Classification – A Name for Your Sample - Microfacies of Carbonate Rocks - page 349

CLASSIFICATION OF LIMESTONES (DUNHAM 1962)

DEPOSITION TEXTURE RECOGNIZABLE DEPOSITIONAL TEXTURE

Original components not bound together during deposition Original components

NOT RECOGNIZABLE

Contains mud Lacks mud were bound together

(particles of clay and fine silt size) and is during deposition as shown

Mudsupported Grainsupported grain by intergrown or lamination

CRYSTALLINE CARBONATE

supported contrary to gravity, (Subdivide according classification

sedimentfloored cavities designed to bear on physical

that are roofed over texture or diagenesis)

by organic or questionable

less the more than organic matter and are

10% grains 10% grains too large to be interstices

MUDSTONE WACKESTONE PACKSTONE GRAINSTONE BOUNDSTONE

EXPANDED CLASSIFICATION (EMBRY and KLOVAN 1971)

ALLOCHTHONOUS LIMESTONE AUTOCHTHONOUS LIMESTONE

ORIGINAL COMPONENTS NOT ORGANICALLY ORIGINAL COMPONENTS ORGANICALLY

BOUND DURING DEPOSITION BOUND DURING DEPOSITION

Less than 10% > 2 mm components no Greater than 10% > 2 mm by organisms

contains lime mud (< 0.03 mm) lime mud components which

Mud supported Grainsupported Matrix > 2 mm build encrust act

less than greater than supported component a rigid and bind as bafflers

10% grains 10% grains supported framework

( > 0.03 mm and
< 2 mm)

BOUNDSTONE

MUDSTONE WACKESTONE PACKSTONE GRAINSTONE FLOATSTONE RUDSTONE FRAMESTONE BINDSTONE BAFFLESTONE

REVISED CLASSIFICATION (WRIGHT 1992)

DEPOSITIONAL BIOLOGICAL DIAGENETIC

Mixed supported Grainsupported In situ organisms Nonobliterative Obliterative

clay and silt grains)
< 10% > 10% grains with no matrix rigid encrusting organisms main many grain most grain crystals

grains grains matrix organisms binding acted to component contacts ascontacts > 10 m

dominant organisms baffle in cement micro are micro

stylolites stylolites

CALCI WACKE PACK GRAIN FRAME BOUND BAFFLE CEMENT CONDENSED FITTED SPARSTONE

MUDSTONE STONE STONE STONE STONE STONE STONE STONE GRAINSTONE

FLOATSTONE RUDSTONE Crystals < 10 m

MICRO

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Grains > 2 mm SPARSTONE

Fig. 8.5. Original, expanded, and revised Dunham classification. Embry and Klovan (1971) introduced the size aspect and
distinguished grains smaller or larger than 2 mm. The new categories floatstones and rudstones correspond to wackestones
and grainstones and packstones, respectively. Other changes concern the subdivision of the boundstone category (see Sect.
8.2). Wright (1992) suggested terms describing diagenetic changes of depositional fabrics. The author emphasizes that the
fine-grained matrix commonly called 'mud' is not necessarily identical with micrite, but corresponds to a matrix consisting
of clay-sized and silt-sized constituents. Note that in this scheme the term mudstone is replaced by calcimudstone and
bindstone by boundstone owing to slight semantic problems.

8.3.2.1 Concepts oids), ooid grainstone (grainstone containing predomi-

nantly ooids). Dunham proposed the notation 'lime' or
'dolomite' for characterizing the mineralogy, but only
the reference to dolomite rocks (e.g. dolomite mud-
stone) appears necessary. The classification is highly
flexible. The rock names should be complemented by
all relevant field or laboratory observations. These can
be sedimentary structures (e.g. medium-bedded, cyclic
bioclast grainstones) and specific textural criteria
(Stromatactis-bearing microbial mudstone). Limestones
with small-scale mixtures of fabric types may be de-
scribed by combinations of names: Peloid wacke/pack-
stone corresponds to a sample with > 10% peloids and
exhibiting wackestone and, to a lesser degree, pack-
stone textures. Such close occurrence of wackestone
and packstone textures may be caused by burrowing.

The original classification includes five textural classes.
Two major groups are distinguished - (1) carbonates
whose original components were organically bound to-
gether during deposition (boundstones), and (2) car-
bonates whose original components were not organi-
cally bound. The second group is subdivided accord-
ing to mud-support (mudstone and wackestone) or
grain-support (packstone and grainstone). The subdi-
vision of mud-supported rocks is based on the < or >
10% grain bulk boundary. These rock names can be
combined with grain type names in various ways: Os-
tracod mudstone (mudstone containing < 10 total rock
volume % ostracods), crinoid packstone (packstone
containing a high percentage of closely-packed crin-