carbonate lecture 4

7/14/2019 Carbonate Lecture 4

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! Some Terminology! Muddy Peritidal Facies! Intertidal-Subtidal Sand Bodies! Reefs and Carbonate Buildups! Pelagic and Resedimented Deep-Water

Limestones

Lecture 4

Carbonate Depositional Systems

CARBONATE PLATFORM

Basin

RampShelf Bank

Basin

Carbonate platforms: geometry, terminology

Platform edge: a critical zone


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Rimmed platform Occurs segmented to continuous rampart with reefs and/or lime

sand shoals along the margin

Absorbs ocean waves and dissipates the storm energy Can restrict water circulation on the platform Generates a variety of lower energy environments Confines the movement of coarse-grained sediment to the lagoon/

shallow platform



Unrimmed platform

Platform (open shelf and ramp) without a margin barrier nearshore, wave-agitated facies grade into deeper water, low-

energy deposits

Sediment can easily be transported into deep water Subtidal accumulation space will be controlled as much by the

depth of wave abrasion as by sea level



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(Tucker, 1999)

Rimmed Shelf Depositional Systems

(Tucker, 1999)

Carbonate Ramp Depositional Systems

! Some Terminology! Muddy Peritidal Facies (see Tucker; Pratt)! Intertidal-Subtidal Sand Bodies! Reefs and Carbonate Buildups! Pelagic and Resedimented Deep-Water

Limestones

Lecture 4



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1. Limestones and dolostones representingcalcareous sediments that are/were deposited in

very shallow water and on muddy tidal flats

2. Wide range of features that can be compareddirectly with modern analogues

Easy to recognize in the field Important paleobathymetric indicators

Muddy Peritidal Facies

(Pratt et al., 1992)

Where do they form?

Typical of microtidal conditions (< 2 m)


The Peritidal Environment


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13

Modern Tidal Flats; Persian Gulf

(Prattetal.,1992)

(Heckel, 1972)

Euryhaline vs Stenohaline Taxa

Modern Tidal Flats; Andros Island

(Scoffin, 1987)


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(Scoffin, 1987)

Modern Tidal Flats; Andros Island

Sedimentary and Biogenic Structures

(Scoffin, 1987)

1. Dominantly lime mudstones, commonly peloidal,although local lenses of coarser sediment

(grainstone) may represent tidal-channel fills.

2. Fenestrae are characteristic features formingdistinctive birdseye/fenestral limestones.

3. Fauna may be restricted in diversity;gastropods with ostracods and bivalves.

Inter- & Supratidal Flat Sedimentation


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4. Thin, coarse layers of skeletal grains may be

transported on tidal flats by storms.

5. Microbial mats and stromatolites; many are

simple planar varieties showing desiccation

cracks and laminoid fenestrae.

6. Small local domal to columnar stromatolites.

7. Bioturbation and rootlet may occur.

Inter- & Supratidal Flat Sedimentation

1. Synsedimentary cemented surface crusts whichmay expand to form tepee structures and may

break up to give intraclasts.

2. Penecontemporenous dolomitization may takeplace, giving fine grained dolomite mosaics.

3. In arid climatic areas evaporite mineralsgypsum-anhydrite-halite will develop.

Inter- & Supratidal Flat Diagenesis

Subtidal Lagoonal Sedimentation

1. Living organisms and accumulating sediments inpredominantly quiet-water areas, depend

largely on the degree of restriction.

2. Sea water may be normal, brackish orhypersaline in terms of salinity.

3. Sediments are variable in grain size, althoughmany are carbonate muds, rich in peloids.

4. Lagoon floor is dominated by euryhaline taxa


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5. Surficial microbial mats and sea grasses may

cover the lagoon floor.

6. Bioturbation is intensive mainly crustaceans and

bivalves.

7. Sedimentary structures poorly developed but

vaguely graded beds of coarser grains and shell

lags may be formed through periodic storm

reworking .

Subtidal Lagoonal Sedimentation

1. Sea floor cementation limited to intraskeletalcavities. Aggregate are common.

2. Microbes play a significant role in skeletalbreakdown and production of micritized grains.

Subtidal Lagoonal Diagenesis

Meter-Scale Peritidal Cycles

1. Facies typically organized in shallowing-upwardsuccessions (submeter to decameter-thick).

2. Basal subtidal unit (A), intermediate intertidalfacies (B) and upper supratidal unit (C) with or

without a capping terrestrial horizons.


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Humid, Low-Energy

Tidal Flats



Arid, Low-EnergyTidal Flats

Middle to Upper Cambrian platform carbonates,Bonanza King Formation, southern Great Basin


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3. Various styles according to energy (low vs high),climate (arid vs humid) and biological evolution

(microbes vs invertebrates vs plants).

4. Asymmetrical organization (ABC) is common.5. Repeated patterns in time ABC/ABC/ABC


Intertidal facies; Finelylaminated, fine-grained

dolomite

Subtidal facies; Dark-gray,thickly-bedded micriticlimestone

Milroy Member of theMiddle Ordovician

Loysburg Formation;Pennsylvania

1

2

3

4

Tidal Flat Carbonate Factory - Source Area

Tidal Flat Source

No Sedimentation

New Tidal Flat

Peritidal Cyclostratigraphy - Autocyclicity

Carbonate Factory - Source Area


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Peritidal Cyclostratigraphy - Allocyclicity

! Some Terminology! Muddy Peritidal Facies! Intertidal-Subtidal Sand Bodies (see Tucker)! Reefs and Carbonate Buildups! Pelagic and Resedimented Deep-Water

Limestones

Lecture 4


(Tucker, 1999)

Intertidal-Subtidal Sand Bodies


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(Tucker, 1999)


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Modern Tidal Flats; Persian Gulf

(Prat

tetal.,1992)

Setting

barrier, beaches, shorefaces and tidal deltasalong ramp shorelines

shoals and banks along rimmed-shelf marginsHydraulic Energy

shallow areas of strong tidal current and waveaction (mostly


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(Tucker, 1999)


Sediment Types

mainly grainstones composed of ooids androunded and sorted skeletal grains

carbonate sands (grainstone-packstone) alsodeposited in deeper waters on carbonate

ramps by the action of storms


(from Aigner, 1985)

Tempestites below the Normal Wave Base


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Hours Y

ears

Minutes

Seconds

Temporal relationships in tempestites

HCSCross-strata

10100CM

Bioturbation

(Modified from Dott, 1983)

8 . WA V E . ND S TO RN4 - DO N4 INA TE DHO RE L INE ND S HA L L O W. I \4 A RINEY S TE MS 1 8 1

Tirne ------->* E= 9 a i;

B

CurrentBe daesponse

Bed statef rn e a n d )

r/Sml l wve ipplesPlanar-laminetedandwave npple onr]sCrosbeddec, oarsesno ano grevelSole narks n base

Typ ica l e r t i ca l uccess ionfs t ruc tu resroduced y as to rm c t ing n a m ix tu re fsand rades nd inegrave l

F A C T E S U C C E S S T O N S NS T O R M . D O M I N A T E D H E L V E SS t o r m - d o m i n a t e dh e l v e s n d c o a s t st e n d o b e i n e a r , nd h e n c e p r o d u c er e l a t i v e l y i m p l e , a b u l a r r o c k u n i t sc o m p a r e d o d e l t a i c co a s t s , w h i chh a v e a n i r r e g u l a r h o r e l i n e n d c o r -r e s p o n d i n g a t e r a l a c i e s c o m p l e x i t y( s e e C h a p t e r1 0 ) . C o a s t a l r o g r a d a -t i o n w i l l p r o d u c e n e s s e n t i a l l y a b u -l a r b o d y i n w h i c h t h e b a s i c s t r a ti -g r a p h i c m o t i f i s a s a n d i e r u p w a r ds u c c e s s i o n h a t r e c o r d s a p r o g r e s -s i v e u p w a r d n c r e a s e n h e n f l u e n c eof waves and cur rent s as t he shore-l i n e p r o g r a d e s .T h e s u c c e s s i o nma yc u l m i n a t e i n s u b a e r i a l b e a c hd e p o s i t s n d e v e n a l l u v i a l e d i m e n t si f h e a c c o m m o d a t i o ns e n t i r e l y i l l e da n d h e o p o f h e s u c c e s s i o n a s no ts u b s e q u e n t l y b e e n r e m o v e d b yt r a n s g r e s s i v e r o s i o n F ig . 2 0 ) . T h ed e t a i l s o f t h e s u c c e s s i o n w i l l v a r yd e p e n d i n g o n v a r i a b l e s s u c h a sa v a i l a b l e g r a i n s i z e s , p r o p o r t i o nofs a n d / g r a v e l o m u d , w a v e a n d t i d a le n e r g y , b i o l o g i c a l a c t i v i t y , s h e l fs l o p e , s u b s i d e n c e a t e a n d r a t e ofs e d i m e n t u p p l y s e e a d d i t i o n a l is -

- = G r1t . + : : : F + Jl r r ---C o m b r n e d l o w Wa n ng osci atory low

Erosion D e p o s i t i o ntrregutr cours,gutters F l a t b e d H u m m o c k y e danisokoprc--+ sotropic 2 -D w a v en p p l e s N o b e df o r m s

F i g u re 1 9 . A- Th e d e v e l o p m e n t f a n i d e a l i z e d v e n t b e d n i n e s a n d s t o n e s a re s u l t f s t o rm -g e n e ra t e do m b i n e d l o w . H i g h - f re -q u e n c y , a v e -g e n e ra t e d s c i l l a t o ry u r re n t s re d o m i n a n t , u t u n i d i re c t i o n a l e o s t ro p h i c l o w d u r i n g h e p e a k o f h e s t o f m p ro v i d e so e t o f f s h o re o m p o n e n t . D u r i n g h e r i s i n g h a s e o f h e s t o rm , e d i m e n t s s u s p e n d e d n d h e m u d d y b e d s e ro d e d , o rm i n g v a r i e t yc f s o l e m a rk s a n d g u t t e rs . As t h e s t o rm s t a r t s o w a n e , n i t i a l l y l a n a r - l a m i n a t e d a n d s d e p o s i t e d n d e r p o w e r f u l o m b i n e d l o w , bu ti h r s v o l v e s o H C S, w h i c h n i l i a l l ym a y b e a n i s o t ro p i c u e o h e n f l u e n c e f h e u n i d i re c t i o n a ll o w c o m p o n e n t .As t h e s t o rmw a n e s ,: o n t i n u e d e d i m e n l e t t l i n g n d e r a rg e l y s c i l l a t o ry l o w p ro d u c e s s o t ro p i c C S, e v e n t u a l l ym a n t l e d y s m a l l w a v e r i p p l e s B . Th e'e s u l t so f h e s m es t o rm c o n d i t i o n s h e n h e s u b s t ra t e s a m i x t u re f s a n d a n d l n e g ra v e l . D u n e s , o t h 2 -D a n d 3 -D , m i g ra t e u r i n gs t ro n g o m b i n e d l o w o p ro d u c e ro s s b e d d i n g , h i c h m a y b e o f u n u s u a l l yo w n c l i n a t i o n u e o h e a f f e c t f s u p e r i m p o s e d a v e m o t i o n .-a rg e s y m m e t r i c a l a v e i p p l e s n d o w -a n g l e o p l a n a r l a m i n a t e d a n d e c o rd h e ra n s i t i o n o d o m i n a n t l y s c i l l a t o ryl o w a s h e s t o rma n e s . Th e w h o l e b e d s m a n t l e d y s m a l lw a v e i p p l e s n d a m u d d ra p e B a s e d n C h e e l , 1 9 9 1 i C h e e l n d L e c k i e , 9 9 3 ) .e d h e s e s t r u c t u r e s o h a v e b e e n c u tand f i l led by o f ishore : d i rec t ed stormi o w s in a n e a r s h o r e e n v i r o n m e n t .l l h e r e x a m p l e s fr o m C r e t a c e o u s' o c k s o l w e s t e r n C a n a d a a r e s i m i l a r1 mny respec t s o t hose o f L4y row1 9 9 2 ) . u t i f i e r n h a v i n g n u b i q u i -: r u s f i l l o f f i n e - g r a i n e d C S a n d r i p -3 r e d s a n d s t o n e (P l in t , 1 9 9 6 ; P l i n t3 n d N u m m e d a l , 0 0 0 ; F i g . 1 8 8 ) ,: J g g e s t i v eof f i l l ing b u t n o t n e c e s - r i l y c u t t i n g ) d u r i n g s t r o n g w a v e3c t ion . Amos e t a l . (2003) observed- i i o r e - n o r m a l u t t e r c a s t s o r m i n g n' l - 40 m of w a t e r o n t h e s h o r e f a c e: 1 S a b l e s l a n d N o v a S c o t i a s h e l f ;: g. 2 ) . G u t t e r o r m a t i o n n d f i l l i n g' : ck a f e w h o u r s a n d o c c u r r e d o n l y: . r r in g s t r o n g c o a s t a l d o w n w e l l i n g: . e t o o n s h o r e i r e c t e d t o r m w i n d s ,: J p p o r t i n g t h e i n t e r p r e t a t io n oft r y r o w 1 9 9 2 ) -G u l t e r c a s t s a r e c o m m o n i n- . . o re f ace s u c c e s s i o n s , a s s o c i a t e d. : h H C S , b u t h e y a l s o o c c u r n h i n -,, I n t e r b e d d e dw a v e - r i p p l e d s a n d -, . i lne a n d m u d s t o n e y p i c a lo f m o r e: ' s h o r e e n v i r o n m e n t s . W h e r er , ^ o r e l i n e sa n b e m a p p e d e g i o n a l l y ,

g u t t e r a s t s n n e a r s h o r eH C S a c i e st e n d t o b e o r i e n t e d h o r e - p e r p e n d i -c u l a r ( L e c k i e a n d K r y s t i n i k , 1 9 8 9 ;[ / y r o w , 1 9 9 2 ; P l i n t , 1 9 9 6 ; P l i n t a n dN u m m e d a l , 2 0 0 0 ; F i g . 2 ) , w h e r e a ss m l l e r u t t e rs y p i c a l f h i n n e r e d -ded, more o f f shore ac ies t end t o bes h o r e - o b l i q u eo s h o r e - p a r l l e lA i g n -e r , 1 9 8 5 ; a r t e t a / . , 9 9 0 iH a y e f a / . ,2 0 0 3 ; V a r b a n n d P l in t , 2 0 0 8 a ; i g .1 8 C ) ; t h e l a t t e r m a y r e c o r dg e o s t r o p h i c l o w s n a r e a s o o d e e pt o have exper ienced s t rong wavea c t i o n .S t orm BedsT h e d e v e l o p m e n t o f a n i d e a l i z e ds t o r m b e d i s s u m m a r i z e d n F i g u r e1 9 4 , w h i c h p o r t r a y s h e r e s p o n s e ff i n e s a n d o n t h e s e a f l o o r o v a r i o u sf l o w s t a t e s u r i n g h e i s i n g n d w a n -i n g s t a g e s o f a s t o r m . F i g u r e 19 8s u m m a r a z e s h e s e d i m e n t a r y t r u c -t u r e s t h a t d e v e l o p u n d e r s i m i l a rh y d r a u l i cc o n d i t i o n s b u t w h e r e t h eb e d c o n s i s t s f a m i x t u r e f s a n d an df i n e g r a v e l .

Tempestites below the Normal Wave Base

(from Plint, 2011)

(from Einsele, 2000)


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(Aigner,1985)

Distal vs proximal Tempestites

Biota

fragments of normal marine organisms distinct trace fossil assemblages

Other Characteristics

scours and channels in tempestites chiefly cross-bedding of all scales; keystone

vugs (intertidal conditions)


Keystone Vugs in Grainstones

Small cavities representing voids left by air and gas bubbles andresulting from air escaping from intergranular pores as they areflooded with marine waters during the flood tidal cycle.

carbonate lecture 4

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