TA2910 07 - Carbonate coasts

8/10/2019 TA2910 07 - Carbonate coasts

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Challenge the future

DelftUniversity ofTechnology

M.E. Donselaar

Carbonate coast deposits


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Sedimentary environments

Continental: fluvial (braided, meandering)

aeolian

lacustrine

Coastal: deltaslinear (clastic, carbonate)

Marine: shelf

deep marine sands

pelagic


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Carbonate coasts: Outline

Occurrence

Coastal types

Reef coasts and sea level fluctuations

Diagenesis Seismic and log response of reefs


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Carbonate coasts: Boundary conditions - 1

Relative lack of clastic deposition

High organic productivity


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Carbonate coasts: Boundary conditions - 2

Photic zone (~ 80-120 m water depth in clear water):photosynthesis

Clear, non-turbid water: clogging of pores

Limited range of temperature fluctuations


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Carbonate coasts: Occurrence

Progressive increase from higher to lower latitudes: increaseof solar illumination

Oceanic upwelling along borders of continents (O2-rich)

http://oceanservice.noaa.gov/education/kits/currents/media/supp_cur04a.html
http://oceanservice.noaa.gov/education/kits/currents/media/supp_cur04a.htmlhttp://oceanservice.noaa.gov/education/kits/currents/media/supp_cur04a.html


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Carbonate minerals

CaCO3Aragonite (orthorhombic)

Calcite (hexagonal)

Low-Mg calcite: < 4 mol. % Mg High-Mg calcite: > 4 mol. % Mg (typically 11-19 mol. % Mg)

Ca(Mg,Fe)(CO3)2 : Dolomite

FeCO3 : Siderite


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Main components

Non-skeletal grains

Biogenic carbonate

Matrix (mud-grade carbonate)


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Non-skeletal grains

Ooids Pisoids

Peloids

http://people.uncw.edu/dockal/gly312/co3diagen/image023.jpg

http://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.html

http://geoinfo.nmt.edu/staff/scholle/graphics/permphotos/035.html
http://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.htmlhttp://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.html


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Ooids and pisoids

Spherical-sub-spherical shape

Ooid: diameter < 2mm

Pisoid: diameter > 2mm

Ooids and pisoids are coated grains: core (grain) coatedwith carbonate lamellae

Carbonate precipitation on moving grain (wave-, tidalaction)

Sediment consisting of ooids: oolite


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Peloids

Spherical, ellipsoidal or angular grains

No internal structure

Size: generally 0.1-0.5 mm

Faecal pellets


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Non-skeletal grains

Link:

http://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.html
http://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.htmlhttp://plaza.snu.ac.kr/~lee2602/atlas2/nonsk.html


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Coastal types

Mainland and barrier island bioclastic coasts

Reef coasts


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Mainland and barrier island bioclastic coasts

Inden & Moore (1983)


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Cross section throughbioclastic carbonate coast



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Bioclastic carbonate coastVertical sequence



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Atoll reef


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Barrier reef coasts

http://www.science.ubc.ca/~geol202/sed/carb/carbhome.html


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Fringing reef coasts

mainland

sea

Fringing reef

Moora Finging reef: http://encarta.msn.com/media_461529282_761572186_-1_1/Moor%C3%A9a_Fringing_Reef.html


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Atoll reef coasts


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Occurrence atoll reefs

Grow around shield volcanoesin oceans

After cessation volcanic activity:erosion and thermal cooling

Volcanic island shrinks in size &submerges

Reef grows upward, centrallagoon surrounded by ring-shaped reef

http://www.unb.br/ig/sigep/sitio033/sitio033english.htm

http://www.uwgb.edu/dutchs/EarthSC202Notes/WAVEeros.HTM
http://www.unb.br/ig/sigep/sitio033/sitio033english.htmhttp://www.unb.br/ig/sigep/sitio033/sitio033english.htmhttp://www.uwgb.edu/dutchs/EarthSC202Notes/WAVEeros.HTMhttp://www.uwgb.edu/dutchs/EarthSC202Notes/WAVEeros.HTMhttp://www.unb.br/ig/sigep/sitio033/sitio033english.htmhttp://www.unb.br/ig/sigep/sitio033/sitio033english.htm


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Zonation carbonate coasts

Selley (1985)


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Sea level changes and reef development

Reef-forming organisms live in the photic zone of sea

Relative rise of sea level: reef grows upward to stay withinphotic zone (aggradation)

Relative fall of sea level: emerged part of reef dies andkarstifies

Stable sea level: reef expands seaward (progradation)

R f t t ti l l


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Reef response to eustatic sea levelfluctuation

Pomar (1991)

Sea level rise: aggradation


Sea level highstand: progradation

Sea level highstand: progradation

Sea level fall: erosion

Sea level fall: erosion



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Porosity


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Dolomitisation

Diagenetic change of calcite by partial replacement of Ca2+ionsby Mg2+ions:

2CaCO3+ Mg2+> CaMg(CO3)2+ Ca

2+

Volume dolomite < calcite caused by smaller ion-size Mg

If dolomitisation is complete the porosity increase is 13%

See also:http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm

Origin: two models

D l iti ti d l
http://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htmhttp://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htmhttp://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htmhttp://mineral.galleries.com/minerals/carbonat/dolomite/dolomite.htm


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Dolomitisation model:Hypersaline Brine Model

Evaporation gypsum precipitation (CaSO4. 2H2O)

Leads to Ca2+depletion and increase Mg/Ca ratio

Leads to increase of Mg concentration

Heavy brine reflux and calcite replacement by dolomite

http://www.science.ubc.ca/~geol256/notes/ch11_dolo_mixing.html


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Reefs on seismic

Selley (1985)


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Reefs on logs


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Carbonate blooms in geological time

http://www.science.ubc.ca/~geol202/sed/carb/carbintr.html


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http://www.science.ubc.ca/~geol202/sed/carb/carbintr.html


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Web links

http://geology.uprm.edu/Morelock/corgeol.htm

http://www.epa.gov/owow/oceans/coral/index.html

http://coralreefs.wr.usgs.gov/
http://geology.uprm.edu/Morelock/corgeol.htmhttp://www.epa.gov/owow/oceans/coral/index.htmlhttp://coralreefs.wr.usgs.gov/http://coralreefs.wr.usgs.gov/http://www.epa.gov/owow/oceans/coral/index.htmlhttp://geology.uprm.edu/Morelock/corgeol.htm


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Compulsory reading

Nichols Chapter 15: Section 15.1Carbonate and evaporite depositional environments

Section 15.3.2 Reefs

TA2910 07 - Carbonate coasts

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