Geology Reference
In-Depth Information
Fig. 16.16. Cool-water coral limestone with deep-water constructional azooxanthellate corals and hydrozoans. The corals
occur within mixed carbonate-siliciclastic deposits, including an up to 8 m thick limestone consisting of a lower floatstone
unit (interpreted as coral thicket) and an upper bioclastic rudstone unit (interpreted as a coral bank). The sample from the
coral bank exhibits slender branching scleractinian corals represented by Dendrophyllia (D) and Oculina (O) and stylasterinid
hydrozoans (S) with still preserved gastropores (white arrow). Marine isopachous fibrous cements form only thin rims (black
arrows). Most interparticle pores are filled with a bright meteoric-phreatic cement.
A deep- and cool-water setting of the coral bank is postulated from the Dendrophyllia-Oculina- community (today flour-
ishing in water depths of about 100 m), low diversity of corals, presence of stylasterinid hydrozoans, presence of planktonic
foraminifera, absence of algae, and the inferred presence of deep currents, which might have provided the nutrient supply
necessary for azooxanthellate corals. Tertiary (Calcare di Mendicino, Late Miocene): Near Cosenza, Calabria, Italy. After
Mastandrea et al. (2002).
Abundant skeletal grains are bryozoans (Fig. 16.15),
mollusk shells particularly high-diversity bivalves, ben-
thic low-diverse foraminifera, echinoderms, and in
Cenozoic limestones barnacles and rhodophycean al-
gae as well. Azooxanthellate and some zooxanthellate
corals started building deep-and cold-water reefs dur-
ing the Tertiary (Fig. 16.16; Pl. 147). Further groups
include brachiopods, serpulid worms and siliceous
sponges recorded by spiculites. These fossils contrib-
uted to the formation of shelf carbonates characterized
by specific skeletal grain associations (Sect. 12.2.1).
The associations have been particularly well studied in
Tertiary temperate and cool-water carbonates (e.g.
Hayton et al. 1995) and used in recognizing paleocli-
mate changes during the Cenozoic but also during the
Late Paleozoic (Brachert et al. 1993; Beauchamp and
Desrochers 1997; Hüneke et al. 2001).
Bioerosion, maceration and dissolution of shells
may cause considerable taphonomic loss in the fossil
record.
Important and abundant groups of modern cold-
water environments are not known or only rarely or
indirectly known from the fossil record because of the
absence or rareness of skeletons. Examples are sea
weeds (brown algae) that form extended kelp forests
in recent high-latitude cold seas, soft sponges, and octo-
corals. Since these organisms provide substrates for
epizoans and epiphytes, the existence of sea weeds, for
example, can be derived from the analysis of attached
organisms.
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