HR: 0800h
AN: PP51D-1357    [Abstracts]
TI: The Massignano Eocene-Oligocene golden spike section revisited
AU: * van Mourik, C A
EM: Caroline.vanMourik@geo.su.se
AF: Department of Geology and Geochemistry, Stockholm UNiversity, Stockholm, S-10691 Sweden
AU: Brinkhuis, H
EM: H.Brinkhuis@bio.uu.nl
AF: Laboratory of Palaeobotany and Palynology, Utrecht University, Budapetslaan 4, Utrecht, NL-3584 CD Netherlands
AB: In common practice, the Eocene/Oligocene (E/O) boundary is linked to the Oi-1 $\delta$ $^{18}$ O benthic isotope event, reflecting the oldest phase of major Antarctic glaciation, calibrated against magnetosubchron C13n. Yet, the IUGS-ratified, current E/O GSSP at the pelagic Massignano Quarry section, central Italy, occurs within the older magnetosubchron C13r, at metre 19 of the 23 m section. To promote further high-resolution stratigraphic and paleoecological studies at Massignano, and to extend the lower Oligocene record, the so-called Massicore was drilled about 110 m south of the stratotype section. By means of high-resolution organic-walled dinoflagellate cyst (dinocyst) analysis, in combination with biotite-rich horizons an almost perfect linear correlation between the core and the quarry was obtained, resulting in the establishment of the Massignano GSSP composite section, spanning from magnetosubchron16-2n to 12r (van Mourik and Brinkhuis, in press). The revised paleomagnetic ages of this interval (P$\ddot{a}$like et al., in prep) were used for a preliminary age model of the composite section. The paleoecological dinocysts proxies were plotted along this agemodel. A straightforward correlation of the (relative) Sea Surface Temperature (SST) curve to the 400 ky eccentricity curve of Laskar et al.'s (2004) was possible. In two intervals (5.60 to 10.50 m and 17 to 35 m) the correlation could be made to the 100 ky eccentricity curve (Laskar et al., 2004). The first astronomical timescale for the Massignano GSSP composite section could be composed, placing the GSSP (19 m) at age of 33.96 $\pm$ 0.05 Ma. The age of the onset of the Oi-1 event appears around 33.55 $\pm$ 0.01 Ma, and towards the top of the section the cold peaks in the SST get more and more pronounced. The cooler conditions are substantiated by the occurrence of restricted high latitude dinocyst species ({\it G. inflata} and {\it Sv. cooksoniae}) from 33.30 $\pm$ 0.01 Ma until the top of the section (van Mourik et al., in prep). Relying also on earlier studies, we demonstrate that the current E/O GSSP criterion, the local extinction of the tropical genus {\it Hantkenina} (planktonic foraminifera) represents an isolated event, not suitable for global correlation. Instead, we argue that selection of the Oi-1 event as E/O criterion, which is also related to the TA4.3/4.4 third order sequence boundary, and the last occurrence of the dinocyst {\it A. diktyoplokum}) would provide a much better basis for global correlation. Moreover, selection of this slightly younger Oi-1 event criterion would place the top of the classic Priabonian Stage back in the latest Eocene, and the base of the Rupelian Stage in the earliest Oligocene. However, since the correlative level is not represented by the surface (quarry) section, but only resides in the cored, not exposed, section at Massignano, a new GSSP site should be selected, for example in one of the other central Italian sections that does span C13n (van Mourik and Brinkhuis, in press).
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 3030 Micropaleontology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting