[meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA 2828

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 7 Jan 2007 01:43:46 -0600
Message-ID: <00f801c7322f$90c50070$b421e146_at_ATARIENGINE>

Hi,

    This is clearly a case where the terminology
has not caught up with what's being described.
There are many ways in which a Meteorite can
age over a geologically significant time period,
or a very short time, for that matter.
    The term "fossil" not only applies to ancient
materials altered in composition, but to situations
where the original materials have been completely
replaced by other minerals which are deposited
in their place, preserving the form, but not the
substance, of the original.
    It's my impression that the very oldest "fossil"
meteorites, those from Sweden that date back
380,000,000 to 410,000,000 years ago, are largely
"replacement" materials.
    Irons are a completely different case. No matter
how ancient the shale, it is the original material, now
completely oxidized, but while the iron atoms are
those of the original object, terrestrialization causes
their original form to be completely lost.
    In a shorter run, the minerals of a stone meteorite
are altered to different minerals while retaining their
original form, and often the agent is water, as was
apparently the case in these much-discussed NWA's.
    Has anyone produced an estimated terrestrial age
for them? (I looked at some of the references but
didn't see any estimates or determinations.) Since
the Sahara was wet until the end of the recent Ice
Age, they need not be particularly ancient.
    Talking about terminology always sounds like
quibbling (sorry). Part of the problem is that the
recovered meteorites that we know about are the
ones lucky enough to land softly in a nice desert
or dry lake or to be found soon enough that they
haven't rotted away, and they DO rot away very
quickly. For example, Iowa is much wetter than
Kansas. Iowa has ONE chondrite that's a Find
(not a Fall); Kansas has nearly 120. (OK, having
Nininger helps some...)
    We were talking a few weeks ago about Tagish
Lake, that is, the ones that got away and have been
underwater for 5 years. I bet they're VERY altered
and terrestrialized by now, unrecognizable sludge,
but you could hardly call them "paleo-meteorites"!
    So, we're talking about meteorites that may be
very ancient or may not be particularly ancient at
all, that may be almost totally replaced, or that may
be almost totally altered but not replaced at all,
that may retain their original forms, or that may
be nothing but a pile of red dirt.
    It doesn't sound to me like a single term applies
reasonably to all these cases. On the basis of how
the terms are used in the other sciences, I don't
see how you could call anything a "fossil" unless
it retains (much of) its original form, and it seems
to me that "altered" should be a milder term than
"terrestrialized," but from what you say it's the other
way around; a thing can be "altered" a little or a lot,
but "terrestrialized" implies a transformation.
    "Paleo-" corresponds to no particular scale of
age, the term being used freely in hundreds of age-
differing contexts, and indeed, age may be irrelevant
to the strange condition of a meteorite that's in the
process of disappearing into the inhospitable and
very hostile environment of Earth (not at all like a
nice clean vacuum where the Sun always shines
and a rock can bask in its rays for all of its days,
and it never rains, not for billions of years).


Sterling K. Webb
----------------------------------------------------------------
----- Original Message -----
From: "Mr EMan" <mstreman53 at yahoo.com>
To: "David Weir" <dgweir at earthlink.net>; "Greg Hupe"
<gmhupe at tampabay.rr.com>
Cc: <Meteorite-list at meteoritecentral.com>
Sent: Saturday, January 06, 2007 11:46 PM
Subject: Re: [meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA
2828


> Under this NomCom guideline NWA2828 isn't "relict" as
> it is hardly altered and should be referred to as a
> paleo meteorite. (Note:If this gets too drawn out all
> meteoritic material is paleo as most is 4.5 billion
> years old). However, paleo is a best choice of the
> three proposed terms.
>
> My take on the three options:
>
> Relict: in petrology and geology is used to describe
> the occurrence of traces of original material after
> alteration. e.g. Serpentine is the hydrated
> alteration product of olivine and the presence of
> olivine or peridot within serpentine would be referred
> to as "relict olivine" etc. Lignite within a coal seam
> is relict lignite. NWA2828 is hardly relict under this
> definition and the NomCom guidelines. However, Relict
> is a valid incorporation of the concept into
> meteorites. Note that Relict is consistent with the
> almost complete alteration to secondary minerals.
> Where "Fossil" may include replacement of the original
> mineral. This is a subtle but important distinction.
>
> Fossil: (Greek Dug or to Dig) Obviously evolved this
> term is in wide use but rarely specified. It is
> usually descriptive of any ancient "organically"
> produced artifact; Trace, imprint, hard or soft
> tissue, premineralized, mineralized segment,
> mummified-- in some fashion altered from its original
> composition or state. By convention and to which
> source one subscribes,a fossil must be older than
> 20,000 OR 2 million years, cannot be derived from a
> living species, nor produced artificially .
> (AFAIRecall). Charcoal from the wildfire caused by
> Canyon Diablo can't be fossil but is paleo. Omitting
> the organically derived stipulation "Fossil" has
> been applied for example, to describe meteorites which
> were found in Ordovician aged sediments where the
> meteorites had been completely altered. It is also
> loosely used to describe ancient geological processes
> NWA2828 doesn't meet the criteria for being fossil.
>
> Paleo: denotes "ancient" and is used to describe
> events or things that are prehistoric--prehistory as
> in what that was not recorded: also to describe a
> process, condition or state occurring before the
> present Paleosoil, paleoatmosphere, paleoclimate, etc.
> The Winona Meteorite has been called paleo and was
> associated with a paleo settlement. Under strict
> reference Wolf Creek, Canyon Diablo, Winona, Lake
> Murray -- all would be paleo meteorites, as would
> anything derived from a prehistoric event as would
> tektites however that distinction need not always be
> applied.
>
> By elimination and like it or not PALEO is a best fit
> for NWA2828. As with any science, this represents the
> discovery of yet another distinction that we need a
> new category for. Both "fossilized" and "relict" seem
> to be subsets of the term "paleo".
>
> Eman
>
>
> --- David Weir <dgweir at earthlink.net> wrote:
>
>>
>> Yea, "fossil" may be accurate or maybe not, but why
>> not use the broader
>> terminology as designated by NomCom in their latest
>> revision in which
>> this new category is proposed?
>>
>> Read it here in section 1.2(c) Relict meteorites:
>>
>>
> http://www.meteoriticalsociety.org/bulletin/nc-guidelines.htm#s12c
>>
>> This section is copied here for your convenience:
>>
>> c) Special provisions are made in these Guidelines
>> for highly altered
>> materials that may have a meteoritic origin,
>> designated relict
>> meteorites, which are dominantly (>95%) composed of
>> secondary minerals
>> formed on the body on which the object was found.
>> Examples of such
>> material may include some types of "meteorite
>> shale," "fossil
>> meteorites," and fusion crust.
>>
>> David
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Received on Sun 07 Jan 2007 02:43:46 AM PST