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Stromatolite Specimen


Bill J

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I was gifted a rock specimen from the estate of a professional geologist.  I was immediately attracted to it as a tall, columnar structure very coral like.  It has been cleanly sawn at the base and it layered, laminae structure immediately indicated stromatolite.  It is about 15 inches tall and 5.5 inches at the base; it weighs about 7 pounds.  At first I thought it was a fossil but these three things stand out contrary to that.  First, it has air voids in it; it is not completely mineralized through.  Second, the external layer is cleanly exposed.  If it was a fossil, the surrounding matrix must have been highly erodible as the fine detail of the outside layer (visible exterior) is remarkable.  Third, consistent with #1 and #2 the "rock" has not been metamorphosed.  We have fossil stromatolites here in Minnesota and they are embedded structure in Mary Ellen Jasper, which is a beautiful rock.  Unfortunately, I have no idea where this came from.  The dad of my friend who gave it to me lived in South Dakota and was in the Pacific Theatre in WWII, but was not known to be much of a traveler otherwise.  Based on my 3 reasons above, I think this may be a specimen of a modern,  extant stromatolite that somehow ended up with the geologist.  I know there are living modern stromatolites with columnar structure at Pavilion Lake BC, and at Lago los Centas in Porvenir, Tierra del Fuego, Chile.  Certainly there are fossil examples of columns too in the record.  Really just looking to see if anyone on this forum has seen anything like this before?  It is beautiful in its own way.  Thanks in advance.  Bill J.20220921_093158.thumb.jpg.b186263ee1765a713d99bc707e7640c8.jpg20220921_093248.thumb.jpg.4cb5296664715a43271a9998d21929c6.jpg

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I think it is maybe a speleotherm/ stalactite/ stalagmite. 

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Or some kind of tufa? Speleothemes are not that porous, usually?

Anyways, not a stromatolithe.

Franz Bernhard

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These are stromatolites in Tierra del Fuego.  There is a morphological similarity, especially the "bends" that appear to match my speciment...plus the exterior "crust-like" surface...

 

image.png.01d3146258f8309d43b587c920279091.png

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Here's another more close-up.  Credit to Jason Frels as the photographer.  This is at a national biological munument in Chile.

 

image.thumb.png.12dc25684d482b67c702ba3e9b897bca.png

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these images of stromatolites are superb, but I still stick to the idea of tufa put forward by Franz.

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15 hours ago, Bill J said:

I think this may be a specimen of a modern,  extant stromatolite that somehow ended up with the geologist.  I know there are living modern stromatolites with columnar structure at Pavilion Lake BC, and at Lago los Centas in Porvenir, Tierra del Fuego, Chile


Can you find a paper about those stromatolites in Chile that show a cross section of one?

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A longitudinal section might show the irregular convex to horizontal layers typical of stromatolites. Without any other information we are only guessing.

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26 minutes ago, westcoast said:

A longitudinal section might show the irregular convex to horizontal layers typical of stromatolites. Without any other information we are only guessing.

I am not an expert. 

But to me, the layers look like they are vertical.

 

Are they horizontal as well ??? 

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Thanks all.  Really good thoughts here.

 

Certainly the pictures of tufa structures are in the running.  Apparently there is new research indicating the presence of a biofilm for at least some types of these to form.  I've not found a picture of a lateral cross-section but would expect it to be layered.  Speaking of cross-sections... 

 

The only cross-section of my specimen is that showing at the base cut.  The "top" is uncut and looks very similar to the base cut, however the laminae are much closer together with minimal voids.  I'll try to get a picture for that.

 

As for a vertical cross-section, that will not be happening with my specimen but it is fully understood how valuable having that would be.  As best I can tell it appears to be layered vertically all the way through so I agree with WestCoast this is just guessing.  So my response to Yoda is no, they do not appear horizontal BUT...  When you look at the bottom off-left of the cross-section you see a hole that might be a tube going up into the structure.  I measured into the hole and its 1 cm going in at most but who knows how long it might have been going the other direction.

 

Back to the tufa hypothesis this certainly is more realistic as these are found here in the US without having to go down to Patagonia.  I may actually have access to some limited lab analysis and that could go a long way on the tufa vs stromatolite front.

 

There is a researcher in Chile that I can reach out to for a possible cross-section image from the other pics shown above.

 

Finally, I'm not sure how a "geologic" process would produce the asymmetrical layer structure that essentially starts at the bottom center and progressively "radiates" the layering up the image.  What I mean is that although this thing is columnar its growth is only on one side.  I attributed that to more of biological process from the cyanobacteria doing their thing that what my occur from progressive wetting/drying cycles in a mineral laden water environment.

 

Thanks again from a newbie.  Bill J. 

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9 hours ago, DPS Ammonite said:


Can you find a paper about those stromatolites in Chile that show a cross section of one?

I'll see what I can come up with.  Thanks for asking.

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Below are figures from "Marco Campos-Venuti 2022 Biominerals microbial life in Agates and other Minerals" showing tufa from Lake Van, Turkey and Mono Lake and Pyramid Lake, Nevada.

 

Tufa Lake Van, Turkey:

 

 

TufaLakeVanTurkey1.jpg.4949e4f5a528f2a2e63ee97cad14e363.jpg

 

TufaLakeVanTurkey2.jpg.0534de9b782ccad93320d1f753fa0869.jpg

 

 

Tufa Mono Lake and Pyramid Lake, Nevada:

 

 

TufaMonoLakeNevada3.jpg.c796f3ca4fb2592a4a662bfa004ad93d.jpg

 

 

Marco Sr.

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45 minutes ago, MarcoSr said:

Below are figures from "Marco Campos-Venuti 2022 Biominerals microbial life in Agates and other Minerals" showing tufa from Lake Van, Turkey and Mono Lake and Pyramid Lake, Nevada.

 

Tufa Lake Van, Turkey:


Looks like best possibility of ones noted.

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17 minutes ago, MarcoSr said:

Below are figures from "Marco Campos-Venuti 2022 Biominerals microbial life in Agates and other Minerals" showing tufa from Lake Van, Turkey and Mono Lake and Pyramid Lake, Nevada.

 

Tufa Lake Van, Turkey:

 

 

TufaLakeVanTurkey1.jpg.4949e4f5a528f2a2e63ee97cad14e363.jpg

 

TufaLakeVanTurkey2.jpg.0534de9b782ccad93320d1f753fa0869.jpg

 

 

Tufa Mono Lake and Pyramid Lake, Nevada:

 

 

TufaMonoLakeNevada3.jpg.c796f3ca4fb2592a4a662bfa004ad93d.jpg

 

 

Marco Sr.

Thanks Marco.  This is great stuff.  At least for the Figure 2.10, the drawing and cross-sections are identified as microbialites, of which stromatolites fall into that category.  Tufa structures apparently have a unique origin story with different biogeochemistry than stromatolites.  Now my question is how to characterize my specimen?  I don't think it qualifies as a fossil, but it's more than just a rock.  Again, thanks.  Bill J.

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I'd classify it as a sedimentary or geologic structure.

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On 1/29/2024 at 9:54 AM, DPS Ammonite said:


Can you find a paper about those stromatolites in Chile that show a cross section of one?

Hello DPS.  As best I can tell Dr. Jorge Rabassa out of Chile is the "expert" among several researchers on the Lago los Cisnes stromatolites.  Here is one of his papers:

 

https://www.academia.edu/79895667/Living_and_fossil_microbialites_in_Laguna_de_Los_Cisnes_Southernmost_Chile_A_duel_between_biotic_and_abiotic_processes

 

I've not seen any cross-sections and would not have seen anything at all if not for Jason Frels taking a vacation trip to Tierra del Fuego and having a day trip out to the "stromatolite park."  I have communicated with him and he's  not a fossil or rock person, just a very good photographer.  In my quest to understand my specimen, I've come to realize that the very hostile conditions in many parts of Chile provide a microbialite laboratory.  I had no idea.  Finally, in case you don't know a little closer to home here's what growing in Pavilion Lake BC:

 

 

170px-Pavilion_Lake_microbialite_towers.jpg         Stromatolites | Silurian Reef | The Field Museum

This was the site of a NASA exobiology research project in the late 2000s.  Pavilion Lake occurs in karst bedrock with high calcium/mineral water quality.  I originally thought this might be where my columnar microbialite came from.

 

Back to Dr. Rabassa, he is the head of the major scientific research institute in Chile.  I'm sure he's open to contact with anyone interested in microbialites.  Bill J.

 

 

 

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On 1/30/2024 at 2:16 PM, MarcoSr said:

 

a columnar microbialite or a microbialitic column

 

Marco Sr.

Thanks again Marco for your feedback.

 

I see from this and other posts you have a strong interest in stromatolites.  Below is a link with some pictures of fossil formations here in Northern Minnesota related to mining of iron formations that's been underway for over 100 years.  The webpage is some notes from a field trip back in 2012 at the former LTV Mine Site now owned by PolyMet.  This is all private property but I myself hope to visit it someday.  What's very cool is that it was of course the cyanobacteria-stromatolites that created the oxygen that precipitated out the dissolved iron in the ancient seas in the first place  That's what the geology of this area is all about.  Here's the link:

 

earthscienceguy: Minnesota Geology Monday - Stromatolites (mnearthscienceguy.blogspot.com)

 

I pulled a couple of pictures:

 

 

39669656-P6225272.jpg  39669476-P6225265.jpg      39669550-P6225268.jpg

 

Again, thanks.  Bill J.

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