112
E. SEIBOLD:
Fig. 9. Regional distribution of the plankton-benthos ratio of foraminifera. Plotted values:
percentage of planktinic foraminifera in the sand fraction
~--~--~--------------------------XI00
percentage of total foraminifera in the sand fraction.
(Based on SARNTHEIN, 1971)
v. Bioturbation
Core analysis and radiography have shown that the sediments of the Persian Gulf
are in general poorly stratified. The primary stratification is in most cases completely
obliterated by bioturbation. Horizontal and vertical burrows, several em in diameter
and tens of cm in length have been found. Some were filled with the neighboring sediment,
but others contained significant enrichments of biogenic particles (MELGUEN, WERNER,
unpublished). Sand-sized particles may be moved upwards in the sediment column a
maximum distance of somewhat over 2 m. The youngest sediments of the Persian Gulf
overlie Holocene and Late-Pleistocene relict sediments formed at a lower sea-level stand.
Oolitic sands, lithified as well as unlithified carbonate-mud pebbles, mollusc shell
fragments, corals and bryozoa are the main components of these shallow-water fossil
sediments. In about 66% of our samples which contained relict sediment the recent
sediment thickness was less than 0.5 m. As a result the content of fossil sediment grains
may be as high as 60% - 80% and thus affects the carbonate content. Within the central
parts of the basins with their reduced sedimentation rates, such phenomena are of regional
importance (SARNTHEIN, 1971).
VI. Organic Carbon Content
Fig. 10 shows the organic carbon content of the sediments. In the Persian Gulf the
content lies below 2% and in the Gulf of Oman above 2%. These values reflect first of
all the primary production. Nutrient deficiency in the western basin is responsible for
holding the organically bound carbon values below 1 %. Secondly, dilution by terrigenous
material is important in areas such as the northern part of the Bay of Hormuz and near
the Iranian coast. On the other hand, terrigenous dilution is of lesser importance in the
Gulf of Oman region. Thirdly, the generally well known relationship between organic
carbon content and sediment grain size plays a role: The coarser the sediment, the lower
the organic carbon content. Examples can be seen from the shallows of the Central Basin.
E. SEIBOLD:
Fig. 9. Regional distribution of the plankton-benthos ratio of foraminifera. Plotted values:
percentage of planktinic foraminifera in the sand fraction
~--~--~--------------------------XI00
percentage of total foraminifera in the sand fraction.
(Based on SARNTHEIN, 1971)
v. Bioturbation
Core analysis and radiography have shown that the sediments of the Persian Gulf
are in general poorly stratified. The primary stratification is in most cases completely
obliterated by bioturbation. Horizontal and vertical burrows, several em in diameter
and tens of cm in length have been found. Some were filled with the neighboring sediment,
but others contained significant enrichments of biogenic particles (MELGUEN, WERNER,
unpublished). Sand-sized particles may be moved upwards in the sediment column a
maximum distance of somewhat over 2 m. The youngest sediments of the Persian Gulf
overlie Holocene and Late-Pleistocene relict sediments formed at a lower sea-level stand.
Oolitic sands, lithified as well as unlithified carbonate-mud pebbles, mollusc shell
fragments, corals and bryozoa are the main components of these shallow-water fossil
sediments. In about 66% of our samples which contained relict sediment the recent
sediment thickness was less than 0.5 m. As a result the content of fossil sediment grains
may be as high as 60% - 80% and thus affects the carbonate content. Within the central
parts of the basins with their reduced sedimentation rates, such phenomena are of regional
importance (SARNTHEIN, 1971).
VI. Organic Carbon Content
Fig. 10 shows the organic carbon content of the sediments. In the Persian Gulf the
content lies below 2% and in the Gulf of Oman above 2%. These values reflect first of
all the primary production. Nutrient deficiency in the western basin is responsible for
holding the organically bound carbon values below 1 %. Secondly, dilution by terrigenous
material is important in areas such as the northern part of the Bay of Hormuz and near
the Iranian coast. On the other hand, terrigenous dilution is of lesser importance in the
Gulf of Oman region. Thirdly, the generally well known relationship between organic
carbon content and sediment grain size plays a role: The coarser the sediment, the lower
the organic carbon content. Examples can be seen from the shallows of the Central Basin.