Paper No. 5
Presentation Time: 9:50 AM
THE AGE OF THE AUSTRALASIAN IMPACT EVENT AND ITS RELATION TO EVENTS AT THE BRUNHES/MATUYAMA BOUNDARY
Tektites are natural glasses formed by melting of upper crustal materials during the hypervelocity impact of an extraterrestrial object. The Australasian strewnfield, covering at least one-tenth of the Earth's surface, is the largest and the youngest of four known tektite strewnfields. The stratigraphic proximity of the Australasian microtektite layers with the Brunhes/Matuyama boundary has prompted the hypothesis that large impacts may trigger geomagnetic reversals. As the Australasian microtektite preceded the Brunhes/Matuyama reversal by estimates of ~12 to 16 kyr, these results are inconsistent with simple geophysical models linking geomagnetic reversals with impact events. Recently, detailed paleomagnetic records from the Pacific and Atlantic Oceans consistently found a decrease in paleointensity approximately 15 kyr prior to the Brunhes/Matuyama transition. In some of these records, a directional excursion to nearly full normal polarity with a low paleointensity remains after demagnetization. The close temporal proximity of the pre-transition low (the so-called precursor) to the B/M transition raised questions about its relationship to the reversal itself as well as to an apparently unrelated event - the Australasian impact, that just occurred before the reversal. A through examination of the question hinges on how accurate one can define the temporal relationships among these events. In this study, we (1) present detailed paleomagnetic records from deep-sea cores through the Brunhes/Matuyama reversal interval in association with well-defined Australasian microtektite layers, (2) reassess the lock-in depth of post-depositional remanence acquisition based upon a compilation of eight deep-sea cores, and (3) test the impact-reversal hypothesis by examining the stratigraphic and temporal relation between the Australasian impact event and the precursor of the B/M reversal.
© Copyright 2003 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.