The Pleistocene of the Eastern Mediterranean
17
For the duration of the Pleistocene there is no indication of a positive difference to be found in this region: out of the big diversity of Pleistocene molluscs
there is no species peculiar to the eastern basin which cannot be found in the
western one. On the contrary, there are many species which never reached the
eastern basin. Other species, frequent in the west, appeared only episodically in
the east.
The Western Mediterranean-between Gibraltar and the Straits of Sicily-is
the classical region in which the universal chronology of the marine Pleistocene
has been established. Such terms as Calabrian, Sicilian, Tyrrhenian-indicating
different levels reached by the eustatic movement of the sea level are in wide use
today and authors like Zeuner (1959) and Fairbridge (1961) see in them a universal pattern.
It is weIl accepted that during the glacial periods-with much water captured
by the increased ice caps-the level of the world ocean was low, perhaps as low as
- 200 m (Fig.5). On the contrary, during the interglacials with the melting of the
caps, sea levels rose, reaching perhaps as much as + 100 m during the earliest of
the three interglacials. It was expected that temperature fluctuations would be
expressed jointly with the level fluctuations. This, however, is not the case for the
Western Mediterranean; only the last interglacial high level (the Tyrrhenian
sensu Blanc, 1969) and that of the two last interglacials (Tyrrhenian I and Ir as
in Zeuner, 1959) show an influx ofwarm water-fauna (Fig. 6).
Zeuner (1959) pointed out that the Pleistocene sea level fluctuations are deviations in a general regressive trend which started with the great late Pliocene
withdrawal of the sea. Other authors emphasize that fossil beaches found at high
levels inland may be eustatic as weIl as "tectogenic", i.e. due to tectonic uplifts.
This is the reason why a correlation between the fossil beach levels and the glacial
stages cannot be seen until the great or second interglacial. The period since can
reasonably weIl be assumed to be tectonically quiet, at least in this part of the
world.
Mars (1963) and Ruggieri (1967) emphasized for the first time that an inversion of the currents in the straits of Gibraltar might be responsible for the appearance or disappearance of cold-water or warm-water species coming into the
Mediterranean (Fig. 7). During glacial periods, the water balance (runoff/evaporation) was positive in the Mediterranean and therefore there was an outflow of
surface water through the straits of Gibraltar and an inflow of deep Atlantic water
over the sill. This inflow brought in the "Celtic" cold water elements (Mars and
Picard, 1958) which characterize the Calabrian, Sicilian and Würm (last glacial)
periods. In the interglacials, evaporation prevailed over runoff and therefore the
currents at Gibraltar were reversed: the Atlantic inflow is at the surface and
brings in warm-temperature and sub-tropical Atlantic species, whereas the outflow of Mediterranean water is over the sill. The cold-water Calabro-Sicilian
species are therefore characteristic of deep water conditions, the subtropical Tyrrhenian species of shallow water conditions. Instead of strictly alternating they
could therefore coexist-unless hydrographie conditions were too extreme; indeed they did so.
In the Calabrian and Sicilian species there is a concomitance of "Celtic"
moIluscs of the Arctica islandica association with Pliocene Paleomediterranean,
17
For the duration of the Pleistocene there is no indication of a positive difference to be found in this region: out of the big diversity of Pleistocene molluscs
there is no species peculiar to the eastern basin which cannot be found in the
western one. On the contrary, there are many species which never reached the
eastern basin. Other species, frequent in the west, appeared only episodically in
the east.
The Western Mediterranean-between Gibraltar and the Straits of Sicily-is
the classical region in which the universal chronology of the marine Pleistocene
has been established. Such terms as Calabrian, Sicilian, Tyrrhenian-indicating
different levels reached by the eustatic movement of the sea level are in wide use
today and authors like Zeuner (1959) and Fairbridge (1961) see in them a universal pattern.
It is weIl accepted that during the glacial periods-with much water captured
by the increased ice caps-the level of the world ocean was low, perhaps as low as
- 200 m (Fig.5). On the contrary, during the interglacials with the melting of the
caps, sea levels rose, reaching perhaps as much as + 100 m during the earliest of
the three interglacials. It was expected that temperature fluctuations would be
expressed jointly with the level fluctuations. This, however, is not the case for the
Western Mediterranean; only the last interglacial high level (the Tyrrhenian
sensu Blanc, 1969) and that of the two last interglacials (Tyrrhenian I and Ir as
in Zeuner, 1959) show an influx ofwarm water-fauna (Fig. 6).
Zeuner (1959) pointed out that the Pleistocene sea level fluctuations are deviations in a general regressive trend which started with the great late Pliocene
withdrawal of the sea. Other authors emphasize that fossil beaches found at high
levels inland may be eustatic as weIl as "tectogenic", i.e. due to tectonic uplifts.
This is the reason why a correlation between the fossil beach levels and the glacial
stages cannot be seen until the great or second interglacial. The period since can
reasonably weIl be assumed to be tectonically quiet, at least in this part of the
world.
Mars (1963) and Ruggieri (1967) emphasized for the first time that an inversion of the currents in the straits of Gibraltar might be responsible for the appearance or disappearance of cold-water or warm-water species coming into the
Mediterranean (Fig. 7). During glacial periods, the water balance (runoff/evaporation) was positive in the Mediterranean and therefore there was an outflow of
surface water through the straits of Gibraltar and an inflow of deep Atlantic water
over the sill. This inflow brought in the "Celtic" cold water elements (Mars and
Picard, 1958) which characterize the Calabrian, Sicilian and Würm (last glacial)
periods. In the interglacials, evaporation prevailed over runoff and therefore the
currents at Gibraltar were reversed: the Atlantic inflow is at the surface and
brings in warm-temperature and sub-tropical Atlantic species, whereas the outflow of Mediterranean water is over the sill. The cold-water Calabro-Sicilian
species are therefore characteristic of deep water conditions, the subtropical Tyrrhenian species of shallow water conditions. Instead of strictly alternating they
could therefore coexist-unless hydrographie conditions were too extreme; indeed they did so.
In the Calabrian and Sicilian species there is a concomitance of "Celtic"
moIluscs of the Arctica islandica association with Pliocene Paleomediterranean,