I Think I Found A Ancient Seashore In Utah

[driller35]

I was doing some rock hunting in in the desert, about the center of Utah and found these strange rock formations in the Mancos Shale of the late Cretaceous (Utah has plenty of strange formations). But these caught my eye because of spacing and alignment. When I looked closer it look like a fine sandstone with a few shell fragments, I thought of Stromatolite but did not see any laminations, When I was able use the internet I found out about Thrombolites and I am fairly sure that's what they are. The formations stretched for over a mile.

A closer look

[Auspex]

These may well be Thrombolites; such in areas around Great Salt Lake have provided case studies of more recent microbial carbonates. I assume your finds are within the footprint of Pleistocene Lake Bonneville?

Micro- and chemical-analysis could confirm their origin.

[Ludwigia]

Certainly is a fascinating looking outcrop. Thanks for sharing!

[driller35]

These may well be Thrombolites; such in areas around Great Salt Lake have provided case studies of more recent microbial carbonates. I assume your finds are within the footprint of Pleistocene Lake Bonneville?

Micro- and chemical-analysis could confirm their origin.

Interesting I had not though of that. On goggle maps the location is 38.994475 -110.351461 at a elevation of 4516'. It is hard to see but there is a line of the formations that run dew south from the road.

[Auspex]

14,500 years ago, Bonneville covered about 40% of Utah; it has been evaporating ever since. Great Salt Lake is just its last super-salty remnant!

[driller35]

I guess I should have called a ancient lakeshore instead.

[Auspex]

Bonneville easily qualifies as an inland sea

[jpc]

If you are in the Mancos these are probably concretions. Look for ammonites in there.

[driller35]

If you are in the Mancos these are probably concretions. Look for ammonites in there.

You are right about the concretions and weathered bedrock have ammonites and other fossils, and I have found some samples. But after Auspexs idea that it was from Lake Bonnevlle I think he is right, because they are not near any bedrock but are just setting on top of the desert sand, I was only off by a 100 million years.

[jpc]

I will admit I have no experience with thrombolites, but I do have a lot of experience with the Pierre Shale, and often enough there will be no outcrop, just concretions and baculites.

[Shamalama]

They look like giant cow patties!

[Auspex]

They seem to be somewhat stratified, and are evidently more resistant to erosion then the surrounding sediment (no doubt that they were buried, and the softer entombing rock has eroded away, leaving them arranged on the same plane as we see them). That they are aligned topographically is distinctive: they are lined-up in a fairly concentrated line. This cannot easily be ascribed to erosional bias; they must have been aligned when they formed.