Corals, coralline algae, diverse bryozoans, microbes.
Bioclastic debris without corals and algae

The first visible level of the reefal unit is formed
by coralline algal thickets associated with a number of coral colonies belonging to the scleractinian
genera Porites and Tarbellastraea. The overlying
unit exhibits more distinctive reef features through
the presence of metric-sized coral patches and
scattered coral colonies. Two different growth
forms of Porites occur (possibly two species): one
with densely packed finger-thick branches, the
other partly massive, partly ramose (often within
the same colony), with branches about 5-10 cm
thick. Coral constructions also contain globular to
ramose colonies of Tarbellastraea with frequent
Lithophaga borings. Thin Porites colonies domi-nate
near the top of the reefal unit. Scleractinian
colonies and mollusc shells (especially bivalves)
are often invaded by a network of boring sponges
corresponding to the ichnogenus Entobia. Among
the samples from Dio'sd, Oosterbaan (1990)
identified the following scleractinian species:
Porites collegniana, Tarbellastraea reussiana, and
Siderastraea crenulata.

Coralline algae also play a major role in the
construction of the framework. They encrust the
surface of coral colonies with up to centimetre-
thick sheaths around thin Porites colonies, or give
rise to bushy outgrowths. Coralline algae are some-
times also associated with bryozoan crusts.
1

The amount of siliciclastic material decreases upward, and at a distinct masses of red algae appear as encrustations covering an area of some 100 m2, possibly a hardground (which is not exposed). Upon parts of this algal build-up coral colonies occur, and locally become dominant (Müller, 1984). The algal-coral build-up is capped by a pebbly horizon and no further beds are exposed here. Further to the NW, a possibly coeval slightly clayey limestone contains abundant Turritella moulds, probably deposited in a sublittoral setting. The transition zone between the build-up and clayey limestone is not exposed. The clayey limestone is covered by a calcarenite ( Müller, 1984),partly grainstone, partly wackestone,with some faunal evidence for slightly decreased salinity.