Geology Reference
In-Depth Information
structures started a fascinating hunt for Holocene and
ancient 'deep-water and cold-water reefs' which is still
going on.
tions in light regime, seasonal sea ice cover, ice shelves,
currents and circulation patterns.
The largest open-shelf cold-water carbonate platform
in the Arctic is
Spitsbergen Bank
in the northwestern
Barents Sea (Henrich et al. 1996; Pl. 4/6). The bank
corresponds to a >80 000 km
2
wide shallow shelf plat-
form bordered by > 400 m deep troughs. Water depths
range from less than 25 m to deeper than 120 m. The
bank is completely covered by sea ice for 6 months.
Melting sea ice causes strong seasonal variations in sur-
face water salinity. The maximum summer tempera-
ture is 2 °C on the bank and 4-6 °C in the marginal
zone. Another bioclastic carbonate production area is
the southwestern
Svalbard shelf
where skeletal carbon-
ate deposition resting on tillites takes place under glacio-
marine conditions in depths between 50 and 80 m
(Andruleit et al. 1996).
Carbonates are produced by (a) barnacles living on
kelp forests and forming mobile sands which are trans-
ported over the shallow platform, and (b) benthic com-
munities (infaunal bivalves, balanids, hydrozoans, soft
corals, sponges, bryozoans) forming buildups on the
deep flanks of the platform. The seamount is covered
by extensive sponge-bryozoan bioconstructions exhib-
iting three distinct facies belts depending on variations
in down-slope food transfer. Different communities
occurring in these belts are biogenic mats with sponge
spicules and bryozoan fragments, sponge bryozoan-ser-
pulid buildups, bryozoan thickets, and sponge-crinoid
mounds (Henrich et al. 1992). Basic patterns of sedi-
ment distribution are coarse, high-energy bioclastic
sands consisting of balanids, bivalves and benthic fora-
minifera on top of the bank and arctic mollusk coquina/
glaciomarine gravel lag deposits over the flanks.
These carbonates differ from other high-latitude shelf
carbonates with or without glaciomarine controls. Post-
glacial or interglacial carbonate sediments capping older
glaciogenic units and not influenced by glaciomarine
settings are known from the Scottish shelf, the Norwe-
gian shelf, off Nova Scotia and Newfoundland, and
western Canada. Carbonate deposition associated with
glaciomarine environments occurs on Antarctic shelves
(Domack 1988; Taviani et al. 1993).
Non-tropical reefs differ significantly from reefs
thriving in shallow warm waters (Table 2.3). High-lati-
tudinal reefs are stressed ecosystems whose biota should
be able to tolerate low water temperatures as well as
sharp seasonal temperature fluctuations, salinity fluc-
tuations and low light influx. Common reef-building
organisms are corals, calcareous red algae, bryozoans,
bivalves (e.g. oysters), serpulids and tube-constructing
sabellarid polychaetes, vermetids, encrusting foramin-
ifera and sponges. Non-tropical reefs comprise coral
reefs, coralline algal reefs, sponge-bryozoan reefs, and
mollusk reefs.
Examples of coralline algal reefs and maerl pave-
ments have been studied on the northern coast of Brit-
tany (France), and the coast of the Troms District in
northern Norway (Freiwald et al. 1991; Freiwald and
Henrich 1994). Oyster reefs, vermetid reefs and ser-
pulid reefs occur in different parts of the Atlantic Ocean
(Milliman 1974). Corals contribute significantly to the
formation of large and extended reef-structures in
deeper cold-water settings (
Lophelia
reefs), but also in
relatively shallow warm-temperate environments
(
Cladocora
banks of the eastern Mediterranean:
Kühlmann 1996; Taviani et al. 2001).
Lophelia
reefs: Huge framework reefs built by the
azooxanthellate coral
Lophelia
cover huge areas of the
deep and cold eastern Atlantic shelf bottoms (Scottish
shelf: Scoffin et al. 1980; Norwegian shelf: Henrich
and Freiwald 1995; Freiwald and Wilson 1998; Faroe
Island: Frederiksen et al. 1992, see Pl. 4/2). The corals
are preserved as frameworks or coarse coral rubble.
Hovland and Thomsen (1997) discuss possible causal
relations between deep-water coral reefs and hydrocar-
bon seeps.
Polar carbonates and arctic sponge-bryozoan mounds:
Parameters other than the rather stable water tem-
perature control polar carbonates influenced by glacio-
marine conditions (Domack 1988; Henrich et al. 1997):
the seasonality of light levels (polar night, polar sum-
mer), winter sea ice coverage versus summer open po-
lar conditions, seasonality in plankton production, and
seasonality in terrigenous sediment discharge by gla-
ciers, meltwater plumes, rivers and release of sea ice
sediment (Henrich et al. 1992, 1997). The richness and
diversity of benthic organisms are controlled by rela-
tively constant (low but stable) temperatures, low fluc-
tuations in salinity, low terrestrial input and fluctua-
Significance of cool-water carbonates:
1
Quantitative and qualitative data of high-latitude
cool-water carbonates are strongly needed in all
speculations on regional and global carbonate bud-
gets.
2
Because the kind of skeletal and non-skeletal grains,
facies, carbonate mineralogy and diagenesis vary
with sea-water temperatures and other factors, the
differentiation of tropical and non-tropical carbon-
