THE MEDITERRANEAN LOWER CRETACEOUS

С. oblongata Zone. It is based on the Range-zone of the index species. Its lower
boundary passes in the upper part of the Lower Valanginian, determined bilaterally.
The upper part of this zone comprises the base of the Hauterivian.
The zone is characterized by Calcicalathina oblongata (W or si.), Micula infracretacea
T h i e г s t., Podorhabdus dietzmanni (Rein h.), Nannoconus bucheri
В г о n п., Zygodiscus diplogrammus (D e f 1., Fer t.), etc.
The nannoplankton microflora is a very promising fossil group for biostratigraphy
(Table 6).
2.3. Hauterivian
The Hauterivian was differentiated byRenevier (1874) who defined it as follows:
"I introduce the term Hauterivian ('marnes d'Hauterive') in order to define
the stage usually referred to as Neocomian or Middle Neocomian in Switzerland."
The stratotype of the Hauterivian is found at Hauterive — Mail, in the northeastern
part of Neuchâtel railway station. The outcrop of this section is rather obscure
today, therefore the characterization of the stage in its type region was complemented
by H a e f e 1 i et al. (1965) with several auxiliary sections at Landeron, Twan and
Russel.
According to the revision introduced by H a f e 1 i et al. (1965), in its stratotype
region the Hauterivian includes the following lithostratigraphic units (in descending
order):
4. Pierre-jaune-zone (=Pierre-jaune de Neuchâtel of R e n e v i e г).
3. Margel-und-Kalk-Zone) (=zone marnocalcaire ofBaumberger,
2. Knollenmergel-Zone J Moulin 1898).
1. Mergel-Zone (=Marnes d'Hauterive of R e n e v i e r).
Owing to Baumberger (1903-1910), many Hauterivian ammonites are
known from the Neuchâtel region, but they originate almost exclusively from the
lower part of the stage. The upper part of the Hauterivian is not well characterized
palaeontologically in the type region. Moreover, the neritic facies of Hauterivian
sediments in the type region of the stage contain facies-determined faunistic successions,
which complicate the correlation with other regions. Therefore, as a whole,
the foundations of the detailed stratigraphy of the Hauterivian were laid with the
investigation of ammonite successions in the Vocontian trough (Southeastern France).
2.3.1. Substages
The law-governed trends in the evolution of the faunas, especially of ammonites,
permits the division of the Hauterivian into two substages: Lower and Upper Hauterivian.
The Lower Hauterivian is distinguished from the Valanginian by the disappearance
of Thurmanniceras, Busnardoites, Sarasinella, Saynoceras and Luppovella,
as well as by the appearance of Crioceratites and Acanthodiscus. It is characterized
by predominance of different species from the genera Acanthodiscus, Crioceratites,
Lyticoceras, Distoloceras, Leopoldia, Olcostephanus, Eleniceras, Spitidiscus, etc.
The Upper Hauterivian is poorer in ammonites. It is characterized by the development
of Balearites, Crioceratites, Subsaynella and Pseudothurmannia, Acrioceras,
Astieridiscus, Plesiospitidiscus, Phyllopachiceras, etc. appear.
In addition to the ammonites, the Hauterivian is also characterized by many
belemnites belonging to the genera Hibolites, Duvalia and Pseudobelus. The first
representatives of Curtohibolites appear in the Upper Hauterivian.
23