Porosity

1. Interparticle

Ooidal grainstone with marine isopachous fibrous cement rims and interparticle (intergranular) porosity (white area in plane polarized light).

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

2. Interparticle

Previous image of an ooidal grainstone in cross-polarized light with the interparticle (intergranular) porosity (in extinction).

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

3. Interparticle

Skeletal grainstone with bioclasts preserved as micrite envelopes due to micritization of the outer rim and dissolution of the skeletal carbonate. Porosity is highlighted by blue epoxy and it is both primary interparticle (intergranular) and secondary mouldic within the grains.

Cretaceous, Miskar Field, offshore Tunisia

4. Interparticle

Skeletal grainstone with bryozoans showing primary interparticle (intergranular) porosity (blue epoxy) and minor secondary mouldic porosity due to partial or complete bioclasts dissolution. Field of view approximately 2 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

5. Interparticle

Skeletal grainstone rich in fusulinid and staffellid foraminifera. Grains exhibit concave-convex contacts and must have been compacted before cementation. Primary interparticle (intergranular) porosity is scarce. Field of view approximately 4.6 mm wide.

Lower Permian, Karachaganak Field, Kazakhstan

6. Interparticle

Skeletal grainstone with primary interparticle (intergranular) porosity (blue epoxy), minor intraparticle (intragranular) porosity and scarce cementation. Numerous grains have micrite envelopes. Field of view approximately 9 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

7. Interparticle

Skeletal grainstone with interparticle (intergranular) porosity. Note micrite envelopes on many grains. There is also minor intraparticle (intragranular porosity). Field of view approximately 1.6 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

8. Interparticle

Primary interparticle (intergranular) porosity in a skeletal grainstone with most of the bioclasts coated by micrite envelopes. There is also minor intraparticle (intragranular) porosity in the benthic foraminifer (Climacammina) in the centre. Field of view approximately 2 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

9. Interparticle

Primary interparticle (intergranular) porosity in skeletal grainstone with echinoderms, foraminifera and green calcareous algae. The green dasyclad fragment of Koninckopora shows also intraparticle porosity.

Carboniferous, Karachaganak Field, Kazakhstan

10. Interparticle

Skeletal grainstone with echinoderms and calcitic green dasyclad algae (Koninckopora) that exhibit primary intraparticle (intragranular) porosity. Field of view approximately 3 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

11. Interparticle

Peloidal skeletal grainstone with high interparticle (intergranular) porosity containing miliolid foraminifera typical of restricted (probably with elevated salinities) platform interior lagoons. Field of view approximately 3 mm wide (left) and 1 mm wide (right).

Cretaceous, Miskar Field, offshore Tunisia

12. Secondary

Particular type of porosity due to complete dissolution of foraminifer shell with the preservation of remnant “shards” of intraparticle cement after foraminifer test walls have been dissolved.

Eocene, Mukta Field, offshore India

13. Intraparticle

Intraparticle (intragranular) porosity in a fusulinid foraminifer. Micrite matrix has been dolomitized and includes some areas with dissolution vug porosity. Field of view approximately 1 mm wide.

Lower Permian, Karachaganak Field, Kazakhstan

14. Intraparticle

Intraparticle (intragranular) porosity in a rugose coral. Field of view approximately 3 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

15. Intraparticle

Intraparticle (intragranular) porosity in a rugose coral. Note the cement and bitumen in the intraparticle pore space. Field of view approximately 3 mm wide.

Lower Permian, Karachaganak Field, Kazakhstan

16. Intraparticle/Dissolution

Cross-section of foraminifer showing intraparticle pore space enhanced by secondary dissolution.

Thin section provided by T. Geel, Vrije Universiteit, Amsterdam

17. Intraparticle/Dissolution

Previous image in cross-polarized light showing the porosity areas of intraparticle and dissolution fully in extinction.

Thin section kindly provided by T. Geel, Vrije Universiteit, Amsterdam

18. Growth framework

Growth framework porosity visible in a polished slab of a red algae bindstone.

Miocene, Mallorca, Spain

19. Breccia porosity

Breccia porosity due to intraformational fracturing in a Miocene breccia composed of Mesozoic limestone clasts.

Miocene, Tarragona, Spain

20. Fenestral porosity

Fenestral porosity in intertidal facies from Central Oman.

Precambrian, Khufai Formation, Central Oman

21. Fenestral porosity

Fenestral porosity in intertidal peloidal grainstone. Field of view approximately 3 mm wide.

Precambrian, Khufai Formation, Central Oman

22. Fenestral porosity

Fenestral porosity in intertidal peloidal grainstone. Field of view approximately 1 mm wide.

Precambrian, Khufai Formation, Central Oman

23. Biomouldic

Skeletal grainstone with fusulinid and bryozoan fragments and a bivalve biomould preserved by the micrite envelope on the outer shell rim. Field of view approximately 9 mm wide.

Lower Permian, Karachaganak Field, Kazakhstan

24. Biomouldic

Secondary porosity put in evidence by the blue epoxy resin with preferential removal of walls of coskinolinid foraminifer to produce mouldic porosity. The intraparticle space is filled by undissolved cement.

Eocene, Mukta Field, offshore India

25. Biomouldic

Mouldic porosity due to dissolution of coskinolinid foraminifer walls. The intraparticle space is filled by undissolved cement.

Eocene, Mukta Field, offshore India

26. Biomouldic

Mouldic porosity due to dissolution of coskinolinid foraminifer walls. The intraparticle space is filled by undissolved cement.

Eocene, Mukta Field, offshore India

27. Biomouldic

Mouldic porosity due to dissolution of gastropods. Field of view approximately 3 mm wide.

Carboniferous, Karachaganak Field, Kazakhstan

28. Biomouldic

Mouldic secondary porosity due to dissolution of a gastropod. Field of view approximately 3 mm wide.

Miocene, Mallorca, Spain

29. Biomouldic

Grainstone of miliolid foraminifera that have been partly to completely corroded with removal of the calcitic shells.

Eocene, Mukta Field, offshore India

30. Biomouldic

Sparite cement on a micrite envelope. The original aragonite of the mollusc shell was leached creating mouldic porosity.

Upper Cretaceous (Turonian), Miskar Field, offshore Tunisia

31. Biomouldic

Rims of sparite cement on shell fragments. Note the micrite envelopes. The original aragonite of the mollusc shells was leached creating mouldic porosity. Intergranular porosity is also seen.

Upper Cretaceous (Turonian), Miskar Field, offshore Tunisia

32. Biomouldic

Mouldic porosity in rudist bivalve grainstone. Field of view approximately 2 mm wide.

Upper Cretaceous (Coniacian), Miskar Field, offshore Tunisia

33. Oomouldic

Oomoulds due to dissolution of aragonitic ooids. Field of view approximately 6 mm wide.

Miocene, Mallorca, Spain

34. Oomouldic

Ooidal grainstone where ooids were dissolved and the oomouldic porosity was filled by late burial cement (ferroan calcite, blue staining with K ferricyanide).

35. Mouldic/Interparticle

Skeletal grainstone containing shelter, interparticle and mouldic porosity. Field of view approximately 9 mm wide.

Carboniferous (Visean), Karachaganak Field, Kazakhstan

36. Cavernous

Cavernous porosity due to limestone dissolution by meteoric water.

37. Late leaching

At first this appears to be primary intraparticle porosity in the stereom of an echinoderm fragment, but the porosity has been created by the selective, late stage dissolution of micrite that had filled the once porous grain.

Eocene, Mukta Field, offshore India

38. Late leaching

Corroded echinoderm fragment with remnant patches of matrix in the stereom and dissolved micrite matrix producing vug porosity.

Eocene, Mukta Field, offshore India

39. Dissolution

Extensive dissolution of the sparry calcite intragranular cements and micritic foraminifer test walls.

Eocene, Mukta Field, offshore India

40. Microporosity

Irregular microporosity within the micrite matrix in foraminifer packstone with Coskinolina.

Eocene, Mukta Field, offshore India

41. Microporosity

Microporosity in the walls of Coskinolina foraminifer and in the cement precipitated in the interparticle space of the foraminifer chambers. The walls are nearly 60 microns thick.

Eocene, Mukta Field, offshore India

42. Microporosity

Microporosity and fine fracture porosity in the micrite matrix filling the cavities in a coral; the former aragonitic corallite walls were replaced by calcite spar but exhibit no porosity.

Eocene, Mukta Field, offshore India

43. Microporosity

Microporosity in a skeletal grain; field of view 0.3 mm.

Upper Cretaceous, Miskar Field, offshore Tunisia

44. Microporosity

SEM image of microporosity in Mississippian (Visean) micrite.

Carboniferous, Mississippian (Visean), Karachaganak Field, Kazakhstan

45. Stylolite dissolution

Late corrosion porosity along stylolite.

Eocene, Mukta Field, offshore India

46. Matrix dissolution

Micrite matrix partly replaced by a hypidiotopic mosaic of dolomite (white). Micrite has been partly dissolved and exhibits secondary porosity (blue epoxy).

47. Dissolution/Intercrystalline

Idiotopic (planar-e) mosaic of (euhedral) dolomite rhomb crystals (white) replacing micrite. The blue areas are secondary porosity between the dolomite crystals (intercrystalline) due to micrite dissolution.

48. Dissolution/Stylolite

Hypidiotopic mosaic of (subhedral, planar-s) dolomite rhomb crystals (white) replacing a skeletal packstone. The blue areas are secondary porosity due to dissolution associated with stylolite formation.

49. Intercrystalline

Intercrystalline porosity in dolomite planar-e (euhedral) idiotopic mosaic.

Upper Cretaceous, Miskar Field, offshore Tunisia

50. Intercrystalline

Intercrystalline porosity in dolomite planar-e (euhedral) idiotopic mosaic.

Upper Cretaceous, Miskar Field, offshore Tunisia

51. Fracture/Dissolution

Late corrosion porosity along fractures.

Eocene, Mukta Field, offshore India