New Backyard Site

[Ludwigia]

You sure are persistent.

[Kane]

So ends five consecutive days at the site, and it is back to work. The finds today were only two.

 

First up, an Acanthopyge contusa cranidium. Nothing new, but despite missing a right lobe, the preservation showing the tubercles is quite good.

[Kane]

I picked this up being hopeful it might be the cranidium of a Terataspis grandis, but jus another Acanthopyge, with its cranidium tipped forward.  

 

Not bad for five days... A bunch of lichids, a new species of brachymetopid for my collection, and a nearly complete Pseudodechenella. 

[Kane]

So, about time to wrap up the field report on this imported fill as nothing new is likely to pop out. 

 

Given the fauna present, most of the fossiliferous rock that contain trilobites conform to what is listed in the Amherstburg Fm., with some outliers from overlying/underlying strata. To that end, apart from the numerous Crassiproetus crassimarginatus which make somewhat poor index fossils given their stratigraphic range, the relative abundance of Acanthopyge contusa became a bit more of a focus.

 

As that species is only known through fragments in the literature, there is no complete body fossil for comparison. I found numerous parts, but never a thorax. The literature shows only pygidia and cranidia, both of which I managed to find. The only fragment not reported and illustrated was the thorax and the genal spines. As I have a few genals, I made a quick attempt at a reconstruction. This is just a two minute sketch in my field book where I "graft" the genals onto what is known in the literature and according to my own specimens. The thorax is a speculation based on Acanthopyge consanguinea, which is a very close relative of about the same geologic age, but found in NY in the Appalachian basin (as opposed to the Michigan basin where my specimens are derived). 

 

The next step will be to formalize the reconstruction as a more detailed and careful illustration.

 

[Al Tahan]

Awesome thread Kane 

[Kane]

Went on a few encore trips to the spot on Friday, Saturday, and Monday. Friday was bitterly cold with a bit of snow on the ground, with Saturday having a few spotty showers. 

 

 A pic of the typical spot. Some of the armour stone is quite large and deeply set, if not interlocked by other stones, making these a challenge to free up for splitting. Larger blocs will not split nicely, tending instead to fracture at a diagonal from the thin bedding planes. Some of these take a few hundred blows of the sledge/chisel combination to break down into more manageable rocks as seen here.

[Kane]

More results typical of the productive light grey stone. Trilobites are more likely to appear where the bryozoans are larger and intact; otherwise, several broken fragments may appear in pulses. 

[Kane]

Recent trilobite partials. Acanthopyge contusa cranidium and genal spine.

[Kane]

Pseudodechenella sp. and two Crassiproetus crassimarginatus. Many more, including cranidia, free cheeks, and other pygidia were left in the field. 

[Kane]

Thoroughly faded Trypaulites erinus. 

[Kane]

I've been able to reasonably reconstruct the stratigraphic sequence of these rocks, emerging as they do from a single location east of this site. Faunal correlations place these in the Amherstburg/Lucas Fms., in the Appalachian basin (south of the Algonquin arch). The contact between the two formations is gradual without a very distinct/abrupt change in lithology. From top to bottom, from observations of the sequence:

 

- Dense, micritic light grey limestone. Poorly fossiliferous. Containing large stromatoporoid colonies, functioning as a kind of cap. These were likely shallow marine and subaerial. Lower material weathers in thin bedded sheets, mostly blank. Moderate to high energy, likely representing a shallowing-upward sequence.

- As above, dominated by Syringopora-like colonies and occasional white skeletal remains of rostroconchs.

- Transition between dense micritic limestone to sandier facies. Dominated by small brachiopods and occasional rostroconchs.

- Sandy, light tan, granular stone, with uneven / turbated bedding surfaces. Lightly fossiliferous, mostly dominated by rostroconchs, and occasional nautiloid orthocones and gastropods (low and high-spired). The molluscs are poorly preserved, sandy, and appear only as steinkerns.

- Mottled grey wackestone with several thin, bituminous partings. Dominated by small Syringopora-like corals and pulses of small rugose corals. Cherty layer pulses with some biomicritic zones.

- Light grey or brown, with wispy and thin bedding planes, abundant light grey chert nodules most likely the result of siliceous sponges. Occasional colonial corals, rostroconchs, bryozoan fragments. Moderate energy environment, and fossils appear as pulses in mostly blank, sandy layers, some with vermicular black "splotches."

- Dark brown, sandier facies. Top of layer may weather greenish grey, and contains several toppled and abraded rugose and branching corals, some of considerable size. Bryozoan fragments, and occasional brachioopods. Between 10-20 cm below this layer may appear pulses of highly fossiliferous beds with smaller branching corals, bryozoans, brachiopds, occasional rostroconch, and rare trilobite fragments.

- Transition layer to light grey stone with thin layers of highly fossiliferous beds sorted by size. Top area commonly contain larger fauna (strophodontid brachiopods, rugose coral, fenestellate byrozoans, large trilobite pygidia, occasional platycerid gastropods, smaller brachiopods and rostroconchs). Transitions rapidly to more sparsely fossiliferous interval for about 10-20 cm containing occasional broken fragments of the preceding. This may be followed by either a busy layer of smaller fragments or a pulse of larger faunal elements. Terminates at base with highly biomicritic, cherty packstone with more abundant but poorly defined crinoidal element.

 

Trilobite appearances and assemblages occur mostly in the the lower layers, becoming less frequent as one progresses upward. Deposits were likely minor reefal complex flanks. Dominant faunal composition points to Amherstburg/Lucas Fms, ruling out Bois Blanc despite one or two outliers. Bryozoans likely played a minor binding role, and marine environment was most probably moderate energy given the presence of the type of larger fauna that remained intact. 

[Shamalama]

Excellent thread, pics, and the ultimate summary is very professional. Well done Mr. Kane!

[Kane]

8 hours ago, Shamalama said:

Excellent thread, pics, and the ultimate summary is very professional. Well done Mr. Kane!

Thanks, Dave! Research and keeping a field notebook are must-additions to the usual collecting kit.  

[Kane]

As the days have been above freezing for the last bit, a lot of the snow has melted. Today was a good day to dig around. Most of the hours were spent with one huge armour stone that weighed likely over a ton. Persistent chiseling, some crowbar action, and I managed to eventually transform the boulder into chips. 

 

Best find of the day was this Acanthopyge contusa pygidium. Despite the unfortunate split, the preservation of this one is quite lovely. 

 

I picked up a few brachs and gastros along the way, too. The one boulder was quite generous, as it provided many fragments of four of the five different trilobites that appear in this material. Before I knew it, looking up at the sky, it was getting closer to sundown so back home I went.

[Shamalama]

Still producing, awesome!

 

[Kane]

Found quite a bit today, but this was the tripmaker. 

Sadly, the positive is pretty poor as these rocks love to explode rather than split. There are a few things that make this one interesting: 1) It is by far the largest example I've found of this lichid at 3.5 cm (1 1/2") wide; 2) It appears to have a feature I have not ever seen in any of the literature -- a prominent tubercle right in the lower middle of the pygidial axis. 

 

[Kane]

But it is the negative where we can see a much clearer outline. Pics with Olympus and iPad.

 

I do question if this is an Acanthopyge contusa at all. This is a mystery.

Here is a comparison with Ludvigsen's image:

 

 

 

The pygidial ribs (and the pygidial tubercle) look like Terataspis but the spines are too short. There are only two Devonian lichids in Ontario, and this one doesn't quite fit either of them. 

[piranha]

58 minutes ago, Kane said:

...It appears to have a feature I have not ever seen in any of the literature -- a prominent tubercle right in the lower middle of the pygidial axis.

 

 

That prominent tubercle is a spine base.  Also compare the similarity of the pleural ribs...

 

[Kane]

It definitely seems to match Terataspis in many respects... but the short termination of the spines is throwing me off! (and on account of other specimens in the same rock that place it in the Amherstburg/Lucas as opposed to Bois Blanc). 

[piranha]

The large size and aberrant features suggest a possible undescribed sub-adult growth stage.  Unfortunately the recorded finds are few and far between.

[piranha]

This may solve the mystery as it appears to be a better match.  This echinolichine also has a distinctive median axial spine: Echinolichas eriopis

 

 

 

Hall, J. & Clarke, J.M. 1888

Palaeontology VII. Containing descriptions and figures of the trilobites and other crustacea of the Oriskany, upper Helderberg, Hamilton, Portage, Chemung and Catskill Groups. Geological Survey of New York, Natural History of New York, Palaeontology: Volume 7:1-236

[Kane]

Thank you so much, Scott! Now that is an exciting prospect!

The corniferous limestone = Onandaga Fm, which pretty much includes the Amherstburg Fm where this material is drawn. Not only that, but Echinolichas eriopis is similar to, yet distinct from E. parallelobatus in Fagerstrom (1961), the latter of which was identified by Ludvigsen in the Formosa Reef as Acanthopyge contusa (1987). All that said, this is possibly the first E. eriopis on this side of the border (or at least that hasn’t been reported yet). 

 

I’ll continue amassing these lichid fragments from this material. They are relatively abundant. 

[digit]

15 hours ago, Kane said:

All that said, this is possibly the first E. eriopis on this side of the border (or at least that hasn’t been reported yet). 

Nice when our explorations push the edge of known science, causing it to expand just a bit.

 

 

Cheers.

 

-Ken

[Kane]

3 minutes ago, digit said:

Nice when our explorations push the edge of known science, causing it to expand just a bit.

 

 

Cheers.

 

-Ken

It certainly is.  That's part of the reason I'm diligently trying to collect as much of the material as possible... just in case!

[Kane]

The usual trilo-bits...