Carbonates and Evaporates

Question 1

carbonate rocks consist primarily of what two carbonate minerals

Answer 1

Limestone - predominately calcite (Calcium carbonate, CaCO3)

Dolomite - Predominately Dolostone (Calcium Magnesium Carbonate, CaMg(CO3)2

Question 2

how are carbonate rocks formed?

Answer 2

through biological and biochemical processes and through inorganic precipitation from seawater

Question 3

what period did the spreading of carbonate rocks start with?

Answer 3

the Cambrian period

Question 4

What percentage of all sedimentary rocks are made of carbonates? And what fraction do these carbonate rocks make up for the worlds petroleum reserves?

Answer 4

20-25%
and
1/3

Question 5

Most carbonates form in what temperature of water?

Answer 5

Warm

Question 6

most carbonate sediments are generated in which zone?

Answer 6

Photic zone

Question 7

True or fales.

Unlike sandstones, most carbonate grains are formed in the environment in which they are deposited?

Answer 7

True

Question 8

Carbonates are not usually found / occur after approx. what depth? And why is that? And what is the name of that depth range?

Answer 8

3500-4000m and this is because the carbonate sediments dissolve here. This depth is called the Carbonate compensation Depth CCD

Question 9

List 4 chemical carbonate rocks

Answer 9

Limestone
Dolostone
Rock Gypsum
Rock Salt

Question 10

List 3 BIOchemical carbonate rocks

Answer 10

Limestones (chalk and coquina)
Chert
Coal

Question 11

Is Coquina a Clastic or Carbonate?

Answer 11

This was a trick question,

Coquina is a clastic carbonate.

Question 12

What is the major rock forming mineral found in mt.rundle?

Answer 12

Calcite (CaCO3)

Question 13

Carbonate reservoirs are predominately composed of what?

Answer 13

chemical precipitates

Question 14

What is a chemical precipitate?

Answer 14

they consist of mineral matters that was precipitated at the place here the rocks first formed and not transported as clastic grains

Question 15

What is the most dominate chemical reservoir rock?

Answer 15

Limestone

Question 16

What is the secretion process? and what are formed by this process?

Answer 16

Rocks of biochemical origin are formed by this process in which animals and plants extract mineral material from solution and transform in into skeletal forms

Question 17

what is the carbonate secreted by living organisms? and how is it formed?

Answer 17

CaCO3 in the form of either aragonite or calcite

Question 18

What are the main biochemical agents in forming limestones?

Answer 18

Algae, bacertia, corals, foraminifera, bryozoa, brachiopods

Question 19

What is the most important rock builder of lime secretions and deposition?

Answer 19

Algae

Question 20

what is the general way dolomite is formed?

Answer 20

formed from limestone as the calcium in calcite is partially replaced by magnesium. Usually as water solutions move through the limestone

Question 21

explain the process of dolomite recrystallization and it’s importance

Answer 21

Magnesium ion migration through layers of limestome form the dolomite and this replacement process causes the recrystallization of the pre-exisiting limestone which enhances the porosity of the carbonate rocks

Question 22

What are the two principal classifications for carbonates?

Answer 22

Folk’s classification: named after Robert Folk

Dunham’s classification: named after Robert Dunham

Question 23

How does Folk’s classification system work?

Answer 23

Based on the presence / absense of Allochem (carbonate particles or grains), matrix and type of cement

Question 24

How does Dunham’s classification system work?

Answer 24

It is based on texture of the rock.

Question 25

Limestones are formed in what environments (4)?

Answer 25

Shallow marine deep marine karsts Lakes

Question 26

High temperature and low pressure and breaking waves favor what?

Answer 26

carbonate precipitation

Question 27

CaCO3 precipitates in warm or cool water?

Answer 27

Warm shallow water

Question 28

What are the four controls on carbonate accumulation?

Answer 28

Temperature Light Agitation of waves Organic activity

Question 29

Are carbonate sediments born or made?

Answer 29

Born

Question 30

What are the four carbonate platforms?

Answer 30

Ramp Rimmed Shelf Epieric platform Isolated platform

Question 31

What is the Carbonate mineralogy consist of?

Answer 31

Aragonite - high temp CaCO3 mineral Calcite - Stable in sea water and near surface crust Dolomite - stable in sea water and near surface

Question 32

Lime muds and skeletal material are lithified into what?

Answer 32

Limestone

Question 33

What are the four keys for the interpretation of a depositional setting of a carbonate?

Answer 33

Grain types Grain packing or fabric Sedimentary structures Early diagenetic changes

Question 34

What is an Ooid?

Answer 34

spherical grains formed by calcite precipitation around the nucleus. Such as shell fragment They are less than 2mm in diameter

Question 35

Where are Ooids found/formed?

Answer 35

Typically form in shallow warm , agitated and carbonate - saturated waters such as those near the bahamas.

Question 36

What kind of sedimentary structures are present in carbonate rocks?

Answer 36

Cross bedding Laminated bedding Mud cracks Trace fossils

Question 37

What are two carbonate marine depositional systems?

Answer 37

Carbonate reefs | Carbonate shelves and platforms

Question 38

What are four examples of Carbonate tectonic extension settings?

Answer 38

Great barrier reef of Australia Bahamas East Africa Red Sea

Question 39

What are three examples of Carbonate tectonic Compression settings?

Answer 39

Persian Gulf Appalachians Australia

Question 40

What is a Karst?

Answer 40

a landscape formed by the dissolution of soluble rocks including limestone, dolomite and gypsum

Question 41

What is a Karst modified reservoir?

Answer 41

Carbonate reservoir

Question 42

Examples of Karst features that can affect reservoir performance

Answer 42

Collapse feature Residual Paleo-Highs Solution - enlarged fractures

Question 43

What are Two factors that shape coral reefs?

Answer 43

The foundation on which they grow | sear level history

Question 44

What are the three major reef types?

Answer 44

Atoll Fringing Pinnacle / Barrier

Question 45

What is an Atoll reef?

Answer 45

circular reef enclosing lagoons

Question 46

What is a Pinnacle reef?

Answer 46

shaped like a tower and rises from the sear floor to form mounds

Question 47

What is a fringing reef?

Answer 47

they grow attached to the shoreline or island

Question 48

Name four carbonate depositional environments

Answer 48

Shelf (reef) margin crest Shelf Platform Basin Shelf base

Question 49

What is a reef margin

Answer 49

forms linear bodies parallel to the basin

Question 50

Why are shelf platform carbonate depositional environments important?

Answer 50

they form major caps to oil fields.

Question 51

What is important to know about the shelf margin slope system?

Answer 51

Gravity dominant sedimentary driver

Question 52

What is important to know about the basin systems?

Answer 52

they are set in the deeper water down slope | they tend to exhibit thin beds of alternating carbonates, silts and shales