Saudi Aramco World: May/June 2014 - page 21

May/June 2014
n the town hall of
Ounianga Kebir,
I meet Aahmat
Moussa Thozi, the
chef de canton.
scientists are not the only ones
interested in history. Through
a translator, Aahmat tells me
the legend of his tribe’s origins.
“There was a very ancient
population that lived next to
this lake. We believe that our
grandfather came out of the
lake. The people who came
out of the lake are linked to
that lake. These localities were
very beautiful, with palms,
dates and a glorious lake.
There are 15 clans in Ouni-
anga. That is how it started.”
Are there cultural clues
here to geological history? It
would take a geo-mythologi-
cal examination
to know for
sure. What exactly does “an-
cient” mean in a land where,
over the seven million years
In a cooling chamber in the basement of the Uni-
versity of Köln’s Institute of Geology and Miner-
alogy, paleoclimatologist Jens Karls searches for
a couple of one-meter sections from the 16-me-
ter (52½') 2010 Lake Yoan “long core.”
As he searches, I spot other labels: Lake
Tivuti, Indonesia; Lake El’gygytgyn, Siberia;
Balkans; Spain; Greenland and Antarctica. It is
a geological tour of world history, all encased in
white plastic tubes.
Karls pulls a Lake Yoan core from its wrap-
ping. I see immediately that this geo-snapshot
of African subsoil is no less beautiful than the
Chadian Sahara and the Lakes of Ounianga
themselves. With the naked eye, I can easily
see and count layers of sediment.
How old is this one? I ask.
“8500 to 10,000 years,” says Karls.
The sample we’re looking at is
actually only half the cylindrical core,
which was sliced lengthwise. This, he
explains, is the “archive half,” used
only for nondestructive measurements
that determine elemental compositions,
magnetism, density, color spectra and
more. It’s tedious work: Some measure-
ments may require 32 hours for each of
the core’s one-meter sections.
“Boring,” says Karls, obviously rel-
ishing all of it and seeming unaware of
his pun in English.
The other half of the core is called
the “working half.” There, says Karls,
“we take the samples for geochemistry,
grain-size pollen analysis and so on.”
Thin sections of the working core
half are cut out with a wire saw, hardened
in epoxy resin and then polished down to a
thickness of 30 micrometers (0.0012"). Under
a microscope, “a most robust age model” is
determined that pinpoints not only year-to-year
changes but “even differences between the
seasons,” he says.
So precise are the analytical tools, he says,
that Karls can look at a single grain of sand in
the lake sediment and, from its surface alone,
determine if it is “from the surrounding sand-
stone hills or if it was transported to the lake
by wind, rivers or mixed transport from some-
where else.”
“We have found the book,” says Karls about
the Ounianga “long core.” “We just have to
translate everything into human language.”
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