(S13) Carbonate Platforms

Question 1

What are the five different forms of carbonate platforms?

Answer 1

Homoclinical ramp, Distally steepened ramp, Unrimmed flat-top platform, Rimmed flat-top platform, Isolated flat-top platform

Question 2

What is an “attached flat top platform”?

Answer 2

A very low gradient top connected to the continent, then a steep slope which is the front margin: Rimmed or unrimmed

Question 3

What is the variation in size of an attached flat top platform?

Answer 3

Few km to >1000km

Question 4

What is another name for an inland sea?

Answer 4

Epeiric sea

Question 5

What is a rimmed platform?

Answer 5

Carbonate shelf with a reef or other carbonate body to act as a rim before the forereef slope

Question 6

Give three examples of facies that a lagoon created by a rimmed platform may be associated with

Answer 6

Shoals, patch reefs, migrating island systems

Question 7

Instead of reefs, unrimmed platform margins are often marked by the development of relatively high-energy facies such as ___.

Answer 7

Ooid shoals

Question 8

Aside from the lack of reef system, what is the two main differences between a unrimmed and a rimmed carbonate shelf?

Answer 8

Unrimmed tend to have lower gradient margins, and a somewhat higher energy platform

Question 9

What is the variation in size of an isolated flat top platform?

Answer 9

Few hundred meters to ~500km long

Question 10

Give a modern example of a larger isolated flat top platform

Answer 10

Bahamas

Question 11

What is the difference between a isolated flat top platform and a reef?

Answer 11

Isolated flat top platforms may be hundreds to km above the sea-floor depth which aggrigated before reef formation

Question 12

What defines an asymmetrical isolated flat-top platform?

Answer 12

Well-developed rimmed margin on one side of platform - usually side with prevailing wind/ocean current favourable for reef growth

Question 13

What forms at the leeward margin of an isolated flat-topped platform?

Answer 13

Grain-shoal islands

Question 14

What forms at the windward margin of an isolated flat-topped platform?

Answer 14

Aggrading reef

Question 15

What is the difference between ramp platforms and other carbonate platforms? (2)

Answer 15

Not flat-topped, do not have steep margin

Question 16

What are the two main subdivisons of carbonate ramps?

Answer 16

Homoclinal and distally steepened ramps

Question 17

What is the difference between homocline and distally steepend ramps?

Answer 17

Homoclinal = gradual gradient, Distally steepend = gradual gradient, then a margin which is slightly steeper at some distance (inner and outer ramp)

Question 18

What do the facies belts on a carbonate ramp range from?

Answer 18

Proximal tidal flats/sabkha to fine/coarse grained shoreline/lagoon to gradually finer down ramp

Question 19

What three facies can ramps be seperated into?

Answer 19

Inner, mid and outer ramp facies

Question 20

What facies can be associated with carbonate ramps? (2)

Answer 20

Patch reef systems, grainstone shoals

Question 21

Give three examples when continental interiors have been flooded by extensive shallow seas

Answer 21

Late Cretacous, Ordovician, Early Carboniferous

Question 22

How is it suggested that epieric platforms were infact very dynamic environments?

Answer 22

Vast shallow-water carbonate factories responding to tectonics and progradation

Question 23

What type of platform is favoured in cooler waters and why?

Answer 23

Ramp platforms - Temperature favours hetrotrophic factories

Question 24

What is “Eustacy”?

Answer 24

Change in sea level

Question 25

What are the eight types of carbonate platforms as suggested by Bosence (2004)?

Answer 25

Fault-block, Salt diapir, Subsiding margin, Offshore bank, Volcanic pedestal, Thrust-top, Delta-top, Foreland margin

Question 26

Who is(are) the author(s) who proposed the idea of eight types of carbonate platforms?

Answer 26

Bosence (2004)

Question 27

What % of global hydrocarbon reserves reside in carbonate reservoirs?

Answer 27

>50%

Question 28

What are the two reasons why carbonate reservoirs are difficult to predict?

Answer 28

Material which makes up the reservoirs has evolved through time, Carbonates more prone to diagenisis with burial

Question 29

Give an example where an entire petroleum system can reside in a single carbonate depositional system

Answer 29

Attached platform margin - steep downslope to deep-marine source rock, top is sealed by salt