Geology Reference
In-Depth Information
duction in cool-temperate, warm-temperate and tropi-
cal/subtropical environments (Halfar et al. 2001).
The distribution of modern tropical warm-water belt
and the northern and southern cold-water belts is con-
trolled by the global circulation patterns of surface cur-
rents and the intensity and availability of nutrient recy-
cling between surface and deep waters (Henrich and
Freiwald 1995). The rocky coasts of open shelf cold-
water belts are characterized by kelp-forests. Kelps are
giant seaweeds (brown algae). The thalli provide habi-
tats for numerous carbonate-secreting organisms (cir-
ripeds, bryozoans, serpulids, crustose coralline algae,
sponges). These epibionts contribute considerably to
carbonate production not only on coastal platforms, but
also in intrashelf troughs and coastal lagoons due to
the drift of algal blades or the transport of pebbles at-
tached to the algae (kelp-drafting).
Modern tropical and non-tropical carbonate sedi-
ments exhibit many biological and sedimentological
criteria (Table 2.2) which are used in discriminating
warm- and cool-water carbonates in the context of fa-
cies analyses of ancient limestones (see Sect. 16.4).
One of the most significant features concerns the
biotic carbonate production in near-coastal shelves:
Subtropical and tropical coasts are fringed by coral
reefs. Non-tropical temperate rocky coasts of the North-
ern Seas are characterized by huge kelp forests which
provide habitats for sediment-producing epibionts (pre-
dominantly barnacles, bivalves, echinoids, and bryo-
zoans).
2.4.4.2 Tropical and Subtropical Shallow-
Marine Carbonates
,
Shelf carbonates
The major settings of subtropical carbonate-produc-
ing shelves fall into two categories: (1) Rimmed shelves
(= protected shelf lagoons), and (2) open shelves (Fig.
2.10). These categories can be subdivided into those
shelves which are influenced by terrigenous input, and
those which are not (Sellwood 1986). This classifica-
tion fits many ancient carbonate shelves. Nevertheless,
some caution is necessary in using recent shelf carbon-
ates as analogues for ancient shelf and platform car-
bonates: Modern shelves have been strongly influenced
by the Quaternary sea-level fluctuations, particularly
by the erosional unconformity formed during the last
Latitudinal
Sea-water Sub-
Latitudinal
Sea-water
range
temperature
division
range
temperature
Beyond the Arctic Circle:
Cold water
polar
>60
°
N and S
>5
°
C
Central Greenland Sea,
POLAR
>50
°
<5 -10
°
C
(to >70
°
N)
Barents Sea,
CARBONATES
N and S
(mean)
Ross Sea, Antarctica
-1.5 to16
°
C
Arctic eastern Canada,
(range)
subpolar
>50
°
to
5 - 10
°
C
Northern Norway,
<60
°
N and S
Western Canadian Shelf
Northwestern Europe
30
°
- 50
°
Cool water
cool-
30
°
to 50
°
5 - 10
°
C
Southern Australia,
TEMPERATE
(60
°
)
~10 -18
°
C
temperate
N and S
Tasmania,
CARBONATES
N and S
(mean)
New Zealand
>10 to 25
°
C
warm -
25
°
to > 30
°
N
10 - 18
°
C
Mediterranean Sea,
(range)
temperate
25
°
to 30
°
S
Off North Africa,
Southwestern Australia
30
°
N
Warm water
subtropical
18 - 22
°
C
Bahama, Florida,
to 30
°
S
Bermuda,
TROPICAL
18 to >22
°
C
Persian Gulf,
CARBONATES
(mean)
Shark Bay
18 to 30
°
C
tropical
>22
°
C
Great Barrier Reef,
(range)
Indian Ocean,
Pacific
Fig. 2.9.
Latitudinal distribution and critical sea-water temperatures of modern tropical carbonates and temperate and polar
carbonate settings. Note that cool-water carbonates can also form in tropical regions, where cold currents reduce sea-water
temperatures (e.g. off the east coast of SouthAmerica, off the west coast of Africa and off the coasts of southern Asia).
