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Abstract

The IUGS Commission on Stratigraphy recently acccepted and ratified a proposal to establish an Eocene/Oligocene (E/O) boundary stratotype section and point (GSSP) in the pelagic Massignano section (central Italy), characterized by the last occurrence of the Hantkeninidae (planktonic foraminifera). However, detailed dinoflagellate cyst zonation of the E/O transition interval in the Mediterranean area indicates that this newly selected ’golden spike’ horizon correlates to the middle part of the classic (marginal marine) Priabonian type section in northeast Italy. The coeval level occurs well below two earlier proposed E/O boundary stratotypes at Priabona.

In this paper, it is outlined that selection of either one of the proposed boundary-stratotypes at Priabona is more suitable than a hantkeninid-based E/O boundary. These boundary levels can be traced in different lithofacies by recognition of either the TA4.3/4.4 sequence boundary, or the last occurrence of the dinoflagellate cyst Areosphaeridium diktyoplokus. Particularly, a sequence stratigraphic concept of the E/O boundary enables a reasonable correlation of the upper boundary of the Priabonian with the base of the Rupelian (i.e., base Oligocene) as recognized in its type-area in Belgium. The acceptance of the position of the ’golden spike’ at Massignano as the top of the Priabonian Stage thus creates a new Priabonian/Rupelian boundary problem at the very time old uncertainties and controversies on the mutual delimitation of these stages are becoming resolved. Since only stage boundaries should serve to define chronostratigraphic units of higher rank, it is concluded that the IUGS Commission on Stratigraphy should re-evaluate the status of the Massignano section as the E/O boundary GSSP.

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