Abstract
During the years 1959-1963 stratigraphical investigations
were carried out in Southern Piemont (Northern Italy) along
five traverses, taken at right angles to the strike of the strata,
which range in age from Eocene to Pliocene.
These sections are important in that they include the rype
sections of some Neogene stages (Langhian, Serravallian and
Tortonian) and some
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classical localities, such as Moliere and
Costa Lupara.
The sequences of these sections (numbered I-V) show large
discrepancies in lithology as well as in the thickness between
the corresponding units. To avoid confusion a number of formations
and members are introduced for each of the sections.
Parts of the sections are barren but in most portions numerous
planktonic foraminifera were found. They could be used to
establish ten biozones, successively I: the semi-involuta Zone, II:
the cerro-azulensis Zone, III: the Globigerina Zone, IV: the
Globigerinoides-Globoquadrina Zone, V: the Globorotalia Zone,
VI: the bisphericus Zone, VII: the Orbulina Zone, VIII: the
menardii Zone, IX: the nepenthes Zone, and X: the obliquus
Zone.
In addition some of the larger Foraminifera were investigated
in more detail, in particular the Nephrolepidina and Miogypsina
species. The embryonic-nepionic apparatus of Lepidocyclina praemarginata
and Lepidocyclina morgani were compared on a biometric
basis. Only a part of the phylogenetic series of the Miogypsinidae
was encountered, namely from M. gunteri to M.
intermedia.
Correlation by means of the zonation with these larger and
planktonic Foraminifera leads to interesting stratigraphic results.
1. In the correlation of the sections II, III and IV only slight
differences with the Italian Geological Map have been met
with, but in the sections I and V there are large deviations
from this map.
2. The type Langhian appears to begin closely above the
Orbulina surface. For the assumed chronological interval
between Helvetian and Tortonian the author suggests to use
the term Serravallian rather than Langhian, because the latter
has commonly been erroneously considered to be the equivalent
of the Burdigalian. The limits between the successive
stages Burdigalian, Helvetian, Serravallian and Tortonian can
be correlated with biozones of planktonic Foraminifera.
3. Furthermore it was found that the beginnings of the genera
Globigerinoides and Globoquadrina do not coincide with the
Oligocene-Miocene boundary. Both genera start their range
in the Late Oligocene already.
4. Among the general conclusions of a paleogeographic nature
we may note, that the transgression over the metamorphic
basement of the Massif of Voltri and Ligurian Alps advanced
in westward direction during Rupelian and probably Chattian
times.
5. In the most eastern section (Tortona-Garbagna area) the
Miocene sequence is not complete, as sediments, corresponding
to at least two of the biozones are lacking here.
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