Jacques:

Looks like massive cylindrical Chert. You need to provide a litholog of Early Eocene Rus Formation to understand the origin of these cherty objects. The photographs do not seem to suggest any Stromatolitic structure. 

Best

Syed

Jaques,

There really isn't too much to go on from your photos. Obviously, a "stromolitic" ("layered stone") texture has to be shown by some sort of cross section (whether broken, slabbed, or polished), while cyanobacterial or "algal" stromatolites occur in fresh-water to marine environments. "Layering" also appears in early diagenetic structures such as caliche concretions the environment of deposition is handy in interpreting a structure as you've photographed. As Syed noted, this simply could be a chert structure--possibly produced by replacement of a carbonate-rich rock(?) with vertical passage of hydrothermal fluids. It is hard to say.

Best,

Ed L.

Does not look like stromatolites, maybe petrified wood, but need to look at sections to see if it has the rings like wood

Hi, from the photos, it doesn;t look like stromatolite !! most probably it is chert concretion. I have working in the Iraqi Southern Desert where the Rus Formation is encountered in many wells, but never have seen stramatolite in the cores.

The cherty structures are certainly not stromatolitic ot formed by cyanobacteria. This could be diagenetic chert replacing carbonate. However look the thin sections for any biogenic evidence.

agree with the others who have responded that it does not resemble the stromatolites I've seen. But the vertical structure is reminiscent of another cyanobacterial formation: tufa. Tufa's form around groundwater seeps where abundant carbonates are available. As cyanobacteria growing around the seep die and degrade, carbonate precipitates form in their place. These can form towers, such as at Lake Van, Turkey or Mono Lake, California.

Lisa:

Superficially these may somewhat resemble "Tufa" which is essentially friable, soft and porous carbonate rock produced by microbial-chemical process. The present photographs do not seem to show such features. Detailed litholog of Rus Formation and petrographic studies might reveal true nature of these objects.

Best

Syed

They don´t look like stromatolites to me. As other colleagues have mentioned, the best way to know if they are, is to have polished sections. I live in Sonora, NW Mexico, where we have stromatolites in the Proterozoic (shallow marine) and the Upper Cretaceous (lake deposits). And they look very differently from your samples.

Interesting photos and discussion.

Need to look at TS and CS in thin sections for texture and structure. as pointed out, the photos are insufficient to justify any concrete conclusion.

Possible options:

Hydrothermal vent deposits (observed in marine sediments deposited in proximity of volcanic vents where the gaseous fluids create tubular deposits of chert / carbonates with a concentric laminate pattern;

Ichnofossils - organic chert / calcite binding along tubular habitats of burrowing organisms - that leave behind such features

Simple fluid escape structures produced during lithification of silicic sediments under special conditions, where the fluids remain trapped in the lower strata and then are triggered into escape through tubular vents....(akin to mud-volcanoes)

....

I am assuming that since these are found in sedimentary rocks, other processes should not be brought into consideration, although even biogenic superficial weathering by soil-dwelling burrowers could also yield such features.

These are just iron nodule and chert concretions commonly found within the Rus Formation.  See Origin of iron nodule paper by Nasir, et al.. you can dwonload from Journal of Qatar University Science Journal

Hi Jaques, your pictures rember me on the trace fossil Paramoudra. This trace fossil is discribed by Bromley from the chalk (Maastricht) of Scandinavia. In Germany are this structures named "Sassnitzer Blumentöpfe". It could be that you have similar structures.

Peter

Peter:

Paramoudra seems a very exciting possibility, as earlier suggested by Vivek. Has anyone guessed about the animal which should be making such Trace fossil?

Vielen Dank und Gruss.

Best

Syed

Hi Jaques, Paramoudra is a very big trace in the Cretaceous but the silicified part is an halo around a relativly small and Long (< 3m) tube. The silicified ring on your first Picture could be such an halo and the central tube is the true trace fossil. As Producer is a worm possible. I do not know the Rus Form. but it should be of marine origin, if the structures are Paramoudra.

All the best

Peter

Good day everybody. First I wish to thank everyone of you for your participation in trying to figure out the mystery behind these structures. I have now completely disregarded the idea/possibility of it being related to stromatolites.  The one I am retaining at the moment is of them being related to the Paramoudra; a comment received from Peter Suhr today....a term i had never heard of before.  More investigations this afternoon on the internet lead me to believe that we are on the right track with this concept.  Also, to answer Peter's question: YES, the Rus formation is of marine origin. It seems that this phenomenom is more widespread that we know of but the name is unknown to most geologists.  I have had a discussion with an archeologist who studied the Eocene Sakesar formation of Pakistan (same age as the Rus in Qatar) and he sent me pictures quite similar to mine. He could never make out the origin of the quartz.

In any case, I am glad about all the comments that my question has generated.   I am still interested in entertaining additional possibilities if someone can propose a better solution than the paramoudras, but I think I need to study everything there is on these paramoudras before the article I am preparing is published....when it does, it will find its way on ResearchGate.

Thank you again very much for all your help

Jacques

Hello Jacques

where in Qatar did you fine these pot stones?

Yes, I agree with Mr. Subhi Naser, they are iron concretions and chert nodules, they are also widely spread in the Dammam Formation with different shapes and sizes