A Trip to the Leighton Formation

[Mainefossils]

Today I took a trip to a new outcrop of the Leighton Formation!

 

My main interest in this new outcrop is to find the source of my original material. The first outcrop I visited actually turned out to be an erratic.  When I first visited there in February the ground was completely frozen. I found a large piece of shale sticking out of the ground, which I proceeded to split, but the rock itself did not come out. This rock yielded about 50 pounds of material on the first trip. 

 

When I returned in June I excavated around the supposed outcrop, and found that it was in a fact an erratic rock. I also found three other large pieces that were also from the Leighton Formation. 

 

Since my first site turned out to be a dud, I am now trying to find new sites. This is the first of three possibly accessible sites to visit. I am mainly looking for the presence of thelodont scales - specifically, those that belong to the species Phlebolepis elegans. I am also looking for a few species that I don't have in my collection yet or I require for research: the tentaculite species T. elongatus, the trilobite species Acastae zerinae, two species in the genus Actinopteria, the undescribed Calymene species that has been mentioned in earlier posts, and eurypterid fragments. 

 

Today was an absolutely beautiful day to do it. It was cool and overcast in the morning, but then cleared up towards the end of the trip - perfect collecting conditions. Here are some pictures of the walk (in chronological order). 

 

 

 

 

 

Once at the outcrop, the Leighton shale member was quite obvious. It was one excellent outcrop, although I didn't find all the species I was looking for. I might have found thelodont scales, but I will not know for certain until I examine the material closely. 

 

The fauna of this formation was similar to that in the erratics I found, with a few marked differences. One is the abundance of the brachiopod species Chonetes bastini, it was the by far most common brachiopod. Also, the characteristic Salopina brachiopod fauna was barely represented in this outcrop - I might have got two specimens of them. Camarotoeichia leightoni was more common, but still relatively scarce compared to the C. bastini. Only the tentaculite species T. elongatus was in the outcrop, the other species of Tentaculite (which I have not identified), was completely absent. The bivalve species Modiolopsis leightoni was amazingly prolific. 

 

On to the geology of the site. Almost the entire outcrop was of made of a highly fractured gray shale that split extremely easily. In this slate, there were occasional pockets of a type of siltstone. The siltstone pockets usually contained a large amount of gastropods of the genus Australonema, with possible fish fragments. There were extremely fossiliferous layers every 5 - 10 centimeters. In between these layers there were still some fossils, but generally there were less molluscs or ostracods. Most of the C. bastini brachiopods were in between the fossiliferous layers. 

 

I only collected from one of the outcrops that was there, two others were situated to the left and right of this one. They had the same general geology and fauna - at least, according to my rather quick check. 

 

Below are a few pictures of the outcrop I collected at: the first is from the front of it, and the second is from behind it. 

 

 

 

Here are a few insitu photos of some of the fossils. The first is of what I guess is an A. zerinae trilobite cephalon, prep will reveal if it actually is. The second is of one of the highly fossiliferous layers I was talking about - notice the enormous profusion of ostracods, with a few brachiopods and mollusks. 

 

 

 

On the way back there were a few red shale pieces I took a look at. I think they are from the Hersey Formation, probably brought in by the tidal current. The first picture shows one of the rocks, and the second is of a brachiopod external mold peeking out. 

 

 

 

I hope to update this thread with further pictures of the fossils collected. To be continued....

 

Thanks for reading! 

Edited August 29, 2021 by Mainefossils

[Wrangellian]

Such a small site, it seems like finding it would be like a needle in a haystack, unless you just happened upon it (and if it were over here I would not have much hope of finding anything in it). Are there larger outcrops of that formation elsewhere?

[Misha]

What a beautiful location and fascinating formation, can't wait to see what other things you got there!

[FranzBernhard]

Thanks for taking us along. Great report with many names I have never heard before .

 

5 hours ago, Wrangellian said:

Such a small site, it seems like finding it would be like a needle in a haystack, unless you just happened upon it

Hey, its already fully exposed in all its glory . I had to "make" most of my outcrops myself this year .

Franz Bernhard

Edited August 30, 2021 by FranzBernhard

[Mainefossils]

Thanks everyone! The new pictures will hopefully be coming soon... I had to sleep, *sigh*, why does this happen each night!   

 

7 hours ago, Wrangellian said:

Such a small site, it seems like finding it would be like a needle in a haystack, unless you just happened upon it (and if it were over here I would not have much hope of finding anything in it). Are there larger outcrops of that formation elsewhere?

 

To the left and right are two other outcrops, which may have been slightly bigger, but not by much. The easiest part on finding this outcrop was that most of the beach was made up of Leighton formation shale - all the gray weathered stone you can see on the beach is actually shale. Just had to find the source. Also, some old geological maps were of some use here. 

 

I have not checked the other two sites I was mentioning, although those might be the next ones I visit. I don't know the size of the outcrop, but as they are similarly situated, I think that they will be relatively the same. 

 

2 hours ago, FranzBernhard said:

Thanks for taking us along. Great report with many names I have never heard before .

 

Hey, its already fully exposed in all its glory . I had to "make" most of my outcrops myself this year .

Franz Bernhard

 

Thank you! It does make me wonder, though, how do you find your new sites? Where do you get your information from? It was relatively easy for me, but you find new sites every year. Do you just start hiking in areas marked as fossiliferous, and find the sites yourself? Or do you find outcrops of the formation you are looking for, and trace it to a new source? Thanks for your time! 

[Mainefossils]

I will start with the "trip-maker" fossils. On the top of the list is, of course, the possible trilobite cephalon, A. zerinae. Below is a much better picture of it. 

 

 

Next is one that I almost left behind.  It is a very nice little Orbiculoidea brachiopod, (one for you @Tidgy's Dad), that weathered almost perfectly out of its host rock. I happened to see it as I was packing up, and was able to extract it. Below are two pictures, first of the brachiopod in closeup, and second of the rock it is in. 

 

 

 

Then, my first Leiopteria rubra mollusk - I originally mistook it for some type of Actinopteria species. I am still not 100% positive on the ID, but it is the closest species. The first picture below is of the cast, and the second of the external mold. 

 

 

 

Also, a complete T. elegontus tentaculite shell, it came out very nice. I noticed that the tentaculites were only found in the fossiliferous layers. Below is a picture of it. 

 

 

To be continued... 

[Mainefossils]

Next will be some of the many C. bastini brachiopods I collected. Most of these specimens have other species on the same rock, which is the reason I brought them back - except a multi - plate. I left plenty of loose ones behind, if anyone wants to go get them! 

 

For now, I will just show a few singles that I brought back - the rest will be shown after they are prepped. 

 

 

 

 

 

To be continued... 

[Wrangellian]

21 hours ago, FranzBernhard said:

Hey, its already fully exposed in all its glory . I had to "make" most of my outcrops myself this year .

Franz Bernhard

I know... You guys have the benefit of more fossiliferous deposits. If I went digging for an outcrop of Haslam Fm, I'd probably be wasting my time. The only reason we find stuff here is because there are rather more widespread outcrops such as riverbanks. Some locations are more abundantly fossiliferous but those are the exception, and they weren't found by randomly digging by hand.

 

I like the tentaculite!

Edited August 31, 2021 by Wrangellian

[FranzBernhard]

1 hour ago, Wrangellian said:

they weren't found by randomly digging by hand.

Well, the digs weren´t completely random, they were guided by very tiny indications already visible . But, well, my fossil friend said: "How did you find that darn sites initially?? I had some problems finding them using your detailed map!"

 

But there are much better stories from this area around. I am not involved, but something will be made public soon. I will post that for sure here on TFF. Its an incredible fossil discovery and story, just about 1-2 km away from my rudist sites...

 

Franz Bernhard

[Wrangellian]

Sounds exciting...

[Mainefossils]

Now onto a few gastropods. 

 

I'll start with one of the siltstone pockets I was talking about. The pictures below are, first of the whole pocket, and second of some of the individual gastropods - I think that they all belong to the genus Australonema. 

 

 

 

 

Then a small one I finished prepping out yesterday. I am really not sure on the species of this one, but I am guessing some sort of platycerid.  

 

 

And another gastropod. I am pretty sure it belongs to the same species as the platycerid above. 

 

 

And a few more puny gastropods. I am not sure on the species of these. 

 

 

 

 

To be continued... 

[Mainefossils]

I think that this will be all for this thread. This shows a few representative specimens - the ones that were fairly obvious at the outcrop. I hope to continue posting new fossils I find, as I split the shale I brought back. Many of these will turn up in the fossil ID thread, as I have come across a fair number of neat little suckers. Thanks so much for reading everyone!