no slide title · wuhan – feb 2008 – unsolved problems in rock mechanics and rock engineering 3...
TRANSCRIPT
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Archeopteryx lithographica
and
An Open-Cast Coal Mine
A bit of a break here: two unusual consulting assignments…
small and large…both related to structural geology
John A Hudson
Lecture 7
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering
A fossil of
Archeopteryx
lithographica
in the Natural
History
Museum,
London, UK
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Tail feather
Approximately 0.5 m across
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 3
The Archeopteryx lithographica fossil is of a
transitional species between dinosaurs and birds.
The generic name, Archeopteryx, is developed from
the Greek words ‘ancient’ and ‘wing’; the specific
name, lithographica, alludes to the fact that the
fossil was found in the Solnhofen limestone in
Bavaria, this rock having been used for printing
purposes.
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Imperial
College
Geological
Museum/
Natural History
Museum
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering
Archeopteryx lithographica: a bird-dinosaur
Natural History Museum
Some dinosaurs were large…
…but Archeopteryx lithographica
was only the size of a chicken
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 6
The fossil was purchased in Victorian times by the Museum in
London, UK, because, as noted by Charig et al. (1986), it is “an
obvious and comprehensible example of organic evolution”.
However, in the 1980s, the authenticity of the fossil was
challenged by N.C. Wickramasinghe and F. Hoyle on the basis
that the fossil had been forged in the nineteenth century by
impressing a modern day feather into a layer of fresh plaster
spread over part of the fossil specimen.
Because dental instruments
had been used to expose
the fossil, it does have an
appearance somewhat of a
plaster model.
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Solenhofen limestone used for
lithographic printing
The rock formation, and hence
the fossil, is of Late Jurassic
age, i.e., around 150 million
years old.
The rock has an extremely fine
grain.
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A Brazilian test on
Solenhofen limestone,
the central crack
illustrating
the rock’s fine grain
This accusation had some credibility because
a) both Wickramasinghe and Hoyle were well known scientists and
b) the specimen does superficially look as though it is made of dental
plaster because of the fine grained uniform nature of the
limestone.
Indeed, the Solnhofen limestone is used as a ‘type’ rock for rock
mechanics testing because of its uniformity and fine grain.
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 9
In addition to the Museum’s own investigations, I was asked to study
the specimen from a rock mechanics point of view.
Did a part of the fossil appear to have been manufactured or not?
This Archeopteryx lithographica fossil is one of the most important in
the world and its authenticity is critically important for evolutionary
studies.
In particular, was the
tail feather impression
artificial? Had it been
created by pressing a
modern feather into a
coating of plaster on
top of a real fossil?
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 10
Rock mechanics approach:
Obtain a core and study longitudinal
slices through the core…
Museum’s response:
Dr Hudson! You don’t understand
paleontological protocol!
Angela Milner
Dr Hudson: Please could
you prove that the rock is
genuine.
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Crack traversing the feather barbs
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 12
Calcite crystals have grown in the fracture.
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A Victorian forger could not have artificially created such a
persuasive mineralised infill of the fracture.
In addition, as above, the en echelon nature of the fracture
formation is illustrated with a zone of staining around the
overlap, which is a phenomenon often observed on the larger
outcrop scale.
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The Museum also justified the fossil’s authenticity by “exactly
matching hairline cracks and dendrites on the feathered areas of
the opposing slabs, which show the absence of the artificial
cement layer into which modern feathers could have been pressed
by a forger”.
This conclusion is further supported by the fracture mineralisation.
This example is an unusual application of rock fracturing
knowledge, but one that once again demonstrates the value of
understanding the formation and characteristics of rock fractures.
Archeopteryx lithographica
A genuine fossil!
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Opencast Coal Mine, UK
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The
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Trucks used on site
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The
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The
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 19
Question: Our trucks are
using more fuel than we
expected, and much more
fuel than at a similar open-
cast site a few kilometres
away.
Please tell us why this is.
Is it our fault, or something
to do with the ground?
At a similar site 3 km
away, we didn’t have this
problem.
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 20 Listric faulting
Coal seam, low friction
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The
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The
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It became apparent that the
near surface strata had
been disturbed by glacial
action.
This glacial action is
somewhat variable as the
glacier travels over irregular
ground: the near surface
ground at this site had been
disturbed…
…whereas that at the
adjacent site had not.
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 25
Prof John Cosgrove explaining the effects of glacial
disturbance, e.g. the existence of small periclines at the site.
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The
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Wuhan – Feb 2008 – Unsolved Problems in Rock Mechanics and Rock Engineering 29
So we weren’t able to save money on the use of the truck
fuel…
…but we were able to show why the near surface soft rock
conditions at this site were different to those at another site a
few kilometres awayi.e. because of localised glacial action.
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End of Lecture 7
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