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TNCollector

Got the itch to collect and study some stromatolites, so I did some searching and feel that I successfully scratched the itch. I found a section of the Cambrian Copper Ridge dolomite that exposes a plethora of stromatolites of various morphologies. Many of them look as if they are straight out of Shark Bay in Australia, with the characteristic domal structure attached to a thinner holdfast on a hard substrate. Stromatolites are formed over a long period of time in tidal zones by colonies of photosynthetic bacteria and/or algae that form sticky layers that trap sediments and concrete them into layers. The colony then grows over the older, cemented colony and the cycle repeats itself. The process is obviously a lot more complicated than that, but I digress.

 

Stromatolites are the oldest confirmed fossils to have been discovered, with the current oldest ones to be confirmed coming from the Strelley Pool Chert formation in Western Australia, dating back to the early Archaen at approximately 3.4 billion years ago. At that point in time, the Earth's atmosphere was largely devoid of oxygen, primarily being composed of CO2. Over the next several billion years, these stromatolites were largely responsible for oxygenating the atmosphere. They may not look like much, but these bacterial colonies were extremely important to creating Earth's biosphere. After the Cambrian explosion, stromatolites began to become quite rare in the fossil record, with multicelluar organisms feeding on them and disrupting the cementation process. After that point and to this day, stromatolites primarily thrive in extreme environments were the animals that feed on them cannot survive. The stromatolites in the Shark Bay, Australia area live in a hypersaline environment created by a seagrass barrier just off the coast. Unfortunately climate-change induced increases in precipitation are causing floods that reduce the salinity of this location and threaten the survival of the stromatolite colonies. 

 

With that information, enjoy these photos of stromatolites. Cube scale is 2cm on each side

 

Large domal type in the position it would have grown in:

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Another domal type, almost spherical in shape, composed of multiple separate colonies that appear to have fused together:

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Another domal type:

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Cross section of broken laminar piece showing growth layers over an oolitic limestone substrate:

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A different one, I hope to polish this face:

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Layers under microscope:

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6.jpg

8.jpg

Edited by TNCollector
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Tidgy's Dad

Lovely specimens. :b_love1:

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Ludwigia

Are these all from Tennessee?

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FossilNerd

We don’t see stromatolites very often. Beautiful. :wub:  Thanks for sharing! 

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TNCollector
3 hours ago, Ludwigia said:

Are these all from Tennessee?

Yes they are. Copper Ridge Dolomite. All of the stromatolites are chertified which preserves a lot of the details that are often missing.

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TNCollector

Got another one to show. I am quite fond of this one. It looks like it literally just came out of Shark Bay! I would like to take some thin slices of these and see if any of the original bacteria are preserved. Stromatolites from some other localities have preserved the bacteria in silica. Reference cube is 2cm on each side.

strom1.thumb.jpg.ed11d907859540d50e3cb48c918809cc.jpg

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Wrangellian

Missed this til now. Nice ones! I'd hesitate to slice that last one. I don't know what your chances are of finding the actual bacteria preserved. Do you have the means to see them and have you tried other pieces that have preserved bacteria?

I'm thinking of starting a 'Show us your stromatolites' topic, where I will show some of mine (once I get some photos) and invite others to show theirs. (I don't think there is such a topic yet?)

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crabfossilsteve

Those are very cool and I especially like the one with the oolitic limestone.  I too wouldn't slice that last specimen.  Too nice as is.

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