450072carbon_sedHandout(1).doc

8/10/2019 450072carbon_sedHandout(1).doc

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HD667 Sedimentary Systems

Carbonate Sedimentology

Wolfgang Schlager

Vrije Universiteit Amsterdam/Earth Sciences

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Contents

0.Introduction

A.Princiles of car!onate sedimentolog"A.1 Production# erosion

A.$.%ro&th otential and dro&ning

A.' %eometr" of shoal&ater car!onate accumulations(.Standard facies model

(.1 Princial controls

(.$ )acies atterns * from ram to rimmed latform

(.' Standard facies !elts+. ,eferences

-n the cover

he island of (ora (ora in the SW Pacific * an eamle of a reefrimmed# troical latform. ,eef!elt at latform margin forms effective !arrier for oceanic &aves# rotecting a &ide lagoon. 2igh

&ater energ" on the ocean side and lo& energ" on the lagoon side of the reef causes reef de!ris to

!e shed referentiall" into the lagoon. )illing of the lagoon !" rogradation of the reef arons 3lightgreen4 is much faster than filling &ith de!ris from the eroding volcanoe on the land&ard side such

that the deeest arts of the lagoon are near the mountain rather than near the reef.

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0.INTRODUCTION

his handout suorts the car!onate sedimentolog" art of course 25667. It is meant as a

teaching aid# not a relacement of the course. 2o&ever# the handout can !e used for selfstud" if itis read in conjunction &ith an introductor" tet# such as 8ones 9 5esrochers 31::$4# uc;er 9

Wright 31::04# or Wright 9 (urchette 31::64.

he course is meant as an introduction to the stud" of car!onate roc;s on the scale of large

outcros to the scale of entire !asins. It also aims at rearing for the interretation of car!onates in

seismic images. +ar!onate etrolog" in thin sections is covered !" ar!onaatgesteenten? !" A. Immenhauser. he anal"sis of diagenetic tetures and theirgeochemical signals is covered !" course 25@:


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A. PRINCIP!S O" CAR#ONAT! S!DI$!NTATION

hree !asic rules cature the eculiar nature of car!onate deositional s"stems car!onate

sediments are largel" of organic origin# the s"stems can !uild &averesistant structures and the"undergo etensive diagenetic alteration !ecause the original minerals are metasta!le. he

imlications of these rules are ervasive. We &ill encounter them throughout the chaters of this

!oo;# starting &ith this first section# &hich !riefl" revie&s the rinciles of gro&th of reefs androduction of sediments as &ell as !asic atterns in the anatom" of car!onate accumulations.

A.%. Prod&'tion o( 'arbonate material

he material for car!onate sediments is etracted from the dissolved load of the sea. In this

resect# car!onates resem!le evaorites and differ from siliciclastics that deend on an eroding

hinterland for sediment sul". hroughout the Phanerooic# the sea &as the rime locus of

car!onate reciitation and organisms the dominant driversF inorganic reciitation &as 3and stillis4 imortant !ut clearl" ta;es second lace !ehind fiation of calcium car!onate as elements of

organic s;eletons. hus# ver" largel"# Gcar!onates are !orn# not madeG 3Hoel P. 8ames4 andcar!onate gro&th and roduction are intimatel" tied to the ocean environment &ith light#

temerature and nutrients eerting the most dominant controls. In different &a"s# a!iotic

reciitation# too# is controlled !" the ocean environment. Shoal&ater car!onate sediments areoceanic sediments# much li;e the elagic sediments of the deesea floor.

+alcite and aragonite are the onl" volumetricall" imortant minerals in marine car!onate

reciitates# !oth the organicall" and inorganicall" controlled variet". +alcite has highl" varia!leadmitures of magnesium. he roerties of lo&magnesian calcite and highmagnesian calcite are

so different that the t&o varieties are often treated as searate minerals. 5olomite is# for all

ractical intents and uroses# a roduct of diagenetic alteration. he chemical# !iological andmineralogical asects of the reciitation of these car!onate minerals in the marine environment is

a comle su!ject !e"ond the scoe of this handout. What &e need to ;ee in mind is that

car!onate reciitation in the marine environment occurs via a!iotic and !iotic ath&a"s and thatthree modes can !e distinguished according to the influence of organisms on the reciitation

rocess

a4 A!iotic mode. he influence of organisms is negligi!le. Preciitation is controlled !" the

thermod"namic saturation state and the reaction ;inetics of the aDueous solution. Eamles)i!rous aragonite cements# ooids.

!4 (ioticall" induced mode of reciitation. -rganisms induce reciitation !ut minerals differ

little from a!iotic reciitates. Eamles are micrite reciitates !" !acteria.c4 (ioticall" controlled mode. -rganisms determine comosition and form of the cr"stals as &ell

as onset and termination of reciitation. Eamles almost all car!onate s;eletons such as

!ivalve shells# coral s;eletons etc.

In the follo&ing# these modes# their most imortant environmental controls and their

com!ination into geologicall" significant car!onate factories &ill !e discussed 3)ig.A$ * A:4.

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"rom )re'i)itation modes to (a'tories

he three modes of car!onate reciitation com!ine &ith variations in erosional regime toform &hat one ma" call car!onate roduction factories.

roical factor"

he troical factor" lies in the hotic environment of the lo& latitudes# a!out '0' 0of the

eDuator. Production is dominated !" s;eletal reciitation &ith a significant a!iotic contri!utionfrom ooids and# ro!a!l"# &hitings. Significant amounts of marine cements are added during earl"

diagenesis &ithin the deositional setting. he micro!ial mode ma" contri!ute via oncoid grains

and stromatolites. he troical factor" sho&s the highest gro&th otential of all car!onate factories.

In addition# it has the strongest tendenc" to !uild rimms at the sea&ard limits of the shoal&aterdomain. hese rims are either !arrier reefs or sand shoals &ith etensive s"ndeositional

lithification. (oth t"es of rims can resist high &ater energ" and !uild into the suratidal one.

ight is argua!l" the most imortant roert" for car!onate reciitation in the troical factor".=ost s;eletal car!onate is secreted !" organisms that erform hotos"nthesis themselves or live in

s"m!iosis &ith hotos"nthetic algae. Photos"nthesis is a comle# and onl" artl" understoodrocess. he !asic reaction ma" !e simlified as

+-$J 2$- J solar energ" K 2+2- J -$

&here 2+2- reresents a simle summar" formula of the organic matter roduced in a

hotos"nthesiing organism. he formula clearl" illustrates the lin; !et&een hotos"nthesis and

car!onate chemistr". Photos"nthesis etracts +-$from the sea &ater# thus increasing its car!onatesaturation and facilitating reciitation of car!onate minerals. Preciitation in the form of +a+-'

has the added advantage for organisms that the" can remove otentiall" deleterious +a$Jions from

the s"stem and !uild a rotective s;eleton.

he lin; !et&een s;eletal car!onate fiation and hotos"nthesis 3and thus light4 elains the

decrease of s;eletal car!onate roduction &ith &ater deth# articularl" in troical environments.he t"ical attern is sho&n in )ig.A@ in general form and in )ig.A using the dominant

+ari!!ean reef !uilding coral =ontastrea annularis as an eamle. he gro&thdeth curve sho&s

a shallo& one of light saturation follo&ed !" a one of raid decrease and a third# dee one

&here gro&th ass"mtoticall" aroaches ero. his gro&th curve can !e derived from the &ellesta!lished eonential decrease of light intensit" &ith deth via a h"er!olic function. he

gro&thdeth atterns of most other car!onateroducing organisms are less &ell ;no&n !ut seem

to follo& similar trends. ight saturation means that light is not a gro&thlimiting factor.

emerature rivals light in its effect on s;eletal car!onate roduction. %enerall"# &armer is

!etter# !ut there eist uer temerature limits for the various car!onatesecreting organisms. hus#the calcif"ing !enthos functions in a temerature &indo& that is different for different organisms.

=ost hermat"ic 3i.e. s"m!iotic4 corals function in the range of $0'00+. he uer temerature

!oundar" sets imortant limits to car!onate roduction# articularl" in restricted lagoons. he most

imortant effect of temerature# ho&ever# is the glo!al onation of car!onate deosits !" latitude


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3)ig.A6# A74. In site of &hat has just !een said a!out the role of light# the !oundar" northern and

southern limit of coral reefs# and thus the !oundar" of troical and cool&ater car!onates# in the

modern oceans is controlled !" &inter temerature rather than radiation. his indicates thatcurrentl" the temerature limit for hermat"ic coral gro&th is reached !efore the light limit. In the

geologic record# this ma" not al&a"s have !een the case.

Salinit" varies relativel" little in the oenmarine environment. he effects of these su!tle

variations on car!onate roduction are not &ell ;no&n. Where access to the oen ocean is

restricted# salinit" varies greatl" and significantl" affects the diversit" of the !iota 3)ig.AL4. hecom!ined effects of salinit" and temerature variations allo& one to su!divide car!onate

environments 3)ig.A:4.

Hutrients. +ontrar" to common eectations# highnutrient environments are unfavora!le forman" car!onate s"stems. Hutrients# to !e sure# are essential for all organic gro&th# including that

of car!onatesecreting !enthos. 2o&ever# the car!onate communities# articularl" reefs# are

adated to life in su!marine deserts. he" roduce their organic tissue &ith the aid of sunlight from

the dissolved nitrate and hoshate in sea &ater and are ver" efficient in rec"cling nutrients &ithinthe s"stem. In highnutrient settings# the car!onate roducers are outaced !" soft!odied

cometitors such as flesh" algae# soft corals or songes. )urthermore# the destruction of reefframe through !ioerosion increases &ith increasing nutrient sul".

+ool&ater car!onate factor"

he cool&ater factor" factor" etends ole&ard of the troical domain# in some laces to

!e"ond the olar circle. It is dominated !" s;eletal material of nonhotos"nthetic !iota 3i.e.!oticall" controlled reciitation4. =ud is a minor comonent derived largel" from a!rasion of

s;eletal arts. -rganic frame!uilders and earl" cementation are scarce or a!sent. +onseDuentl"#

there is articall" no rim!uilding caa!ilit" and the deositional geometr" is that of a ram. heaccumulation rates are significantl" lo&er than in the troical factor" 3see


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5iscussion of car!onate roduction &ould !e incomlete &ithout considering erosion as a sort

of negative roduction. In the contet of this discussion# erosion stands for the removal of

sedimentar" roc; from the lace of deosition. =echanical erosion is a ;e" rocess in altering theoriginal roduction outut !ut in car!onates# t&o other rocesses are imortant chemical

dissolution and !ioerosion !" !oring# etching or rasing organisms 3)ig.A104.

=echanical erosion

It is distri!uted ver" unevenl" over car!onate deositional environments. It is most intensive atlatform margins &here the construction of reefs and lithified sand shoals drasticall" alters the

eDuili!rium rofile !et&een the sediment ile and the &ave energ" resent in the &ater column.

Siliciclastic s"stems that easil" adjust to the oceanCs energ" regime develo shelf !rea;s on average

around 100 m. ,eefs or car!onate sand shoals ma" !uild to sea level at the same osition andmodern coral reefs are a!le to &ithstand all !ut the most intensive oceanic &ave regime in the

troics. It is o!vious that mechanical erosion is intensive in these settings and constant

freme!uilding is reDuired to reair the damage. In considering the effects of mechanical erosion it

should !e noted that seafloor lithification is common and geologicall" coeval &ith deosition. hisgreatl" reduces the rate of mechanical erosion and ma;es iles of car!onate sediment more

resistant to lateral dislacement.

+hemical erosion.

At resent# the surface &aters of the ocean are nearl" ever"&here saturated &ith resect to calcite.

5issolution in shoal&ater car!onate settings is restricted to the most solu!le mineral hases#

magnesian calcites &ith ver" high magnesium contents and aragonite grains of ver" small sie 31micron or less4. 2o&ever# seafloor dissolution is intensive in the dee ocean.

(ioerosion.

Erosion !" organisms is much more intensive in limestones and dolomites that in silicate roc;s.

here are several reasons for this. +ar!onate minerals generall" are more solu!le than silicates can!e easil" etched !" organic acidsF the" are also softer than silicates and thus easier to a!rade

organic hard arts. )inall"# s;eletal car!onate contains a!undant food in the form of organic matter

!et&een the car!onate minerals. he intensit" of !ioerosion varies enromousl". It is most intensive

in the intertidal one of the troics &here it acts li;e a !iological sa& that cuts horiontal notches inthe limestones and creates the sectacular limestone cliffs 3)ig.BBBBBBBBB4. (ioerosion increases

&ith the nutrient content of the sea &ater. his effect causes much damage to reefs that are close to

a hinterland &ith agriculture !ecause runoff of dissolved agricutural fertiliers increases thenutrient content of the sea and greatl" intensifies !ioerosion.

A.+ ,ro-t )otential o( soal-ater 'arbonate systems

Siliciclastic deositional s"stems deend on outside sediment sul" for their accumulation. In

car!onate settings# the a!ilit" to gro& u&ard and roduce sediment is an intrinsic Dualit" of the

s"stem# called the gro&th otential. +oncetuall"# one should distinguish !et&een the a!ilit" to

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!uild u verticall" and trac; sea level# the aggradation otential# and the a!ilit" to roduce and

eort sediment# the roduction otential. he aggradation otential is articularl" critical for

survival or dro&ning of car!onate latformsF the roduction otential is a crucial factor for therogradation and retreat of car!onate latforms and the infilling or starvation of !asins.

he gro&th otential is different for the different factories &ith the troical factor" having thehighest# the cool&ater factor" the lo&est gro&th otential. his relationshi is disla"ed in

)ig.A11. he figure also sho&s that car!onate sedimentation rates decrease &ith increasing length

of the time san in &hich the rate has !een measured * a universal attern of the sediment record.his attern reflects the fact that sedimentation and erosion are eisodic or ulsating rocesses and

the record is riddled &ith hiatuses of highl" varia!le duration 3)igs.A1$4. We assume that the uer

limit of o!served sedimentation rates is an aroimation of the gro&th otential of car!onate

factories.

he gro&th otential also differs for different facies !elts of a factor". he troical factor"

sho&s man" eamles of this ;ind. =ost imortant is the difference !et&een the gro&th otential

of the rim and interior of troical car!onate latforms. he gro&th otential of the rim issignificantl" higher than that of the latform interior. When confronted &ith a relative sealevel rise

that eceeds the gro&th otential of the interior# a latform &ill raise its rim and leave the lagoonemt" 3Gemt" !uc;etG4.

A.+ ,eometry o( soal-ater 'arbonate a''&m&lations

Interreting deositional geometr" is an imortant ste to&ards redicting the anatom" ofsedimentar" roc;s in the su!surface. -ne advantage of sediment anal"sis !" deositional geometr"

is that it can !e erformed not onl" on easil" accessi!le outcros !ut also on seismic or georadar

radar rofiles and hotos of inaccessi!le outcros. %eometr" contains significant information onthe internal structure and the deositional histor" of a formation. his discussion deals first &ith

!asic controls on the geometr" of car!onate accumulations and the suita!le terminolog" for their

descrition. Su!seDuentl"# &e turn to characteristic atterns associated &ith the three car!onatefactories or secific deositional environments.

Prin'i)les o( 'arbonate de)ositional geometry

he geometr" of car!onate deosits results from the satial atterns of roduction and the

suerosed effects of sediment redistri!ution !" &aves and currents. )our commonl" occurringatterns in car!onate geometr" are directl" related to rinciles of car!onate roduction and the

h"drod"namics of the &ater column.

14 +ar!onate factories !uild u and tend to raise a!ove the adjacent sea floor. he reason for this

tendenc" is the !enthic origin of most car!onate sediment. (enthic organisms do not li;e !eing

!uried alive. he" thrive in areas &here lateral influ of sediment is modest such that insitu

car!onate roduction can outace it and raise the sea floor in the ones of intensive roduction.

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+ar!onate latform.

+ar!onate latform is a &idel" used and rather loose term. he dictionar" definition recisel"

catures the essence of the usage of this term in car!onate sedimentolog"


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regime on the sloe# shifting the !alance !et&een erosion and deosition of tur!idit" currents. his

in turn changes sediment geometr" on the sloe and the rise 3)ig.A$14.

c4 he angle of reose of loose sediment is a function of grain sie. Engineers have Duantified thisrelationshi for manmade dums and the same numerical relationshis have recentl" !een sho&n

to al" to largescale# geological features 3)ig.A$$ through A$4. he most imortant control on

the angle of reose is the degree of cohesion of the sediment.

he change in deositional regime &ith changing sloe angle is largel" caused !" the degree of

sediment !"assing on the sloe. he sediment source of the vast majorit" of car!onate sloes isthe latform. hus# sediment enters the sloe on the uer end and is distri!uted do&nsloe !"

various modes sediment gravit" transort. At gentle sloe angles# the cometence and caacit" of

the transorting agents decreases steadil" a&a" from the sediment source at the latform margin.

+onseDuentl"# sedimentation rates decrease and time lines converge !asin&ard. As declivit"increases# the vigor of sediment gravit" flo&s increases such that significant volumes of sediment

!"ass the stee sloe and come to rest on the adjacent !asin floor. (asin&ard of the !"ass sloe a

sediment aron develos as a series of laterall" coalescing tur!idite fans. hese arons are

comara!le to the continental rises of dee ocean !asins. he" are dominated !" tur!idites. In aglo!al surve"# 2eeen 9 har 31:L4 suggested that the !oundar" !et&een sloes and rises in the

ocean t"icall" lies at a!out 1.@0 3tanS K 0.0$4.

Steeening of sloes !e"ond the realm of !"assing roduces erosional sloes &here the

sediment !udget of the sloe is entirel" negative and more material is eorted !" erosionaltur!idit" currents and !" sluming and !asal sloe failure than the sloe receives from the

latform.

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)ig. A1 +ar!onate reciitation modes and car!onate factories. =arine car!onatereciitation ma" !e free of organic influence 3a!iotic4# induced !" organisms !ut not

further influenced !" them 3!ioticall" induced4 or totall" regulated !" organisms

3!ioticall" controlled4. -n large scales# the reciitation modes com!ine to differentcar!onate roduction s"stems or


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)ig.A$ he deth &indo&s of car!onate roduction. Production vs. deth estimated for the three

factories. 5ata for roical factor" are &ell ;no&n# cool&ater factor" and mound factor" are oorl"

constrained.

1'

0 m

100

200

300

400

500 ?

?

tropical mound cool

PRODUCTION vs. DEPTH

genuine

drowning

possible


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)ig.A' Production of the troical factor" from terrestrial elevation to su!hotic deth. In most

terrestrial environments# car!onate roc;s are !eing eroded# i.e. roduction is negative# !ecause

rain&ater is undersaturated &ith resect to car!onate. =aimum roduction is in the uer art ofthe hotic one# &hence it decreases aroimatl" eonentiall" &ith deth.

1@

mean

lo& &ater

lightsaturation

!ase of hotic Eone in clear &ater

&ater

deth

inm

eters

100

0 A0 100

roduction rate in M of maimum

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)ig.A@ +hange of light intensit" and troical car!onate roduction &ith &ater deth.ight disla"s a simle eonential decrease &ith &ater deth. he roduction of organic matter

can !e related via a h"er!olictangent function to light intensit"F roduction sho&s a shallo& one

of light saturation# &here light is not a gro&thlimiting factor# follo&ed !" raid decrease oforganic gro&th &ith &ater deth. In the troical car!onate factor"# organic roduction can !e ta;en

as a good estimate of car!onate roduction. In troical and su!troical environments# the one of

light saturation reaches to a!out $0 m for corals# the euhotic one to a!out 100 m. After (osscher9 Schlager 31::$4# modified. he dashed curve 3light etinction4 o!e"s the eDuation

I K I0e;

he !old curve of organic gro&th 3+hal;er in (osscher 9 Schlager# 1::$4 has the form

PK Pmatanh 3I/ I;4IK light intensit" at deth

I;K light intensit" at !ase of saturated oneP K organic roduction K &ater deth

; K etinction coefficient of light# deends on tur!idit" and other roerties

one of light saturation K interval &here light is not a gro&thlimiting factoreuhotic one K one a!ove comensation deth 3!iolog"4 or one &ith a!undant gro&th of

hotos"nthetic organisms.

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)ig.A Sigmoidal gro&th curves * a common attern in car!onates. Poulations of organisms

resond to the oening u of ne& living sace in three stes first# gro&th lags !ehind the creation

of living sace# second# oulation gro&th eceeds the rate of change in sace# finall"# oulation

gro&th is limited !" the rate of gro&th in living sace. A sigmoidal gro&th curve results from thisthreeste gro&th. =ost car!onate s"stems are controlled !" organic gro&th and thus follo& this

la&.

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)ig.A6 emerature control on reefs. ,ecent coral reefs are limited in the north and south !" theosition of the $00isotherm for the coldest &inter month# sho&n here as a !old line. ,eefs indicatd

!" stiles. After (osscher 9 Schlager 31::$4.

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)ig.A7 Protection against &ater tur!ulence and restriction of echange &ith the oen sea are t&o

indeendent varia!les that can !e used to classif" car!onate deositional environments in arotectionrestriction matri. he a!ove version is rather crude# refinement for secific case studies

is easil" ossi!le.

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)ig.AL he cliffs of a Pacific island illustrate several rinciles of car!onate erosion. Erosion ismost intensive in the intertidal one &here !ioerosion and &ave a!rasion com!ine to undercut the

island roc;s# roducing nearvertical sea cliffs. Intertidal erosion is also resonsi!le for the &atercovered terrace in the foreground and the overhanging !each at the foot of the cliff. Hote uliftedfossil intertidal one higher in the cliff. >arst erosion 3!" car!onatedissolving rain&ater and

lants4 creates the gentle landforms a!ove the cliffs and modifies the uer arts of the cliffs. In the

shallo&marine environment# car!onate erosion is normall" outaced !" reciitation.

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)ig.A: Sedimentation rates of the three car!onate factories lotted against the length ofthe time interval of o!servation. ,ates decrease &ith increasing length of time in all

factories. roical rates are highest and !est documented. +ool&ater rates are lo&er

overall 3!" a factor of @4F occasionall" high shortterm rates are caused !" reingand local traing of sediment. ,ates of the mound factor" nearl" eDual troical rates in

the domain of $.10* 107"r. heir short term rates are oorl" ;no&n. 5ou!le line is

estimate of gro&th otential of average troical latformF angular line is uer limit oflargest availa!le set of car!onate accumulation rates. he decrease of sedimentation

rates &ith increasing length of o!servation is a fundamental roert" of all sediment

families. After Schlager 3in ress4.

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)ig.A10 Shoretosloe rofiles of siliciclastics# cool&ater car!onates and rimmedcar!onate latforms.

a4 Siliclastics &ith a!undant sediment sul". ,esult is sea&ard diing surface in eDuili!rium

&ith deeening &ave !ase.!4 ,immed car!onate latforms. -n troical latforms# the &aveeDuili!rium rofile is grossl"

distorted !" the construction of &averesistant reefs and Duic;l" lithif"ing sand shoals# !othoccurring mainl" at the latform margin . Platforms are !asicall" dishshaed and eDuili!riumrofiles develo onl" locall" in arts of the lagoon. When sealevel eceeds the gro&th

otential of the latform# a sea&ard sloing ram ma" recede the gro&th of a rimmed rofile.

c4 +ar!onate rams are accumulations &ithout rims that resem!le the siliciclastic eDuili!rium

rofile. +ool&ater car!onate follo& this attern. roical latforms commonl" sho& rams asa transient stage during raid transgressions !efore a rim can develo.

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)ig.A11 U&ard gro&th of car!onate latforms &ith constant sloe reDuires deosition of ever

larger volumes of sediment on the flan;s. In the case of a coneshaed atoll# the gro&th of volume3V4 is roortional to the sDuare of the height of the cone. In case of a linear latform margin# the

gro&th of V is roortional to the height of the latform. ,eal latforms ro!a!l" fall !et&een

these t&o etremes. he stead" increase in sloe volume ma" limit the gro&th of ver" tall

latforms such as oceanic atolls. Smaller latforms seem to comensate for this effect !" increasein sloe angle and/or raid filling of the !asin. Schlager 31:L14.

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)ig.A1$ =odern su!marine sloe angles of car!onate latforms and siliciclastic s"stems in Atlantic

and Pacific. +ontours of 1# $ and @M of total samle 3H4 in unit area. H 3car!onates4 K @1'# H

3clastics4 K 7$. +ar!onates steeen &ith height !" !uilding slumresistant sloes. After Schlager

9 +am!er 31:L64.

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)ig.A1' Sloe angle and the !alance of erosion and deosition on sloes. As sloe angle increases#the vigor of tur!idit" currents increases too and changes the deositional regime on the sloe from

accretion to erosion. ("ass sloes reresent an intermediate stage. he" receive mud from the

erennial rain of sediment# &hereas coarse material travelling in large tur!idit" currents is s&etfarther into the !asin. After Schlager 9 +am!er 31:L64.

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)ig.A1@ %rainsie vs. angle of reose of loose material. his relationshi elains much of thedifference in sloe angle of coarse# mudfree sloe sediments and mudd" sloes. After >ir;!" in

>enter 31::04# modified.

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#. Carbonate (a'ies models

+ar!onate roc;s often over&helm the untrained e"e !" a !e&ildering variet" of tetures#structures and grain t"es. Patch" diagenesis adds to the imression of almost chaotic diversit" and

irregularit". Uon closer insection# the situation is not nearl" as !ad. If car!onate sediments are

characteried !" sedimentar" structure# teture and grain ;ind# a recurring succession of facies!elts can !e recognied in shoreto!asin transects. hese facies aear throughout the Phanerooic

and &ith onl" slight modification also in the late Precam!rian. his surrising ersistence indicates

that the evolution of organisms in this time interval had onl" a modif"ing effect on the !asiccar!onate facies. he standard car!onate facies seem to cature trends dictated !" other arameters

such as the distri!ution of gro&th rates as a function of deth and distance from shore# the degree

of rotection from the action of &aves and tidal currents# and the degree of restriction in the &ater

echange &ith the oen sea. -n the sloes# the declivit" and the the !alance !et&een sedimentationand erosion are crucial controls. hese rinciles are discussed in the net section# follo&ed !" a

resentation of facies on rams and rimmed latforms.

#.% Prin'i)al 'ontrols on 'arbonate (a'ies )atterns

We have seen a!ove that the troical car!onate factor"# !" far the most roductive car!onate

s"stem# roduces nearl" all its sediment in a narro& deth range that etends onl" fe& tens of

meters do&n from sea level. he sea&ard erimeter of this highl" roductive one tends to !erotected !" an elevated# &averesistant rim. his car!onate gro&th function generates a latform

geometr" &ith t&o !asicall" different deositional settings the ver" flat to s&et !" &aves and

tidal currents# and the stee sloes shaed !" gravit"driven sediment transort. he terms


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morholog" of rimmed latforms is eculiar to troical car!onates. he same situation eists &ith

regard to deositional facies.

he succession of tetures and sedimentar" structures on car!onate rams can !e directl"

matched &ith siliciclastic shelf models. =ore secificall"# one can correlate the facies attern of

attached rams &ith that of the siliciclastic !eachoen shelf model 3,einec; 9 Singh# 1:L0#'L$@$'4 and the facies succession of detached rams &ith the siliciclastic shelflagoon model 3,einec;

9 Singh# 1:L0# @$@@$:4.

here is no siliciclastic analogue for rimmed latforms. 2o&ever# the facies attern of rimmed

latforms can !e derived from the siliciclastic !eachshelf model or from the car!onate ram model

!" inserting a &averesistant rim 3comosed of reefs or artl" lithified sand shoals4 and adjusting

the facies for the effects of this rim. In the clima stage of latform evolution# the &averesistantrim sits at the latform edge# directl" ato the sloe. his osition is rather sta!le !ecause of the

d"namics of latform gro&th a rim that originall" forms in a more !an;&ard osition &ill raidl"

rograde if it roduces more sediment than is needed to match relative sealevel riseF such ecess

roduction is li;el" considering the high roductivit" of rims. At the latform edge# the rate ofrogradation slo&s do&n !ecause the high sloe reDuires much larger sediment volumes for the

same amount of rogradation 3)ig.A1:4. hus# further rogradation &ill !e slo&er !ut the sloe&ill tend to steeen to the angle of reose !ecause of the high sediment sul" from the roductive

rim.

-n the latform side# the rim sheds ecess sediment ranging in sie from cla" to !oulder.

(e"ond the reach of rim de!ris# an oen lagoon ma" develo &ith a !ottom rofile in eDuili!rium

&ith &ave action. 2o&ever# at the clima stage of latform evolution this lagoon is largel" filled

and relaced !" tidal flats that eand sea&ard almost to the latform rim.

he succession of facies on rimmed troical latforms has !een cast into a standard facies

model !" Wilson 31:74. (ased on t&o decades of case studies !" numerous researchers# WilsonCs31:74 model of standard facies has assed the test of time &ith fl"ing colors. It is reroduced in

)ig.(1. 5esite the remar;a!le succes of the model# certain modifications or additions are called

for. he" are illustrated in )igs.($ and discussed !elo&.

he standard model is


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Another characteristic of the Wilson model is that it uses a discrete horiontal scale &ith shar

!oundaries !et&een facies. In nature# these facies !oundaries ma" !e gradational and irregular. )orinstance# the su!division of sloes in facies ' and @ is often imossi!le and a com!ined !elt '/@

ma" !e more aroriate. he !oundar" !et&een facies 7 and L is often ver" gradual. In these

instances is refera!le to designate a com!ined facies !elt 7/L and eress increasing restriction !"!iotic indices or a larger num!er of su!facies.

he standard model sa"s nothing a!out &ind&ardlee&ard differentiation. =ost latformsdevelo as"mmetries in resonse to dominant &ind directions 3)igs. $@# $4. Seismic surve"s

reveal these as"mmetries !etter than most other techniDues.

#.+ Te standard (a'ies belts

1A4 5ee Sea

Setting (elo& &ave !ase and !elo& euhotic oneF art of dee sea# i.e. reaching through thethermocline into the realm of oceanic dee &ater.

Sediments Entire suite of deesea sediments such as elagic cla"# siliceous and car!onate ooe#hemielagic muds including tur!iditesF adjacent to latforms &e find mitures of elagic and

latformderived materials in the form of erilatform ooes and muds.

(iota Predominantl" lan;ton# t"ical oceanic associations. In erilatform sediments u to 7Mshallo&&ater !enthos.

1(4 +ratonic dee&ater !asins

Setting (elo& &ave !ase and !elo& euhotic one !ut normall" not connected &ith the oceanicdee&ater !od".

Sediments Similar to 1A !ut in =esooic+enooic rarel" ever elagic cla"F hemielagic muds

ver" commonF occasionall" anh"driticF some chertF anoic conditions fairl" common 3lac; of!iotur!ation# high organic content4.

(iota Predominantl" ne;ton and lan;ton# coDuinas of thinshelled !ivalves 3Posidonia t"e4#

occasionall" songe sicules.

$4 5ee shelf

Setting (elo& fair&eather &ave !ase !ut &ithin reach of storm &aves# &ithin or just !elo&

euhotic oneF forming lateaus !et&een active latform and deeer !asin 3these lateaus arecommonl" esta!lished on to of dro&ned latforms4.

Sediments =ostl" car!onate 3s;eletal &ac;estone# some grainstone4 and marl# some silicaF &ell

!iotur!ated# &ell !edded.(iota 5iverse shell" fauna indicating normal marine conditions. =inor lan;ton.

'4 oeofsloe aronSetting =oderatel" inclined sea floors 3over 1.04 !asin&ard of a steeer sloe.

Sediments =ostl" ure car!onates# rare intercalations of terrigenous mud. %rain sie highl"

varia!leF t"ical are &elldefined graded !eds or !reccia la"ers 3tur!idites or de!risflo&

deosits4 intercalated in mudd" !ac;ground sediment.

$L


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(iota =ostl" redeosited shallo&&ater !enthos# some dee&ater !enthos and lan;ton.

@4 SloeSetting distinctl" inclined sea floors 3commonl" 0 to nearvertical4 sea&ard of latform margin.

Sediment Predominantl" reed latform material &ith elagic admitures. 2ighl" varia!le

grain sieF end mem!ers are gentle mudd" sloe &ith much sluming and sand" or ru!!l" sloe&ith stee# lanar foresets.

(iota =ostl" redeosited shallo&&ater !enthos# some dee&ater !enthos and lan;ton.

4 ,eefs of latform margin 3)ig.(@4

Setting 3I4 -rganicall" sta!ilied mud mounds on uer sloe or 3II4 rams of ;noll reefs and

s;eletal sands or 3III4 &averesistant !arrier reefs rimming the latform.

Sediments Almost ure car!onate of ver" varia!le grain sie. =ost diagnostic are masses oratches of !oundstone or framestone# internal cavities &ith fillings of cement or sediment#

multile generations of construction# encrustation and !oring and destruction.

(iota Almost eclusivel" !enthos. +olonies of frame!uilders# encrusters# !orers along &ith large

volumes of loose s;eletal ru!!le and sand.

64 Sand shoals of latform margins 3)ig.(@4Setting Elongate shoals and tidal !ars# sometimes &ith eolianite islandsF a!ove fair&eather &ave

!ase and &ithin euhotic one# strongl" influenced !" tidal currents.

Sediments +lean lime sands# occasionall" &ith DuartF artl" &ith &ellreserved cross !edding#artl" !iotur!ated.

(iota Worn and a!raded !iota from reefs and associated environments# lo&diversit" infauna

adjusted to ver" mo!ile su!strate.

74 Platform interior normal marine

Setting )lat latform to &ithin euhotic one and normall" a!ove fair&eather &ave !aseF called

lagoon &hen rotected !" sand shoals# islands and reefs of latform marginF sufficientl"connected &ith oen sea to maintain salinities and temeratures close to those of adjacent

ocean.

Sediments ime mud# mudd" sand or sand# deending on grain sie of local sediment roductionand the efficienc" of &inno&ing !" &aves and tidal currentsF atches of !ioherms and

!iostromes. errigenous sand and mud ma" !e common in latforms attached to land# a!sent in

detached latforms such as oceanic atolls.

(iota Shallo&&ater !enthos &ith !ivalves# gastroods# songes# arthroods# foraminifers andalgae articularl" common.

L4 Platform interior restrictedSetting As for facies 7# !ut less &ell connected &ith oen ocean so that large variations of

temerature and salinit" are common.

Sediments =ostl" lime mud and mudd" sand# some clean sandF earl" diagenetic cementationcommonF terrigenous influ common.

(iota Shallo&&ater !iota of reduced diversit"# !ut commonl" &ith ver" large num!ers of

individualsF t"ical are cerithid gastroods# miliolid foraminifers.

$:


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:A4 Platform interior evaoritic

Setting as in facies 7 and L# "et &ith onl" eisodic influ of normal marine &aters and an arid

climate so that g"sum# anh"drite or halite ma" !e deosited !esides car!onates. Sa!;has# saltmarshes and salt onds are t"ical features.

Sediments +alcareous or dolomitic mud or sand# &ith nodular or coarsecr"stalline g"sum or

anh"driteF intercalations of red !eds and terrigenous eolianites in landattached latforms.(iota ittle indigenous !iota ecet !luegreen algae# occasional !rine shrim# a!normal salinit"

ostracodes# molluscs.

:(4 Platform interior !rac;ish

Setting oor connection &ith the oen sea just li;e :a !ut &ith a humid climate such that fresh

&ater runoff dilutes the small !odies of onded sea&ater and marsh vegetation sreads in the

suratidal flats.Sediments +alcareous marine mud or sand &ith occasional fresh&ater lime mud and eat la"ers.

(iota Shoal&ater marine organisms &ashed in &ith storms lus a!normalsalinit" ostracodes#

fresh&ater snails and charoh"tic algae.

WilsonCs 31:74 standard facies are also caa!le of reresenting the situation on car!onaterams. -n attached rams# the succession includes facies 7 assing into facies $. -n detached

rams# the succession starts on the land&ard side &ith facies L or 7# deending on the degree of

restriction# includes the !arrier as facies 6# follo&ed on the sea&ard side !" facies $. he criticaldifference to rimmed latforms remains even if the same facies categories are used to descri!e the

situation. he diagnostic criteria are the sloe facies ' and @. -n rimmed latforms# facies $ is

searated from the rim facies 6 !" a sloe &ith facies ' or @. 2omoclinal rams lac; sloe facies

altogether# &hereas distall" steeened rams sho& sloe facies ' or @ sea&ard of facies $. UsingWilsonCs 31:74 standard facies for descrition of rams is advantageous !ecause rams often

grade u&ard into rimmed latforms. ,immed rofiles and ram rofiles ma" also alternate in

sace &here the rim inde is lo&.

'0


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)ig.(1 S"nosis of standard facies !elts revie&ing second order !odies of sediment and standard

microfacies associated &ith each !elt. After Wilson 31:74.

'1


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)igs.($. +ommonl" o!served modifications of WilsonCs 31:74 standard facies in shoreto!asintransects.

'$


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)ig.(' ,immed margins are common on car!onate latforms. ,eefs 3facies 4 are imortant rim!uilders# !ut earl"lithified# stac;ed sand shoals 3facies 64 can !e eDuall" effective in defending

latforms. A rimCs effectiveness in rotecting the interior deends largel" on its continuit"#

measured !" the rim inde 3see chater A4. ,eef and sand shoals ma" also occur together on alatform magin.

''


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)ig.(@ Wind&ardlee&ard as"mmetr" in a seismic cross section of %reat (ahama (an;3E!erli 9 %ins!urg# 1:LL4. -n the shallo& latform to# sediment moves redominantl"

&est&ard under the influence of the easterl" trade &inds. As a result of this as"mmetric

sediment movement# &ind&ard !an; margins are sediment starved# aggrade verticall"and sho& good evidence for seismic reefs. Westfacing# lee&ard margins are &ell

sulied &ith latform sediment and rograde. Aarent lac; of reefs on the rogradinglee&ard margin on the right is ro!a!l" caused !" raid shift of reef gro&th andfreDuent interrutions !" sediment duming. Progradation ultimatel" filled the !asin and

no& the latform etends all the &a" across.

'@


35/36

C. R!"!R!NC!S

(osscher# 2.# and Schlager# W.31::$4 +omuter simulation of reef gro&th.Sedimentolog"# v. ':# .0'1$.

)ischer# A.%. 31:L$4 ongterm oscillations recorded in stratigrah". In (erger# W. 9

+ro&ell# 8.+. 3eds4# +limate in earth histor". 3Hat.Ac.Press4 Washington# .:710@.%rigg#,.W. 31:L$4. 5ar&in Point a threshold for atoll formation. +oral ,eefs# v.1# .$:

'@.

2ardie# .A. 9 Shinn# E.A. 31:L64 idal flats. In +ar!onate deositional environments#modern and ancient. Part '. +olorado School of =ines Nuarterl"# v.L0# no.'# 7@ .

8ames# H.P. 9 >endall# A.+. 31::$4 Introduction to car!onate and evaorite facies

models. In Wal;er# ,.%. and 8ames# H.P.# )acies =odels resonse to sea level

change. 3%eological Association of +anada4 Stittsville# -ntario# .$6$7.8ames# H.P. 9 =acint"re# I.%. 31:L4 ,eefs. +ar!onate deositional environments#

modern and ancient. Part 1. +olorado School of =ines Nuarterl"# v. L0# no.'# 70 .

8ones# (.W. 9 5esrochers# A. 31::$4 Shallo& latform car!onates. In Wal;er# ,.%. 9

8ames# H.P.# )acies models. 3%eol. Assoc. +anada4 St. 8ohnOs# H)# +anada# .$77'01.>enter# 8.A.=. 31::04 +ar!onate latform flan;s sloe angle and sediment fa!ric.

Sedimentolog"# v.'7# .7777:@.ees# A. 31:74 Possi!le influence of salinit" and temerature on modern shelf

car!onate sedimentation. =arine %eolog"# v.1:# .1:1:L.

=ont"# +..V.# (osence# 5.W.8.# (ridges# P.2. 9 Pratt# (.,. 31::4 +ar!onate mudmounds# their origin and evolution. Int. Assoc. Sedim. Sec. Pu!l.# $'# '7.

=orse# 8.W. 9 =ac;enie# ).. 31::04 %eocemistr" of sedimentar" car!onates.

5eveloments in Sedimentolog". 3Elsevier4 Amsterdam# v.@L# 707.

Heumann# A.%. 9 =acint"re# I. 31:L4 ,eef resonse to sealevel rise ;eeu# catchu or giveu. Proceedings of the )ifth International +oral ,eef +ongress# ahiti# v.'#

. 10110.

Plotnic;# 8.E. 31:L64 A fractal model for the distri!ution of stratigrahic hiatuses.8ournal of %eolog"# v.:@# no.6# .LLL:0.

Posamentier# 2.W.# 8erve"# =.. and Vail# P.,. 31:LL4 Eustatic controls on clastic

deosition I. SEP= Sec. Pu!l. @$# .10:[email protected]# 2.W. 9 Vail# P.,. 31:LL4 Eustatic controls on clastic deosition II

seDuence and s"stems tract models. SEP= Sec. Pu!l. @$# .1$1@.

Purser# (.2. 31:7'4 he Persian %ulf. 3Sringer4 (erlin# .1@71.

,ead# 8.). 31:L4 +ar!onate latform facies models. AAP% (ull.# v.6:# .1$1.,eince;# 2.E. 9 Singh# I.(. 31:L04 5eositional sedimentar" environments. 3Sringer

Verlag4 2eidel!erg# $ndedition#1.

Sand!erg# P. 31:L4 Hons;eletal aragonite and +-$ in the Phanerooic andProterooic. In SundDuist# E. and (roec;er# W.# he car!on c"cle and atmosheric

+-$ Hatural variations Archean to Present. %eoh"sical =onograhs# v. '$# .L

:@.Schlager# W. 31:L14 he arado of dro&ned reefs and car!onate latforms. %SA (ull.

v. :$# .1:7$11.

Schlager# W. 31::$4 Sedimentolog" and seDuence stratigrah" of reefs and car!onate

latforms. Amer.Assoc.Petrol.%eol. +ourse Hotes Series# v.'@# .171.

'


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Schlager# W. 31::'4 Accommodation and sul" a dual control on stratigrahic

seDuences. Sedimentar" %eolog"# v. L6# .1111'6.

Schlager# W. 3in ress4 Sedimentation rates and gro&th otential of troical# cool&aterand mound car!onate s"stems. %eol. Soc. ondon# Sec. Pu!l.

Schlager# W. 9 +am!er# -.# 31:L64 Su!marine sloe angles# dro&ning unconformities

and selferosion of limestone escarments. %eolog"# v.1@# .76$76.Schlanger# S.-. 31:L14 Shallo&&ater limestones in oceanic !asins as tectonic and

aleoceanograhic indicators. In Warme# 8.E.# 5ouglas# ,.%. 9 Winterer# E.. 3eds4#

he dee sea drilling roject a decade of rogress# Soc.Econ.Pal.=in.# Sec.Pu!l.# '$#.$0:$$6.

Schroeder# =. 31::14 )ractals# chaos# o&er la&s. 3)reeman4# He& or;# @$: .

uc;er# =.E. 9 Wright# V.P. 31::04 +ar!onate sedimentolog". 3(lac;&ell Scientific

Pu!lications4 -ford# @:6.Vail# P.,. et al.# 31:774. Seismic stratigrah" and glo!al changes of sea level# in Pa"ton#

+.E. 3ed4# Seismic stratigrah" alications to h"drocar!on eloration# AAP%

=em.# $6# .@:$1$.

Wilson# 8.. 31:74. +ar!onate facies in geologic histor". 3Sringer Verlag4# He& or;#@71 .

Wright# V.P. 9 (urchette# .P. 31::64 +hater : Shallo&&ater car!onate environments.In ,eading# 2.%. 3ed4# Sedimentar" environments rocesses# facies# stratigrah".

3(lac;&ell Scientific Pu!lications4 -ford# .'$':@.

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