorrectdotforeachenvironment,thenconnecttheshadeddotstodrawthesea-levelcurve. ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢ ¢
Medium-beddedmicritewithlimesandlenses;clamcoquina,patchreefs
Algallaminateddolomite;mudcracks.,gypsum
Grey-greenhummockybedsofpackedbiomicriteinterbedddwithveryburrowedbiomicrite
Thinlylaminatedblackmicrites
*Startingfromthebottomofthestratigraphiccolumn,markintheboxnexttoeachboundarylinebetweenfacieswhetherthefacieschange,movingupwardsinthecolumn,representsthatsealevelistransgressing(T)orregressing(R).
Trans.orRegress.
T/R*