Difference between revisions of "Carbonate sedimentary rocks classification"

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In oil and gas industry, classifying carbonate rocks is a major step in core and thin section description. Two classification systems have been widely used in the industry:  
 
In oil and gas industry, classifying carbonate rocks is a major step in core and thin section description. Two classification systems have been widely used in the industry:  
# Folk (1959<ref name=Flk1959>Folk, R. L., 1959, [https://archives.datapages.com/data/bulletns/1957-60/data/pg/0043/0001/0000/0001.htm Practical petrographic classification of limestones]: AAPG Bulletin, v. 43, p. 1–38.</ref>, 1962) Classification  
+
# Folk (1959<ref name=Flk1959>Folk, R. L., 1959, [https://archives.datapages.com/data/bulletns/1957-60/data/pg/0043/0001/0000/0001.htm Practical petrographic classification of limestones]: AAPG Bulletin, v. 43, p. 1–38.</ref>, 1962<ref name=Flk1962>Folk, R. L., 1962, [https://archives.datapages.com/data/specpubs/carbona2/data/a038/a038/0001/0050/0062.htm Spectral subdivision of limestone types], ''in'' W. E. Ham, ed., Classification of carbonate Rocks-A Symposium: [https://archives.datapages.com/data/alt-browse/aapg-special-volumes/m1.htm AAPG Memoir 1], p. 62-84.</ref>) Classification  
# Dunham (1962) Classification  
+
# Dunham (1962<ref name=Dnhm>Dunham, R. J., 1962, [https://archives.datapages.com/data/specpubs/carbona2/data/a038/a038/0001/0100/0108.htm Classification of carbonate rocks according to depositional texture], ''in'' W. E. Ham, ed., Classification of Carbonate Rocks: [https://archives.datapages.com/data/alt-browse/aapg-special-volumes/m1.htm AAPG Memoir 1], p. 108–121.</ref>) Classification  
 
Both classifications provide an indication of depositional energy setting and reservoir quality.
 
Both classifications provide an indication of depositional energy setting and reservoir quality.
  
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* Wentworth (1922){{note|a}} [a]
 
* Wentworth (1922){{note|a}} [a]
 
* Bramkamp & Powers (1958)
 
* Bramkamp & Powers (1958)
* Folk (1959<ref name=Flk1959 />,1962)
+
* Folk (1959, 1962)<ref name=Flk1959 /><ref name=Flk1962 />
* Dunham (1962)
+
* Dunham (1962)<ref name=Dnhm />
 
* Leignton & Pendexter (1962)
 
* Leignton & Pendexter (1962)
 
* Todd (1966)
 
* Todd (1966)
* Embry & Klovan (1971)
+
* Embry & Klovan (1971)<ref name=EmbryKlvn>Embry, A. F., and J. E. Klovan, 1971, A late Devonian reef tract on northeastern Banks Island, N.W.T: Bulletin of Canadian Petroleum Geology, v. 19, no. 4, p. 730–781.</ref>
 
* Wright (1992)
 
* Wright (1992)
 
* Hallsworth & Knox (1999)
 
* Hallsworth & Knox (1999)
Among all of the attempts, Folk (1959<ref name=Flk1959 />, 1962) and Dunham (1962) extended by Embry & Klovan (1971) classifications were widely accepted.  
+
Among all of the attempts, the Folk<ref name=Flk1959 /><ref name=Flk1962 /> and Dunham<ref name=Dnhm />, extended by Embry & Klovan<ref name=EmbryKlvn />, classifications were widely accepted.  
  
 
==Folk Classification==  
 
==Folk Classification==  
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* Pelmicrite: consists of pellets with microcrystalline matrix (Figure 10).
 
* Pelmicrite: consists of pellets with microcrystalline matrix (Figure 10).
 
<gallery mode=packed heights=300px widths=300px>
 
<gallery mode=packed heights=300px widths=300px>
File:GeoWikiWriteOff2021-Abdulwahab-Figure7.png|{{figure number|7}}Intramicrite
+
File:GeoWikiWriteOff2021-Abdulwahab-Figure7.png|{{figure number|7}}Intramicrite<ref>[http://sepmstrata.org/microscopic_gallery_details.aspx?gid=165&pg=1&gcid=9 SEPM Strata Microscopic Gallery]</ref>
File:GeoWikiWriteOff2021-Abdulwahab-Figure8.png|{{figure number|8}}Oomicrite  
+
File:GeoWikiWriteOff2021-Abdulwahab-Figure8.png|{{figure number|8}}Oomicrite<ref>[http://www.sepmstrata.org/microscopic_gallery_details.aspx?gid=207&pg=3&gcid=11 SEPM Strata Microscopic Gallery]</ref>
 
File:GeoWikiWriteOff2021-Abdulwahab-Figure9.png|{{figure number|9}}Biomicrite
 
File:GeoWikiWriteOff2021-Abdulwahab-Figure9.png|{{figure number|9}}Biomicrite
 
File:GeoWikiWriteOff2021-Abdulwahab-Figure10.png|{{figure number|10}}Pelmicrite
 
File:GeoWikiWriteOff2021-Abdulwahab-Figure10.png|{{figure number|10}}Pelmicrite
Line 94: Line 94:
 
==Dunham Classification==  
 
==Dunham Classification==  
 
===Dunham’s Criteria===
 
===Dunham’s Criteria===
Dunham classification system is based on three depositional textural features:
+
[[w:Dunham classification|Dunham's classification system]] is based on three depositional textural features:
 
* The presence or absence of lime mud.
 
* The presence or absence of lime mud.
 
* The abundance of grains.[j]  
 
* The abundance of grains.[j]  
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===Extended Dunham Classification (1971)===
 
===Extended Dunham Classification (1971)===
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure18.png|thumbnail|500px|{{Figure number|18}}Extended Dunham classification (1971)]]
+
Embry and Klovan<ref name=EmbryKlvn /> expanded the original Dunham classification due to the lack of:
Embry and Klovan expanded the original Dunham classification due to the lack of:
 
 
* Classifying coarse-grained (>2mm) rocks.  
 
* Classifying coarse-grained (>2mm) rocks.  
 
* Subdividing organically-bound rocks (boundstones).  
 
* Subdividing organically-bound rocks (boundstones).  
 
The extended Dunham Classification is shown in Figure 18.  
 
The extended Dunham Classification is shown in Figure 18.  
 +
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure18.png|center|framed|200px|{{Figure number|18}}Extended Dunham classification (1971)]]
  
 
====Coarse-Grained Rocks Classification====
 
====Coarse-Grained Rocks Classification====
 
* Floatstone: a matrix-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 19).   
 
* Floatstone: a matrix-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 19).   
 
* Rudstone: a grain-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 20).
 
* Rudstone: a grain-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 20).
 +
<gallery mode=packed heights=250px widths=250px>
 +
File:GeoWikiWriteOff2021-Abdulwahab-Figure19.png|{{figure number|19}}Floatstone 
 +
File:GeoWikiWriteOff2021-Abdulwahab-Figure20.png|{{figure number|20}}Rudstone
 +
</gallery>
 +
 
====Organically-Bound Rocks Subdivision====
 
====Organically-Bound Rocks Subdivision====
 
* Bafflestone: in situ organically-bound rock in which organisms act as baffles (Figure 21).
 
* Bafflestone: in situ organically-bound rock in which organisms act as baffles (Figure 21).
 
* Bindstone: in situ organically-bound rock in which organisms encrust and bind (Figure 22).
 
* Bindstone: in situ organically-bound rock in which organisms encrust and bind (Figure 22).
 
* Framestone: in situ organically-bound rock in which organisms build a rigid framework (Figure 23).[k]
 
* Framestone: in situ organically-bound rock in which organisms build a rigid framework (Figure 23).[k]
 +
<gallery mode=packed heights=250px widths=250px>
 +
File:GeoWikiWriteOff2021-Abdulwahab-Figure21.png|{{figure number|21}}Bafflestone
 +
File:GeoWikiWriteOff2021-Abdulwahab-Figure22.png|{{figure number|22}}Bindstone
 +
File:GeoWikiWriteOff2021-Abdulwahab-Figure23.png|{{figure number|23}}Framestone
 +
</gallery>
  
 
===Depositional Energy Setting and Reservoir Quality Indications===
 
===Depositional Energy Setting and Reservoir Quality Indications===
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Rudstones and framestones are usually formed in high-energy settings (above wave base).  
 
Rudstones and framestones are usually formed in high-energy settings (above wave base).  
 
Organically-bound rocks show good reservoir quality if the skeletal growth is interconnected.
 
Organically-bound rocks show good reservoir quality if the skeletal growth is interconnected.
 
==Gallery==
 
 
 
 
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure19.png|thumbnail|Fig. 19 Floatstone [19]]] 
 
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure20.png|thumbnail|Fig. 20 Rudstone [20]]]
 
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure21.png|thumbnail|Fig. 21 Bafflestone [21]]]
 
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure22.png|thumbnail|Fig. 22 Bindstone [22]]]
 
[[File:GeoWikiWriteOff2021-Abdulwahab-Figure23.png|thumbnail|Fig. 23 Framestone [23]]]
 
  
 
==Notes==  
 
==Notes==  
Line 161: Line 162:
  
 
==References==
 
==References==
{{reflist}}  
+
{{reflist}}
20. ^ [3] [4] [5] [9] Folk Classification. Wikipedia. https://en.wikipedia.org/wiki/Folk_classification#cite_ref-2
 
 
 
21. ^ [6] Gregg, Jay. (December 18). Limestone Petrology. Missouri S&T. https://web.mst.edu/~greggjay/carbonate_page/lsgallery/pages/c-ACS190_10.htm
 
 
 
22. ^ [7] (2021, March 29). Microscopic Gallery. SEPM Strata. http://sepmstrata.org/microscopic_gallery_details.aspx?gid=165&pg=1&gcid=9
 
 
 
23. ^ [8] (2021, March 29). Microscopic Gallery. SEPM Strata. http://www.sepmstrata.org/microscopic_gallery_details.aspx?gid=207&pg=3&gcid=11
 
 
 
24. ^ [10] Sahraeyan, Mohammad. (2013, June). Sedimentary Basin Analysis of Sachun Formation in Southwestern Iran: Implication for Sedimentary Environments and Tectonic Setting. ResearchGate. https://www.researchgate.net/figure/Photomicrographs-showing-micrite-and-pelmicrite-in-the-argillaceous-limestone-facies-of_fig8_262337097
 
 
 
25. ^ [12] [18] K. Bjørlykke (ed). Petroleum Geoscience: From Sedimentary Environments to Rock Physics, DOI 10.1007/978-3-642-34132-8_5, Ⓒ Springer-Verlag Berlin Heidelberg 2015.
 
 
 
26. ^ [13] Mudstone. Wikipedia. https://en.wikipedia.org/wiki/Mudstone
 
 
 
27. ^ [14] Carbonate Rock Classification. Carbonateworld. https://carbonateworld.com/carbonate-atlas/carbonate-rock-classification/images/wackstone/
 
 
 
28. ^ [15] [16] F. Jerry Lucia. Estimating Permeability in Carbonates Using the Rock-Fabric Method. Bureau of Economic Geology. https://www.beg.utexas.edu/lmod/_IOL-CM07/cm07-step02a.htm
 
 
 
29. ^ [17] Ardakani, Omid H. (2013, June). Diagenetic evolution and associated mineralization of Middle Devonian carbonates, southwestern Ontario, Canada. ResearchGate. https://www.researchgate.net/figure/Thin-section-photomicrographs-of-Middle-Devonian-rocks-A-Syntaxial-and-equant-calcite_fig3_235413575
 
 
 
30. ^ [19] [20] Al-Awwad, Saad F. & pomar, Luis. (2015, May 21). Origin of the rudstone–floatstone beds in the Upper Jurassic Arab-D reservoir, Khurais Complex, Saudi Arabia. ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0264817215001634
 
 
 
31. ^ [21] Khanaqa, Polla. (2018, December). Stratigraphy and Facies Analysis of the Govanda Formation from Western Zagros, Kurdistan Region, Northeastern Iraq. ResearchGate. https://www.researchgate.net/figure/a-Photo-of-the-Coral-
 
Bafflestone-of-Barda-Balaka-Outcrop-Between-the-stems-Fine_fig12_330094098
 
 
 
32. ^ [22] Bindstone. Bureau of Economic Geology. https://www.beg.utexas.edu/lmod/_IOL-CM02/st21-ancbindstone.htm
 
 
 
33. ^ [23] Camuera, Jon. (2014, July). Origin and palaeo-environmental significance of the Berrazales carbonate spring deposit, North of Gran Canaria Island, Spain. ResearchGate. https://www.researchgate.net/figure/A-Framestone-facies-composed-of-parallel-plant-moulds-coated-with-calcite-B-Plant_fig4_283498781
 
 
 
==Sources==
 
1. Lokier, Stephen W.; Al Junaibi, Mariam (2016). "The petrographic description of carbonate facies: are we all speaking the same language?". Sedimentology. 63 (7): 1843–1885. doi:10.1111/sed.12293
 
 
 
2. Folk, R. L., 1959, Practical petrographic classification of limestones: AAPG Bulletin, v. 43, p. 1–38.
 
 
 
3. Folk, R.L., 1962, Spectral subdivision of limestone types, in Ham, W.E., ed., Classification of carbonate Rocks-A Symposium: American Association of Petroleum Geologists Memoir 1, p. 62-84.
 
 
 
4. Dunham, R. J., 1962, Classification of carbonate rocks according to depositional texture, in Ham, W. E., ed., Classification of Carbonate Rocks: AAPG Memoir 1, p. 108–121.
 
 
 
5. Embry, Ashton F.; Klovan, J. Edward (1971-12-01). "A late Devonian reef tract on northeastern Banks Island, N.W.T". Bulletin of Canadian Petroleum Geology. 19 (4): 730–781.
 
  
6. K. Bjørlykke (ed). Petroleum Geoscience: From Sedimentary Environments to Rock Physics, DOI 10.1007/978-3-642-34132-8_5, Ⓒ Springer-Verlag Berlin Heidelberg 2015.
+
==Other Sources==
 +
* Gregg, Jay. (December 18). Limestone Petrology. Missouri S&T. https://web.mst.edu/~greggjay/carbonate_page/lsgallery/pages/c-ACS190_10.htm
 +
* Sahraeyan, Mohammad. (2013, June). Sedimentary Basin Analysis of Sachun Formation in Southwestern Iran: Implication for Sedimentary Environments and Tectonic Setting. ResearchGate. https://www.researchgate.net/figure/Photomicrographs-showing-micrite-and-pelmicrite-in-the-argillaceous-limestone-facies-of_fig8_262337097
 +
* K. Bjørlykke (ed). Petroleum Geoscience: From Sedimentary Environments to Rock Physics, DOI 10.1007/978-3-642-34132-8_5, Ⓒ Springer-Verlag Berlin Heidelberg 2015.
 +
* Carbonate Rock Classification. Carbonateworld. https://carbonateworld.com/carbonate-atlas/carbonate-rock-classification/images/wackstone/
 +
* F. Jerry Lucia. Estimating Permeability in Carbonates Using the Rock-Fabric Method. Bureau of Economic Geology. https://www.beg.utexas.edu/lmod/_IOL-CM07/cm07-step02a.htm
 +
* Ardakani, Omid H. (2013, June). Diagenetic evolution and associated mineralization of Middle Devonian carbonates, southwestern Ontario, Canada. ResearchGate. https://www.researchgate.net/figure/Thin-section-photomicrographs-of-Middle-Devonian-rocks-A-Syntaxial-and-equant-calcite_fig3_235413575
 +
* Al-Awwad, Saad F. & pomar, Luis. (2015, May 21). Origin of the rudstone–floatstone beds in the Upper Jurassic Arab-D reservoir, Khurais Complex, Saudi Arabia. ScienceDirect. https://www.sciencedirect.com/science/article/pii/S0264817215001634
 +
* Khanaqa, Polla. (2018, December). Stratigraphy and Facies Analysis of the Govanda Formation from Western Zagros, Kurdistan Region, Northeastern Iraq. ResearchGate. https://www.researchgate.net/figure/a-Photo-of-the-Coral-Bafflestone-of-Barda-Balaka-Outcrop-Between-the-stems-Fine_fig12_330094098
 +
* Bindstone. Bureau of Economic Geology. https://www.beg.utexas.edu/lmod/_IOL-CM02/st21-ancbindstone.htm
 +
* Camuera, Jon. (2014, July). Origin and palaeo-environmental significance of the Berrazales carbonate spring deposit, North of Gran Canaria Island, Spain. ResearchGate. https://www.researchgate.net/figure/A-Framestone-facies-composed-of-parallel-plant-moulds-coated-with-calcite-B-Plant_fig4_283498781
 +
* Lokier, Stephen W.; Al Junaibi, Mariam (2016). "The petrographic description of carbonate facies: are we all speaking the same language?". Sedimentology. 63 (7): 1843–1885. doi:10.1111/sed.12293

Latest revision as of 14:09, 19 December 2023

Wiki Write-Off Entry
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Author Zainab Al Abdulwahab
Affiliation Saudi Aramco
Competition 2021 Middle East Wiki Write Off

In oil and gas industry, classifying carbonate rocks is a major step in core and thin section description. Two classification systems have been widely used in the industry:

  1. Folk (1959[1], 1962[2]) Classification
  2. Dunham (1962[3]) Classification

Both classifications provide an indication of depositional energy setting and reservoir quality.

History

Various classification systems had been proposed for both academia and industry purposes:

  • Wentworth (1922)Template:Note [a]
  • Bramkamp & Powers (1958)
  • Folk (1959, 1962)[1][2]
  • Dunham (1962)[3]
  • Leignton & Pendexter (1962)
  • Todd (1966)
  • Embry & Klovan (1971)[4]
  • Wright (1992)
  • Hallsworth & Knox (1999)

Among all of the attempts, the Folk[1][2] and Dunham[3], extended by Embry & Klovan[4], classifications were widely accepted.

Folk Classification

Folk’s Criteria

Folk's classification system is based on three basic components of limestone:

  • Allochems (sediment grains): framework component of the rock. There are four major types of allochems in Folk system: intraclasts, oolites, fossils, and pellets.
  • Microcrystalline lime mud: matrix component of the rock < 4 μm in size.
  • Sparry calcite cement (sparite): pore-filling component precipitated during deposition.

Major Families Classification

Based on the relative proportions of matrix and pore-filling components surrounding the framework component, Folk defined three major families plotted on a triangular diagram (Figure 1).

  • Family I: sparry allochemical limestone that consists of allochems cemented by sparry calcite cement.[b]
  • Family II: microcrystalline allochemical limestone that consists of > 10% allochems within lime mud.
  • Family III: microcrystalline limestone (micrite) that consists of 0-10% allochems within mud. In other words, composes almost entirely of mud.[c]

Folk defined a fourth family based on in situ organic growth deposits: biolithite.[d]

Subdivision of Major Families

Family I and II of Folk’s system could be subdivided based on the type of allochems presented. The most important types of allochems are: intraclasts, oolites, fossils, and pellets respectively. A total of eight subdivisions are diagrammatically presented in Figure 2.[e]

Family I subdivisions

  • Intrasparite: consists of intraclasts with sparry calcite cement (Figure 3).
  • Oosparite: consists of oolites with sparry calcite cement (Figure 4).
  • Biosparite: consists of fossils with sparry calcite cement (Figure 5).
  • Pelsparite: consists of pellets with sparry calcite cement (Figure 6).

Family II subdivisions

  • Intramicrite: consists of intraclasts with microcrystalline matrix (Figure 7).
  • Oomicrite: consists of oolites with microcrystalline matrix (Figure 8).
  • Biomicrite: consists of fossils with microcrystalline matrix (Figure 9).
  • Pelmicrite: consists of pellets with microcrystalline matrix (Figure 10).

Depositional Energy Setting and Reservoir Quality Indications

Generally, Family I rocks are formed in high-energy settings and show good reservoir quality, especially if they are partially cemented. Oosparite is considered to be the best reservoir quality rock. It is usually characterized by good porosity & permeability, good sorting, and cross-bedding. It is mainly formed near strong offshore currents such as submarine shoals.[f] Family II & III rocks are formed in low-energy settings and show poor reservoir quality. They usually formed in deep water and restricted settings where the current is not strong enough to winnow away the lime mud.[g] [h]

Spectral Subdivision of Limestones

Figure 11 

In 1962, Folk proposed the spectral subdivision. He subdivided the 3 major families into eight types forming a sequential transitional spectrum of energy level in which the first type represents the lowest energy, and the last type represents the highest energy (Figure 11).

Criteria

  • For rocks dominated by lime mud, Folk considered the percentage of allochems presented.
  • For rocks dominated by sparry calcite cement, Folk considered the sorting and rounding of allochems presented.

Subdivisions

Folk proposed a total of eight types representing a gradational transition of energy level from low to high. Considering, for instance, fossils to be the major allochems in the system[i], the sequential subdivisions are:

  1. Micrites and dismicrites: rocks consist entirely of lime mud.
  2. Fossiliferous micrites and dismicrites: rocks consist of 1-10% allochems.
  3. Sparse biomicrites: rocks consist of 10-50% allochems floating in the matrix.
  4. Packed biomicrites: rocks consist of > 50% packed allochems.
  5. Poorly washed biosparites: rocks consist of almost equal amounts of lime mud and sparry calcite cement in which the current was not strong enough to winnow away all lime mud particles.
  6. Unsorted biosparites: poorly sorted rocks in which the current was strong enough to winnow away lime mud particles, but the allochems are still not sorted.
  7. Sorted biosparites: well-sorted rocks in which the allochems are still not well-rounded and abraded.
  8. Rounded biosparites: well-sorted and well-rounded rocks in which the allochems underwent intense abrasion.

Dunham Classification

Dunham’s Criteria

Dunham's classification system is based on three depositional textural features:

  • The presence or absence of lime mud.
  • The abundance of grains.[j]
  • The presence of in situ organic binding

Dunham (1962) Classification

Figure 12 Dunham classification system for carbonate rock (1962)

The original Dunham classification system composes of six classes summarized in Figure 12:

  • Mudstone: a mud-supported rock with < 10% grains, and original components are not organically bounded together during deposition (Figure 13).
  • Wackestone: a mud-supported rock with > 10% grains, and original components are not organically bounded together during deposition (Figure 14).
  • Packstone: a grain-supported rock with lime mud presented, and original components are not organically bounded together during deposition (Figure 15).
  • Grainstone: a grain-supported rock with lime mud absent, and original components are not organically bounded together during deposition (Figure 16).
  • Boundstone: a rock with the presence of organic components bounded together during deposition.
  • Crystalline: a rock with unrecognizable depositional texture (Figure 17).

Extended Dunham Classification (1971)

Embry and Klovan[4] expanded the original Dunham classification due to the lack of:

  • Classifying coarse-grained (>2mm) rocks.
  • Subdividing organically-bound rocks (boundstones).

The extended Dunham Classification is shown in Figure 18.

Figure 18 Extended Dunham classification (1971)

Coarse-Grained Rocks Classification

  • Floatstone: a matrix-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 19).
  • Rudstone: a grain-supported rock with > 10% of grains >2mm and original components are not organically bounded together during deposition (Figure 20).

Organically-Bound Rocks Subdivision

  • Bafflestone: in situ organically-bound rock in which organisms act as baffles (Figure 21).
  • Bindstone: in situ organically-bound rock in which organisms encrust and bind (Figure 22).
  • Framestone: in situ organically-bound rock in which organisms build a rigid framework (Figure 23).[k]

Depositional Energy Setting and Reservoir Quality Indications

Generally, mud-supported rocks: mudstones and wackestones are formed in low-energy settings and show poor reservoir quality. Grain-supported rocks: packstones and grainstones are formed in high-energy settings and show good reservoir quality. Grainstones is considered to be the best reservoir quality rock, especially if it is partially cemented. It is usually characterized by good porosity & permeability, and good sorting. Floatstones and bindstones are usually formed in medium-energy settings (below average wave base). Rudstones and framestones are usually formed in high-energy settings (above wave base). Organically-bound rocks show good reservoir quality if the skeletal growth is interconnected.

Notes

  1. [a] Early carbonate classification is grain-size based system: Calcilutite (grains < 63 μm), calcarenite (63 μm < grains < 2mm), calcirudite (grains > 2mm).
  2. [b] This family has restricted limits because cement by itself cannot form a rock and the supported framework component (allochems) has limited packing.
  3. [c] If the microcrystalline limestone had been disturbed either by bioturbation or soft-sediment deformation, the term “disturbed microcrystalline limestone” or “dismicrite” could be assigned.
  4. [d] Examples of biolithites are: algal biolithite and coral biolithite.
  5. [e] Naming of a subdivision is a composite of two parts. The first part refers to the name of the allochem. The second part refers to the family type. For Example, intrasparite: intra- refers to intraclasts, and –sparite refers to family I.
  6. [f] Oosparites are more common than Oomicrites because the need of strong current to form these rocks.
  7. [g] Intrasparites are more common than intramicrites because the need of strong current to transfer course rock fragments.
  8. [h] Both biosparites and biomicrites are common. However, biosparites are usually more rounded and abraded because of the strong current.
  9. [i] The subdivisions could be applied considering other types of allochems: intraclasts, oolites, and pellets.
  10. [j] The abundance of grains defines the nature of the framework. In other words, whether it is mud-supported or grain-supported.
  11. [k] The term “boundstone” is retained if the organic bounding type is not recognized.

References

  1. 1.0 1.1 1.2 Folk, R. L., 1959, Practical petrographic classification of limestones: AAPG Bulletin, v. 43, p. 1–38.
  2. 2.0 2.1 2.2 Folk, R. L., 1962, Spectral subdivision of limestone types, in W. E. Ham, ed., Classification of carbonate Rocks-A Symposium: AAPG Memoir 1, p. 62-84.
  3. 3.0 3.1 3.2 Dunham, R. J., 1962, Classification of carbonate rocks according to depositional texture, in W. E. Ham, ed., Classification of Carbonate Rocks: AAPG Memoir 1, p. 108–121.
  4. 4.0 4.1 4.2 Embry, A. F., and J. E. Klovan, 1971, A late Devonian reef tract on northeastern Banks Island, N.W.T: Bulletin of Canadian Petroleum Geology, v. 19, no. 4, p. 730–781.
  5. SEPM Strata Microscopic Gallery
  6. SEPM Strata Microscopic Gallery

Other Sources