Carbonate rocks are special because they have a strong link to biological processes. Carbonate sediments are formed biologically rather than through inorganic processes. The composition of carbonate rocks can provide precise information about the depositional environment, unlike siliciclastic rocks. Carbonates can form through various processes, including mechanical deposition, chemical precipitation, and in situ growth. They are classified based on their grain composition, matrix, and cement using ternary diagrams and schemes from Dunham and Folk.

1. Carbonate Rocks

2. Strong link with the “biologic world”
carbonate sediments are born, not made (James, 1984)
“Organic world” has stronger
and more complex relationship
with the environment than the
inorganic one.
A qz grain is a qz grain at the present time
as well as in the Cambrian.
An actual reef works in a different way than
a Cambrian reef.
The study of carbonate rocks
allows paleoenvironmental
recostructionof high detail
Why carbonate rocks are special?

3. Lateral transport of carbonate sediments
is usually very limited .
Why carbonate rocks are special?

4. The composition of a carbonate rock gives very often precise information
on the depositional environment.
The composition of a siliciclastic rock does not give in general information
of the original depositional setting
Why carbonate rocks are special?

5. Carbonates can be the final product of different processes
 mechanical deposition
 chemical precipitation
 in situ growth (build-up)
Why carbonate rocks are special?

6. Classification of carbonate rocks

7. Fundamental to understanding sedimentary rocks is the distinction of three basic components:
GRAINS (termed allochems by Folk), MATRIX (carbonate mud), and porosity or porosity-filling
CEMENT. Typical carbonate rocks are plotted here on a ternary diagram using those three end
members.
Ternary Plot of Major Limestone Constituents

8. Carbonate Rock-Petrography
Carbonate Rocks are made of :
Grains or allochems
Matrix or mud
Cement
matrix cement
grains grains

9. Grains
non-skeletal grains
skeletal grains/bioclasts
non-skeletal grains
Carbonate Rock-Petrography
skeletal grains

10. Carbonate sediments and rocks
(lithified sediment hardened by diagenetic
processes, such as cementation, compaction,
mineral recrystallization)
Carbonate rock classification: Dunham (1962) based on
DEPOSITIONAL TEXTURE: information about energy of the
depositional environment.
MOST IMPORTANT and COMMONLY in USE!!
Carbonate rock classification: Folk (1951) based on grain
composition and presence of micrite or cement: information about
the origin of the grains and of the depositional environment.
NOT CURRENTLY IN USE!!
Carbonate Classifications

11. Dunham (1962) Limestone Classification
The distinction as to whether a rock is supported by matrix (mud) or framework (grains) is
fundamental to this scheme. The four basic terms for normal (non-crystalline) limestones can be
further modified with terms describing constituent grains or other features. The most difficult
aspect of this classification, in many cases, is in deciding whether a rock with large and irregular
(skeletal or intraclastic) grains, or one that has undergone substantial post-depositional
compaction, was originally mud- or grain-supported.
Dunham classification is based on depositional texture

12. Embry& Klovan (1971) Limestone Classification
In Embry and Klovan (1971) scheme,for biogenic limestones, the term “floatstone” replaces Dunhamʼs
“packstone”. For coarser, grain-supported biogenic limestones, the term “rudstone” was coined. In
addition, an organically bound rock can be termed a “bafflestone”, a “bindstone”, or a “framestone”,
depending on the nature of the organic structures. These last three terms, in particular, have been widely
adopted by those working on reefs, bioherms, and other biogenic carbonates.

13. EMBRY & KLOWAN (1971)
Dunham (1962) Limestone Classification

14. 1. Original components bound
together at the time of deposition:
BOUNDSTONE
1a. Organisms build a rigid
framework:
FRAMESTONE (corals)
1b. Organisms act as baffle:
BAFFLESTONE (algae, bryozoans)
1b. Organisms encrust and bind:
BINDSTONE (Stromatolites, red
algae)
Carbonate rock classification: Dunham (1962) + Embry and
Klovan (1972)
2. Original components not bound together at
the time of deposition
2a. Less 10% grains > 2mm
-When mud-supported and grains are < 10%:
MUDSTONE
-When mud-supported and grains are > 10%:
WACKESTONE
-When grain-supported with micrite matrix
filling the pore space: PACKSTONE
-When grain-supported, no micrite matrix
(sediment) but cement (precipitate) or unfilled
pore space: GRAINSTONE
2b. More 10% grains > 2mm
-Matrix supported: FLOATSTONE
-Grain supported: RUDSTONE

16. Peloidal grainstone with intraclasts and bioclasts

17. Bioclastic grainstone

18. Lime mudstone

19. Bioclastic Packstone with intaclasts

20. Oolithic-bioclastic Grainstone

21. Bioclastic Packstone

22. Oolithic Grainstone

23. Bioclastic Wackestone

24. Bioclastic Packstone with intraclasts

25. Bioclastic Grainstone

26. Oolithic-peloidal Packstone

27. Boundstone
Algal boundstone
(bindstone)
Finely laminated, algal boundstone
(Stromatolite).
Coral boundstone
(framestone)

28. From Baccelle & Bosellini (1965)