THE MEDITERRANEAN LOWER CRETACEOUS

lagoon and brakish environments. The Aptian-Albian sections from the continent
and from its margin demonstrate gradually facial changes from shallow-sea to deepsea
pelagic sediments. A similar dependence is also established for the Agadir — Essaouira
Basin and its continuation into the ocean, with the exception of a number
of intraformational hiatuses with some alternations of marine and continental sediments.
A similar picture is also observed in the continental part of Meseta.
Generally speaking, the Lower Cretaceous in the coastal basins of the continent
(Tarfaya — El Aaiun and Agadir — Essaouira) demonstrates a change of marine
for non-marine environment, with predominant development of deltaic facies
which correlate well biostratigraphically and palaeoecologically with the flysch facies
of the boreholes at Sites 370 and 397. Moreover, the thick turbidites in the Moroccan
Basin (Site 370) are in sharp contrast to the pelagic carbonates and black
shales in the more southern area (Site 367). Interesting is also the development
of the black shale facies in the upper part of the Lower Cretaceous, which suggest
practically oxygen-free environment.
3. NORTHERN AFRICA
The Lower Cretaceous is developed in marine facies in Algeria and Tunisia, whereas
in Libya, Egypt and Sahara it is represented by continental deposits.
3.1. Algeria
The Lower Cretaceous is developed in the Sahara Atlas, the High Plateaux and in
the Tellian Atlas.
In the western part of the Sahara Atlas the Lower Cretaceous is represented
by sandstones and sandy claystone ("continental intercalaire"), whereas in the east
in the same zone —• by sandstones and evaporites (Sahara type).
In the High Plateaux the Lower Cretaceous is of terrigenous-carbonate type.
All stages are developed (Fig. 17).
The Bulgarian geologists who investigated the High Plateaux (Tchounev
et al., 1969; К о 1 e v et al., 1970; Z i d a r о v et al., 1973 — oral communication
of unpublished data) distinguished three main lithostratigraphic units connected
with the Lower Cretaceous: the Oued Mina Carbonate Formation, the Berthelot
Sandstone Formation and the Remailia Limestone Formation. The succession
of these Formations can be seen very well along the Frenda — Tiaret road near the
Oued Mina cascade.
The Remailia Limestone Formation lies transgressively and slightly discordantly
over the Upper Jurassic dolomites of the TIemsen Formation (Tchoumatchenc
о— oral communication). It is represented by various limestones (biodetritic,
intraclastic and organogenic), dolomites and marls. The limestones contain poorly
preserved traces of bivalvs, gastropods and corals, while the marls are rather rich
in foraminifera. Their thickness is 80-90 m.
Fauriella cf. boissieri (P i с t.) is found at the base of this Formation near Djebel
Recheiga. This species marks the lower boundary of the Formation as Berriasian.
Exogyra mines С о q., Harpagodes jaccardi (P i с t., Cam p.), Nerinea spp., Trigonia
sp., as well as foraminifera: Choffalella decipiens S с h 1., С. zireggensis S i g.,
Ammobaculites subaequalis M j a t I., Dorothia sp., etc. occur near the Oued Mina
cascade.
These faunistic finds define the interval from the Berriasian to the Lower Hauterivian.
The Berthelot Formation lies with a clear lithological boundary higher up.
It is represented predominantly by sandstones with intercalations of aleuritic clay-
87