Sedimentary!Rocks! T. Perron 12.001 - - PDF document

sedimentary rocks t perron 12 001 we ve heard about
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Sedimentary!Rocks! T. Perron 12.001 - - PDF document

Sedimentary!Rocks! T. Perron 12.001 Weve!heard!about!igneous!rocks.!Formed!by!cooling!& !crystallization!of!melts.!If! you!sample!a!random!part!of!Earths!interior,!odds!are!pretty!good!youll!get!an!


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! 1! Sedimentary!Rocks! We’ve!heard!about!igneous!rocks.!Formed!by!cooling!& you!sample!a!random!part!of!Earth’s!interior,!odds!are!pretty!good!you’ll!get!an! !crystallization!of!melts.!If! yard?!Soil,!which!is!made!largely!of!rock!fragments.]!Usually!you’ll!hit!sediment,!and! igneous!rock.!What!about!Earth’s!surface?![Q:!What!do!you!hit!if!you!dig!in!your! those!can!be!transformed!back!into!rock.! ! Toda (we’ll y:! !ta Fa lk t !l e! a

  • f!

ter,!in!t rocks! he!l at!the!surface,!and!the!processes!they!r !how ecor ! ectures!on!plate!tectonics,!about !they!get d!along!the!way !to!the!surfa ! ce)! Let Wis ’s! co st ns art in ! ! w (PPT) ith!a! ,!from!a!paper!by!Whitey!H story!about!some!enigmatic!features!in! agadorn!et!al.!(Geology,!2002).! a!~500!Ma!rock!ou Lik tcrop e!al !in! ! good!stor “The%follow ies,!it!is!a!tragedy.! l! ing%scenario%for%medusoid%stranding,%decay,%and%burial%is% hypothesized.%Jellyfish%were%blown%or%swam%into%a%shallow%embayment.%The%tide% ebbed%and%escape%behaviors%were%initiated%…%During%mass%strandings,%most% jellyfish%settle%on%the%surface%with%their%subumbrella%down,%and%they%commonly% pump%their%bells%in%an%attempt%to%escape%from%stranding%…%This%escape%behavior%

  • ften%compounds%their%fate,%because%they%pump%much%of%their%stomach%and%

internal%cavities%full%of%sand,%thus%exacerbating%their%fate%through%extreme%sand% loading.%…%The%only%structure%often%preserved%within%the%umbrellar%center%is%a% ! convex%sediment%mound%formed%either%through%pulsing%of%the%dying%jellyfish%or% Tragic!indeed decomposition%of%the%sediment .!But!this!is!a!great!example!of!the!rich!information!stored!in! Aladen%gastrovascular%cavity.”% sedimentary!rocks.!! ! We wate !co r!d uld epth !als !and

  • !us

!wav e!the e !gr !ene ain!s rgy iz .!In!fact,!my!group!has! e!and!ripple!wavelength bee !o n!d f!th

  • e

ing !sand to!interpret!ripple!patterns!preserved!in!sedimentary!rocks![PPT:!Myrow!photo!of! !experiments!to!try! stone!to!infer!

  • utcrop!with!defects,!and!time!lapse!of!experiment].!!

! Let’s!make!a!table!of!the!different!stages!that!different!kinds!of!sedimentary!rocks! pass!through.!This!will!help!you!interpret!the!samples!you!examine!in!the!lab.!

  • T. Perron – 12.001
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! 2! ! Source!Rock! ! (Silici)clastic*sedimentary*rocks* Chemical/Biological*sed*rocks* ! Physical!processes!

  • Me

fragmentation!of!bedrock! chanical!weathering!–!

  • Er

surfa

  • sion!

Transport ce!in! –!detachment!from! ! sou –!moved!away!from! rce!area!

  • sou

wind rce! Finin ,!ic a e rea )!or !b !gr y!fl av u i id! smaller!particles!during! g ty (water,! !–!breakdown!i ! nto! transport! Chemical!processes!

  • Chemical!weathering!
  • Dissolution!–!usually!in!

H2O!

  • Alteration!–!to!

different!minerals!by! chemical!reactions!

  • Transport!–!in!solution!

Breakdown! Deposition!

  • Me

trans ch po ani r c t!e al! ne –!du rgy e! ! to!drop!in! Precipitation!

  • Inor
  • ganic!d
  • addi

ue!to tio !satur

  • loss!of!s

n!o

  • lv

f!s ent!by

  • lute

ati !e !

  • n!
  • f!sil

Biotically!mediated!(e.g.!shells! ica change!in!sol !or!carbonate ub )! ility v ! ap! Sedimentation! Burial*!

  • In!a!d

In!a!place!wher More!sediment!deposited!on!top! epression!or e!Ear !bas th’s in!(ocean,!lake,!valley) !surface!is!sinking!(Gulf ! !of!Mexico)! Diagenesis!(alteration!of!rock)!!!Lithification!(transformation!into!rock)!

  • Pressure,!heat,!different!fluids!lead
  • Dew

Compaction! !to…!

  • Chem!

at rea erin ct g ion ! Addition!of!miner ! s! als,!including!cementation! Lithification! Sedimentary!Rocks! ! *N bas

  • te!the!pr

ins,!which es !o ervation!bias n!contain!bo .!In!gener back!yard!in!western!MA!will!probably!not!form!a!sedimentary!rock! fte dies!of al,!s !wate ed r !r .!T

  • cks

he!s !r

  • ecor

il!yo d u!d !what!is ig!up!i !happening!in! n!your!suburban! ! because!it!is!eroding!rather!than!being!deposited!&!buried.! in!that!location,! Differen

  • Differen

t!kinds! t

  • f!

!source!material!(rock)! sed!rocks!result!from! ! Different!pathways!through!the!process!we!just!sketched!out!

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! 3! Knowing!the!names!& valuable !categories!that!have!been!devised!to!describe!sed!rocks!is! clastic,!b ,!and!your i !textbook!chapter!will!help!with!that.![PPT:!textbook!tables!on! Equally !

  • /chem]!

especial !important! ly:! is!knowing!how!a!rock!records!different!parts!of!this!pathway,! ! 1. 2. Which!transport!agent(s)?!H flow?!

  • w!strong?!If!water,!how!much,!and!what!kind!of!

Tectonic/geographic!settings!of!source!& Pacific!rim,!or!“passive”!like!eastern!N.!America?!Steep!river!exiting! !sink.!“Active”!margin!like!the! 3. mountains,!large!river!floodplain,!beach,!or!sea!floor?! Climate.!Glacial?!Tropical?!Desert?! How !

  • 4. Biological!activity.!Production,!deposition,!alteration!of!sediments.!
  • !ca

Ind n!w icator e!look s ! ! Prominent!recent!examples!of!geologists!applying!these!ideas! !of at !thes a!sed!rock e!four! !a fa nd!deduce!t ctors!in!cla hese!t stic!and!chem hings?!Rest /bio! !of!l sed! ect rock ure: s ! ! !

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! 4! ! Clastic( Chemical/Biological( 1.! st trans rengt Typ po e! h! r &! t!age

  • f!

nt!

  • Gra

Gra Bould in!si in!sha er ze! /gr pe! –! ave pr –!tr

  • p!to!tr

l/s

  • more!easily!

ans and po /s ans rt!d ilt/clay! por istanc t!ener –!256/2/0.05/0.005!mm! e.!L gy.! arger!grains!round!

  • Grain!sorting!–!change!in!transport

processes)![hand!samples (river!profile)!or!time!(e.g.!fining!up)![PPT]! Bedforms! !energy!in!space!

  • (shape!of!sed!surfa

,!recall!ripple!example]! ce!due!to!transport! Symmetry!!

  • Orie
  • n!

!bi

  • Amplitude!

dunes!make!thick!XQ ntati ! ! !fl !tr

  • w

/uni ans !energy,! !d po be ir d r e t!d s c ) ti ![P i w r

  • e

nal!f P ind! c T ti ]

  • !

vs.! lo n! w w ! ater!(eolian!

  • Reworking!of!chem./

can!apply!clastic!methods Diagenetic!textures,!e. bi g

  • .!ooids

!s ! ed!r !

  • cks,!

2.! geogr set sou Tect t rce! ing! aphic!

  • nic!

&!

  • f!

sink &! !

  • Mineralogy!–!source!rock!type!varies!with!tec!setting!
  • Quar

faster,!so!distal!sediments!more!qtz tz!content!–!mafic!minerals,!feldspar!break!down!

  • Grain!size!–!proxy!f

Qrich! Ind river! irect,!via!tr vs.!large!del ans t por a

  • r

)! t!agent!& !topograph !ener ic!s gy lope !(st !and eep!coa !tec!ac sta ti l v ! ity!

  • Species!composition!

Presence!of!clastic!component! higher!energy,!near!shore! !

  • !

Rock!type! (silica)!made!of!diatoms,! made!of!foraminifera! radiolarian –!limestone!(car ![PPT]!!!CCD [PPT] ! bo ,!cher nate t! )! 3.!Climate!

  • Chem!weathering!of!gra

!

  • !

ins!

  • Sequence!of!deposits!

Coarser!grains! !colder ! ! climate!change! Indirect,!via!transport!medium!(e.g.,!glacier!vs.!wind!vs.! river)!

  • Redox!state!

Presence!of!evaporit Species!composition! –!BIFs!

  • e!

C pr hemical!composition!–!climate!

  • xies!(lecture!later!in!course)!

4.! acti B vi iol ty

  • gica

! l!

  • Bi

C Sed!str lasts!made!of!biogenic!material!

  • turbati

uctur

  • n

es,!esp!fossils ! !

  • Species!composition!
  • Mi

dolomitization?)! neralogy!(microbial!role!in! Sed!str stromatolites,!fossils!in!general!! uctures!–!reefs,!

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! 5! Case!Studies! 1.! ! Snow

  • ball!Earth!
  • Present!them!with!diamictite/tillite!with!dolostone!stratigraphically!above,!say!

An!idea!that!goes!back!to!mid;20th!century!

  • de

environment!and!climate?! posited!in!marine!sediment,!and!BIF!found!in!deeper!water.!What!kind!of!

  • Then!say!paleomag!inclinations!indicate!deposition!near!equator,!in!Neoproterozoic!

(~ The!st 600

  • ry!(popul

;800Ma).!Gl arized!b aciers!a y!J.!K t!the! irschvi equator? nk!@!C ! Harva

  • rd):

altech!&!P.!Hoffman/D.!Schrag!@!

  • Gl

Ice

  • b

! al a Ocean!sealed!off!from!atmosphere! ft !gl ed! ciation! ris! !!ice!@

  • sits!

!equa

  • ;ra

deb dep glacia tor!(“ l!sed! snow in!ocea bal n l!Ea ![PPT] rth” ! )!

  • CO2

!oceans!become!anoxic!!

  • Sudden!input!of!C

!from!volcanoes!causes!strong!greenhouse! alters!from!limestone!to!dolostone![PPT]! O2 ! ! into!ocean!causes!deposit ! ion!of!“ !!melts!ice! cap!carbonate”,!which!

  • Oceans!become!oxic!

(magnetite,!Fe3O4,!or!hematite,!Fe !dissolved!Fe!

2O3

is! ,!inter

  • xidized!

bedded!wi and!precip th!sh it ale at !o es! r!c

  • u !as! IFs!

! he t rt)![P B PT]! ! This!is!a

  • Extreme!wind!&

ice! !giant!wave!r !waves!due!to!crazy!weather!and!sea!level!rise!from!melting! This!is!inferred!to!have!happened!not!just!once,!but!a!few!times! ipples![PPT]! Global!gl !cont aciat roversia ions!!Do!you!b l!story,!a uy!it nd!t ?!What!are!some!potential!problems!with!this!hypothesis?! here!is!debate!about!these!interpretations!of!sed!rocks.! ! 2.!Evidence!for!water!at!Meridiani!Planum,!Mars,!from!the!Opportunity!Rover !

  • !!
  • Was

Oppo !Mar rtuni s!e ty!s ver e !we nt!to t? !Me !

  • evidence!of!hematite!(Fe

rid O iani!Planum!because!spectra!collected!from!orbit!showed! Evidence!from!sed!rocks!exposed!in!wall!of!Endurance!C

  • ),!often!found!in!aqueous!environment!!

Clastic!sed!rocks!

2 3

" rater![PPT]:! " " Derived!from!wx!of!basalt! “F Cross esto ;

  • st

n”!c ratifica ross t ;lamination!with!sinuous!crests!interpreted!to!be! ion!–!wind!or!water?!Probably!wind,!given!size.![PPT]!

  • Chem!sed!rocks!

" diagnostic!of!transport!in!water![Dave!Rubin!animation]!

  • Jarosite!and!other!hydrous!sulfate!salts!suggest!formation!in!water;

Diag " " en et rich!environme H features! nt! ematite!concretions!–! ic! “Vugs”!–!voids!left!by!mineral!dissolution,!matrix!intact![PPT]! “blueberries”![PPT]! ! These!interpretations,!too,!are!not!without!controversy.!What!do!you!think:!was!Mars!wet?!

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MIT OpenCourseWare http://ocw.mit.edu

12.001 Introduction to Geology

Fall 2013 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.