Carbonate Rock Diagenesis

Meteoric

1. Meniscus Cement

Peloidal grainstone with peloids (likely due to micritisation of ooids) bounded by calcite cement with meniscus fabric (cement precipitated at grain contacts where water is retained for capillary tension in the vadose zone). Interparticle porosity highlighted by blue epoxy.

Holocene, Bahamas

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2. Meniscus Cement

Grainstone consisting of peloids (likely due to micritisation of ooids) and partly dissolved ooids (dissolution affected the non micritised aragonitic laminae coating the ooids) with meniscus calcite cement (cement precipitated at grain contacts where water is retained for capillary tension in the vadose zone). Interparticle and secondary disspolution porosity highlighted by blue epoxy.

Holocene, Bahamas

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3. Meniscus Cement

Previous image in crossed polarizers of a peloidal and partly dissolved ooids grainstone with meniscus calcite cement (cement precipitated at grain contacts where water is retained for capillary tension in the vadose zone). The view in cross polarisers shows complete extinction in correspondence of the interparticle pores.

Holocene, Bahamas

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4. Meniscus Cement

Ooidal sediment from recent tidal bars (NW Andros, Bahamas) bounded by meniscus calcite in the vadose zone. To notice that recent ooids are tangential with concentric orientation of aragonite crystals.

Holocene, Bahamas

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5. Meniscus Cement

Ooidal sediment from recent tidal bars (NW Andros, Bahamas) bounded by meniscus calcite in the vadose zone. Previous image viewed in cross polarised light showing the interparticle porosity in black.

Holocene, Bahamas

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6. Meniscus Cement

Ooidal grainstone from an inner ramp shoal barrier in the Mississippian of South Wales showing micritic meniscus cement of possible meteoric vadose origin followed by equant sparite in irregular rims and mosaic. The clear sparite could be of phreatic meteoric environment or of burial diagenesis origin.

Mississippian, South Wales, UK

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7. Pendant Cement

Pennsylvanian phylloid algae mound with micritic crusts and micrite envelopes around biomouds. The lower part shows prismatic cement with pendant, gravity controlled fabric typical of the meteoric vadose zone.

Pennsylvanian, New Mexico, USA

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8. Pendant Cement

Detail of previous image with prismatic cement with pendant, gravity controlled fabric typical of the vadose zone. Red colour, iron oxide related impurities increase downward as gravity controlled as well.

Pennsylvanian, New Mexico, USA

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9. Pendant Cement

Previous image in crossed polarisers with prismatic cement with pendant, gravity controlled fabric typical of the vadose zone.

Pennsylvanian, New Mexico, USA

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10. Vadose Cement

Pisoidal grainstone showing: a) pisoids of possible vadose origin with concave-convex grain contacts (vadose compaction: concave contacts between grains because of partial dissolution in the vadose zone); b) pendant calcite cement (vadose zone) precipitated on the lower part of the pisoids; c) in the lower part of the thin section a coarse and leached equant calcite cement might be of meteoric phreatic origin.

Lower Jurassic, High Atlas, Morocco, cf. Verwer et al. (2009b), Merino-Tome'’ et al. (2012)

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11. Meteoric Dissolution

Peloidal and pisoidal grainstone with grains bounded by irregular rims of equant to bladed calcite lined by micrite crusts. There might have been influence of meteoric waters dissolving partly the first rim of marine cement, followed by meniscus micrite and renewed marine cementation as radial fibrous.

Permian, New Mexico, USA

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12. Meteoric Dissolution

Previous image in crossed polarisers with grains bounded by irregular rims of equant to bladed calcite lined by micrite crusts. This cement of possible meteoric origin shows irregular and discontinuous growth but it might also have been partly dissolved before the micrite encrustation and the following radial fibrous marine cement.

Permian, New Mexico, USA

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13. Calcrete

Ooidal grainstone deposited during late Pleistocene, exposed to subaerial meteoric alteration and formation of calcrete palaeosol with laminar texture. Red colour is due to Fe oxide concentration in terrestrial settings.

Pleistocene, Florida Keys, USA

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14. Calcrete

Detail of previous image of ooidal grainstone deposited during late Pleistocene exposed to subaerial meteoric alteration and calcretisation (ooid dissolution, micritisation and iron oxide crusts).

Pleistocene, Florida Keys, USA

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15. Calcrete

Previous image in crossed polarisers of ooidal grainstone deposited during late Pleistocene, exposed to subaerial meteoric alteration and calcretisation (ooid dissolution, micritisation and iron oxide crusts).

Pleistocene, Florida Keys, USA

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16. Calcrete

Calcrete palaeosol from Mississippian inner ramp facies in South Wales. Typical features of alpha type calcretes: circumgranular cracks and glaebules (cf. Wright 1994).

Mississippian, South Wales, UK

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17. Calcrete

Calcrete palaeosol from Mississippian inner ramp facies in South Wales. Typical features of alpha type calcretes: circumgranular cracks, glaebules, angular clasts of pedogenised lithified deposits and iron oxide seams (cf. Wright 1994).

Mississippian, South Wales, UK

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18. Microcodium

Peloidal (micritised grains) grainstone with abundant interparticle porosity and minor calcite meniscus cement containg Microcodium (rosettes of calcite prisms) in the centre. This calcite structure is indicative of root calcification in presence of fungi (cf. Košir 2004).

Pleistocene, Bahamas

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19. Microcodium

Skeletal rudstone/packstone with quartz grains, coralline red algae and lithoclasts and fragments of reworked Microcodium.

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

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20. Microcodium

previous image in crossed polarisers, skeletal rudstone/packstone with quartz grains, coralline red algae and lithoclasts and fragments of reworked Microcodium.

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

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21. Microcodium

Oligocene reef facies affected by alteration by Microcodium (rosettes of calcite prisms) attributed to calcification of root cells of plants in the presence of fungi (cf. Košir 2004). Microcodium is indicative of subaerial exposure and development of vegetation cover.

Oligocene, Central Apennine, Italy

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22. Meniscus Cement

Skeletal grainstone with micrite meniscus cement precipitated in vadose conditions (above the water table and with air + water in the pore space). Vadose cement has been followed by cementation of equant calcite spar.

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23. Laminar Calcrete

Dense laminar calcrete overlying calcified root mat calcrete.

Oxfordian, Upper Jurassic, Rocha Forte, Portugal

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24. Pendant Cement

Pendant fibrous, inclusion-rich cement precipitated in vadose conditions.

Devonian, Western Canada

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25. Microcodium

SEM image of Microcodium, mm-sized aggregate of prismatic calcite crystals that form on limestone unit affected by exposure to subaerial conditions. Microcodium most likely represents root cell calcification effect of plants in the presence of fungi and Ca-rich, nutrient-poor soils.

cf. Kosir (2004)

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26. Microcodium

Microcodium mm-sized aggregate of prismatic petal-like crystals that occur in limestone unit affected by subaerial exposure to subaerial conditions. Microcodium most likely represents root cell calcification effect of plants in the presence of fungi and Ca-rich, nutrient-poor soils.

cf. Kosir (2004)

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27. Microcodium

Foraminifera packstone obliterated by Microcodium growth due to subaerial exposure and soil formation.

cf. Kosir (2004)

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28. Microcodium

Outcrop photo of a rock altered by Microcodium growth due to root cell calcification in the presence of fungi following soil formation.

cf. Kosir (2004)

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29. Microcodium

Limestone unit completely altered and replaced by Microcodium formation due to root calcification in the presence of fungi, following subaerial exposure and development of soil.

cf. Kosir (2004)

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30. Alveolar structure

SEM image of needle fibre calcite present in alveolar septal structure, a fungal mycelial product in palaeosols.

Mississippian, UK

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31. Alveolar structure

SEM images and photomicrographs of alveolar septal structure from present-day vadose profiles; curved septa in pores, especially root tubes, are produced by calcification in fungal mycelial bundles in palaeosols.

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32. Alveolar structure

Alveolar septal structure from present-day vadose profiles; curved septa in pores, especially root tubes, are produced by calcification of needle fiber calcite in fungal mycelial bundles in palaeosols.

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33. Calcified roots

Calcified root mat from Mississippian calcrete. Many laminar calcretes are calcified root mats. Field of view is approximately 1 mm wide.

Llanelly Fm., Mississippian, Wales, UK

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34. Microkarst peloid infill

Peloidal infill of microkarst cavity. Peloids are produced by grainification of limestone affected by soil formation by circum-granular cracking and displacement by wetting and drying cycles. Field of view approximately 9 mm wide.

Bembridge Limestone, Eocene, UK

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35. Sphaerosiderite

Sphaerosiderite from a nodular bed associated with rootlets horizon.

Pennsylvanian, Brynmawr, South Wales, UK

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36. Sphaerosiderite

Sphaerosiderite from a nodular bed associated with rootlets horizon.

Pennsylvanian, Brynmawr, South Wales, UK

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meniscus cement

peloid

meniscus cement

dissolved ooid laminae

meniscus cement

dissolved ooid laminae

tangential ooid

meniscus cement

tangential ooid

meniscus cement

radial ooid

meniscus micritic cement

pendant cement

pendant cement

pendant cement

pendant cement

circumgranualr cracks

glaebules

angular clasts

Microcodium

peloid and meniscus cement

Microcodium

coralline red algae

Microcodium

quartz grains

Microcodium

meniscus micrite

laminar calcrete

root traces

pendant cement

Microcodium

Microcodium

Microcodium

Microcodium

Microcodium

needle fiber calcite

alveolar septal texture

alveolar structure

needle fiber calcite

peloids

Meteoric

CLOSE

meniscus cement

peloid

meniscus cement

dissolved ooid laminae

meniscus cement

dissolved ooid laminae

tangential ooid

meniscus cement

tangential ooid

meniscus cement

radial ooid

meniscus micritic cement

pendant cement

pendant cement

pendant cement

pendant cement

circumgranualr cracks

glaebules

angular clasts

Microcodium

peloid and meniscus cement

Microcodium

coralline red algae

Microcodium

quartz grains

Microcodium

meniscus micrite

laminar calcrete

root traces

pendant cement

Microcodium

Microcodium

Microcodium

Microcodium

Microcodium

needle fiber calcite

alveolar septal texture

alveolar structure

needle fiber calcite

peloids