Page 67 - Atlas of Sedimentary Rocks Under The Microscope

�· --

Carbonate rocks

Limestone Classification

Two of the most popular limcslonc classifications are those of Folk
(1959, 1962) and Dunham (1962). These are summarized in Tables 3
and 4 and Fig. E.

Table 3. Classification of limestones according to
Original components not organically bound together during deposition Components
organically Dunham (1962) Rock names are in
bound during capita/ letters
deposition
no
contains carbonate mud carbonate
mud
mud-supported
grain-supported
< 10% allochems > 10% allochems
MUDSTONE WACKESTONE PACKSTONE GRAINSTONE DOUNDSTONE

T a b l e 4 Classification of limestones based on the
volumetric > 10% allochems < 10% allochems
allochem scheme of F o l k ( 1959, 1962) Rock names
composition Sparry calcite > Micrite > 1-10% allochems < I % "' are in capita/ letters
Micrite Sparry calcite allo- ""
chems �
...
6
v
> 25% INTRASI1ARITE INTRA MICRITE Intraclasts ..<:
0
Intraclasts INTRACLAST- :.0
BEARING -o
Q
MICRITE "'
"'
>25% OOSPARITE OOMICRITE "' ·- ..c .....
v
�
Ooids E Ooids (.)
.,
..c 0010- � � -o <.>
"' o. _
-o � el -e
!!! _g BEARING
"' · o .::
"' 3:1 BIOSPARITE OIOMJCRJTE (;j MICRITE � i .�
Q.
CI'I
(j ]. c "' - "0
c
"' ... rl) � "' f- - !-;: : ;:l
] " ·- "' -o Bioclasts o. �
" '
... c
c
::s
� 0 o - 8 3: I .D FOSSILII'EROUS � ... 1-
"'
"' - Q.
N � :.0 to BIOPELSPARITE OIOPELMICRITE � MICRITE "' w
�
v � . 2' 1:3 � u !-
v � i ;;:
!-
... Peloids :J
v PELOID- 0
§ 1:3 PELSPARITE I'ELMICRITE BEARING ;;
0 MICRITE
>
Over J micrite matrix Subequal Over i spar cement
()-1% 1-10% 1()-50% Over 50% spar& Sorting Sorting Rounded &
Allochems Allochems Allochems Allochems micrite poor good abraded
Poorly-
Micrite & Fossiliferous Sparse Packed washed Unsorted Sorted Rounded
'
dismicrite micrite biomicrite b1ospante b1ospante b1ospante b1ospante
- Micrite matrix B Sparry calcite cement
F i g . E The range in textures shown by carbonate rocks, illustrated using the rock names of the F o lk classification ( a f t e r Folk, 1959)
62