[meteorite-list] Tektite QUESTION

From: Keith <littlejo_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:28 2004
Message-ID: <Pine.SOL.4.33.0209201218220.22358-100000_at_katie.vnet.net>

First, a good on-line article is:

Wang, J., Q. Zhao, X. Chen, R. Wang, and P. Wang (2000)
Age estimation of the mid-Pleistocene microtektite event
in the South China Sea: A case showing the complexity of
the sea-land Correlation. Chinese Science Bulletin.
Vol. 45 No. 24, pp. 2277-2280. (December 2000)

http://www.scichina.com/ky/0024/ky2277.pdf

It can be obtained using the above URL.

On Fri, 20 Sep 2002 09:15:27 +0200
in [meteorite-list] Tektite QUESTION,
Bernd Pauli HD wrote:
>Michael Blood wrote:
>>I am sure I have it in more than one text SOMEWHERE,
>>but can anyone tell me quick short the estimated age
>>of the Austro-asian strewn field Tektites?
>>
>>"Sterling K. Webb" wrote:
>>
>>The figure given for the age of the Australasian field
>>has been estimated at 770,000 to 780,000 years for the
>>past 30 or 40 years; however, somewhere on a posting
>>on CCNET which I can no longer find (&%$!), attempts
>>to refine the precision of those isotopic ages came
>>up with a figure about 10% to 12% older, more like
>>850,000 to 900,000 years, which made sense as there
>>have always been a few australites with anomalous ages
>>(about 10% older). Maybe we should just call it
>>somewhere short of a million.
>
>Hello Michael and List,
>BARNES V.E. (1990) Tektite research 1936-1990
>(Meteoritics 25-3, 1990, 149-159).
>
>p. 155: Ages of tektites
>
>Lovering et al. (1972) determined that the stratigraphic
>age of australites is between 24 000 and 16 000 years,
>which is at considerable variance with the 700 000-year
>age found for australites and the rest of the tektites in
>the Australasian strewnfield by fission-track
>(Fleischer and Price, 1964) and potassium-argon (K/Ar)
>dating ...text deleted...

The stratigraphic age assigned by Lovering et al. (1972)
was found to be found badly flawed by Shoemaker and
Uhlherr (1999). Lovering et al. (1972) studied the
occurrence australites within the the Lake Torrens Plain
in South Australia. They argued on the basis of what
they considered to be the excellent state of preservation
of the tektites found in the Lake Torrens Formation; the
nearest Pleistocene outcrops being 15-25 km away; and
their occurrence in wind blown sand that the tektites
are in situ and, thus, contemporaneous with the Lake
Torrens Formation. Since the Lake Torrens Formation has
been dated at 16,000 to 24,000 BP, Lovering et al. (1972)
argued that these tektites fell at some time around
16,000 to 24,000 BP.

Shoemaker and Uhlherr (1999) reinvestigated the tektites
from the Lake Torrens Formation. He found that the
tektites in the Lake Torrens Formation did not come from
wind-blown sands but rather alluvial sands. Also, he
found the tektites came from older Pleistocene deposits,
Hanson Plain Sand, that locally underlies the Lake
Torrens Formation. Contrary, to what Lovering et al.
(1972) concluded, they found a plausible local source
for the tektites and evidence that the tektites found in
the Lake Torrens Formation were reworked from the Hanson
Plain Sand. As a result, Shoemaker and Uhlherr (1999)
disputed the age assigned by Lovering et al. (1972) to
the tektites found in the Lake Torrens Formation since
they found clear evidence that these tektites were not
in situ but rather reworked from older Pleistocene
sediments.

Gill (1965) argued for a Holocene age for australites as
being only as old as 7,300 BP. In the Port Campbell area
of Victoria, Australia, Gill (1965) recovered 14
australite samples within a soil profile lying above a
hardpan soil zone. Wood and charcoal from the hardpan
dated to about 7,300 BP. Another australite was found
in a hardpan dated to about 5,700 BP. Unfortunately,
Gill (1965) completely disregards the fact that soils
are very dynamic systems and are churned by a number
of processes as discussed by Johnson (1990) and Johnson
et al. (1987). Within soils, materials of vastly
differing ages, e.g. wood, charcoal, Aboriginal
artifacts, and tektites, can be and are typically and
randomly mixed together. The tektites simply were present
in the soils before the formation of the hardpans and the
age of the hardpans provide absolutely no evidence about
the age of the tektites. the charcoal and other material
dated were simply mixed into the soil by pedoturbation
and lack any association with the australites and only
date the hardpans, if anything at all.

Gill (1965) also argued that the tektites were in situ
because they are the " include the best preserved
tektites in the world." However, Fudali (1993) showed
that Gill (1965) was greatly mistaken about the degree
of preservation about these tektites. In fact, contrary
to what Gill (1965) argued, Fudali (1993) demonstrated
tektites exhibit significant signs of weathering and
transport. Fudali (1993) also found that the specimens
that Gill (1965) described constitute only a very small
fraction of the tektites to be found. Thus, Gill (1965)
came to a badly flawed conclusion about them being in
situ because he failed to realize he had studied a
sample badly biased towards the more showy "perfect
specimens" and unrepresentative of the state of
preservation of local tektites in general. Finally,
Fudali (1993) found that these australites in reality
were not in situ the australites and appeared to be
coming from sandy sediments older than and lying
below the hardpans.

If a person looks into the published literature, the
age estimates offered by Gill (1965) and Lovering et
al. (1972) have been very effectively discredited by
Fudali (1993) and by Shoemaker and Uhlherr (1999).

References Cited:

Fudali, R. F., (1993) stratigraphic age of australites
revisited. Meteoritics. vol. 28, no. 1, pp. 114-119.

Gill, E. D. (1965) Quaternary geology, radiocarbon
datings, and the age of australites. In: International
studies on the quaternary-inqua cong., 7th, boulder,
colorado, pp. 415-432. Special Paper no. 84, Geological
Society of America, Boulder, CO.

Lovering, J. F., B. Mason, G. E. Williams, and D. H.
McColl (1972) Stratigraphical evidence for the
terrestrial age of australites. Journal of the Geological
Society of Australia. vol. 18, Part 4, no. 4,
pp. 409-418.

Johnson, D. L. (1990) Biomantle evolution and the
redistribution of earth materials and artifacts. Soil
Science. vol. 149, no. 2, pp. 84-102.

Johnson, D. L., S. D. Watson, D. N., Johnson, and R. J.
Schaetze (1987) Proisotropic and proanisotropic processes
of pedoturbation. Soil Science. vol. 143, no. 4,
pp. 278-292.

Shoemaker, E. N., and H. R. Uhlherr (1999) Stratigraphic
relations of australites in the Port Campbell Embayment,
Victoria. Meteoritics and Planetary Science. vol. 34,
no. 3, pp. 369-384.

Another Reference

Fudali, R. F., A. J. Miller, And A. W. R. Bevan (1991)
Australites from northern Australia. Meteoritics.
vol. 26, no. 2, pp. 153-155.

Have Fun

Keith Littleton
New Orleans, LA
Received on Fri 20 Sep 2002 12:36:36 PM PDT