carbonatesoceans1.csusb.edu/340/carbonates.pdf · • ramps. modern biogenous carbonate ......
TRANSCRIPT
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