Sedimentary Rocks And Fossils

Front 1

Dominant minerals

Back 1

1. Cations + (CO3)2-
2. Most common cations
- Larger Ca2+
- Smaller Mg2+

Front 2

Dominant minerals: Aragonite

Back 2

1. Open orthorhombic structure
2. Can accomodate cation substitution
3. Unstable
4. CaCO3

Front 3

Dominant minerals: Calcite

Back 3

1. More closed rhombohedral structure
2. High Mg calcite (>5% Mg)
3. Low Mg calcite
4. CaCO3

Front 4

Dominant minerals: Dolomite

Back 4

CaMg(CO3)2

Front 5

Carbonate deposition controls

Back 5

1. Temperature
2. Pressure
3. Agitation
4. Organic activity
5. Minor siliclastics
6. Light

Front 6

Temperature

Back 6

1. Precipitates in warm water
2. Dissolves in cold water
3. CCO diagram (carbonate concentration depth)

Front 7

Agitation

Back 7

1. Currents and waves allow CO2 to escape
2. Promotes carbonate precipitation

Front 8

Organic activity

Back 8

1. Many organisms precipitate CaCO3 from seawater
2. Many organisms remove CO2 from water
- Promotes precipitation of CaCO3

Front 9

Absent/limited presence of Siliclastics

Back 9

Abundant silicalastics will overwhelm carbonate production

Front 10

Light

Back 10

1. Photosynthesis requires light
2. Nearly all carbonate production occurs at depths where light can penetrate (<20 m)
3. Carbonate not produced inmuddy water

Front 11

Distribution though time: Precipitation of Modern Cabonates

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1. Inorganic
- Caves (travertine)
- Springs (tufa)
2. Organic
- Reefs
* Shallow marine
* Low silicates
* Warm water 40 degrees North or South of Equator

Front 12

Distribution thought time: Precipitation of Ancient Carbonates

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Abundant Proterozoic-Phanerozoic
- Controlled by:
* Tectonics
* Orogenic evolution

Front 13

Modern Carbonates: Lithification of Carbonates

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1. Non-marine
- Shallow carbonate lacustrine mud
2. Shallow marine
- Continental shelves where siliclastics are low
3. Deep marine
- Abyss above the carbonate compensation
4. Others
- Limestone rubble
- K-horizon in soil (caliche)

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Ancient Carbonates: Lithification of Carbonates

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1. Non-marine
- Rare (preservation?)
2. Shallow marine
- Abundant Proterozoic-Mesozoic
- Broad shallow seas that covered continents
3. Rare
- Not preserved
- Not abundant carbonate plankton
4. Others
- Rare (preservation?)

Front 15

Limestone components

Back 15

1. Allochems
- Skeletal
- Non-skeletal
2. Orthochems

Front 16

Allochems: Skeletal clasts

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Fossil fragments (biocasts)

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Allochems: Non-skeletal clasts

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1. Coated grains (Ooids/ooliths)
2. Chemical or biochemical
3. Intrabasinal

Front 18

Allochems: Non-skeletal clasts

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1. Peloids
- Sand-sized clasts of micro-crystalline carbonate
- Intra-basinal origin
* Fecal pellets
* Recrystallization as allochem

Front 19

Allochems: Non-skeletal clasts

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Grain aggregates
- Weakly held together by microbial mats
- Local intrabasinal

Front 20

Allochems: Non-skeletal clasts

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Limestone clasts
- Ripped up and transported
* Intrabasinal
* Estrabasinal
- Equal siliciclastic rock fragments

Front 21

Orthochems

Back 21

1. Micrite (carbonate mud)
- equals silicicclastic matrix
2. Spar (carbonate cement)

Front 22

Dunham Classification

Back 22

1. Empasizes texture
- Allochems or grains
- Mud of any compostion
- Primary spar cement
* Grain supported
- Secondary spar
* Recrystallization of micrite
* Not grain supported

Front 23

Dunham Classification: Limestones

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1. Unbound
A. Contains mud
- Mud supported
* Mudstone (<10% grains)
* Wackestone (>10% grains)
- Grain supported
* Packstone (<10% mud)
B. Grainstone
2. Boundstone (reef)

Front 24

Depositional texture not recognizable

Back 24

1. Crystalline carbonate
2. Allochems NOT grain supported floating in spar

Front 25

Dolomite

Back 25

1. CaMg(Co3)2
2. Forms naturally in unrealistic conditions
3. Penecomtemporanous replacement of Mg for Ca
* High ph environments
* Precipitation of gypsum, anhydrite, to use Ca cation
* Mg becomes abundant in brine and replaces Ca
4. Secondary replacement of Ca by Mg from high Mg fluid

Front 26

Dolomite

Back 26

1. Ancient dolomite widespread, modern dolomite limited
- Past environments were different than today
- Most dolomite is by recrystallization over long time spans