surely the tablecloth is more appropriately named an oversized 'nappe-kin'.
I think the deep allochthonous salt in the Gulf of Mexico would resonate
under the name of 'deep allochthonous salt siesta' or perhaps 'deep
allochthonous period of post-prandial rest'..
-----Original Message-----
From: Tectonics & structural geology discussion list
[mailto:[log in to unmask]]On Behalf Of Peel, Frank FJ
Sent: 10 March 2004 08:05
To: [log in to unmask]
Subject: Salt nappes
Colleagues,
Looks like we have a good answer to Mallickarjun Joshi's original question,
and the consensus is that we can continue to use the word nappe for a big
allochthonous sheet, especially in France, with some reservations (or for a
table cloth in a restaurant in France, another circumstance where it's good
to have a reservation).
It also looks as though the oil company useage of "salt nappe" as a generic
word for giant allochthonous salt sheets is ok by Olivier Merle's definition
(but someone will have to define the word "giant").
In that case, it's probably a good time to go ahead and give a name to a
deep allochthonous salt nappe in offshore Louisiana, which I've been working
on intermittently for a couple of years. It appears that the frontal 15-30km
(at least) of the deep salt there is not the autochthonous Louann, but is
emplaced to the south over much younger sediments. It's been lumbering
under different names like "the frontal allochthon", " the salt mass
formerly known as Louann", "the allochthonous deep salt" or "the deep thing
that looks a bit like the younger Sigsbee salt nappe".
So, anyone got a good name suggestion? "Afternoon Nappe" has already been
used....
Cheers
Frank Peel
Principal Structural Geologist
BHP Billiton Petroleum
From: Matsen Broothaers
Subject: Re: nappe
Hi all,
In Olivier Merle's book "Emplacement mechanisms of nappes and thrust sheets"
the term nappe or thrust sheet is presented "to describe huge displacements
(several tens of kilometres) on a surface close to the horizontal".
Furthermore, "the word 'nappe' is of French origin meaning tablecloth and
reflects the three-dimensional form of these geological structures which
overlay a large surface whilst having a relatively moderate thickness".
Hence, no particular geometry (recumbent folds) is implied; the displacement
or allochthony is the important factor. For the recumbent folds the term
"fold-nappe" is used, as also presented in the discussion in a Geological
Society Special Publication (McClay & Price 1981). They use the term "thrust
nappe" to denote " an allochthonous tectonic sheet which has moved along a
thrust fault".
Matsen Broothaers
<http://www.kuleuven.ac.be/geology/hsg/SG&T>
EOM
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