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Re: Tektite Question
larrydavison schrieb:
> With all the recent discussion of asteroids hitting the earth. I have
>
> this question for the list.
> Has there been any research done with the idea that Tektites were
> formed
> when a large asteroid hit the earth? As there appears to be only 4
> known
> major sites with tektites.
> New studies that I have read about indicate additional sites with
> tektites with varying ages from 5 thousand to 65 million.
> Because we have never seen the cause, are they the effect?
> Can this be a logical assumption? Thanks for your attention.
>
> Larry D.
Hello Larry, hello List Members,
I’d say, yes - at least Mr Hartung thinks so. In his paper Australasian
Tektite Source Crater? Tonle Sap, Cambodia (J.B. Hartung, Inst.
Geochem., Univ. Vienna, A-1010 Vienna, Austria / Meteoritics 25-4, 1990,
pp. 369-370), you find among other details:
1) Australasian tektites may be grouped into three classes: flanged
buttons, splash forms and Muong Nong. This sequence of classes
correlates with decreasing distance from the source crater.
2) Ideally, the source crater should exist within the strewnfield of
Muong Nong Tektites. Muong Nong tektites have been found predominately
in the countries of Cambodia, Laos, Thailand and Viet Nam.
3) Tonle Sap (Grand Lake) is a relatively long lake (length : width =
4:1) located in Cambodia at 13° N, 104.5° E, well within the Muong Nong
tektite strewnfield, and is, therefore, at the right place.
4) Based on comparisons of the Australasian tektite strewnfield with
those related to the Ries (24 km) and Bosumtwi (10 km) craters, the
Australasian tektite source crater should have dimensions near 100 km.
Tonle Sap is 100 km long and up to 35 km wide, ... . Tonle Sap is the
right size.
5) About two thirds of the way along its length Tonle Sap necks down to
a width of 15 km, thereby dividing the lake in two parts. Laboratory
experiments involving impacts at small angles above the horizontal
produce elongated, segmented or double craters. If the impact that
produced Australasian tektites was highly oblique and if some allowance
is made for crater filling, then Tonle Sap is the right shape.
6) A great circle containing the long axis of the lake passes through
that part of Australia where the most flanged button tektites have been
found. Tonle Sap has the right orientation.
7) The mere presence of Tonle Sap indicates it was formed only recently,
on a geologic time scale. The 1 Ma age of Australian tektites is also
recent, on the same scale. Tonle Sap was formed at approximately the
right time.
8) Finally Tonle Sap is a rare lake, if not unique. Other large lakes
have readily identifiable reasons for being; glacier withdrawal,
tectonic motion or arid-climate depressions. Tonle Sap is not involved
with any of these processes, so a rare event may be called upon to
explain its presence. Why not impact?
9) I conclude that the Australasian tektites and their strewn field
resulted from the impact of an object a few km in diameter moving from
the NW to the SE at a very low angle of incidence with respect to the
Earth's surface. The object contacted the Earth near what is now the
northwest end of Tonle Sap.
Regards, Bernd
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