Paper No. 239-1
Presentation Time: 1:30 PM-5:30 PM
MICROFOSSIL MELTING BY THE EWING IMPACT
NUNES, Alice A.1, ABBOTT, Dallas H.2, and GLATZ, Christy A.2, (1) Environmental Biology, Barnard College, 3009 Broadway, New York, NY 10027, an224@columbia.edu, (2) Lamont-Doherty Earth Observatory, PO Box 1000, Palisades, NY 10964-8000

The Ewing Crater located in the abyssal equatorial Pacific struck the earth at 7-11 Ma in the early late Miocene. Cores located in the ejecta blanket of the Ewing crater contain tektites, impact spherules, and platy magnetite as well as microfossils. We first examined ocean cores to locate the possible zones associated with the Ewing Impact using visual cues such as sharp dark laminated layers. We measured the magnetic susceptibilities of the cores in close proximity to the crater site, believing that those having abnormally high susceptibilities were possibly impact layers. Samples were sieved into 150 and 63-micron fractions. Using a binocular light microscope, the samples were examined for evidence of an impact namely tektites, spherules, and platy magnetite. Particles were then examined under the scanning electron microscope. Various sponge spicule microfossils have been found that appear to be intermediate between tektites and sponges. The distal portions of these microfossil aggregates have the charactaristic tear-dropped ablated surface texture of tektites. Central zones of the particles are smooth with one half being more ablated than the other. Structures located on the less ablated sides of the fossil appear vascular where broken off. The usual sponge symmetrical or geometric shape was distorted and the individual sponge spicules bent backward. This suggests that tektites are not always formed from completely melted terrestrial substances ejected into the atmosphere under high temperatures and pressures. Partially melted siliceous and calcareous particles are also formed.

2002 Denver Annual Meeting (October 27-30, 2002)
Session No. 239
Impact Stratigraphy (Posters)
Colorado Convention Center: Exhibit Hall
1:30 PM-5:30 PM, Wednesday, October 30, 2002
 

© Copyright 2002 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.