Dictyonema sp. graptolite from the Coburg Formation

The second the three Graptolites species that I've found in the Coburg formation is Dictyonema sp.  It appears as a net like carbon coating on the rock face. Mostly you find them on small fragments of rock but occasionally you will get a big slab where you can get a feel for how big some of the colonies could get. Dictyonema is a genus that is extant from the Ordovician all the way thru to the Devonian but it is hard to get a species because most fossils are not preserved well enough.

On this sample, there is also some Melanostrophus sp. Graptolites.

Here is a link to the Baltic fossil ID website, FOSSIILID.info which has some more examples of this Graptolite.

Here are other examples of this Genus that I've collected in the Silurian aged Rochester shale, and Devonian aged Windom shale.

The Coburg formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 130 to help identify these fossils.

Melanostrophus sp. graptolite from the Coburg Formation

Graptolites are mysterious lifeforms that lived primarily in the early Paleozoic era. They often formed colonial structures that floated in the water column. Melanostrophus sp. is an odd member of the group in that it does not form straight, segmented colonies. Instead they have curved or wavy structures. According to William Hessin's book "South Central Ontario Fossils", some paleontologists have considered Melanostrophus sp as a type of annelid worm. Whatever the case, this fossil is somewhat common in the upper layers of the Coburg formation and appears as a black carbonaceous coating on limestone surfaces.

The Coburg formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
This fossil was collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 264 to help identify it.

Sowerbyella sericea brachiopod from the Coburg formation

One of the more common brachiopod fossils found in the Coburg formation is Sowerbyella

sericea. This genus ia also common throughout the Ordovician across the US.  S. sericea is a rectangular shaped shell that has a convex pedicle valve with a concave brachial valve. In the Coburg formation it is often found on the surface of limestone layers covered by shale. At other times I've found them within the limestone layers when I am splitting rocks. At that time they will take on a shiny, silvery sheen as the shells are un-weathered and possibly damaged from the splitting.

Here is a plate with dozens of examples of this species present.

On the back side of the plate are some of the un-weathered fossils I mentioned earlier.

This is another sample where the specimens of Sowerbyella sericea overlap one another in a kind of pavement. This is likely the result of a storm current that swept up the fossils and deposited them in a jumbled heap.

The Coburg formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 125-126 to help identify them.

Isotelus "mafritzae" trilobite from the Coburg Fm.

One of the big draws to the Coburg formation exposure in the St. Mary's Cement Quarry is the abundance of Isotelus sp. Trilobites. Pieces of molts are very common but it is not uncommon to find complete specimens as well. There are two species of Isotelus found in the Coburg fm., I. latus and Isotelus “mafritzae” (note that this is an informal name as the species has never been formally described). The latter is the most common while the former is know primarily from huge isolated pieces of it's shell. The easiest way to tell the two apart is that  I. latus has a more rounded cephalon and pygidium.

This is a partial molt of Isotelus “mafritzae” that appears to have the cephalon tucked under, but after some prep work by a friend it was found to just be a thorax and pygidium. Still it's a nice articulated specimen that I just need to trim some excess matrix from.

This is an inverted specimen of Isotelus “mafritzae” that unfortunately has had most of the shell weather away. The impression of the exoskeleton is still in the rock which is nice, but the reason I kept it is that the hypostome is still intact and in place. The hypostome is a part of the mouth on trilobites and has a slightly different shape in each genera.  More often you find this part loose and isolated in the rock so this is a nice example of it in life position.

Here is an isolated pygidium of an Isotelus “mafritzae”.  They are typically very smooth with a slightly raised central lobe that is more pronounced as it gets to the thorax.

The Coburg formation is Ordovician in age (late Ordovician, Katian/Mohawkian stage).
These fossils were collected from the St. Mary's Limestone Quarry in Bowmanville, Ontario. I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, pg. 197-199 to help identify them and provide some of the descriptive information I wrote above..

St. Mary's Cement Quarry site overview

I'm going to start a series of posts that will focus on the fossils I have found in the Coburg and Whitby formation at the St. Mary's Cement Quarry in Bowmanville, Ontario.  I have been fortunate enough to get into the quarry three times in the last two years and I need to consolidate what I have collected and get everything labelled and named.  The quarry is private property and is actively worked my visits are as a member of a local club, Gem and Mineral Club of Scarborugh, during official club trips.

A view from inside the quarry

The quarry mines primarily the Coburg formation but the very top most layers are part of the Whitby formation while the very bottom most belong to the Verulam formation.  This exposes a nice chunk of upper Ordovician rock that is rich with fossils. The Coburg formation is primarily composed of  limestone beds with some thin layers of inter-bedded shale. The layers tend to vary from 1"-12" thick.  The Coburg formation has two members within it's layers, the Hillier and the Hallowell. The Hillier member comprises the majority of the Coburg with the Hallowell confined to the lower portion above the Verulam formation. The largest difference between the members is that the Hallowell has thicker limestone beds with a coarser grain.

I have found Trilobites, Crinoids, Cephalopods, Corals, Bryozoans, Graptolites, Ostracods, Pelecypods, and Brachiopods during my trips. I primarily hunt for fossils by looking at the surface of the rocks in a pile and see if I find anything of interest. If not I will try to split the rock and look some more. Sometimes you find the best fossils when you split.  Not many of the fossils weather loose and are easy to pick up. The limestone is a little bit harder and more erosion resistant and there are less fossil in the shaly layers.

A big pile of Coburg formation to search.

The Whitby formation is primarily represented by a thick section of black shales known as the Collingswood member. Typically black shales don't often have many fossils but the Collingswood surprises you with a decent amount of variety. I've found Trilobites, Cephalopods, Ostracods, Pelecypods, Gastropods, and Brachiopods in my searches. The primary method to find the fossils is splitting the thin bedded shales.

The Verulam formation is at the bottom of the quarry and is not extracted as much as the Coburg. It is more shaly and not as desirable for some construction purposes.  I've not spent much time collecting in the Verulam at Bowmanville as I tend to spend my time in the Coburg or Whitby formations. The fauna of the Verulam is similar to the overlying Coburg formation but with slightly different genera or species. It is easier to pick up loose specimens from the Verulam formation as the limestone seems to be a little softer and the shaly layers have more fossils.

As I mentioned before, this is an active quarry and we are sometimes limited as to where we can collect. As you can see from the picture below, the quarry machinery is quite large and would not notice if you were in their way.

That's it for the introduction, The next post will start on the fossils that I have found from this quarry so far.

I used William Hessin's book "South Central Ontario Fossils", 2009, Self Published, as a source for the technical info in this post