Carbonates

The other white meat….

Processes that affect compositionally controlled marine facies

1. Influx of terrigenous sediment2. 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/grapestonePeloid

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 lagoon reef flat

reef crest or algal ridge

reef front

wall fore reefpatch reef

spur & groove

higher salinity more delicate morphologies massive

leafy

Wave EnergyTides dominate

Cross-section of typical reef system

Controls for reef development 1

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

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

Controls for reef development 2

b. water depth• progradation• build to MLW

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

Controls for reef development 3

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

CompositionCementMorphology

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

Edge of Patch ReefSan Salvador, Bahamas

Diversity of Organisms on patch reefSan Salvador, Bahamas

San Salvador backreefnote carbonate sands and ripples

Porites spp. and octocoralsreef flat, San Salvador, Bahamas

Porites spp. and octocorals 2reef flat, San Salvador, Bahamas

Patch reef and diversSan Salvador, Bahamas

Acropora palmata and Solenastrea sp.San Salvador, Bahamas

Backreef Framework morphologiesSan Salvador, Bahamas

Meanderina sp.

Millipora sp.

Crinoid, cryptic reef inhabitantSan Salvador, Bahamas

Porites porites, patch reefSan Salvador, Bahamasnote golden-brown colorfrom Zooxanthellaein ectoderm

San Salvador, Bahamaslagoon floor with ray and commensal jack 1

San Salvador, Bahamaslagoon floor with ray and commensal jack 2

Large sponge on lagoon floorSan Salvador, Bahamas

note fragments of coral branches littering lagoon floor from hurricane

Calcareous algae in lagoon

Serpulid polychaete and calcareous algae (Halimeda sp.)lagoon, San Salvador, Bahamas

Chlorophytic algaeSan Salvador, BahamasMajor producers of calcareous sedimentfrom left: Penicillus spp. (3 specimens) Udotea sp., Halimeda sp., and Acetabularia sp.

Backreef lagoonSan Salvador, Bahamas

Thallassia sp. meadowSan Salvador, Bahamas

white flecks on grass blades = benthic Elphidium sp. forams

Udotea sp. calcareous algae in Thalassia sp. Meadow

San Salvador, Bahamas

Sea urchins in Thallassia sp. MeadowSan Salvador, Bahamas

Echinoid grazing in Thalassia sp. meadowSan Salvador, Bahamas

San Salvador, Bahamasbackreef lagoon and hardground with aeolianites 1

San Salvador, Bahamas backreef lagoon and hardground with aeolianites2

Beachrock forming along beachSan Salvador, Bahamas

Typical beach and lagoonSan Salvador, Bahamas

note white cliffs in background are lithified Pleistocene aeolian dunes formed during last glacial sea-level drawdown

Pleistocene brain coral, Cockburnetown fossil reef

San Salvador, Bahamas

Cockburnetown, San Salvador Pleistocene fossil reef along exposed reefcrest—lagoon

sediments to right

Cockburnetown, San SalvadorPleistocene fossil reef flat—note Acropora

cervicornix (staghorn coral) branches in lower part of photo

Eleuthera Cay, Bahamas from air

I-80 Silurian Patch Reefjust west of Chicago, IL

major skeletal organisms = brachiopod Kirklandia spp.

Bear Lake, IdahoHard-water lacustrine system

Aqua color due to micrite precipitation in lake

Devonian Columbus LimestoneLake Erie, Ohio

Stromatolites on bedding planes

Shingle Pass, Egan Range, NevadaCross-section through margin of Paleozoic Carbonate Platform

Middle Cambrian on left, Devonian on RightNote siliciclastic influx in white band near center (mid Ordovician

Eureka Quartzite)Carbonates are organic rich, forming the gray bands in the photo

Typical dolomitized carbonate platform sedimentation

(organic rich, shallow biostroms and tidal flats),Ordovician Fish Haven Dolostone, Lakeside Mts, Utah