THE MEDITERRANEAN LOWER CRETACEOUS

of alternation of marls and clayey limestones. Limestones predominate at the base
of this part, whereas marls passing into compact claystones become gradually imposed
higher up.
The Formation is in a complex tectonic position — in the frontal part of the
Chouala nappe, therefore it is difficult to characterize its boundaries. Many ammonites
occur among the sediments of this Formation.
Fit;. 18. Lithostratigraphic units in the northern part of the High Plateaux between the Oued Mina
and Ouled Mimoun
The following Berriasian ammonites are found in the Chouala area in the lower
part of the Formation: Berriasella calisto (d'O r b.), Berriasella cf. privasensis
(P i с t.), Fauriella boissieri (P i с t.), Spiticeras sp. indet. and Leptoceras studeri (О о s t.).
Valanginian ammonites follow above the beds of this association: Thurmanniceras
cf. thurmanni (P i с t.), Kilianella sp. indet., Olcostephanus (O.) leptoplanus
(B a u m b.), and slightly higher up: Saynoceras verrucosum (d'O r b.), Neocomites
neocomiensis neocomiensis (d'O r b.), Olcostephanus sp. indet., Neolissoceras
grasianum (d'O r b.), etc.
A very rich Valanginian association was found at Ain en Nessissa: Phylloceras
spp., Neocomites neocomiensis neocomiensis (d'O г b.), N. neocomiensis premolicus
(Say n), Л', neocomiensis subquadratus (Say n), Olcostephanus (Olcostephanus)
astierianus (d'O г b.), Olcostephanus (Rogersites) atherstoni (S с h a r p e) and O. (R.)
psilostomus (N e u m., U h 1.).
The middle part of the investigated Formation is of Hauterivian age, which
is proved by the find of Crioceratites sp. indet., Olcostephanus sp. indet. and Phyllopachiceras
sp. at Sidi Seba Achir.
The upper part of the Formation is of Barremian age. The following species
are found at Sidi Ounes: Barremites nabdalsa (С о q.), B. aff. difficilis (d'O r b.),
Subpulchellia sauvagensis (Her m.), S. ochleafi (N i с к.), Spilidiscus pulrinatus
В u s п., Holcodiscus spp. and Hamulina sp. indet. A little higher: B. nabdalsa
(С о q.), Pulchellia compressissima (d'O r b.), Holcodiscus perezianus (d'O r b.),
Spitidiscus querolensis В u s n. and Hypophylloceras barremense В u s п., followed
above by: Pseudosaynella strettosioma (U h 1.), Hypophylloceras barremense
В u s п., Subpulchellia sp. and B. nabdalsa (С о q.). At Ras el Masraf and at Sidi
Aek: Pulchellia ouachensis (С о q.), Subpulchellia sauvageani (Her m.), Spitidiscus
nemglonensis (Say n), Spitidiscus sp. indet., Eotetragonites duvali (d'O r b.), Pseudosaynella
strettosioma (U h 1.), etc.
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