GSSP for the Eocene - Oligocene Boundary.


Definition:

The base of the Oligocene Stage is defined in the Massignano section about 10km southeast of Ancona, Italy. The GSSP is at the base of a 0.5m thick greenish-grey marl bed. At this level, both the planktonic foraminifera Hantkenina and Cribrohantkenina, Eocene genera of the Hantkeninidae, become extinct.


Location:

The Massignano Section is located on the Adriatic coast of Italy near Ancona in the Monte Conero area. It is an abandoned quarry on the east side of the Ancona-Sirolo road near the village of Massignano. The section is located at latitude 43°3213N and longitude 13°3536E (Geol. Map of Italy: F.118, Ancona). The GSSP is situated at 19m above the base of the section.
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Sedimentology:

The Massignano section, which covers the late Eocene to Early Oligocene, is 23m thick and consists of reddish and greenish grey marls and calcareous marls. The lower part is in the Scaglia Variegata Formation (12.3m) and above this is the Scaglia Cinera Formation (10.7m). The sediments of the Massignano section are completely marine with no evidence of any hiatus. The GSSP is at the base of a greenish-grey 0.5m thick marl bed, 19m above the base of the section.
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Primary Markers:

Foraminifera:
The planktonic foraminifera Hantkenina and Cribrohantkenina, Eocene genera of the Hantkeninidae, become extinct at the GSSP.

Secondary Markers:

Nannofossils:
The GSSP is within calcareous nannofossil zones NP21 and CP16a.

Paleomagnetics:
The Massignano section lies within magnetic polarity reversal 13R1.

Radiomentric Age:
Radiometric ages (K-Ar and 40Ar-39Ar) have been obtained from biotites. The date of 34.6+0.3Ma at 14.7m above the base of the section indicates that the age of the GSSP at 19m is younger and is estimated to be 34 Ma.

References:

Premoli Silva, I. and Jenkins, D. G., 1993. Decision on the Eocene-Oligocene boundary stratotype. Episodes 16/3, p.379 - 382.