THE MEDITERRANEAN LOWER CRETACEOUS

Delga (1969) distinguished three basic types: (1) fine sandy flysch ("flysch gréseux
fin de Guerrouch"); (2) sandy flysch ("flysch greseux-micacé"), and (3) flysch
with calcareous microbrecchias ("flysch à microbrèches calcaires"). Similar flysch
types may be observed in many Mediterranean zones.
The transition zone between the platform of the High Plateaux and the pelagic
area to the north is outlined to the southwest of Constantine. In this zone (Monts
de Batna — Aures) the Lower Cretaceous is markedly terrigenous or terrigenous-carbonate
(Bureau, 1971).
The development of the Berriasian and Valanginian is interesting, because they
are well substantiated palaeontologically only in the investigated zone in the Constantine
region. At Ravin Bleu (M. de Batna) there are clayey-carbonate sediments
with intercalations of sandstones and siltstones, from the transition between the
neritic and the pelagic zones, in which Donze, Guiraud, Le Hégarat
(1974) have found rich calpionellid and ammonite associations, known from the
classical outcrops in the Mediterranean Region.
3.2. Tunisia
The Lower Cretaceous in Tunisia is connected with three main tectonic zones: the
Tunisia Depression, the complex of intracratonnal basins and unstable neritic basins
in Central Tunisia and Tunisian Sahara.
In the southernmost (Sahara) part of Tunisia the base of the Lower Cretaceous
(Berriasian-Hauterivian) is built of continental terrigenous sediments and evaporites.
Carbonates are developed further north in the southern periphery of the sea
basin. The Barremian in this zone is represented by coarse terrigenous continental
sediments: conglomerates and sandstones with intercalations of red sandy claystones.
This is the classical "continental intercalaire" with thickness up to 1000 m.
Remains of vertebrates and plants are found. There are no traces of sea organisms.
A similar type of sedimentation continued during the Aptian as well, but with the
appearance of dolomites and clayey dolomites during the Late Aptian. This marks
the beginning of a lagoon environment in Sahara.
Purbeckian-Wealdian type of facies are developed to the north of the Sahara
zone: sandstones, dolomites, claystones and gypsum (Merbah el Asfer Formation).
They contain remains of vertebrates, silicified trees, bivalvs, gastropods, as well
as some rare marine species.
The Barremian and the Lower Aptian are represented by terrigenous sediments:
sandstones, conglomerates and red claystones (Bateun el Rhezae Formation). Higher
up the Aptian and Albian sections are built of limestones, massive dolomites
and gypsum-bearing marls. At Dj. Tebaga de Medine they lie transgressively on
Permian or Jurassic rocks (Burollet, Manderscheid, 1965).
In the east and northeast the continental terrigenous facies are replaced by carbonates
belonging to the typical Mediterranean Lower Cretaceous. Their southern
boundary at the end of the Albian Age marks the starting point of the Trans-
Sahara Late Cretaceous transgression.
Burollet (1956) outlined three main zones of Lower Cretaceous development
in Central Tunisia: Dj. Nara zone, Kasserine zone and zone of the Periatlas
basin.
The lower part of the series (Berriasian-Valanginian) is discovered in the Djebel
Nara zone (North-South axis). The section starts with the marls of Sidi Kralif
(earlier designated as "Argiles de Sidi Kralif"). These are grey marls with intercalations
of limestones and clayey limestones. The marls are rich in fossils, among which
many pyritized ammonites are known (Breitstroffer, 1937; A r n о u 1 d-
S a g с t, 1951). The ammonite successions demonstrate the development of the
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