Week 5

Question 1

Carbonate minerals

Answer 1

Calcite

Aragonite

Dolomite

Question 2

Calcite

Answer 2

CaCO3

Trigonal rhombohedral

Layered with central Ca2+

Most common in rock record

Question 3

Aragonite

Answer 3

CaCO3

Orthorhombic

Metastable over 10-100s of million years - alters to calcite

Most common in corals/molluscs

More MECHANICALLY stable

Question 4

Dolomite

Answer 4

Ca.Mg(CO3)2

Alteration of calcite - Mg from meteoric waters

More resistance to weathering (unless powdered b/c increases SA)

Buff colour due to Fe

Can have high Mg calcite but dolomite is 50:50

Question 5

Types of allochems

Answer 5

Ooids

Peloids

Skeletal grains

Forms

Coccoliths

Question 6

Ooids

Answer 6

= less than mm carbonate spheres, grow around a nucleus

Higher energy = concentric circles

Sheltered = radial

Question 7

Peloids

Answer 7

= no internal structure, amalgamations of carbonate mud

Can be subdivided into pellets/intraclasts

More elongated than voids because haven’t rolled/nucleated in the same way

Question 8

Forams

Answer 8

= structure that single-celled organisms leave behind

Round, smooth

More structured than ooids/peloids

Question 9

Coccolith

Answer 9

= microscopic plates that form a coccolithophore

Major component of chalk

Question 10

Types of autochems

Answer 10

Sparry cement/sparite

Micritic cement/micrite

Question 11

Sparite

Answer 11

Forms from calcite in pore fluid; so saturated that can form without deforming grains

Acicular/fibrous/drusy/granular

Question 12

Acicular =

Answer 12

needle-like

Question 13

Fibrous =

Answer 13

Thicker than acicular but fibrous

Question 14

Drusy =

Answer 14

void-filling and pore-lining cement

Quick precipitation due to high saturation of calcite

Later availability lower = slows down

= crystals of different sizes

Question 15

Granular =

Answer 15

calcite cement with relatively equidimensional pore-filling small crystals

Question 16

Micrite

Answer 16

Muddy
Fine crystals of calcite/clay

Can be washed in OR during diagenesis

Question 17

Cathodoluminesence

Answer 17

Bombard with electrons and see dolomite rhombus with phases of growth due to varying Mg levels

Question 18

Lime mud inputs

Answer 18

(MOST SIGNIFICANT)
Disaggregation of calcareous green algae

Mechanical disaggregation of carbonate grains

Bioerosion

Chemical/biochemical precipitation

Tidal flats erosion

Disaggregated pellets

Question 19

Lime mud outputs

Answer 19

Pellet formation

Into solution

Mud transported offshore in suspension

Deposition on tidal flats

Question 20

Different origins of carbonate

Answer 20

CLASTIC

EVAPORITIC

BIOGENIC

Question 21

Clastic origin

Answer 21

Calcilutite

Calcarenite (all ooids)

Calcirudite

Question 22

Evaporitic origin

Answer 22

When <50% seawater removed

Minor carbonates

~FeO/aragonite

Question 23

Biogenic origin

Answer 23

N.B. Reef growth 1.5-6m/kyr

More than clastic

T/light are primary controls

(T)tropical
- top most water

(C)ool water
- controlled precipitates

(M)ud-mound
- micrite

Question 24

Effect of mud on carbonates

Answer 24

Provides nutrients = good BUT block light

BALANCE

Question 25

Carbonate response to HST

Answer 25

More accommodation space

Can ‘drown’ system

Photic zone 80-200km

Question 26

Carbonate response to TST

Answer 26

Increasing accommodation space

Matches SL = thick packages

Question 27

Carbonate response to FST

Answer 27

Exposed BUT resistant to erosion
- early lithification/skeletal framework

“Limestone pavements” (karstic sediments)

Preserved in rock record (unlike sandstones)

Question 28

Carbonate difference in diagenesis

Answer 28

Early lithification reduces mechanical compaction

Question 29

Carbonate factory deposition type: T

Answer 29

Controlled by photic zone (~80m depth)

Lead to production of reefs/platforms

Question 30

Carbonate factory deposition type: C

Answer 30

Rates of carbonate precipitation = v low

Show similar responses as clastic systems

Question 31

Carbonate factory deposition type: M

Answer 31

High slopes due to biogenic cements

Glues together into mounds

Question 32

CCD through time

Answer 32

Not constant

Varies due to T and acidity

Question 33

Lysocline =

Answer 33

~2000m, starts to dissolve

Question 34

Volume of water remaining = 50%

Evaporite precipitated…

Answer 34

CARBONATES

• minor
• some iron oxide and aragonite
• only accounts for small % of total solids

Question 35

Volume of water remaining = 20%

Evaporite precipitated…

Answer 35

CALCIUM SULPHATE

Solution is denser

Gypsum (<42’C) or anhydrite (>42’C)

Question 36

Volume of water remaining = 10%

Evaporite precipitated…

Answer 36

ROCK SALT (HALITE)

Brine (solution) v dense

Question 37

Volume of water remaining = 5%

Evaporite precipitated…

Answer 37

POTASSIC AND MAGNESIUM SALTS

SO: ionic strength (potential) of evaporating seawater has a strong control over minerals that form

Precipitation of various magnesium sulphates/chlorides and finally NaBr and Kcl

Potassium and magnesium salts (Kainite/Carnallite/Sylvite)

Question 38

Carbonate response during LST

Answer 38

Carbonates = biogenic sediments = dependent on light

Area that is submarine smaller = production reduced and distribution limited
BUT access to sunlight improved = some places enhanced

Question 39

Clastic response to LST

Answer 39

Smaller area of continental shelf = easier to get over littoral fence = more turbidites/mass flow deposits