170
deep to pennit significant brine concentrations, but
during the late Miocene thick salt deposits were generated in these basins (Sect. 6.4.3). As in the Black
Sea, the Red Sea and the Persian Gulf experienced
drastic changes during their history, leading to pronounced variations in their sedimentary records
(Sect. 4.3).
4.2.4 A Composite Basin: the Mediterranean Sea
The Mediterranean Sea is divided into a western and
an eastern deep basin by a sill between Sicily and the
North African coast (Fig. 4.2b). The eastem basin in
particular is characterized by a large excess in evaporation over precipitation, leading to relatively high
water temperatures and salinities. Three different
water masses can be distinguished in this type of basin: surface water, intennediate water, and deep bottom water, which interact in several ways. Intennediate and bottom waters are fonned in winter, when
cooling of surface water in marginal regions, such as
the northern Adriatic Sea, leads to an increase in density. The intennediate water flows back over the midbasin sill and out as an undercurrent through the
Strait of Gibraltar into the Atlantic Ocean. The deep
water is somewhat cooler, and it circulates more
slowly than the other water masses. It mixes to some
extent with intennediate water and flows out into the
Atlantic.
Today, the oxygen content of the deep water is
fairly high in both basins, but during the early Holocene and during several intervals within the late Quaternary, the bottom water in the eastern basin, including the Adriatic Sea, was more stagnant and repeatedly depleted of oxygen. This is documented by a
number of thin sapropel layers within hemipelagic to
pelagic sediments.
During the last ~0.3 Ma, up to more than ten discrete,
basin-wide, organic-rich sapropellayers formed in the eastern Mediterranean. The nature of these layers has been
Iively debated in recent years because they may result from
several processes: changes in sea level and/or water circulation, as weil as c1imate change (e.g. Jung et aI. 1997;
Schmiedl et aI. 1998). Several authors have postulated that
the sapropels are associated with periods of high, monsoonal precipitation in eastern Africa and the general climatic changes on the nearby land masses (Rossignol-Strick
1985; Ten Haven et aI. 1987; Murat and Got 1987). Fresh
water flooding by the Nile River may have caused the influx of land-derived organic matter and have provided nutrients for high marine organic productivity. In addition,
the increased freshwater discharge may have favored the
formation of stratified waters and thus prevented convective overturn and ventilation ofbottom water.
Because of the presence of tephra 1ayers in wide regions
of the Mediterranean, precise radiometric age determinations for Quaternary sediments could be carried out (e.g.
Keller et aI. 1978; Kraml 1997), in addition to stable oxygen isotope determinations.
Chapter 4 Adjacent Seas
Whether or not a current reversal in the Strait of Gibraltar occurred during the transition from the last glacial
phase to the Holocene, as well as whether additional reversaIs resulted from earlier Pleistocene c1imatic changes, is
controversial (Diester-Haass 1973; Huang and Stanley
1974). A simulation of the oceanographic situation in the
Mediterranean has shown that anti-estuarine circulation
was maintained at the straits of Gibraltar and Siciliy also
during the last glacial maximum (Myers and Haines 1998).
For further details about the sediments ofthe Mediterranean see, e.g., Stanley (1972, 1977), Emelyanov (1972),
Wezel (1980), Stanley and Wezel (1985), Van Hinte et al.
(1987), (Bouma 1990). Ocean drilling and associated seismic studies have provided additional information about the
tectonic and sedimentary history ofthis complex basin. The
plate tectonic evolution of the Mediterranean is discussed,
e.g., by Westaway (1994) and Comas et aI. (1996). The
Miocene evaporites, backarc basin formation, and mud
diapirism of the Mediterranean are mentioned in Sects.
6.4.3 and 12.5.
All the larger and smaller subbasins of the Mediterranean Sea contain similar fills, showing the following
sequence (from top to bottom):
- Pliocene to Quaternary predominantly clastic sediments.
- Miocene evaporites (cf. Sect. 6.4.3).
- Older deep-water sediments.
The present-day basinal sediments of the Mediterranean are largely hemipelagic muds with low to medium carbonate contents produced mainly by
foraminifera and coccoliths. In addition, several midsized fans in front ofmajor rivers (e.g., Rhone, Ebro,
Nile, Rhone) and many smaller ones are observed.
Sedimentation rates are in the order of 10 to 30
cm/ka, but may be considerably higher in some areas,
particularly where mud flows and mud turbidites play
a role.
4.2.5 Basins with Horizontally Separated Inflow
and Outflow
Some marginal ocean basins have a horizontally separated inflow and outflow (Fig. 4.3b; Pickard and
Emery 1982). Due to the gain or loss of heat, salinity
and fertility in the adjacent sea, the characteristics of
the outflowing water may deviate considerably from
those of the inflow. Consequently, organic producti on and sediments may differ on the intlowing and
outflowing sides of the marginal sea. Present-day
examples of this basin type are the Caribbean Sea
(the American counterpart of the Mediterranean) and
larger, marginal parts of the world oceans, such as
the Norwegian-Greenland Sea.
The Caribbean Sea. The intlow of surface water
into the modem Caribbean Sea consists of a portion
deep to pennit significant brine concentrations, but
during the late Miocene thick salt deposits were generated in these basins (Sect. 6.4.3). As in the Black
Sea, the Red Sea and the Persian Gulf experienced
drastic changes during their history, leading to pronounced variations in their sedimentary records
(Sect. 4.3).
4.2.4 A Composite Basin: the Mediterranean Sea
The Mediterranean Sea is divided into a western and
an eastern deep basin by a sill between Sicily and the
North African coast (Fig. 4.2b). The eastem basin in
particular is characterized by a large excess in evaporation over precipitation, leading to relatively high
water temperatures and salinities. Three different
water masses can be distinguished in this type of basin: surface water, intennediate water, and deep bottom water, which interact in several ways. Intennediate and bottom waters are fonned in winter, when
cooling of surface water in marginal regions, such as
the northern Adriatic Sea, leads to an increase in density. The intennediate water flows back over the midbasin sill and out as an undercurrent through the
Strait of Gibraltar into the Atlantic Ocean. The deep
water is somewhat cooler, and it circulates more
slowly than the other water masses. It mixes to some
extent with intennediate water and flows out into the
Atlantic.
Today, the oxygen content of the deep water is
fairly high in both basins, but during the early Holocene and during several intervals within the late Quaternary, the bottom water in the eastern basin, including the Adriatic Sea, was more stagnant and repeatedly depleted of oxygen. This is documented by a
number of thin sapropel layers within hemipelagic to
pelagic sediments.
During the last ~0.3 Ma, up to more than ten discrete,
basin-wide, organic-rich sapropellayers formed in the eastern Mediterranean. The nature of these layers has been
Iively debated in recent years because they may result from
several processes: changes in sea level and/or water circulation, as weil as c1imate change (e.g. Jung et aI. 1997;
Schmiedl et aI. 1998). Several authors have postulated that
the sapropels are associated with periods of high, monsoonal precipitation in eastern Africa and the general climatic changes on the nearby land masses (Rossignol-Strick
1985; Ten Haven et aI. 1987; Murat and Got 1987). Fresh
water flooding by the Nile River may have caused the influx of land-derived organic matter and have provided nutrients for high marine organic productivity. In addition,
the increased freshwater discharge may have favored the
formation of stratified waters and thus prevented convective overturn and ventilation ofbottom water.
Because of the presence of tephra 1ayers in wide regions
of the Mediterranean, precise radiometric age determinations for Quaternary sediments could be carried out (e.g.
Keller et aI. 1978; Kraml 1997), in addition to stable oxygen isotope determinations.
Chapter 4 Adjacent Seas
Whether or not a current reversal in the Strait of Gibraltar occurred during the transition from the last glacial
phase to the Holocene, as well as whether additional reversaIs resulted from earlier Pleistocene c1imatic changes, is
controversial (Diester-Haass 1973; Huang and Stanley
1974). A simulation of the oceanographic situation in the
Mediterranean has shown that anti-estuarine circulation
was maintained at the straits of Gibraltar and Siciliy also
during the last glacial maximum (Myers and Haines 1998).
For further details about the sediments ofthe Mediterranean see, e.g., Stanley (1972, 1977), Emelyanov (1972),
Wezel (1980), Stanley and Wezel (1985), Van Hinte et al.
(1987), (Bouma 1990). Ocean drilling and associated seismic studies have provided additional information about the
tectonic and sedimentary history ofthis complex basin. The
plate tectonic evolution of the Mediterranean is discussed,
e.g., by Westaway (1994) and Comas et aI. (1996). The
Miocene evaporites, backarc basin formation, and mud
diapirism of the Mediterranean are mentioned in Sects.
6.4.3 and 12.5.
All the larger and smaller subbasins of the Mediterranean Sea contain similar fills, showing the following
sequence (from top to bottom):
- Pliocene to Quaternary predominantly clastic sediments.
- Miocene evaporites (cf. Sect. 6.4.3).
- Older deep-water sediments.
The present-day basinal sediments of the Mediterranean are largely hemipelagic muds with low to medium carbonate contents produced mainly by
foraminifera and coccoliths. In addition, several midsized fans in front ofmajor rivers (e.g., Rhone, Ebro,
Nile, Rhone) and many smaller ones are observed.
Sedimentation rates are in the order of 10 to 30
cm/ka, but may be considerably higher in some areas,
particularly where mud flows and mud turbidites play
a role.
4.2.5 Basins with Horizontally Separated Inflow
and Outflow
Some marginal ocean basins have a horizontally separated inflow and outflow (Fig. 4.3b; Pickard and
Emery 1982). Due to the gain or loss of heat, salinity
and fertility in the adjacent sea, the characteristics of
the outflowing water may deviate considerably from
those of the inflow. Consequently, organic producti on and sediments may differ on the intlowing and
outflowing sides of the marginal sea. Present-day
examples of this basin type are the Caribbean Sea
(the American counterpart of the Mediterranean) and
larger, marginal parts of the world oceans, such as
the Norwegian-Greenland Sea.
The Caribbean Sea. The intlow of surface water
into the modem Caribbean Sea consists of a portion