[meteorite-list] British Lower Eocene London Clay Tektites

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Thu, 24 May 2007 01:08:25 -0500
Message-ID: <006c01c79dc9$f189dd80$f54de146_at_ATARIENGINE>

Hi, Aubrey, List


Here is a photo of Australasian micro- and
mini- microtektites found in the Indian Ocean:
http://www.nio.org/projects/shamprasad/figure2%20.htm
Note the similaritity of shapes. These are slightly
(but not too much) larger than the London Clay
micros.

Here is a small photo of Eocene micromicrotektites
from the Chesapeake Bay Crater:
http://meteor.pwnet.org/img/impact_13.jpg
There is a clear resemblance to the
London Clay micros. Note the high
frequency of the amber-colored micros.

Photo of Chicxulub microtektites:
http://geophysics.ou.edu/impacts/chicxulubtektites.jpg
Note the surface degradation. These are "clean"
samples. Eventually, microtektites of this age are
altered into clay nodules and escape notice.

Paper (with photos) of possible (very) small
Devonian microtektites:
http://www.wanfangdata.com.cn/qikan/periodical.Articles/zgkx-ed/zgkx2000/0003/000309.htm
(The ones that were 100 to 200 micrometers
were sectioned and the surface SEM'ed; results
are shown in a table below the photo; scroll down.)

    First, microtektites degrade much faster than larger
tektites. By faster, however, I mean tens of millions of
years, though. These objects are remarkably "fresh"
looking. One asks why have they not degraded in 35
million years?

    Answering my own question, the high transparency
suggests a very high silica content. This would account
for their degree of preservation. The black appearance
that most of us think of as "typical" of tektites is the
result of high iron content. I gather that they have been
securely tucked away in the London Clay for all that
time and not exposed nor over-wetted.

    I'm tempted to say that the shapes alone are almost
sufficient to identify them as tektites; it looks like an
illustration of Baker's famous paper on tektites form.
However, what's needed is a) a bulk composition by
SEM, and b) a determination of water content by
infrared spectroscopy (which is non-destructive and
much more accurate than destructive extraction; polish
off two surface windows and scope through the clean
interior).

    Even after 35 million years, a tektite glass is going to
be distinctly drier than ANY volcanic glass and most
impact glasses. I was frankly amazed that the finder
would dismiss these as volcanic in origin. They look
nothing like volcanic microspherules. If someone is
in a more expensive mood, another good test would
be the flourine-boron ratios, which serves as a kind of
"thermometer" for the temperature of formation. This
would easily demonstrate that they were non-volcanic.
(Personally, I find the "volcanic" suggestion outlandish.)

    If I had to vote without tests, I'd vote "yes" to their
being a tektite glass, but just as with mysterious iron
objects that come crashing through one's roof, a test
is really required. Since there is an ongoing controversy
about a proposed multi-ringed impact feature in the North
Sea (or is it only a salt basin?), with paper in Nature, etc.,
http://bromans.blogspot.com/2007/03/great-north-sea-impact-crater-vs-salt.html
maybe the pro-Impactisitas would pay for some testing?
Nothing like a handful of tektites to bolster your impact!


Sterling K. Webb
-------------------------------------------------------------------
----- Original Message -----
From: Aubrey Whymark
To: meteorite list ; britishandirishmeteoritesociety at yahoogroups.com
Sent: Wednesday, May 23, 2007 7:46 PM
Subject: [meteorite-list] British Lower Eocene London Clay Tektites


Hi

I just wanted to draw attention to these possible microtektites from the
Lower Eocene London Clay in England. The finder, Michael Daniels, has very
kindly provided a number of images and some notes.

http://www.tektites.co.uk/13.html

What do people think of these possible microtektites? Are they comparable
with other microtektites found? Interestingly some of the microtektites seem
to have extra 'spikey' features (see photos) - is this normal?

Thanks, Aubrey
www.tektites.co.uk

P.S. out of contact from 26th May for a bit.
Received on Thu 24 May 2007 02:08:25 AM PDT