Georgian Bay Formation in mosquito-filled creekbed

[markjw]

There is a bit of Georgian Bay formation in my neighbourhood. It is littered with trace fossils and guarded by swarms of mosquitos.

This area surrenders its treasures very reluctantly. There are a few little bryozoan pieces and not much else that I can see.

 

The exception is a single outcrop from which I've pulled some sedimentary rock and found shell imprints. Some are quite wonderful, and there are several species. I think they might have these genus names: Ambonychia, Rafinesquina, Zygospira. The rocks also have all kinds of "colonies" in them, but I cannot identify them and they are not easy to make out.

[Monica]

Hi Mark!

 

This is indeed the bivalve Ambonychia radiata:

 

Nice finds for our area! 

 

Monica

[JUAN EMMANUEL]

Hey Mark, those are good finds.

I have red information from William A. Hessin’s book South-Central Ontario Fossils that the Upper Member of the Georgian Bay Formation is present in Oakville around Bronte Creek just north of a certain railway. This member bears a lot of reef types of fossils like Favistina, Stromatocerium and Prismostylus, similar to what I’ve been finding in Streetsville, Mississauga. Have you ever explored an area in Oakville similar to what I’ve mentioned? The fossils you’ve shown look like they belong to the Lower Member of the formation. 

[markjw]

Hi Juan Emmanuel:

I went looking for that exact place...parked at a Tim Hortons! But I found absolutely nothing except a piece of errant fossilized sponge (I think). Eventually the way was blocked by a giant cliff that was obviously Queenston shale. Very disappointed I couldn't identify the area described in the book.

 

Same with 16 mile creek at Kerr Street (not mentioned in Hessin). Barren bedrock, but found a nice erratic: A big fossilized coral. (Also fossil filled ballast under the road overpass!)

 

I have geological map 2337 which shows exact boundaries of bedrock, but the map stops short at Oakville. The intruding bit of Georgian Bay formation is near the Petro Can refinery, and encompasses lower Jacobs Creek, which is where I found the above fossils. The map is great for your old haunts at Streetsville.

[Al Tahan]

Very nice report. Thanks for sharing