Carbonates

The other white meat….

Processes that affect compositionally controlled marine facies

1. Influx of terrigenous sediment

2. Rate of organic productivity• Siliciclastic deposition occurs when 1 > 2

• Carbonate deposition occurs when 2 > 1

Distinctive characteristics of carbonate marine facies

• Carbonate allochems are typically not transported far from their source (i.e. they have local provenance).

• Carbonate allochems are mostly biogenous.

Major carbonate facies

• Biostrom• Bioherm– Hermatypic organisms– Reef

• Platforms• Ramps

Modern biogenous carbonate producers

• Chlorozoan facies– Anthozoa and calcareous green algae

• Foramol facies– Benthic foraminifera, mollusks, cirrepedia,

bryozoa, rhodophyta

Controls on Carbonate Deposition

1. Latitude– Controls temperature

• Temperature controls secretion and growth

• Cold H2O increases solubility

• (increases CO2 solubility, therefore increases

carbonic acid)

Surface sea temperatures

• Polar <5 ºC • Subpolar 5-10 ºC• Temperate 10-25 ºC• Subtropical 15-30 ºC• Tropical >25 ºC

Major carbonate production occurs in the 20-25 ºC isotherm

(Approx 30º North to 30º South latitude)

• 23-27 ºC = ideal for biogenic carbonate formation– Minimum temp = 18 ºC (dormancy of chlorozoan secretion)

– Maximum temp = 30 ºC (cessation of secretion, often death)

Latitude control on non-skeletal allochems

• Oöids/Grapestones• Oncoids• Peloids

• Intraclasts Oolith/grapestone

Peloid

Absent

0º

Pole

50º

30º

Non-skeletal Allochems

Modern cold-water carbonate producers (non cor-algal)

• Occur in temperate to subpolar regions – Ostrea spp., serpulids,

brachiopods, etc.

Chlorozoan

Foramol

0º

Pole

50º

30º

Skeletal Associations

Survival of selected cor-algal producers

• Solenastrea spp. occurs in 10 ºC waters offshore N. Carolina

• Porites spp. can tolerate temps to 40 ºC (very hardy, initial colonizer after hurricanes)

Latitude also controls

• Upwelling (abundance of dissolved nutrients)• Biodiversity • Ambient solar radiation• Reflection and refraction (less red-yellow at

higher latitudes)

2. Siliciclastic supply

• Fouls carbonate-producing tissues (e.g. mesenteries, mantles, etc.)

• Inhibits organic productivity

3. Depth

• Controls photic zone – eulittoral (<20 m) to sublittoral (around 200 m)– Carbonate production hinges on photosynthesis and

photosynthethic symbionts (e.g. Zooxanthellae)

• Colonial hermatypics common in photic zone• Solitary carbonate-producers typify greater depths

• Controls evaporation in upper water column

4. Salinity

• Balance between evaporation and precipitation/influx of H2O

• Varies with latitude• Osmotic flow from

saline to FW• Rapid ∆ = extinction• Slo ∆ = adaptation 0º

Pole

50º

30º

36

37

36

353433

3535

Salinity ‰

5. Turbulence and Substratum

• Current velocity• Wave energy• Hardgrounds and stability• Spur and Groove• Whitings

6. Nutrients

• Concentrated in areas of upwelling

Reef Development

• Rigid framework, “impediment to travel”• Modify their own environment• Bioherms (contain biolithite or

boundstone)

back reef or lagoonreef flat

reef crest or algal ridge

reef front

wall fore reefpatch reef

spur & groove

higher salinity more delicate morphologies massive

leafy

Wave EnergyTides dominate

Controls for reef development

a. Hermatypic organisms– high growth rate– encrust and bind– two types

• clonal (e.g. corals, bryozoans)• rapid ontogeny (eg. Ostrea)

Controls for reef development

b. water depth• progradation• build to MLW

∆ sea level• catch-up• keep-up• drowning• exposure

Controls for reef development

c. water circulation, currents, nutrients– controlled by

• tectonics• coriolis force• latitude• upwellings

Origins of micrite

• Dominate backreef and lagoon• Micritization

– Endolithic fungii

• Aragonite needles– calcareous algae– recrystallize easilly

• Whitings– fish stir up bottom– bacteria (USGS)

Diagenetic Environments

• Vadose (zone of aeration)– either Meteoric (FW) or Marine

• Phreatic (FW)• Phreatic (zone of FW-Marine mixing)• Phreatic (Marine)

Cement and Environment Environment Cement

CompositionCement

Morphology

Characteristics

Vadose •low Mg CC = FW•Mg enriched CC = marine

•pendant•meniscus

•fm of vuggy porosity•pref dissoln arag•calcrete and rhizocretions•pisoids

Phreatic (FW) •equant•isopachous•drusy•bladed spar•syntaxial overgrowths

•active circulation = rapid cementation •stagnant = little or no cementation

Phreatic (mixing)

Dolomite •recrystallization, cuts across grain boundaries

only one method of dolomite formation

Phreatic (Marine)

•aragonite•Mg enriched CC

•isopachous fibrous

•stagnant = slo to none•active = mesh of needles•micritization Mg

reef

0º

Pole

50º

30º

0º

Pole

50º

30º

36

37

36

353433

3535

Salinity ‰

Chlorozoan

Foramol

0º

Pole

50º

30º

Skeletal Associations

Oolith/grapestone

Peloid

Absent

0º

Pole

50º

30º

Non-skeletal Allochems

teepee diagrams

bOrilnk

backreef

porites and octocorals

porites and octocorals2

patch reef and divers

acropora palmata and solenastrea

millipora and meanderina

crinoid

porites

lagoon and ray

sponge in lagoon

lagoon and ray2

calcareous algae in lagoon

serpulid and calc algae

lagoon

urchins in thallassia meadow

thallassia meadow

calc algae in meadow

urchin

chlorphytic algae

backreef lagoon and hardground with aeolianites

beachrock

backreef lagoon and hardground with aeolianites2

beach and lagoon

fossil brain coral cockburnetown reef

ss fossil reef along axis

Eleuthera Key beach to wall

san salv key from air

I-80 Siluriun Reef

bear lake

Dev Cols ls stroms at lake erie

Shingle Pass, Egan Range

83la dolo sequence

cockburnetown fossil reef flat

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