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Se uence

Strati ra hthestudyofrockrelationswithinatimestratigraphicframeworkofrepetitive,genetically

relatedstrata

bounded

by

surfaces

of

erosion

or

nondeposition,ortheircorrelativeconformities.

Importantbecauseitplacesstrataintoapredictable,cronostratrigraphic

accommodationspace

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baselevel

will

result

in

divisions

of

the

.

T eterm sequence was ntro uce yS oss

etal.(1949)todesignateastratigraphicunit

oun e

ysu aer a

uncon orm t es.

e

identified6majorunconformitiesinNorth

mer ca.

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Correlativeconformities

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.

forcebehind

sequence

formation

at

all

levels

.

+globalsealevelchart.

Thisis

why

it

is

all

about

relative

sea

level

changevs.sealevelchange.

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Accommodationspace

(i.e.relative

sea

level

change)

EUSTACY

Posamentier, 198

SUBSIDENCE UPLIFT

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Accommodationspaceequation

Space is created by

chan in in tectonic Space is filled with

+ = +T:Tectonicsubsidence

E=rateofEustaticsealevelrise

subsidence and Eustasy water and sediments

S:sedimentationrate

W:water

depth

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boundary)

depositionalsystems

3 Parase uence set stackin atterns: ro radational

aggradational,retrogradational)

4)Parasequence

(boundedbyflooding surfaces)

5)Floodingsurface

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linkedand

coexisting

today

(fluvial,

delataic,

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geneticallyrelated

strata

bouned

by

. .

relatedconformities.

recordononecycleofrelativesealevel

mportant:every

epos t ona

sequence

s

boundedaboveandbelowbyunconformities

orcorre at vecon orm t es.

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Systemtract(subdivisionofthedepositionalsystem)Genetica y

associate

stratigrap ic

units

t at

were

eposite

uring

speci ic

phasesoftherelativesealevelcycle(Posamentier,etal,1988)and

representedintherockrecordasthreedimensionalfaciesassemblages.They

, ,

andparasequence

stacking

pattern

(Van

Wagoner

et

al.,

1988)

The original 3 system track

HST

LST

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Highstandsystemstract(HST):

Durin suchaslowriseinrelativesealevel sedimentsu l is

>

rise,

driving

a

seaward

building

of

the

coast

known

as

progradationalstacking.TheHSTwillcontainanincreasingly

.

systemstract,eustaticsealevelbeginstofall,butsubsidence

>fall,

such

that

relative

sea

level

is

rising,

albeit

at

ever

slowerrates.

Eventually,astherateofeustaticfallincreases,iteventually

,

level(Falling

stage

system

track

+Sequence

boundary).

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,

equalsthe

rate

of

subsidence

and

is

then

,

aslowrelativeriseinsealevel.Justasinthe

,

outpacedbysedimentationrate,leadingtoa

thelowstandsystemstract(LST).

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Transgressivesystems

tract

(TST)

,

ofrelative

sea

level

rise

also

increases

and

,

leadingtoretrogradationalparasequence

.

calledthetransgressivesystemstract(TST).

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Transgressivesurface

(System

tract)

Maximum oo ingsur ace Parasequence

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Thekeyverticalsuccessioninall

depositionalsequences:

Frombottomtotop:

1) Sequenceboundary

ow tan system

Track(LST)

3) Transgressive surface

4) Trans ressive s stem

track(TST)

5) Maximumflooding

surface

track(HST)

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Howdoyourecognizeasequence

boundary?

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PARASEQUENCEPARASEQUENCE

Geneticallyrelated,relativelyconformable

floodingsurfacesandtheircorrelativesurfacesBedsandbedsetsarepartofthesameprogradational

event

Thedepositsofasimpleprogradationoftheshoreline

Van Wagoner et al., 1990

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Surfacemarkedbydeeperwaterstratarestingon

shallowerwaterstrata

Canbecausedby:Van Wagoner et al., 1990

re a ver se nsea eve ue otectonicsubsidenceorfaulting

Eustac

Simpledeltalobecompaction looding Surfacelooding Surface

Van Wagoner, Mitchum, Campion and Rahmanian 1990

looding Surfacelooding Surface

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Systemtracksandparasequences

arearranged

into

parasequence

sets

Asuccessionof eneticall related

parasequencesthatformadistinctivestacking

attern

exam le:

ro radatioal

retrogradational,aggradational)

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Stackingpatterns

Sedimentation>accomodation

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Stackingpatterns

Sedimentation=accomodation

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Stackingpatterns

Sedimentation

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Rate of sediment supply Rate ofaccommodationm

od

ati

on vs

Sediment Su lAggradationalParasequence

comm

odatio

n

ate

ofa

cco

ProgradationalParasequence

edimentsup

ply=

In

creasing

Increasing rate ofsediment supply

Sediment bypass

0

ati

on

Sequence Boundary

faccomm

o

96_0118_13

RegionalIncision

Loss

(modified from Shanley and McCabe,1996)

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Transition from marine

o non mar ne

After Catuneanu, 2006

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Whatarewelookingat?(CretaceousMancosShalenearWoodside,Utah)

Tidal influence

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HST

LST

HST

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LowStandsystemTract

, ,rates>accomodation rates, shallowing

upward

L t d t t t

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Lowstand systems tract

T i t t t

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Transgressive systems tract

Highstand systems tract

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Highstand systems tract