[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Antarctica - Part 2a

Smithsonian Contributions to the Earth Sciences, Number 23

Catalog of Antarctic Meteorites, 1977-1978

Field Occurrences and Collecting Procedures

W.A. Cassidy

Historical Background

In 1969, a Japanese glaciological team was establishing a triangulation
chain on an ice field adjacent to the Yamato Mountains in order to
measure local flow in the Antarctic ice sheet. During this procedure,
one of their number, Renji Naruse, picked up a meteorite. Visual
searching in the area quickly produced eight more specimens, all lying
on the ice (Yoshida, et al., 1971), which were returned to Japan for
examination. In 1973, Makoto and Masako Shima described four of these
specimens at the Meteoritical Society meeting in Davos, Switzerland
(Shima and Shima, 1973). I attended the meeting out of a general
curiosity about new meteorites and an interest in the exotic locale in
which these had been discovered. During the oral presentation I suddenly
realized Shima was describing four distinct subclasses of stony
meteorites that had been found within the remarkably small area of 50
square kilometers. Normally, meteorite specimens encountered in such
concentrations result from a shower of fragments from the same parent
and, therefore, are all of one subclass; it was startling to find as
many as four types of stony meteorite reported within such a restricted
area.
It seemed necessary to postulate some mechanism of concentration to
explain how this could have occurred. The obvious suggestion, made by
Yoshida et al. (1971), was that the concentration mechanism has
something to do with Antarctic ice: Meteorites falling in Antarctica
fall onto a moving medium and there might be a potential in this for
concentrating specimens from different falls. Whatever the mechanism, it
did not seem likely that in a continent as large as Antarctica such an
occurrence would be unique.
I discussed these matters with Professor Takesi Nagata, Director of the
National Institute of Polar Research, Tokyo, during one of his stays as
a visiting professor in our department at the University of Pittsburgh.
As a result of these discussions, he directed the 1973-74 Japanese field
party to make additional meteorite searches at the Yamato Mountains
site. These produced twelve additional specimens (Shiraishi, et al.,
1976). Thus encouraged, Japanese field parties found 663 during austral
summer 1974-75 (Yanai, 1976), and 307 in 1975-76 (Matsumoto, 1978). The
total Japanese collection as of this writing, midway through 1979, now
numbers an almost incredible 991 meteorite specimens found within an
area of 300-400 square kilometers at Yamato Mountains.
My initial proposal to the Division of Polar Programs, National Science
Foundation, submitted in May 1974, was to search for meteorites during
field season 1975-76 on ice patches accessible by helicopter from
McMurdo Station. It was not funded, but I was encouraged to resubmit it
for the following year. In the proposal, I pointed out the anomalously
high concentration of meteorites found lying on the ice at the Yamato
Mountains and suggested that other areas on the Antarctic ice sheet
should bear similar numbers of meteorites. These locations would
probably be ones where ablation, or wasting away of the ice surface, is
occurring, while the ice being lost is constantly being replaced by
newer ice arriving from the interior of the continent.
My proposal was funded for field season 1976-77. For several years,
Japan had enjoyed cooperative research programs with the United States
and New Zealand, working out of McMurdo Station and Scott Base,
respectively, both bases being located on Ross Island. Ajoint U.S.-Japan
field search for meteorites in areas accessible by helicopter from
McMurdo Base was established. It was agreed that all specimens found
would be cut in half and distributed equally between the United States
and Japan. The first year's field party consisted of Keizo Yanai of the
National Institute for Polar Research, Tokyo, Edward Olsen of the Field
Museum of Natural History, Chicago, and myself.
Yanai had a valuable store of previous Antarctic experience and had been
heavily involved in the Yamato Mountains meteorite recoveries. Olsen had
earlier been in Greenland. Therefore, I was the only member of the group
without previous experience of Arctic or Antarctic conditions. Our plan
was to establish a series of field camps, beginning with one or two at
low elevations under relatively mild climatic conditions, from which we
could make forays on foot to search for meteorites. We planned to work
up to more difficult sites gradually, mainly so that I could become
accustomed to conditions of extreme cold. Our first campsite, therefore,
was at the lower end of the Wright Upper Glacier, a valley glacier that
carries ice directly off the Antarctic ice plateau. The glacier is fed
principally by ice coming over the Airdevronsix Icefall, but it also
receives a small increment from a minor ice mass between Mt. Fleming and
Mt. Baldr.


Best regards,

Bernd

----------
Archives located at:
http://www.meteoritecentral.com/list_best.html

For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------