Re: [meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA 2828
Hi Jeff and list, Thank you Jeff for the educating insight you have provided me, and others on this topic. The more complicated these get, the more I am drawn into all aspects of meteoritics. It certainly draws my attention away from the negative Moroccan influence I endure while acquiring these interesting "messengers" from our neighbors just outside our blue boundaries! Thank you again for all who have contributed to this very educational thread, this makes it all worth while in the long run! Best regards, Greg Greg Hupe The Hupe Collection NaturesVault (eBay) [EMAIL PROTECTED] www.LunarRock.com IMCA 3163 - Original Message - From: "Jeff Grossman" <[EMAIL PROTECTED]> To: Sent: Sunday, January 07, 2007 9:52 AM Subject: Re: [meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA 2828 > As I was heavily involved in developing the NomCom rules, let me give > my take on this whole discussion: > > Our actions were stimulated by the Osterplana "fossil" meteorites, as > they are commonly called in the literature. For those who don't know > these, they are a group of several dozen objects embedded in > Ordovician age carbonate rocks in Sweden. Many of these have > chondritic structures, with chondrule textures clearly > visible. Others are simply dark clasts in the limestone. The only > primary meteoritic mineral left, if anything, is some chromite, and > everything else has been replaced by secondary, terrestrial > minerals. Thus, the chondrules are pseudomorphs and the chromite is > relict. Brunflo is a similar occurrence found in another quarry. > > We needed a guideline to cover the naming of these objects, but the > usual guidelines for meteorites were inadequate. These meteorites > present a continuum of cases, from ones we were comfortable calling > "fossil" meteorites (they preserve the original structure and can be > classified, mostly as L chondrites) to ones that nobody can or will > ever classify, or even prove beyond a reasonable doubt to be > meteoritic in origin. > > Now combine these occurrences with other things in the > literature. There are meteoritic clasts in some terrestrial rocks > that survive with most of their primary minerals and structures > intact. The Morokweng meteorite described in Nature by Maier et al > last year was also called a "fossil" meteorite, but only the metal > and sulfide were replaced by secondary minerals; silicates are little > altered. For the purpose of meteorite nomenclature, we would want to > treat this case like any other meteorite found on Earth... it's a > meteorite by any reckoning. I don't know the details, but perhaps > NWA 2828 is a similar case. > > We also have things around like iron shale, which I don't think > should be distinguished from cases like the Osterplana objects, as > Sterling Webb does. Both types can contain some of the chemical > signature or structure of the original meteorite and are largely > composed of secondary minerals. However, these are not fossils, as > they are not preserved in the geologic record. They are the products > of weathering meteorites at the earth's surface. But from a > nomenclature perspective, they need to be treated the same as the > Osterplana objects. > > This is why we came up with the operational term "relict > meteorite." It covers all objects that are largely altered, but > which have relict signatures indicating a meteoritic origin, > including composition, texture, isotopes, or whatever. Relict does > not mean fossil. Some relict meteorites are fossil meteorites, like > the classifiable Osterplana specimens and Brunflo, and some are not, > like a highly weathered, barely recognizable stone from the Sahara, a > piece of iron shale from Arizona, or a chip of fusion crust collected > on the Antarctic ice (like LAP 04531). Conversely, some fossil > meteorites are not relict meteorites, like the Morokweng stone. The > terms relict and fossil are independent of each other. (I have no > opinion on this term "paleometeorite" which I have not seen defined.) > > One last comment. The Wlotzka weathering scale (W0-W6) is not > applicable to anything but ordinary chondrites. This is why we can't > just extend it to W7 and use it to cover all highly weathered meteorites. > > jeff > > At 12:46 AM 1/7/2007, Mr EMan wrote: >>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
Re: [meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA 2828
As I was heavily involved in developing the NomCom rules, let me give my take on this whole discussion: Our actions were stimulated by the Osterplana "fossil" meteorites, as they are commonly called in the literature. For those who don't know these, they are a group of several dozen objects embedded in Ordovician age carbonate rocks in Sweden. Many of these have chondritic structures, with chondrule textures clearly visible. Others are simply dark clasts in the limestone. The only primary meteoritic mineral left, if anything, is some chromite, and everything else has been replaced by secondary, terrestrial minerals. Thus, the chondrules are pseudomorphs and the chromite is relict. Brunflo is a similar occurrence found in another quarry. We needed a guideline to cover the naming of these objects, but the usual guidelines for meteorites were inadequate. These meteorites present a continuum of cases, from ones we were comfortable calling "fossil" meteorites (they preserve the original structure and can be classified, mostly as L chondrites) to ones that nobody can or will ever classify, or even prove beyond a reasonable doubt to be meteoritic in origin. Now combine these occurrences with other things in the literature. There are meteoritic clasts in some terrestrial rocks that survive with most of their primary minerals and structures intact. The Morokweng meteorite described in Nature by Maier et al last year was also called a "fossil" meteorite, but only the metal and sulfide were replaced by secondary minerals; silicates are little altered. For the purpose of meteorite nomenclature, we would want to treat this case like any other meteorite found on Earth... it's a meteorite by any reckoning. I don't know the details, but perhaps NWA 2828 is a similar case. We also have things around like iron shale, which I don't think should be distinguished from cases like the Osterplana objects, as Sterling Webb does. Both types can contain some of the chemical signature or structure of the original meteorite and are largely composed of secondary minerals. However, these are not fossils, as they are not preserved in the geologic record. They are the products of weathering meteorites at the earth's surface. But from a nomenclature perspective, they need to be treated the same as the Osterplana objects. This is why we came up with the operational term "relict meteorite." It covers all objects that are largely altered, but which have relict signatures indicating a meteoritic origin, including composition, texture, isotopes, or whatever. Relict does not mean fossil. Some relict meteorites are fossil meteorites, like the classifiable Osterplana specimens and Brunflo, and some are not, like a highly weathered, barely recognizable stone from the Sahara, a piece of iron shale from Arizona, or a chip of fusion crust collected on the Antarctic ice (like LAP 04531). Conversely, some fossil meteorites are not relict meteorites, like the Morokweng stone. The terms relict and fossil are independent of each other. (I have no opinion on this term "paleometeorite" which I have not seen defined.) One last comment. The Wlotzka weathering scale (W0-W6) is not applicable to anything but ordinary chondrites. This is why we can't just extend it to W7 and use it to cover all highly weathered meteorites. jeff At 12:46 AM 1/7/2007, Mr EMan wrote: >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
Re: [meteorite-list] Fossil, Relict, or Paleo- was "Fossil" NWA 2828
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" <[EMAIL PROTECTED]> To: "David Weir" <[EMAIL PROTECTED]>; "Greg Hupe" <[EMAIL PROTECTED]> Cc: 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 > min
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 <[EMAIL PROTECTED]> 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 __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
