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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*