III. PHYSICAL AND VEGETATIONAL ASPECTS OF THE SAHARA
111
T A B L E I
S U C C E S S I O N O F C L I M A T O - S E D I M E N T A R Y E V E N T S H A V I N G O C C U R R E D O V E R T H E
W E S T E R N A L G E R I A N S A H A R A D U R I N G T H E C O U R S E O F T H E
P L I O - Q U A T E R N A R Y "
Geologie
periods
0 Year
Holocene
8000 yrs B. C.
Upper
Pleistocene
c c ΠΠΠ
DDjUUU
Middle
Pleistocene
— 250,000
Villafranchian
— 2,000,000
Pliocene
— 8,000,000
Climatic
manifestations
1000 B.C.
Neolithic humid
4500 B.C.
12,000 B.C.
Upper Pleistocene
Pluvial or
Last Pluvial
- - >40,000 B.C.
?
Pluvial(S) of the
Middle Pleistocene
?
"
,
Climatic revolution
of the
Upper Villafranchian
?
Climatic revolution
of the
Pio - Villaf ran chian
?
?
Neogene climatic
revolution
"From Conrad (1969).
Sedimentary phenomena
or
morphologic evolution
Ergs
Low terraces
Lacustrine erg formation,
turfs
Great Western Erg formation
Sandy terrace of the Saoura
Small lacustrine cycle with
Cardium and Ostracod vestiges (Ahnet, Chech erg)
Chech erg formation
Fossil ergs (Great Eastern
Erg)
Incrusted or armored intercalary glacis
Conglomeritic terrace
Regouging of the valleys
Fossil ergs
Late silicifications
Incrusted or armored upper
glacis
High terraced wadis
Great lacustrine cycle
Great deepening of the valleys
Small hamadas
Late silicifications
Fluvio-lacustrine sedimentation of the Plio-Villafranchian (Lates,
Siluridae,
Crocodiles, Ostracod s,
Characinidae )
Sketching of the hydrographie
network
Erosion of the Neogene
hamadas
Late silicifications
Hamadas lacustrine sedimentation (turfs, limestones,
dolomites, sandstones)
Average
climatic tendency
Hyperar id
Arid to subarid
Hyperarid
Subarid
Arid to hyperarid
Subarid
Arid to hyperarid
Attenuated subarid
A r i d ?
Attenuated subarid
to semiarid
A r i d ?
Semiarid