Thursday, September 29, 2011

Cererithyris arkelli

Today's fossil is Cererithyris arkelli from the Bathonian stage of the Jurassic (164-167 mya). These were collected from Luc sur Mer in the providence of Normandy, France. It is a Terebratulid and shows just a little bit of plication (the zig-zag folds) near the front edge of the mature shells.






Thanks to my good friend Gery, who collected these himself, for sending me these fossils!

Tuesday, September 27, 2011

Coenites verticillatus from the Louisville Limestone

I've shown you some specimens of Coenites that I collected from the Louisville Limestone in this past post. Today I have another species called Coenites verticillatus. It is distinguished from other species in that the diameter of the colony is much larger and it has a unique growth pattern.

As you can see from the above specimen, Coenites verticillatus seemed to grow on the periphery or sides of the coral reef. It would form a column like shape between a base and the lower surface of another coral. In the first picture you can see that the top of the column spread out once it contacted another surface. Thanks to Mike and Kenny for showing me the spot where I found this.

Sunday, September 25, 2011

Pleurodictyum from the Jeffersonville Limestone

The specimens shown below are of Pleurodictyum and came from a site that was mixed Louisville Limestone and Jeffersonville Limestone. I can't say for sure which formation it came from but more than likely it came from the Jeffersonville. I base this on the diameter of the corallites which could correspond to two species known from the Jeffersonville Limestone: P. planum or P. maximum.

The Jeffersonville Limestone is middle Devonian in age (Eifelian) while the Louisville Limestone is upper Silurian (Ludlow). They are separated by about 20 million years and yet the Jeffersonville rests unconformably on top of the Louisville. This is what makes things tough to identify when rocks and soils developed from the two are mixed.

Friday, September 23, 2011

Diplotrypa franklini

As I've said before many times, Bryozoans are very hard to ID down to the species level. Even to get to the genera level is tough unless there is some readily identifiable physical feature. So how can I say with any confidence that the Bryozoan specimens below are likely Diplotrypa franklini? Simple, I read about it.

Here are a couple of specimens, note the rounded shape and layered structure. The shape is due to the colonies being overturned during storm events and the bryozoan growing back around to the newly upturned surface. The layering is the result of annual growths and is highlighted by the selective preservation of some layers by Silica while other remain Calcite.

You can make out the pore structure very well on weathered specimens.

These are a couple of specimens that I etched out of the limestone with acid.

The locality I found these at near the Juniata River in Juniata county, PA. There is a small borrow pit and railroad cut that slice through layers of rock from the Silurian aged Keyser formation. I found out about this exposure by reading an issue of Pennsylvania Geology, the official publication of the Pennsylvania Geological Survey, which discussed the paleoenvironment that these Bryozoans came from. Here is a link to a .pdf of the issue. Within the article they note that there are nine different species of Bryozoan that can be found at the site but the most prevalent is Diplotrypa franklini. So while I can't examine the micropores with an electron microscope or thin slice a colony I can say, with a fair amount of certainty, that the specimens I found are likely to be from the most common and abundant species present.

A piece of advise from me to anyone who wants to seek out the site, stay off the railroad tracks as they can be dangerous because of train traffic. 

Wednesday, September 21, 2011

Marble Hill Bed fossils

The fossils I'm featuring today are from the Marble Hill Bed. This is a layer within the Ordovician (Richmondian) aged Whitewater formation and is found in a geographically small area near Bedford, KY. Within the unit is a very limited fauna that is dominated by Mollusks most of which are Paupospira bowdeni(Loxoplocus bowdeni). It has been interpreted as a shelf edge bar deposit.

Here are some of the fossils that can be found within the bed. Clockwise from left, Orthoceras nautiloid, Cyclonema gastropods, Paupospira gastropods and Cycloconcha Pelecypods.

One of the interesting aspects about this bed that has been studied is that the shell material of the fossils has been recrystallized from the original Aragonite to the more stable Calcite. The recrystallization was very unusual because the lamellar microstructure of the shell structure has been preserved. This is different from how mollusks are generally preserved within other parts of the Ordovician formations which is by casts of the internal body space or by dissolution and redeposition of the shell by Calcite.

Thanks to Mike at Louisville Fossils and our mutual friend Herb for the fossils. Mike has write ups of Paupospira and Cycloconcha on his site.

Monday, September 19, 2011

Callixylon newberryi

The Devonian is the time period during which the first "trees" evolved. This is evidenced by fossilized wood that is found within sediments that were laid down in the ocean. The piece below is a portion of Callixylon newberryi and was given to me by my friend Herb who found it in Kentucky within the New Albany Shale.

You can see wood grain structure when viewed closely. Mike over at Louisville Fossils has some magnified pictures of one piece.

The New Albany Shale is a series of thin bedded black shales that were deposited in the Upper Devonian to Lower Mississippian. It corresponds to the Antrim Shale of the Michigan Basin, the Ohio Shale of eastern Ohio and eastern Kentucky, the Chattanooga Shale of Tennessee and central Kentucky and the Kettle Point formation in Ontario (technically part of the Antrim shale).

Saturday, September 17, 2011

Flexicalymene from Ohio

I've explored many outcrop of Ordovician rock in the Cincinnati region of Ohio/Kentucky/Indiana but never have I found a whole trilobite. The local collectors are so efficient that even parts can be hard to find. My friend Herb had the unfortunate experience of listening to me grumble about this fact so he gave me this enrolled specimen of Flexicalymene. He found it near Waynesville, OH in the Whitewater Formation which is Ordovician in age (Richmondian stage of the Cincinnatian series which corresponds to the Ashgill stage in Europe and Katian stage of the ICS).

Thanks to Herb for giving me this fossil. One day I hope to find one for myself "in the wild".

Thursday, September 15, 2011

Nautilus from Caen, France

Nautilus are cephalopods related to the Ammonites and look similar but their shells have less complex chambers. Whereas in Ammonites the walls that separate the chambers can be very complex and intrcate (sometimes resembling fractal patterns), Nautilus generally are plain and simple. Kind of like the Amish of the Cephalopod world. The specimen below is from Caen, France and is from the lower Jurassic (Toarcian stage). You can see that some of the replaced shell is still in place.

Thanks to Gery for this fine specimen.

Tuesday, September 13, 2011

Zeilleria humeralis

Zeilleria humeralis is another Jurassic (Oxfordian) age brachiopod and this one was found at the beachside cliffs of Villers sur Mer, France.


Thanks go out to my friend Gery for sending me this specimen.

Sunday, September 11, 2011

Romingerella major from Kentucky

These are some specimens of a fossil coral called Romingerella major from the Louisville Limestone near Louisville, KY. These have been silicified and the original calcite skeletons replaced by Quartz. The process is not always the most detailed and produces features called "Beekite" (rounded blobs of Quartz) that often obscure the finer surface details.

It was thanks to this specimen that I was able to determine the species. Note the star like structures that surround the corralites.

This species may also be Thecia major but the book that I used to ID the specimen (E. C. Stumm. 1964. Silurian and Devonian Corals of the Falls of the Ohio. The Geological Society of America-Memoir 93 1-184 [A. Miller/K. Layou]) indicates that is should be called Romingerella major. As I can't find any more current reference I'm going to stick with the Stumm book.

Thanks to Mike and his cousin Kenny for showing me around Louisville.