Stratigraphical and micropaleontological data on the tertiary of Southern Piemont (Northern Italy)

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 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.