106
E. SEffiOLD:
II. Carbonate Content
Except for near-shore areas along the Iranian coast, the sediments of the Persian
Gulf nearly always contain more than 50% carbonate minerals (Fig. 4, see also HARTMANN et ai., 1971). These values reach 80% towards Arabia and on shallows within the
Gulf. Fig. 5 shows that an increase in carbonate content generally parallels an increase
in mean grain diameter and vice versa. This fact alone suggests that near the Iranian coast
organisms are the primary contributors of carbonate to the sediments; the contribution
of carbonate through river inflow and the bioturbate mixing of relict sediments will be
discussed below.
EMERY (1956) pointed out that for the entire Gulf area the mean biogenic carbonate
content of the sediments lies between 60% and 87%, of which 54- 69% are shell
fragments. Typical samples from the main sedimentary environments are given in
Table 1.
The silt fraction of the sediment (0.02 - 0.06 mm) is currently under investigation.
It is difficult, even with the use of a scanning electron microscope, to differentiate between
recent, subfossil, and fossil remains. Biogenic carbonate generally forms between 1/2 and
1/3 of the silt fraction (FOTTERER, unpublished).
III. Benthic Organisms
Benthic organisms are the most important contributors of carbonate to the sediment
of the Persian Gulf. In the Gulf of Oman, however, benthic organisms take second place
to the planktonic organisms as carbonate contributors. Current results indicate that
coarse biogenic carbonate sediment particles are rarely subject to more than very
local transport (exceptions: near-shore currents in shallow water, outflow channel
on the Biaban Shelf). This is suggested by the coincidence of living and dead benthic
foraminifera fauna (HAAKE, LUTZE, unpublished). Therefore, these biogenic remains
may generally be regarded as autochthonous and are direct indicators of the above
mentioned environmental conditions. The areas influenced by the inflow from Iranian
rivers are recognizable by an abundance of ostracods (Fig. 6) and benthic foraminifera in the sediment. These areas are further characterized by land-plant fragments
which are transported on the bottom like sand particles and which have been found up
to 30 km . off-shore (SARNTHEIN, 1971). Benthic foraminifera are indicators of water
depth. For example Quinqueloculina crassicarinata COLLINS occurs predominantly at a
depth of 30 m (Fig. 7). Some of the depth zones characterized by a particular fauna
become somewhat deeper as the mouth of the Gulf is approached. This may indicate
dependency of certain fauna on water properties (Figs. 2 and 3; HAAKE, 1970; LUTZE,
unpublished). On the continental slope at water depths greater than 200 m, benthic
foraminifera decrease in numbers; this decrease is even more pronounced in the benthic
mollusks (SARNTHEIN, 1971).
E. SEffiOLD:
II. Carbonate Content
Except for near-shore areas along the Iranian coast, the sediments of the Persian
Gulf nearly always contain more than 50% carbonate minerals (Fig. 4, see also HARTMANN et ai., 1971). These values reach 80% towards Arabia and on shallows within the
Gulf. Fig. 5 shows that an increase in carbonate content generally parallels an increase
in mean grain diameter and vice versa. This fact alone suggests that near the Iranian coast
organisms are the primary contributors of carbonate to the sediments; the contribution
of carbonate through river inflow and the bioturbate mixing of relict sediments will be
discussed below.
EMERY (1956) pointed out that for the entire Gulf area the mean biogenic carbonate
content of the sediments lies between 60% and 87%, of which 54- 69% are shell
fragments. Typical samples from the main sedimentary environments are given in
Table 1.
The silt fraction of the sediment (0.02 - 0.06 mm) is currently under investigation.
It is difficult, even with the use of a scanning electron microscope, to differentiate between
recent, subfossil, and fossil remains. Biogenic carbonate generally forms between 1/2 and
1/3 of the silt fraction (FOTTERER, unpublished).
III. Benthic Organisms
Benthic organisms are the most important contributors of carbonate to the sediment
of the Persian Gulf. In the Gulf of Oman, however, benthic organisms take second place
to the planktonic organisms as carbonate contributors. Current results indicate that
coarse biogenic carbonate sediment particles are rarely subject to more than very
local transport (exceptions: near-shore currents in shallow water, outflow channel
on the Biaban Shelf). This is suggested by the coincidence of living and dead benthic
foraminifera fauna (HAAKE, LUTZE, unpublished). Therefore, these biogenic remains
may generally be regarded as autochthonous and are direct indicators of the above
mentioned environmental conditions. The areas influenced by the inflow from Iranian
rivers are recognizable by an abundance of ostracods (Fig. 6) and benthic foraminifera in the sediment. These areas are further characterized by land-plant fragments
which are transported on the bottom like sand particles and which have been found up
to 30 km . off-shore (SARNTHEIN, 1971). Benthic foraminifera are indicators of water
depth. For example Quinqueloculina crassicarinata COLLINS occurs predominantly at a
depth of 30 m (Fig. 7). Some of the depth zones characterized by a particular fauna
become somewhat deeper as the mouth of the Gulf is approached. This may indicate
dependency of certain fauna on water properties (Figs. 2 and 3; HAAKE, 1970; LUTZE,
unpublished). On the continental slope at water depths greater than 200 m, benthic
foraminifera decrease in numbers; this decrease is even more pronounced in the benthic
mollusks (SARNTHEIN, 1971).