Geology Reference
In-Depth Information
Cold-water reefs.
Biotas that may have been im-
portant in ancient temperate-water reefs include cal-
careous red algae, encrusting foraminifera, bryozoans,
serpulids and sabellariids, spiculate demosponges, fas-
ciculate ahermatypic and hermatypic corals, vermetid
gastropods, and bivalves (e.g. oysters). These groups
form reefs within ramp and platform environments,
characterized by the low diversity at a species, family
or phylum level, the abundance of stress-tolerant taxa
(e.g. cyanobacteria, bryozoans), arrested ecologic suc-
cessions (dominated by pioneering taxa), the absence
of distinct zonation patterns and often limited dimen-
sions by comparison to tropical reefs (Copper 1994).
ate sediment of the mounds is fine-grained. It consists
predominantly of bioclastic framestones, packstones
and wackestones. Framebuilders are only azooxan-
thellate organisms (dendroid and arborescent sclerac-
tinian corals; fanlike hydrozoans and octocorals). The
breakdown of skeletons due to strong bioerosion as well
as the baffling effects of coral colonies were respon-
sible for the accumulation of micritic carbonate sedi-
ment. Early diagenesis is responsible for arrested ma-
rine-meteoric cementation. During late diagenesis the
aragonite of the skeletons was dissolved and replaced
by calcite (Weidlich and Bernecker 1991).
These reefs have been compared with modern coral
'lithoherms' formed by ahermatypic corals in the Straits
of Florida (Neumann et al. 1977) and off the Little
Bahama Bank (Mullins et al. 1981) in deep-water set-
tings between 600 and 700 m, with strong bottom cur-
rents providing oxygen and nutrients for the biota. Simi-
larities to Fakse include growth of current-oriented coral
thickets, strong sediment trapping and baffling, and
extensive bioerosion.
16.4.2 Case Study: Early Tertiary Cool-
Water Coral Reef
Under 'Basics' for this section and the keyword K021
(see CD) one can find important references dealing with
ancient cold-water carbonates from the Ordovician,
Carboniferous and Permian, Cretaceous and Tertiary.
Examples of cold-water carbonates from the Ordovi-
cian are shown on Pl. 106/1, from the Early Permian
on Pl. 106/2, and from Tertiary temperate carbonates
on Pl. 106/3 and Pl. 107/1.
Basics: Ancient coldwater carbonates
Beauchamp, B. (1994): Permian climatic cooling in the Ca-
nadian Arctic. - Geological Society of America, Special
Paper,
288
, 299-346
Beauchamp, B., Desrochers, A. (1997): Permian warm- to
very cold-water carbonates and cherts in Northwest
Pangaea. - In: James, N.P., Clarke, A.D. (eds.): Cool-wa-
ter carbonates. - SEPM, Special Publication,
56
, 327-347
Bernecker, M., Weidlich, O. (1990): The Danian (Paleocene)
coral limestone of Fakse, Denmark: a model for ancient,
aphotic, azooxanthellate coral mounds. - Facies,
33
, 103-
138
Brookfield, M.E. (1988): A mid-Ordovician temperate car-
bonate shelf: the Black River and Trenton Limestone
Groups of Southern Ontario, Canada. - Sedimentary Ge-
ology,
60
, 137-153
Carannante, G., Esteban, M., Milliman, J.D., Simone, L.
(1988): Carbonate lithofacies as paleolatitude indicators:
problems and limitations. - Sedimentary Geology,
60,
333-
346
Hayton, S., Nelson, C.S., Hood, S.D. (1995): A skeletal as-
semblage classification system for non-tropical carbon-
ate deposits based on New Zealand Cenozoic limestones.
- Sedimentary Geology,
100
, 123-141
Hünecke, H., Joachimski, M., Buggisch, W., Lützner, H.
(2001): Marine carbonate facies in response to climate
and nutrient level: the Upper Carboniferous and Permian
of Central Spitsbergen (Svalbard). - Facies,
45
, 93-136
James, N.P., Clarke, A.D. (eds., 1997): Cool-water carbon-
ates. - SEPM, Special Publication,
56
, 440 pp.
Mastandrea, A., Muto, F., Neri, C., Papazzoni, C.A., Perri,
E., Russo, F. (2002): Deep-water coral banks: an example
from the 'Calcare di Mendicino' (Upper Miocene, North-
ern Calabria, Italy). - Facies,
47
, 27-42
Willumsen, M.E. (1995): Early lithification in Danian
azooxanthellate scleractinian lithoherms, Fakse quarry,
Denmark. - Beiträge zur Paläontologie,
20
, 123-131
Further reading:
K021
Pl. 147 shows the microfacies of Early Tertiary cold-
water coral reef limestones from Denmark. These lime-
stones represent one of the finest examples of ancient
cool-water coral reefs.
The Fakse quarry and the nearby Stevns Klint lo-
cality south of Copenhagen, Denmark, are classical lo-
calities for studying the Cretaceous-Tertiary boundary
and its events as well as understanding cold-water
mounds and reefs (Pl. 147). In this area uppermost
Maastrichtian bryozoan chalky wackestones forming
low asymmetrical mounds are overlain by the just cen-
timeter-thick Danian Fish Clay, which passes upward
into the
Cerithium
Limestone exhibiting a prominent
hardground at the top. The surface of this hardground
is overlain by bryozoan mound complexes of bryozoan
floatstone and packstone (Fig. 16.15) with black flint
layers (Surlyk and Damholt 2001). These bryozoan
mounds as well as ecologically zoned coral mounds
were formed below the photic zone on the deep-water
shelf of the Danish-Polish Trough. The water depth is
assumed to have been 100 to 300 m (Surlyk 1997).
The coral mounds with a height up to 30 m, a maxi-
mum length of 200 m, and a width of 80 m exhibit an
asymmetrical shape that was controlled by paleocurrent
directions (Bernecker and Weidlich 1980). The carbon-
