THE MEDITERRANEAN LOWER CRETACEOUS

3. Blueish and yellowish marls with spongia and brachiopods (marnes d'Arzier);
2. Zoogenic limestones with Natica leviathan and Nerinea (marbre bâtard);
1. Grey marls and oolitic limestones with Toxaster granosus, bivalvs and gastropods
(Mergel und Kalkzone).
Only the upper part of this formation belongs to the Valanginian, the lower part
being Berriasian.
Ammonites occur very seldom in the stratotype of the Valanginian. Therefore,
in order to facilitate correlation, Busnardo etal. (1979) characterized in detail
the so-called hypostratotype of the Valanginian at Angles and at Barret-le-
Bas (Southeastern France). In this region the Valanginian is connected with pelagic
deposits containing many ammonites, calpionellids, belemnites, ostracods, foraminifera
and nannofossils (Table 6).
On the basis of the successions in this section, Busnardo et al. (1979)
identified eight ammonite zones with twenty subzones, as well as zones according
to foraminifera, ostracods, calpionellids and nannoflora.
The ammonite zones found in the so-called hypostratotype of the Valanginian
are of local significance. Some of the zones are based on species and/or associations
which are more widespread in other countries. For example, the appearance
of Thurmanniceraspertransiens (S a y n) in Valanginian sections in Bulgaria marks
the base of the Valanginian. Busnardoites campylotoxus (U h 1.) and Saynoceras
verrucosum (d'O г b.), which are given as index species for the middle zones of the
Valanginian, are widespread in the upper part of the stage in Bulgaria.
2.2.1. Substages
The Valanginian is subdivided into two substages. The differentiation is based on
the ammonite distribution. The Lower Valanginian is characterized by the mass
propagation of the genera Kilianella, Thurmanniceras and Sarasinella, which are less
represented in the Upper Valanginian and have sharply changed species composition.
Ammonite genera Neocomites, Olcostephanus, Bochianites, Saynoceras, Luppovella,
Busnardoites and Neohoploceras are extensively represented in the Upper
Valanginian.
2.2.2. Biostratigraphic Zones
Ammonite Zones
Two zones should be accepted as standard zones in the Valanginian. In some
regions the space of this stage may be subdivided into more zones, which, however,
have limited distribution.
The Lyon Colloquium (1963) adopted two standard zones of the Valanginian:
lower — Kilianella roubaudiana Zone, and upper — Saynoceras verrucosum Zone,
which correspond to the Lower and Upper Valanginian, respectively.
K. roubaudiana Zone. It is based on the Range-zone of Kilianella roubaudiana. Its
lower boundary is marked by the disappearance of Berriasella, Fauriella, Tirnovella,
and by the appearance of Kilianella, Thurmanniceras and Neocomites.
The zone is characterized by K. roubaudiana (d'O г b.), K. lucensis (Say n),
K. ischnotera (Say n), Thurmanniceras thurmanni (P i с t., Cam p.), T. pertransiens
(Say n), T. salientinum (Say n), T. crassicostatum N i к., T. otopeta
T h i e u 1., Clavithurmannia foraticostata T h i e u I., Sarasinella trezanensis (Lor y),
S. eucyrta (Say n), S. walkeri (U h ].), Neocomites beaumugnensis S a y n and
Spiticeras (AT.) gratianopolitense D j a n.
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