(EPS 321) (EPS 321) CARBONATES AND EVAPORITESCARBONATES AND EVAPORITES

Prof. Dr. Mahmoud A. M. ArefProf. Dr. Mahmoud A. M. Aref

Department of Petroleum Geology & Sedimentology, Department of Petroleum Geology & Sedimentology, Faculty of Earth Sciences, Faculty of Earth Sciences, King Abdulaziz University, King Abdulaziz University,

Jeddah, Saudi ArabiaJeddah, Saudi Arabia

Lecture 05: Components of carbonate sediments: Lecture 05: Components of carbonate sediments: 2) Skeletal components. 2) Skeletal components.

II II -- Skeletal componentsSkeletal components

It's a reflection of the distribution of carbonateIt's a reflection of the distribution of carbonate--secreting invertebrate through time and space.secreting invertebrate through time and space.Environmental factors that control distribution and Environmental factors that control distribution and development of organisms aredevelopment of organisms are::

1. depth, 1. depth, 2. salinity, 2. salinity, 3. substrate,3. substrate,4. turbulence.4. turbulence.

EPS 321 Lecture 05

Identification of skeletal particles Identification of skeletal particles in thin section arein thin section are

Shape (size) Shape (size) two dimensional viewtwo dimensional viewInternal structure may be altered due to diagenesis.Internal structure may be altered due to diagenesis.Mineralogy (staining).Mineralogy (staining).

EPS 321 Lecture 05

A. MOLLUSCAA. MOLLUSCA

Occupying marine, brackish and fresh water environments.Occupying marine, brackish and fresh water environments.Mode of life:Mode of life:InfaunalInfaunal, , epifaunalepifaunal, , vagilevagile (crawlers), nektonic (free(crawlers), nektonic (free--swimming), swimming), planktonicplanktonic (free(free--floating).floating).e.g. e.g. RudistsRudists (Cretaceous) and Oyster form reef(Cretaceous) and Oyster form reef--like structure.like structure.Mineral composition: aragonite or calcite.Mineral composition: aragonite or calcite.Aragonite dissolution filling with Aragonite dissolution filling with drusydrusy sparitesparite..Calcite retain original structure.Calcite retain original structure.Bivalves fragments are elongate, rectangular to curved grains, Bivalves fragments are elongate, rectangular to curved grains, disarticulated.disarticulated.

A.1. Bivalves:A.1. Bivalves:

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BivalvesBivalves

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A.2. A.2. GastropodesGastropodes::

Shallow marine, Shallow marine, hypersaline and brackish hypersaline and brackish water environment.water environment.BenthicBenthicThey are composed of They are composed of aragonite that dissolve and aragonite that dissolve and filled with filled with drusydrusy sparitesparitecement.cement.

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GastropodesGastropodes

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A.3. A.3. CephalopodesCephalopodes::

Wholly marine animals, nektonicWholly marine animals, nektonic--planktonicplanktonic mode of life, mode of life, pelagic deep water environment.pelagic deep water environment.Composed of aragonite that dissolve and filled with Composed of aragonite that dissolve and filled with drusydrusysparitesparite cementcementLarge in size and septa are characteristics Large in size and septa are characteristics

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CephalopodesCephalopodes

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B. Brachiopods:B. Brachiopods:

Shallow marine, benthic, sessile organismsShallow marine, benthic, sessile organismsStructure similar to bivalves, composed of lowStructure similar to bivalves, composed of low--Mg Mg calcite, thin outer layer of calcite fibers normal to calcite, thin outer layer of calcite fibers normal to the wall, and thick inner layer composed of oblique the wall, and thick inner layer composed of oblique fiber.fiber.

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BrachiopodsBrachiopods

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Brachiopod

Brachiopod

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C. CoralsC. CoralsComposed of lowComposed of low--Mg calcite that Mg calcite that preserve internal preserve internal microstructure as microstructure as septa and tubule.septa and tubule.Shallow marine, Shallow marine, clear waterclear water

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CoralsCorals

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D. D. EchinodermataEchinodermata

Wholly marine, Wholly marine, composed of single composed of single calcite grain.calcite grain.

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EchinodermataEchinodermata

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E. E. BryozoaBryozoaColonial marine Colonial marine organisms, composed organisms, composed of aragonite or highof aragonite or high--Mg Mg calcitecalciteConsists of Consists of foliaceousfoliaceouscalcite with rounded calcite with rounded holes filled with calcite holes filled with calcite spar or sediment.spar or sediment.

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BryozoanBryozoan

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F. ForaminiferaF. ForaminiferaMarine, microscopic Marine, microscopic organisms, loworganisms, low-- to highto high--Mg Mg calcitecalcite

PlanktonicPlanktonic foraminifera foraminifera (Globigerina) dominate in (Globigerina) dominate in pelagic deposits, chalk, marlspelagic deposits, chalk, marls

Benthic foraminifera in Benthic foraminifera in shallow seas.shallow seas.

EPS 321 Lecture 05

ForaminiferaForaminifera

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The contribution of algae and The contribution of algae and microbes to limestone through:microbes to limestone through:

providing skeletal carbonate particles providing skeletal carbonate particles trapping grains to form laminated trapping grains to form laminated sedimentssedimentsattack particles through the boring attack particles through the boring activities.activities.

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RhodphytaRhodphyta (Red algae)(Red algae)

Composed of cryptocrystalline calcite within Composed of cryptocrystalline calcite within and between cell walls (cellular and between cell walls (cellular strstr.).)They coat, bind and cement substrate.They coat, bind and cement substrate.

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RhodphytaRhodphyta (Red algae)(Red algae)

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B. B. ChlorophytaChlorophyta (green algae)(green algae)

Death of these plants Death of these plants produce sand sized produce sand sized particles, or fine particles, or fine carbonate sediment carbonate sediment (lime mud)(lime mud)

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Micrite envelopesMicrite envelopesProduced by Produced by endolithicendolithic bacteria that bore into the skeletal debris, followed bacteria that bore into the skeletal debris, followed by filling of the cavities.by filling of the cavities.

The processes of grain degradation produce totally The processes of grain degradation produce totally micritizedmicritized grains, i.e. grains, i.e. peloidpeloid which is devoid of internal skeletal structure.which is devoid of internal skeletal structure.

Indicate deposition in the Indicate deposition in the photicphotic zone (100 zone (100 200 m depth)200 m depth)

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(EPS 321) CARBONATES AND EVAPORITESII - Skeletal componentsIdentification of skeletal particles in thin section areA. MOLLUSCAA.2. Gastropodes:A.3. Cephalopodes:B. Brachiopods:C. CoralsD. EchinodermataF. ForaminiferaThe contribution of algae and microbes to limestone through:Rhodphyta (Red algae)B. Chlorophyta (green algae)Micrite envelopes