20
H.-J. Bolle
3 Past Climates and Vegetation in the Mediterranean Basin
3.1 Late Cretaceous Period to Pliocene Epoch (135 Ma - 1 Ma B.P.)
Traces of vegetation, primarily pollen, and of animals, sediments, dunes or geohydrological structures allow to draw conclusions with respect of the water, wind
and temperature regime in ancient times and the development of vegetation and
climate. 100 Ma B.P. the Sudan and Arabia were positioned near the equator and
southern Europe at 30 degree North. The African plate separated from the South
American one and moved towards the Eurasian plate from which it was separated
by the Tethys Sea (which was a broad seaway linking what we now call the North
Atlantic and Indian oceans until 20 million years ago). The Sahara at that time was
still in the tropics and southern Europe had a climate like the northern African coast
has nowadays. The first Saharian sand deposits, indicating its desertification, have
been found at the ground of the Atlantic Ocean from the Oligocen (33 - 28 Ma B.P.)
on (Sarnthein, 1978). 11 - 5 Ma old wood was found from trees which were adapted
to dry climate. Due to the northward movement of the African plate since 65 Ma
B.P. land masses slowly build up around the western part of the Tethys Sea and
formed the Mediterranean basin. In the East the brackish Paratethys Sea was left
over from which later on the Carpathian lakes, the Black Sea, the Caspian Sea, and
the Aral Sea formed. When the African continent collided with the Asian one the
Middle East mountains formed and interrupted the conection to the Indian Ocean.
The Balkan mountains blocked the drainage of the Paratethys Sea and northern
rivers into the Mediterranean. Around 15 Ma B.P. the Mediterranean basin had
approximately its present shape but its geographical position was still a few degrees
further South and the climate became dry. The continued northward movement of
the African plate build up the Iberian-Moroccan mountains which closed the
connection to the Atlantic Ocean between 10 and 6 Ma B.P. (Hsti, 1983). Due to this
complete isolation and the geographical position in the dry belt some four million
km 3 water evaporated and the basin fell dry and left a salt-covered surface with the
exception, maybe, of a few brackish lakes. Prior to the geological evidence that the
Mediterranean basin had been a desert, French and Italian paleontologists had
postulated a "salinity crisis" during the "Messinian" period between 6 and 5 Ma B.
P. to explain the extinguishment of species that cannot survive in sea water with
high salinity. It seems to be that the Balkan barrier got permeable for some rivers
around 5.5 Ma B.P. when the Paratethys broke up into the smaller lakes and seas
and some brackish lakes developed in the Mediterranean basin. Also major rivers
like the Rhone and Nile poured water (and with it gravel) into the dry basin. Around
5.2 Ma B.P. the North Atlantic Ocean broke through the Iberian-Moroccan barrier
and opened what we now call the Strait of Gibraltar. The much lower lying
Mediterranean basin regained its water volume by what must have been a gigantic
waterfall. Later on the Bosporus barrier eroded and the Mediterranean Sea was
connected with the Black Sea and northern rivers as well.
H.-J. Bolle
3 Past Climates and Vegetation in the Mediterranean Basin
3.1 Late Cretaceous Period to Pliocene Epoch (135 Ma - 1 Ma B.P.)
Traces of vegetation, primarily pollen, and of animals, sediments, dunes or geohydrological structures allow to draw conclusions with respect of the water, wind
and temperature regime in ancient times and the development of vegetation and
climate. 100 Ma B.P. the Sudan and Arabia were positioned near the equator and
southern Europe at 30 degree North. The African plate separated from the South
American one and moved towards the Eurasian plate from which it was separated
by the Tethys Sea (which was a broad seaway linking what we now call the North
Atlantic and Indian oceans until 20 million years ago). The Sahara at that time was
still in the tropics and southern Europe had a climate like the northern African coast
has nowadays. The first Saharian sand deposits, indicating its desertification, have
been found at the ground of the Atlantic Ocean from the Oligocen (33 - 28 Ma B.P.)
on (Sarnthein, 1978). 11 - 5 Ma old wood was found from trees which were adapted
to dry climate. Due to the northward movement of the African plate since 65 Ma
B.P. land masses slowly build up around the western part of the Tethys Sea and
formed the Mediterranean basin. In the East the brackish Paratethys Sea was left
over from which later on the Carpathian lakes, the Black Sea, the Caspian Sea, and
the Aral Sea formed. When the African continent collided with the Asian one the
Middle East mountains formed and interrupted the conection to the Indian Ocean.
The Balkan mountains blocked the drainage of the Paratethys Sea and northern
rivers into the Mediterranean. Around 15 Ma B.P. the Mediterranean basin had
approximately its present shape but its geographical position was still a few degrees
further South and the climate became dry. The continued northward movement of
the African plate build up the Iberian-Moroccan mountains which closed the
connection to the Atlantic Ocean between 10 and 6 Ma B.P. (Hsti, 1983). Due to this
complete isolation and the geographical position in the dry belt some four million
km 3 water evaporated and the basin fell dry and left a salt-covered surface with the
exception, maybe, of a few brackish lakes. Prior to the geological evidence that the
Mediterranean basin had been a desert, French and Italian paleontologists had
postulated a "salinity crisis" during the "Messinian" period between 6 and 5 Ma B.
P. to explain the extinguishment of species that cannot survive in sea water with
high salinity. It seems to be that the Balkan barrier got permeable for some rivers
around 5.5 Ma B.P. when the Paratethys broke up into the smaller lakes and seas
and some brackish lakes developed in the Mediterranean basin. Also major rivers
like the Rhone and Nile poured water (and with it gravel) into the dry basin. Around
5.2 Ma B.P. the North Atlantic Ocean broke through the Iberian-Moroccan barrier
and opened what we now call the Strait of Gibraltar. The much lower lying
Mediterranean basin regained its water volume by what must have been a gigantic
waterfall. Later on the Bosporus barrier eroded and the Mediterranean Sea was
connected with the Black Sea and northern rivers as well.