Geology Reference
In-Depth Information
Fig. 8.2.
Framestone
. More precise names are 'branched coral framestone' or '
Retiophyllia
framestone' Densely spaced
scleractinian coral colonies are still in life position. The corals form extended thickets. The coral limestone exactly fits the
original definition of a framestone (in-situ sedentary fossils that built a three-dimensional framework) and also corresponds
to the definition of framestones based on a guild character (dominance of the constructor guild). Note the difference in
comparison with Pl. 41, also showing a framestone. Late Triassic: Adnet near Salzburg, Austria. Sawed quarry wall. The
Adnet reef is a spectacular example of Triassic reefs (Bernecker et al. 1999). Width of the picture 80 cm.
of
bindstone, framestone
and
bafflestone
(Embry and
Klovan 1971; see Pls. 41 and 42; Fig. 8.1), and fol-
lowed by a wealth of special terms proposed in order
to characterize different reef fabrics, reef rocks became
more and more ambiguous and perplexing.
Current reef research make it clear that the Embry
and Klovan's classification does not cover all the modes
in which sessile organisms contribute to the formation
of reefs. Hence, there is a great temptation to coin rock
names describing all possible modes of reef building.
Recognizing the complex manner in which organ-
isms contribute to the construction of organic frame-
works. Tsien (1981) and Cuffey (1985) proposed addi-
tional rock names, especially for 'reef limestones' (see
Box 8.1). Tsien's biocementstone and coverstone are
useful and handy terms. They describe biological pro-
cesses different from those addressed by Embry and
Klovan:
•
Biocementstone
(Fig. 8.3) describes a fine-grained
texture, predominantly controlled by microbes and al-
gae that colonize reef debris and produce microcrys-
talline cements as metabolic by-products. Biocemen-
tation is an important factor in the formation of mud
Fig. 8.3.
Biocementstone
. Many reef limestones are charac-
terized by the abundance of micritic or sparry carbonate ce-
ments and the intimate association of cements with micro-
biota, e.g. calcimicrobes, sponges. The thin section shows
sponge-like fossils (black) bound by submarine cements.
Early Cambrian (Krol Formation): Lesser Himalaya, India.
Scale is 5 mm.
