Page 88 - Carbonate Facies in Geologic History

Slope and Basin (Standard Facies Belts 1, 3, and 4) 75

all algal genera, they have great importance in the carbonate regime of clear
tropical marine water. Simpler forms are probably essential to carbonate produc-
tion from seawater. Furthermore, algae which secrete preservable calcareous skel-
etons can be divided into several major groups, each with its own ecological
character. A series of descriptive work resulting from a lifetime of study by John-
son (1957, 1961, 1967) is available in the American literature and furnishes perti-
nent information on the taxonomy of calcareous algae and their environmental
interpretation. See also Horowitz and Potter (1971, p.75-80) for key to identifica-
tion and for references in European literature to works by Pia, Ott, Elliot and
Maslov. The most comprehensive review of the geological application of these
forms is by Ginsburg et al. (1971) from whose "Notes for a Short Course" the
Fig.III-3 and Table III-l are derived.

Glossary of Sedimentary Structures in Carbonate Rocks

About 80 commonly recognized sedimentary and organic structures in carbonate
strata are described below. They are grouped according to the standard facies
belts which occur along a typical shelf-margin profile, but numbered consecu-
tively. A few of the smaller structures are discussed in this Chapter also under
microfacies. The references appended to most of the categories are not complete
but were chosen for availability and for good illustrations.

Slope and Basin (Standard Facies Belts 1,3, and 4)
1. Flysch-bedding
Rhythmically monotonous marine sequences composed of thin (10 cm-50 cm)
resistant limestones interbedded with somewhat thinner marls or calcareous
shales. The limestones are poorly fossiliferous, and graded when composed of
calcisilt or fine calcarenite (Thomson and Thomasson, 1969, p.69; Wilson, 1969,
p.8; and AGI Glossary, 1973, p.270)(Plate XXVII B).
2. Bouma sequences
Characteristic and ideal successions of five intervals making up one complete
sequence of a turbidite. One or more of the intervals may be missing. The inter-
vals from the top: (E) pelitic; (D) upper parallel laminations; (C) current ripple
laminations; (B) lower parallel laminations ; and (A) graded coarse sediment (Bou-
ma, 1962; Thomson and Thomasson, 1969).
3. Mudflows with exotic blocks - debris flows
Boulders and blocks up to 10 feet and larger in diameter surrounded by mud
flow material, i.e., much finer matrix (Thomson and Thomasson, 1969, p.65).
4. Flute casts
A sole mark, a raised subconical structure, the up-current end of which is
rounded or bulbous, the opposite end flaring out and merging with the bedding
plane. Formed by filling of an erosional scour or flute (Pettijohn and Potter, 1964,
p.307).