Stansbury Island Fossil Hunting Research Part 2

[Earth Chemistry]

 This is a continuation of my last post with @UtahFossilHunter going back to the island last minute before the snow flies. This time we tried another outcrop of the Undifferentiated Cambrian (now determined to be the Chisholm Formation) on the search for fossils. Link to Part 1

Here is the map on my last post.


This is the Chisholm Formation at the foot of the mountain.

We went up farther on the mountain and found a contact zone. Being a large dipping anticline going down the slope at an angle, the rock layers get older on the bottom then the top. Other places on the island the rock layers are rotated sideways so we kept going right and slightly down more.

We kept going up and we found some Bonneville gravel.

 Further along we found lots of a good structural rock with en echelon fractures from nearby faults. But no fossils. We decided to check a few other rock layers again just in case. The Ordovician Garden City Formation had absolutely nothing. So we went back down and drove to another place where the Silurian Laketown Dolomite outcrops so we hike up and..... 

We found our first Silurian fossil!

We didn't expect anything to be in this formation. Unlucky for us, it was on a boulder so we thought we had to take out a chunk of it. UtahFossilHunter and I had forgot our chisels but we had our hammers. So for ten minutes we kept trying to break off the chunk it was sitting in. You can see in the pictures the fossil was on a ledge. The bedding layer below was a large chert nodule layer so every time we hit it you could hear little shards zooming by like ricocheted bullets. After that ten minutes while watching the snow clouds make their way across the Utah-Nevada border, we decided to take a risk and try popping the fossil out just underneath the shell. That risk payed off and it came out whole. The lesson here is if you know you might be looking in hard rock layers don't forget your chisels. 


 

[ynot]

6 minutes ago, Earth Chemistry said:

We found our first Silurian fossil!

No pictures - it did not happen.

Where is the pictures?

[Earth Chemistry]

Bonneville gravel

[Earth Chemistry]

Just now, ynot said:

No pictures - it did not happen.

Where is the pictures?

Technical difficulties they’re incoming now

[Earth Chemistry]

En echelon fractures

[Earth Chemistry]

Silurian gastropod!

[Earth Chemistry]

[Earth Chemistry]

The gastropod is heavily recrystalized and the matrix metamorphosed due to the faulting nearby. This layers fossils are so sparse we did not think it contained any.

[Earth Chemistry]

The fossil-less Chisholm Formation

[Tidgy's Dad]

Very interesting. 

Thanks for sharing and especially congratulations on the gastropod find! 

[Earth Chemistry]

The impending doom of snow

[DeepTimeIsotopes]

Some more landscape pics: 

The, also fossil lacking, Garden City Formation

[DeepTimeIsotopes]

A panoramic of the view from the Chisholm Formation

[DeepTimeIsotopes]

An updated stratigraphy column

Green is now abundant fossils

Red is no fossils

Yellow is rare fossils

[Raggedy Man]

 

 

[Tidgy's Dad]

Nice work, chaps!