4.3 Modern Examples, Sedimentary History
Pleistocene carbonate-rich layers in deep-sea sediments are not necessarily coeval in the Atlantic and
Pacific Oceans (e.g. Grötsch et al. 1991). Oceanic
circulation including the so-called conveyer belt is
further discussed in Sect. 5.2.
4.3 Sedimentary History of So me
Modern Adjacent Seas
4.3.1 The Black Sea
The young sedimentary history of the Black Sea is
particularly interesting (Fig. 4.4), but still not clear.
The specific development of this basin in the Neogene was strongly affected by (I) repeated changes in
its connection with the Mediterranean Sea and the
world oceans, and (2) by significant climatic variations. The latter caused the late Miocene (Messinian)
"salinity crisis" and the Quatemary high-frequency,
high-amplitude sea-Ievel fluctuations in the Mediterranean. The modem euxinic state of the basin with
estuarine water circulation (see above) evolved in the
Holocene.
The tectonic setting and pre-Miocene history of the Black
Sea basin are discussed, e.g., by Okay et al. (1994) and
Robertson (1996). The Neogene his tory of the Paratethys,
including the Black Sea, has been studied by Steininger
and Rögl (1984) and Rögl (1998). In the late Eocene, the
fonner wide Tethys Ocean was replaced in the west by the
Mediterranean Sea and in the east by the intercontinental
Eurasian Paratethys basin. The latter became finally enclosed during the Miocene and experienced an endemic
evolution. It was separated into subbasins, the western one
being the Black Sea. The Bosphorus Strait seems to be a
complex feature produced by both fluvial processes and
graben tectonics (Gökalnn et al. 1997). It exists in its present fonn since the Wünn glacial.
The results of deep-see drilling have been reported by
Degens and Ross (1974), Hsü (1978), Degens and Stoffers
(1980). Water exchange with the Mediterranean has been
dealt with by Stanley and Blanpied (1980) and Aksu et al.
(1999). The Holocene sapropels have attracted much interest (e.g. Glenn and Arthur 1985; Calvert and Fontugne
1987; Arthur and Dean 1998; Calvert and Karlin 1998).
Miocene-Pliocene Development
The present-day connection ofthe Black Sea with the
Mediterranean via the Bosphorus Strait existed in the
past probably only for short time intervals, i.e. in the
Miocene and late Pleistocene. During these periods,
the depositional environment and sediments of the
Black Sea were influenced by inflowing marine waters (Fig. 4.4e, Sections A and C). In the late Miocene, the Black Sea and Caspian Sea were euxinic
basins with marine fauna. During the subsequent "salinity crisis" in the latest Miocene (Sect. 6.4.3), the
173
Black Sea (as well as the Caspian Sea) were closed
off from the Tethys ocean and transformed to
intracontinental seas of variable salinity. This is indicated by the presence of endemie fauna and lacustrine shallow-water carbonates (Fig. 4.4e).
In the long interval between the late Miocene and late
Pleistocene (Fig. 4.4, Section B), the Black Sea was a fresh
to slightly brackish water lake with predominantly carbonate deposition. Climatic variations generated altemating
marly and ca1careous beds with abundant siderite concretions accumulated under changing redox conditions. The
organic matter of the last lake phase is predorninantly of
terrestrial origin (Calvert and Fontugne 1987).
The Holocene Black Sea
The modem history of the Black Sea began ~7.5 ka
B.P. when the Holocene transgression had reached
the sill depth of the Bosphorus Strait and enabled the
spillover of sea water into the former fresh to brackish water lake. It took another 4000 to 6000 years
until the present-day environment was established.
Saline, anoxie bottom waters expanded and finally
filled the maj or part of the basin.
During this transitional interval, organic productivity in the surface water was particularly high because of vertical mixing of water masses and nutrient
. recycling. This led to the accumulation of laminated
sapropel rich in organic matter (up to about 15% organic carbon) and a carbonate content in the order of
10%. Later, the stratification of the Black Sea became more stable and the organic productivity dec1ined. The last 1 to 2 ka in Black Sea evolution are
characterized by a shallow, stable chemocline, separating oxygenated, fairly fertile surface water from a
thick deep-water mass. Coccolith-carbonate production diluted the organic carbon concentration of the
deep-water sediment. A typical deep-water sequence
is shown in Fig. 4.4d, but intercalations of mud flow
deposits are omitted, which may occur between the
uppermost two units. The deep-water mass is anoxie
and contains considerable quantities of H 2 S, NH 3 ,
and P (Fig. 4.4b and c).
Most of the hydrogen sulfide is produced by bacterial sulfate reduction within the water column. After a peak in
organic carbon deposition (in tenns of carbon concentration) ~5 ka B.P., the concentration of organic carbon in the
sediment decreased. The uppennost, varved coccolith ooze
on the abyssal plain commonly contains between 1% and
4% of organic carbon and between 15% and 55% of carbonate. The accumulation rate of organic carbon is low in
the Black Sea in comparison to that of modem, highly productive coastal upwelling zones (Sect. 5.3.4).
Consequently, the formerly widely held opinion that
the Black Sea provides a particularly effective
depositional environment for hydrocarbon generation, should be significantly modified. Such a favor-
Pleistocene carbonate-rich layers in deep-sea sediments are not necessarily coeval in the Atlantic and
Pacific Oceans (e.g. Grötsch et al. 1991). Oceanic
circulation including the so-called conveyer belt is
further discussed in Sect. 5.2.
4.3 Sedimentary History of So me
Modern Adjacent Seas
4.3.1 The Black Sea
The young sedimentary history of the Black Sea is
particularly interesting (Fig. 4.4), but still not clear.
The specific development of this basin in the Neogene was strongly affected by (I) repeated changes in
its connection with the Mediterranean Sea and the
world oceans, and (2) by significant climatic variations. The latter caused the late Miocene (Messinian)
"salinity crisis" and the Quatemary high-frequency,
high-amplitude sea-Ievel fluctuations in the Mediterranean. The modem euxinic state of the basin with
estuarine water circulation (see above) evolved in the
Holocene.
The tectonic setting and pre-Miocene history of the Black
Sea basin are discussed, e.g., by Okay et al. (1994) and
Robertson (1996). The Neogene his tory of the Paratethys,
including the Black Sea, has been studied by Steininger
and Rögl (1984) and Rögl (1998). In the late Eocene, the
fonner wide Tethys Ocean was replaced in the west by the
Mediterranean Sea and in the east by the intercontinental
Eurasian Paratethys basin. The latter became finally enclosed during the Miocene and experienced an endemic
evolution. It was separated into subbasins, the western one
being the Black Sea. The Bosphorus Strait seems to be a
complex feature produced by both fluvial processes and
graben tectonics (Gökalnn et al. 1997). It exists in its present fonn since the Wünn glacial.
The results of deep-see drilling have been reported by
Degens and Ross (1974), Hsü (1978), Degens and Stoffers
(1980). Water exchange with the Mediterranean has been
dealt with by Stanley and Blanpied (1980) and Aksu et al.
(1999). The Holocene sapropels have attracted much interest (e.g. Glenn and Arthur 1985; Calvert and Fontugne
1987; Arthur and Dean 1998; Calvert and Karlin 1998).
Miocene-Pliocene Development
The present-day connection ofthe Black Sea with the
Mediterranean via the Bosphorus Strait existed in the
past probably only for short time intervals, i.e. in the
Miocene and late Pleistocene. During these periods,
the depositional environment and sediments of the
Black Sea were influenced by inflowing marine waters (Fig. 4.4e, Sections A and C). In the late Miocene, the Black Sea and Caspian Sea were euxinic
basins with marine fauna. During the subsequent "salinity crisis" in the latest Miocene (Sect. 6.4.3), the
173
Black Sea (as well as the Caspian Sea) were closed
off from the Tethys ocean and transformed to
intracontinental seas of variable salinity. This is indicated by the presence of endemie fauna and lacustrine shallow-water carbonates (Fig. 4.4e).
In the long interval between the late Miocene and late
Pleistocene (Fig. 4.4, Section B), the Black Sea was a fresh
to slightly brackish water lake with predominantly carbonate deposition. Climatic variations generated altemating
marly and ca1careous beds with abundant siderite concretions accumulated under changing redox conditions. The
organic matter of the last lake phase is predorninantly of
terrestrial origin (Calvert and Fontugne 1987).
The Holocene Black Sea
The modem history of the Black Sea began ~7.5 ka
B.P. when the Holocene transgression had reached
the sill depth of the Bosphorus Strait and enabled the
spillover of sea water into the former fresh to brackish water lake. It took another 4000 to 6000 years
until the present-day environment was established.
Saline, anoxie bottom waters expanded and finally
filled the maj or part of the basin.
During this transitional interval, organic productivity in the surface water was particularly high because of vertical mixing of water masses and nutrient
. recycling. This led to the accumulation of laminated
sapropel rich in organic matter (up to about 15% organic carbon) and a carbonate content in the order of
10%. Later, the stratification of the Black Sea became more stable and the organic productivity dec1ined. The last 1 to 2 ka in Black Sea evolution are
characterized by a shallow, stable chemocline, separating oxygenated, fairly fertile surface water from a
thick deep-water mass. Coccolith-carbonate production diluted the organic carbon concentration of the
deep-water sediment. A typical deep-water sequence
is shown in Fig. 4.4d, but intercalations of mud flow
deposits are omitted, which may occur between the
uppermost two units. The deep-water mass is anoxie
and contains considerable quantities of H 2 S, NH 3 ,
and P (Fig. 4.4b and c).
Most of the hydrogen sulfide is produced by bacterial sulfate reduction within the water column. After a peak in
organic carbon deposition (in tenns of carbon concentration) ~5 ka B.P., the concentration of organic carbon in the
sediment decreased. The uppennost, varved coccolith ooze
on the abyssal plain commonly contains between 1% and
4% of organic carbon and between 15% and 55% of carbonate. The accumulation rate of organic carbon is low in
the Black Sea in comparison to that of modem, highly productive coastal upwelling zones (Sect. 5.3.4).
Consequently, the formerly widely held opinion that
the Black Sea provides a particularly effective
depositional environment for hydrocarbon generation, should be significantly modified. Such a favor-