18 March 2012

Fossil interlude: Eighteen Mile Creek, New York

Posted by Jessica Ball

The weather has been freakishly nice for March in Buffalo, so yesterday I decided to chuck any ideas of getting work done and went fossiling with a friend instead. The area where I live sits right on top of the Devonian Onondaga limestone, so I’m already surrounded by a very fossiliferous unit (it’s full of things like coral and brachiopods and crinoids). But for a special locale, it’s worth it to head down to Eighteen Mile Creek, which flows into Lake Erie about 12 miles southwest of Buffalo.

Looking southwest along the lakeshore cliffs

The scenery is lovely here – to get to the fossil site, you take a short hike through woods that border the creek and the marshy areas at the lake outlet. But the best part is at the end of the walk: Trilobites!

Well, trilobite bits.

Eighteen Mile Creek is one of the best places in Western NY to find trilobites (and other fossils as well). It exposes the Wanakah Shale, another Devonian unit. Here’s what UB’s Geology Department website has to say about it:

“At its type locality north of Eighteen Mile Creek along Lake Erie shore, the Wanakah Shale consists of about 19.8 m of medium gray, soft, fossiliferous shale and shaly mudstone with several calcareous bands and zones of larger concretions. The highest beds of the Wanakah Shale exposed just below the Tichenor Limestone contain a high diversity fossil assemblage termed the Demissa and Stictopora beds of Grabau (1898, 1899). These units yield over 80 species of macrofossils and are particularly rich in brachiopods and bryozoans.

“At Eighteen Mile Creek, the Tichenor Limestone is a resistant, 30-40 cm thick ledge-forming crinoidal biospharite and biomicrite. It contains numerous large rugose corals (Heliophyllum, Eridophyllum) and heads of the tabulate coral Favosites hamiltoniae, large crinoid columns, fenestellid bryozoans and brachiopods. The large bivalves Plethomytilus, Actinopteria, and Goniopora, are locally abundant in the upper surface of the Tichenor Limestone.”

To give you a better idea of the stratigraphy, here’s a diagram of local Devonian units:

Courtesy of Dr. Jorg's sed/strat website (http://www.geology.buffalo.edu/contrib/people/faculty/gly216trip.htm)

Walking along the beach is one easy way to find fossils, but you can also bring along a rock hammer and split chunks of the shale apart (this tends to be where the trilobites show up). We did both, and here are some of our finds:


Brachiopods are really easy to find on the beach, since they seem to stand up to wave action pretty well. I think this is Athyris spiriferoides

Rugose (or horn) corals are also really common, in both the shale units and the limestone.

Occasionally, the rugose coral gets REALLY BIG.

A slice of a rugose coral - it looks a little bit like a really big crinoid stem from this angle, but the crinoids here don't get that large.

There are a lot of concretions in the shale, and they're usually a little crystalline at the center. The color bands are also really common.

Despite the fact that it's shale here (and presumably a low-energy environment), it's hard to find trilobites that aren't broken up. So you see a lot of trilobite butts (pygidiums? pygidii?)

But just occasionally, you find a really awesome trilobite in one piece - like this one! A Phacops rana rana, if this website is correct: http://www.fossilguy.com/sites/18mile/

I didn't even have to break any rocks to find this guy - he was just laying there on the beach.

I think he's a little pyritized, which would explain why he stuck together when all his buddies were going to pieces.

Oxide minerals (maybe pyrite?) tend to show up in this botryoidal form here. These are all over the beach as well, and I think they can be just as interesting as the fossils!

Because Buffalo is an industrial town, there are also some interesting remnants of that industry on the Lake Erie shoreline, like these glassy bits of slag.

But everyone comes for the fossils. And it was a beautiful day for it!

For more information on Western NY Geology (and fossiling at Eighteen Mile Creek and other locales), check out these links: