Geology Reference
In-Depth Information
terms describe the identity of the colonizing organism,
the nature of the substrate, and the location of the colo-
nists (on the surface or within the surface). The classi-
fication was inspired by the carbonate classification sys-
tem used by Folk (Sect. 8.3.2). Each term consists of
two or three roots: The last root refers to the identity of
the colonizing organism (animal, -zoan; plant, -phyte,
or either, -biont). The preceeding root describes the type
of the substrate (rock, -litho-; animal, -zoo-; plant, -phyto-;
or any organic hardpart of unknown or uncertain sta-
tus, living or dead, -skeleto). The location of the coloniz-
ing organisms is indicated by the prefix epi- or endo-.
The collective term sclerobiont is used for any kind of
animal or plant fouling any kind of hard substrate.
Sclerobionts include encrusters pressed closely to the
surface of the substrate (Fig. 9.7), sessile organisms
that are cemented or organically anchored to the sub-
strate surface and grow into the water column (Fig. 9.9),
and borers that enter the substrate.
9.2.1 Criteria and Constraints of Encrusters
Biogenic crusts are formed by sessile benthic organ-
isms including microbes, algae, foraminifera, sponges,
bryozoans, corals as well as serpulids and mollusks.
Encrusting organisms are solitary or colonial. The lat-
ter exhibit various growth forms (Jackson 1979, Tay-
lor 1992) comprising runners (linear forms, e.g. some
bryozoans), sheets, mounds, plates (with punctuated
bases), vines (linear to branched, semierect forms) and
trees (erect forms). Sheets and mounds are common
growth forms of reefal encrustations, producing crusts
oriented parallel to the substrate (Fig. 9.7) and indicat-
ing strong competition for space. Erect upright encrus-
tations (Fig. 9.9) point to low sediment input.
The success of encrustation depends on a number of
factors including the size, structural complexity and sta-
bility of the substrate, the biochemical conditioning,
Fig. 9.7.
Characteristic hard substrate encrusters.
The bivalve shell (B) was first encrusted by an association consisting of
sessile foraminifera (SF;
Miniacin
a), serpulids (
Ditrupa
, D) and squamariacean red algae (SRA; today called peyssonnelaceans).
Corallinacean red algae (CRA) form the later phase of the encrustation. Note intensive boring of the shell (black arrows)
prior to the biogenic encrustation. Borings are infilled with fine bioclastic sediment. By contrast, the borings in the squam-
ariacean algae are occluded by cement (white arrow). Applying the terminology proposed by Taylor and Wilson (2002) for
organisms inhabiting hard substrates, the crust sequence consists of more or less synchronous episclerozoans and
episclerophytes represented by squamariacean red algae, followed by epizoophytes represented by corallinacean red algae.
Late Tertiary (Middle Miocene): St. Margarethen, Burgenland, Austria. Scale is 5 mm.
