2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 43-2
Presentation Time: 9:00 AM-6:00 PM

CONSTRAINING THE AGE OF THE MATUYAMA-BRUNHES REVERSAL USING INTERCALIBRATED 40AR/39AR AND ASTRONOMICAL AGES OF THE BISHOP TUFF AND AUSTRALASIAN TEKTITE

RIVERA, Tiffany A., Isotope Geology Lab, Boise State University, 1910 University Dr, Boise, ID 83725, tiffanyarivera@gmail.com, STOREY, Michael, QuadLab, ENSPAC 11.1, Roskilde University, Universitetsvej 1, PO Box 260, Roskilde, 4000, Denmark, PALIKE, Heiko, National Oceanography Center, Southampton, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, England, and ZEEDEN, Christian, Utrecht University, Budapestlaan 4, Utrecht, 3584 CD, Netherlands

Recent high-resolution δ18O records from North Atlantic (I)ODP cores, with reliable paleomagnetic signals, have placed the mean age of the Matuyama-Brunhes (MB) geomagnetic polarity reversal ca. 8 ka younger than previous estimates when correlated to ice-volume age models (Channell et al., 2010). However, this age offset is not synchronous with a new astronomically intercalibrated 40Ar/39Ar age for the normal-polarity Quaternary Bishop Tuff, stratigraphically above the MB boundary by approximately 15 ka. In order to best constrain the age of the boundary, an astronomically calibrated radio-isotopic age is needed on a datable unit from the reversed-polarity side of the MB boundary. The Australasian tektite is a suitable unit from the Matuyama chron for dating the MB boundary because the positions of microtektite layers relative to the MB boundary have been documented in (I)ODP and other drill cores. Previous analyses of the drill cores have estimated the duration between the tektite layer and the MB boundary between 8 and 12 ka, and an astronomical age has been assigned to this unit (Horng et al., 2002). Using a Nu Instruments Noblesse multi-collector noble gas mass spectrometer, we present 40Ar/39Ar step-heating and fusion age data, relative to the astronomically calibrated Fish Canyon sanidine, on the Australasian tektite, and have updated the tuning model for this layer using the La2004 orbital solutions. Using 40Ar/39Ar ages for these two units that bracket the boundary along with sedimentation rates determined through drill core analysis, we approach the MB boundary from both sides to arrive at a boundary age that is consistent with independent astronomical ages proposed for the polarity transition. This novel approach provides a best-fit age for the MB boundary that incorporates radio-isotopic dating, astrochronologies, and sedimentation rates.

The research leading to these results has received funding from the European Community's Seventh Framework Programme [FP7/2007-2013] under grant agreement no. 215458.

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 43--Booth# 297
EARTHTIME Geochronology: Improving Age Interpretations through Integration and Intercalibration (Posters)
Minneapolis Convention Center: Hall C
9:00 AM-6:00 PM, Sunday, 9 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 127

© Copyright 2011 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.