The Ancient Ordovician Sea Floor

[Walter Piorkowski]

Leitz Ortholux microscope
4X Leitz projection eyepiece plus 1/3x relay lens

Image No.1
Horizontal Field of View 10.25mm
13 images at .005 inch increments
Nikon 1.2x Plan Achromat objective
Diffused Fiber Optic Illumination

Image No.2
Horizontal Field of View 10.25mm
15 images at .005 inch increments
Nikon 1.2x Plan Achromat objective
Diffused Fiber Optic Illumination

Canon 50D
Zerene PMax and Photoshop 7 processing.


Last summer a field trip was taken to a local quarry to do some fossil hunting. The quarry, in Dixon Illinois, exposes a 450 million year old epeiric sea floor that back then covered the American Midwest. The orientation of the North American continent at the time put Illinois close to where the Bahamas are today. All life of the period has now been turned into limestone of the Platteville Group.

Bits and pieces from the processing of larger specimens have ended up under the microscope. Most of the microscopic animal life that was deposited is in pieces or pretty well crushed up but intact shells of some clams survive as in image number two.

In image number one I believe the circular objects are crinoid ossicles. And I believe that I have identified the infant clam resting upon the more massive adult as both Hesperorthis concave Cooper.
Walt

[Peter M. Macdonald]

Walter,

There are a number of identifiable piecs of other things as well as the large shell and the crinoid ossicles.

At the top of the right edge of the first picture is a moult casting of the tail section (pygidium) of a trilobite. It is cut through by the edge of the frame. We are looking at the inside surface of the cuticle.

In the same picture there are a number of pieces of bryozoa. At the left edge, just above the centre is a small piece of a stick shaped bryozoan. There are other pieces at the bottom right and between the topmost two crinoid ossicles. Looks like some of these pieces had a roll about the seabed for a time before being fossilised, whilst others are much fresher. In particular, the trilobite and the lowest bryozoan are very fresh, with nicely defined markings. The crinoid ossicles and the bryozoan between them have been abraded by being rolled about.

In the lower image, the large quadrangular object at the bottom right is probably a piece of coral. This too has been abraded sufficiently that it is not possible to make a firm exclusion of another pirce of bryozoan, but coral is far more likely.

Regards,

Peter

[gjones]

Very interesting photos and discriptions!

[Walter Piorkowski]

Hello Peter. Thank you so much for fleshing out the details that your skilled eyes picked up in my images. This knowledge answers some questions and will add to the enjoyment that I will get out of examining these fossils in the future.

Thanks for looking Grant.
Walt