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GLGY Sed Strat > Carbonate Diagenisis > Flashcards

Carbonate Diagenisis Flashcards

1
Q

What is percentage of carbonate rocks in the sedimentary record?

A

Around 13%

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2
Q

Epeiric platform is characterized by ……

A

Warm, shallow in land sea

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3
Q

What is a carbonate platform?

A

Term applied to any shallow marine environment where carbonates accumulate.

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4
Q

Facies boundaries !!!

A

One rock have different specifics characteristics related to the environment that was deposited.

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5
Q

In the fore reef talus we would find a pile of broken of corals, so we can infer that the …………and …………. will be different

A

Substrate and organisms

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6
Q

What structures can we find in a reef front?

Those are the …………of the reef

A

Bafflestone
Bindstone
Framestone

Core

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7
Q

What structures can I find in the reef crest?

A

Bindstone

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8
Q

What structures can I find in the back reef?

A

Bafflestone

Floatstone

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9
Q

What structures can I find in the sand apron part of the reef?

A

Rudstone and grainstone

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10
Q

What structures can I find in a lagoon environment?

A

Packstone and wakestone

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11
Q

Reefs have a major impact on the environment. They ……….waves, decreasing the energy of the environment.

A

Break or baffle

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12
Q

What structures can we expect to find on the fore reef talus and back reef?

A

Rudstone and grainstone

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13
Q

When tides move sediment in and out, little particles get coated with calcium carbonate and thus forming……………

A

Ooids

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14
Q

A rock formed by ooids is called……..

A

Oolite

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15
Q

Carbonate sand shoals:

Where ooids form, is a very specific environment, where shallow, warm and gently agitated waters make a perfect depositional setting for carbonates. Can we expect planar bedding in this setting?

A

No because we will have increase Bioturbation!!

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16
Q

Describe the environmental setting you would find in a lagoon?

A

Low energy environment
Increased nutrients
Very fine grained sediment
Increased Bioturbation

Lagoon- warm, shallow waters promote evaporation and concomitant increase in salinity- hyper-saline solution- precipitation of calcium carbonated

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17
Q

We can start altering the sediment as soon as it was deposited.
True/false

A

True

Eogenesis - immediately post deposition.

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18
Q

Diagenic processes:

Microbial micritization : transforms the original grains (recrystalization) or coats the grains with a micritic envelope, due to the action of……….

Cementation: process occurring when you have ………………..pore water.

Pore fluids are supersaturated with respect to cement phase
There are no kinectic factors inhibiting precipitation.

A

Microbes

Supersaturated or hipersaline

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19
Q

How do we modify salinity?

A

Evaporate water
Temperature
pH

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20
Q

What is cement?

A

Crystals precipitated in a fluid-filled space, growing attached to a substrate; commonly aragonite, HMC, LMC, Dolomite ( others are less common)

!!!! Precipitated as opposed to deposited!!!!!!!

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21
Q

Diagenic processes:

What is Neomorphism?

A

Transformation between one mineral and itself or a polymorph. It is thought to be a “wet” process, meaning that it is occur across a thin, interstitial fluid film.

E.g., taking a calcite and growing a bigger calcite grain.
Replacement of aragonite shells or cement by calcite.
Recrystalization of a lime mud to produce coarser crystals.

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22
Q

Diagenic processes:

Dissolution: occurs when fluids are…………..with respect to a given mineral. Particularly important in meteoric settings; also related to Lysoclines in deeper marine settings.

A

Undersaturated

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23
Q

What are Lysoclines?

!!!!!!

A

Change in salinity wit depth in oceans!!!

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24
Q

What are the characteristics of meteoric water?

A

Acidic- low pH

Under saturated with carbonates.

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25
Q

What is the difference between precipitation and dissolution?
!!!

A

Precipitation happens when the pore space is supersaturated and dissolution happens when the pore water is undersaturated.

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26
Q

What is the difference between non-rimmed and rimmed carbonate platforms?

A

Decreased energy in rimmed shelf because energy is wasted in the corals (reef).
High energy in non-rimmed platform causing completely different types of organisms and sedimentary structures to be there. Consequently you will have different Bioturbation in each setting.

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27
Q

Diagenetic processes:

Mechanical compaction: processes occurring under increased overburden when grains are translocated for closer packing, fractured, crushed. It results in …………. unless you have…………….

!!!!!

A

Decreased porosity

Early cementation

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28
Q

Diagenetic processes:

Chemical compaction: produced by ………. Process results in a “ ……………..” Between the adjacent grains and, ultimately, dissolution seams and ………….., surfaces that are marked by the remaining, relatively insoluble materials (clay, oxides, organic matter)

!!!!!!!!

A

Pressure-enhanced dissolution
Fitted fabric
Stylolites

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29
Q

What is Fitted fabric?

A

One grain intertwined to the other

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30
Q

As we increase mechanical and chemical compaction, with increase in pressure, water is pushed out of the porous, forming dewatering, flame, ball/pillow structures. It can happen in ……………settings too

A

Carbonates

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31
Q

Marine diagenesis:

Occurs on: …………

A

Shallow waters depth: where the carbonate is!!!!

The sea floor
Tidal flats
Beachs

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32
Q

Marine diagenesis:

Shallow waters (to shelf (200m) and slope depths:
Good potential for cementation depending on:
………

Deep waters:
High pressure, low water temperature and high partial pressure of CO2 lead to dissolution Because seawater becomes more …………..

A

Shallow waters: decreased porosity
Salinity
Temperature
Pressure

Deep waters: Increase porosity
Undersaturated (1st with respect to aragonite then HMC, then LMC. Acidity breaks things up increasing porosity.

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33
Q

Isopachous cement?

A

Is a cement of precipitated minerals that form rims of nearly equal thickness around the grains in a sedimentary rock during diagenesis. Common in sub aqueous environment.

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34
Q

The interesting is what happens to pore water. When we have waves in a high energy environment, we are not just moving water at the surface, we are moving water in and out of the……..

A

Pore spaces

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35
Q

Marine diagenetic setting:

Active shallow marine setting: wave/ tides pumping pore waters through reefs and shoals, producing: Aragonite And HMC cements forming ……………..’coats’ composed of needles,fibers, blades on grains/ skeletons

Intragranular cements, that is, within shells such as gastropods and forams.

A

Isophacous

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36
Q

Marine diagenenic:

Less active (stagnant) marine setting: modern muddy sands in relatively protected settings, characterized by:
Early more localized Cementation of grains into aggregates, intragranular cements.
Intense microbial...................

Microbes don’t live in places with high energy.

A

Micritization

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37
Q

Marine diagenesis:

Marine phreatic settings as in intertidal- supratidal zones such as:…….., ………., producing:

………… Cement in lower intertidal zones and meniscus cements in ……….. (Low/high) Intertidal zones ( vadose Zones)

Micrite coats

A

Beach rock and tidal flats

High

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38
Q

Marine diagenesis:

Water table separates a zone of intermittent drying & saturation, called ………
from a zone that is constantly wet (permanently fluid-saturated , called ………….

A

Vadose zone

Phreatic zone

39
Q

Vadose zone?

A

Intermittent wet (above low tide)

40
Q

Phreatic zone?

A

Constant wet (below low tide)

41
Q

What is vugs?

A

Gaps/holes/spaces in the sediment often formed by secondary dissolution.

42
Q

How do we form larger crystals in the phreatic zone?

A

Change in pH
Change in temperature
Change in pressure
Change in concentration of solution

The pore spaces are continuously soaked, which allows a slow and long periods of growth (large crystals)

43
Q

Meteoric diagenisis:
In phreatic zone:

Cement growth is more continuous with ……………..

LMC in blocky, approximately ……………rims or pore-filling

Phreatic zone cements are ……………..to burial cement.

A

Larger crystals
Equant
Transitional

44
Q

Meteoric diagenesis:
Vadose zone!

Calcareous soil horizons can form (calcretes, …………..soils)

LMC calcite is precipitated in distinctive forms:…………., pendant

A

Caliche

Meniscus

45
Q

Vadoze zone: …………….wet. They form calcretes, desert pavements, early diagenesis, calcite and concrete nodule.

A

Periodically (dry and wet)

46
Q

Phreatic zone:……………. that is continuously growing and getting significantly larger

A

cement

47
Q

Ooids form………..cement in marine phreatic zone.

A

Meniscus

48
Q

Unlike marine water, fresh water has very little Ca2+ and carbonate, so it becomes a little …………….

A

Acidic

49
Q

Large crystals are indicative of………………zone

A

Phreatic

50
Q

Once aragonite needles, transformed into LMC – this is a ……………process!

A

Neomorphic process

51
Q

Burial diagenesis:

CaCO3 rocks enter this setting either:

Directly from the marine setting, with marine pore fluids, or-

After ……………………… where mineralogy is partly stabilized and fluids are fresh or mixed (marine-meteoric)

A

Meteoric diagenesis

52
Q

Burial diagenesis:

Subsurface conditions include:
Higher pressure and……….
Higher ……………

Low rates of fluid flow:

  • ……….
  • ……….
A

Temperature
Salinity (but not always) very generalized statement!

Low porosity
Low permeability

53
Q

Sparry calcite: is a crystalline mosaic of calcite crystals in which individual crystals are easily discernable with an optic microscope. In carbonates, sparry calcite forms as a cement during diagenesis within……………..porosity or ……………. of aragonite.

A

Primary

Neomorphism

54
Q

Burial diagenesis: Common processes include:
Mechanical compaction

Chemical compaction e.g pressure solution producing……………. and “fitted fabric”

Cementation of typically coarse sparry calcite (LMC)

Neomorphism and recrystalization of any remaining …………and HMC

Burial ……………

A

Stylolites
Aragonite
Dolomitization

55
Q

Dolomitization:

If you precipitate ………….., you take …….out of the system, increasing the concentration of Mg. think of Mg:Ca

A

Calcium carbonate

Ca2+

56
Q

What is the importance of dolomite?

A

Common petroleum reservoir rock

Used in cement

57
Q

Dolomite Isomorphs:

Substitute……. and …….. To form the Isomorphs.

Ankerite (CaFe(CO3)2)
Kutnahorite (CaMn(CO3)2)

Dolomite has a range of composition but we still call it dolomite

A

Iron and manganese

58
Q

Dolomite Isomorphs:

Most commonly, partial substitution of iron results in………………..dolomite:

CaMgFe(CO3)2

A

Feroic

59
Q

We call it dolostone if it made of ………..or more of dolomite.

A

50%

60
Q

Dolomitization is the replacement of ….. With……

A

Ca2+ with Mg

61
Q

The vast majority of dolomites are thought to have formed via………. Of pre-existing carbonate minerals.
E.g calcite and aragonite

Replacements can ( but doesn’t alway) result in …………….. of the original limestone fabric.

A

Replacement

Destruction

62
Q

Dolomitization:

Probably a replacement. What so we need?
Pore fluids - large amounts of …… Into the system.

Get rid of aragonite and…………(lots of Ca+)
Move fluid into the system, replenishing with………

A

Mg
Gypsum
Mg

63
Q

Dolomitization requirements

Pore fluids wit elevated Mg:Ca ratio
Evaporation of seawater(to form …….)
Precipitation of …………. and gypsum ( remove ……)

Some sort of ………..
Must be long- term as LOTS of Mg is needed to dolomitize large volumes of carbonates

A

Brine
Ca2+
Advection

Max enrichment with Mg is obtained with temperatures passing 60 C (really bad to reproduce on land)

64
Q

According to one model:

(1) Ca2+ + Mg2+ + 2(CO3 2-). – CaMg(CaCO3)2

Dolomitization is not ……………of dolomite from sea water.

A

Direct precipitation

65
Q

According to the replacement model:

(2) Mg2+ + 2(CaCO3)– CaMg(CO3)2+ Ca2+

Replacement of calcium with magnesium. We need max enrichment of Mg2+

Requires addition of Mg2+ and removal of Ca2+

It has been demonstrated that can happen but why does not work?

A

Lot easier at high temperatures past 60C but we can’t find this occurring naturally and flowing through a carbonate platform.

So temperature is the problem!!!

66
Q

Meteoric diagenisis:
In phreatic zone:

Cement growth is more continuous with ……………..

LMC in blocky, approximately ……………rims or pore-filling

Phreatic zone cements are ……………..to burial cement.

A

Larger crystals
Equant
Transitional

67
Q

Meteoric diagenesis:
Vadose zone!

Calcareous soil horizons can form (calcretes, …………..soils)

LMC calcite is precipitated in distinctive forms:…………., pendant

A

Caliche

Meniscus

68
Q

Vadoze zone: …………….wet. They form calcretes, desert pavements, early diagenesis, calcite and concrete nodule.

A

Periodically (dry and wet)

69
Q

Phreatic zone:……………. that is continuously growing and getting significantly larger

A

cement

70
Q

Ooids form………..cement in marine phreatic zone.

A

Meniscus

71
Q

Unlike marine water, fresh water has very little Ca2+ and carbonate, so it becomes a little …………….

A

Acidic

72
Q

Large crystals are indicative of………………zone

A

Phreatic

73
Q

Once aragonite needles, transformed into LMC – this is a ……………process!

A

Neomorphic process

74
Q

Burial diagenesis:

CaCO3 rocks enter this setting either:

Directly from the marine setting, with marine pore fluids, or-

After ……………………… where mineralogy is partly stabilized and fluids are fresh or mixed (marine-meteoric)

A

Meteoric diagenesis

75
Q

Burial diagenesis:

Subsurface conditions include:
Higher pressure and……….
Higher ……………

Low rates of fluid flow:

  • ……….
  • ……….
A

Temperature
Salinity (but not always) very generalized statement!

Low porosity
Low permeability

76
Q

Sparry calcite: is a crystalline mosaic of calcite crystals in which individual crystals are easily discernable with an optic microscope. In carbonates, sparry calcite forms as a cement during diagenesis within……………..porosity or ……………. of aragonite.

A

Primary

Neomorphism

77
Q

Burial diagenesis: Common processes include:
Mechanical compaction

Chemical compaction e.g pressure solution producing……………. and “fitted fabric”

Cementation of typically coarse sparry calcite (LMC)

Neomorphism and recrystalization of any remaining …………and HMC

Burial ……………

A

Stylolites
Aragonite
Dolomitization

78
Q

Dolomitization:

If you precipitate ………….., you take …….out of the system, increasing the concentration of Mg. think of Mg:Ca

A

Calcium carbonate

Ca2+

79
Q

What is the importance of dolomite?

A

Common petroleum reservoir rock

Used in cement

80
Q

Dolomite Isomorphs:

Substitute……. and …….. To form the Isomorphs.

Ankerite (CaFe(CO3)2)
Kutnahorite (CaMn(CO3)2)

Dolomite has a range of composition but we still call it dolomite

A

Iron and manganese

81
Q

Dolomite Isomorphs:

Most commonly, partial substitution of iron results in………………..dolomite:

CaMgFe(CO3)2

A

Feroic

82
Q

We call it dolostone if it made of ………..or more of dolomite.

A

50%

83
Q

Dolomitization is the replacement of ….. With……

A

Ca2+ with Mg

84
Q

The vast majority of dolomites are thought to have formed via………. Of pre-existing carbonate minerals.
E.g calcite and aragonite

Replacements can ( but doesn’t alway) result in …………….. of the original limestone fabric.

A

Replacement

Destruction

85
Q

Dolomitization:

Probably a replacement. What so we need?
Pore fluids - large amounts of …… Into the system.

Get rid of aragonite and…………(lots of Ca+)
Move fluid into the system, replenishing with………

A

Mg
Gypsum
Mg

86
Q

Dolomitization requirements

Pore fluids wit elevated Mg:Ca ratio
Evaporation of seawater(to form …….)
Precipitation of …………. and gypsum ( remove ……)

Some sort of ………..
Must be long- term as LOTS of Mg is needed to dolomitize large volumes of carbonates

A

Brine
Ca2+
Advection

Max enrichment with Mg is obtained with temperatures passing 60 C (really bad to reproduce on land)

87
Q

According to one model:

(1) Ca2+ + Mg2+ + 2(CO3 2-). – CaMg(CaCO3)2

Dolomitization is not ……………of dolomite from sea water.

A

Direct precipitation

88
Q

According to the replacement model:

(2) Mg2+ + 2(CaCO3)– CaMg(CO3)2+ Ca2+

Replacement of calcium with magnesium. We need max enrichment of Mg2+

Requires addition of Mg2+ and removal of Ca2+

It has been demonstrated that can happen but why does not work?

A

Lot easier at high temperatures past 60C but we can’t find this occurring naturally and flowing through a carbonate platform.

So temperature is the problem!!!

89
Q

Dolomitization model: Addition of both Mg2+ and CO3 2- to the system.

CaCO3 + Mg2+ + CO3 2- – CaMg(CO3)2

Eliminates the removal of Ca2+ as a requirement

What is the problem?

A

Kind of the same thing of number replacement . The only difference is that you don’t have to eliminate Ca2+, you can only have to cram Mg2+ into CaCO3

90
Q

Dolomitization:

What are we trying to replace?

A

The Ca2+ and CaCO3

91
Q

Dolomitization:

What are we trying to do?

We have Mg2+ and we are trying to insert in a …….. structure to make dolomite

A

carbonate

92
Q

Dolomitization:

Where does it take place?

A

Carbonate platforms and in temperate climate, around 30 from the equator.

93
Q

What is a Sabkhas?

A

Marine lake that is filled periodically (coastal lagoon)

94
Q

What is Neomorphism?

A

Is a term used by folk to cover the combined processes of inversion ( eg. Transformation of aragonite to calcite) and recrystalization ( change in size or shape of a crystal with little or no change in chemical composition or mineralogy)

GLGY Sed Strat (4 decks)

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