Paper No. 9
Presentation Time: 10:00 AM
NEW HIGH-PRECISION GEOCHRONOLOGY FROM THE LATE EOCENE OF NORTH AMERICA AND ITALY
SAHY, Diana1, FISCHER, Anne
2, TERRY Jr, Dennis O.
3, CONDON, Daniel
1 and KUIPER, Klaudia
2, (1)NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, United Kingdom, (2)Faculty of Earth and Life Sciences, Vrije Universiteit, 1085 De Boelelaan, Amsterdam, 1081 HV, Netherlands, (3)Earth and Environmental Science, Temple University, 326 Beury Hall, 1901 N. 13th St, Philadelphia, PA 19122, dihy@bgs.ac.uk
The Eocene – Oligocene transition was a time of rapid climate deterioration from global greenhouse to icehouse conditions, evidence of which is preserved in the form of stable isotope records and changes in fossil assemblages in both marine and continental settings. The availability of accurate and precise temporal constraints is essential for evaluating these data in terms of the possible causes, duration, rate, and scale of both climate change and biologic evolution. As part of the GTSnext project (www.gtsnext.eu), we are working on developing high precision U-Pb (zircon) and
40Ar/
39Ar (sanidine) geochronology of air fall tuffs, integrated with magnetostratigraphy, biostratigraphy, and astronomical tuning, in order to derive an improved geochronologic framework for the Late Eocene – Early Oligocene. This data set will facilitate enhanced integration of continental and marine records.
Several key sections from both marine and continental settings were selected for this project based on the availability of volcanic ash horizons and the availability and quality of published biostratigraphic and magnetostratigraphic records. 29 ash layers were sampled in the continental White River Group of North America at Flagstaff Rim near Casper, WY and Toadstool Geologic Park near Crawford, NE. Tephra layers from marine deposits were sampled in the Marche-Umbria basin along the Adriatic coast of central Italy, in the Massignano section (which contains the GSSP for the Eocene-Oligocene boundary), and the nearby Monte Cagnero section. In total, the selected sections cover an interval of about 5 Myr, from the top of chron C16n.2 to the base of C11n.
Here we present preliminary results of ID-TIMS U-Pb dating of zircons from 16 ash layers from both the USA and Italy and compare these with previously published radio isotopic and magnetostratigraphic data. Our results show some discrepancies between the U-Pb data and the magnetostratigraphy of the Flagstaff Rim section and indicate that some of the earlier 40Ar/39Ar studies from the White River Group were systematically too old by ~ 1 Myr.
