ABSTRACT: In common practice, the Eocene/Oligocene (E/O) boundary is linked to the Oi-1 d18O benthic isotope event, reflecting the oldest phase of major Antarctic glaciation, calibrated against magnetosubchron C13n. Yet, the IUGS-ratified, current E/O Global Stratigraphic Section and Point (GSSP) at the pelagic Massignano quarry section, central Italy, occurs within the older magnetosubchron C13r. To extend the Massignano record further into the early Oligocene, to include the critical C13n episode missing in the surface section, a core was drilled in the direct vicinity of the quarry section. First correlations between the core and the quarry section have recently been proposed. In this paper, we use high-resolution organic-walled dinoflagellate cyst (dinocyst) analysis to significantly improve correlation between the two sections. In addition, we build on earlier studies, and demonstrate that the current E/O GSSP criterion, which is based on the local extinction of the tropical planktonic foraminifera genus Hantkenina represents an isolated event that is not suitable for global correlation. Instead, we argue that selection of the Oi-1 event be the main criterion for the determinating the E/O boundary, and that this provides a much better basis for global correlation, Moreover, the Oi-1 is also related to the TA4.3/4.4 third order sequence boundary and the last occurrence of the dinocyst Areosphaeridium diktyoplokum. Selection of this slightly younger criterion would place the upper boundary of the classic Priabonian Stage back in the latest Eocene, and the base of the Rupelian Stage in the earliest Oligocene. Since the proposed correlative Oi-1 event level is not represented in the surface (quarry) section, but only resides in the cored section at Massignano, a new GSSP site should be selected, for example in one of the other central Italian sections that does span C13n.
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