Classification – A Name for Your Sample - Microfacies of Carbonate Rocks - page 342

Both, Folk (1959) and Dunham (1962) proposed names
for limestones whose formations were dependent on
sessile benthic organisms. Folk uses the term biolithite
as a sackname for autochthonous reef rocks exhibiting
corals, algae and other organisms in growth position. The
name should be discarded in favor of the other sackname
boundstone introduced by Dunham. The author's ex-
amples include coral limestones with corals in living po-
sition, stromatolite limestones, and limestones exhibit-
ing dense intergrowth of various encrusting organisms.
The difference between geological and biological
thinking: Dunham did not specify how the organisms

contribute to rock-building processes. Problems arose
as subsequent modifications of the Dunham classifica-
tion tried to take a more stringent look at the inferred
role of organisms in reef-building: Geologists are inter-
ested in distinguishing reef rock types by organic struc-
tures. Biologists and paleontologists examine the signifi-
cance of reef builders for the buildup of reefs (Fig. 8.1).

Subdivision of autochthonous carbonates
More and more names for smaller and smaller dif-
ferences? Beginning with the well-founded subdivision
of boundstones into the genetically defined categories

Box 8.1. Genetic-descriptive terms used for limestones built predominantly by sessile organisms (autochthonous lime
stones: reef carbonates and microbialites). The author of the original definition is marked by an asterisk.

Bafflestone - Carbonate rocks containing in-situ stalk-shaped and branching fossils that trapped sediment during deposition
by acting as bafflers, slowing down water movement and allowing sediment to settle (*Embry and Klovan 1971).
Minimally transported members of the baffler guild predominate in the samples. Pl. 41/1, Pl. 116/3
Bindstone - (a) Carbonate rocks containing in situ laminar, tabular, or encrusting fossils which encrusted and bound
sediment during deposition (*Embry and Klovan 1971). In bindstones the in-situ fossils do not form a three dimen-
sional framework as they do in framestone. (b) Carbonate rocks dominated by encrusting organisms that encrust or
bind debris together, forming a framework (Tsien 1981). (c) Carbonate rock containing in-situ fossils that encrust and
bind sediment during deposition. The matrix and not the in-situ fossils form the supporting framework of the rock;
fossils may represent as little as 15% of the rock volume (Fagerstrom 1987). Pl. 6/5, Pl. 8/1-2, Pl. 123/3
Biocementstone - Carbonate rocks formed by algae and bacteria which produce micrite cement and trap, stabilize, and
support lime mud (*Tsien 1981, 1984).
Bioconstructed limestones - Limestones characterized by 'colonial framework builder organisms with interstitial mate-
rial' (Carozzi 1989).
Biolithite - A 'sackname'. Limestone constructed by organisms that grew in place, forming a rigid framework that
bound sediment and remained in place (* Folk 1959). The name should not be used for limestones containing broken
off fragments of reef organisms.
Branchstone - Reef carbonate rocks, characterized by branching colonies consisting of densely-spaced, touching skel-
etal elements with only minor sediment in between; e.g. some modern Acropora thickets (* Cuffey 1985). Compare
Fig. 8.1C.
Cementstone - (a) Reef limestones composed of >50% spar of early and late diagenetic as well as neomorphic origin
(*Fagerstrom 1987). The cement volume may exceed that of organic framework or internal sediment. Pl. 50/6, Pl.
145/1. (b) Limestones composed almost totally of fibrous cement (commonly replaced and/or recrystallized), in
which grains or in-situ biogenic material does not constitute a framework (*Wright 1992). Describes a diagenetic
fabric!
Coverstone - Carbonate rocks dominated by in-situ tabular or lamellar organisms covering, protecting and stabilizing
broken debris (*Tsien 1981, 1984). Includes a part of 'bindstone', sensu Embry and Klovan (1971). Pl. 78/4
Cruststone - Reef limestone consisting of densely packed organic crusts growing one upon the other (*Cuffey 1985).
Pl. 51/7
Framestone - (a) Carbonate rocks containing in-situ massive sedentary fossils that built a rigid, three-dimensional
supporting framework at the time of deposition (*Embry and Klovan 1971). (b) Reef frameworks dominated by the
constructor guild (Fagerstrom 1987). Pl. 42/1, Pl. 79/1, Pl. 116/2, Pl. 149/2
Globstone - Reef carbonate rocks, consisting of colonies attached one upon the other (* Cuffey 1985).
Lettucestone - Reef carbonate rocks, built up by calcified organisms characterized by lettuce-like growth forms (e.g.
phylloid algae), aiding in the formation of a framework and intra- and interskeletal trapping of sediment. The de-
scriptive name recalls the similarity of the growth form to that of composite plants, e.g. cabbages (*Cuffey 1985).
Platestone - A limestone composed of an in-situ accumulation of algal plates, e.g. of phylloid algae (* Davies and
Nassichuk 1990). Pl. 58/1
Shellstone - Carbonate rock characterized by shells (e.g. bivalves or brachiopods) cemented upon one another (e.g.
oyster banks). Most shells are in contact; there is no or only little sediment between the shells (* Cuffey 1985). Pl. 87/4.