Our Local Fauna

A fossil's "life" and a fossil's "death"

Fossils are any evidence of past life. Some theorists argue that many things we take for granted, such as concentrated gold deposits and possible even clouds, may be in part a result of past life (and thus fossils).

Not only do certain very unusual conditions have to be met at the time of death for organisms to be preserved but fossils also have to survive other dangers. Over time fossils may ride the earth's crust to great depth where pressures warp and compress fossils. At these great depths the heat can be so great as to actually melt the rock.

Even if fossils survive these threats over millions of years continents can travel hundreds of kilometres. If the rock strata is forced upward it can be exposed to erosion. Just as sedimentation once buried the fossil, the earth's processes run in reverse, bring air, water and fragmentation, so that rock that took millions of years to be laid down is soon ground into dust.

As a final challenge the Cenozoic ice ages sent a series of great glaciations, sheets of ice hundreds of metres tall that scoured the land every few thousand years, taking away the surface until they were scraping bare rock and moving surface material hundreds of kilometres.

Two key local geological events to remember

To begin we will start with the sea Iapetus 465 million years ago (during the Ordovician), an ancient and alien living world, which put down much of the areas limestone (as well as the fossiliferous shale). Imagine this place first, for more time will have elapse before the first even takes place then has elapsed since.

Sometime, most likely in the Jurassic, the crust we currently stand on was under tension, it was being pulled apart and it, well..., it sunk. The result is the "Bonnechere graben": Essentially all of the rock strata in the Ottawa valley is considerably lower than its counterparts outside of the valley. This is important because it protected early paleozoic rocks from the glaciers that would eventually sweep the land.

The second major event, as you may have guessed, are the last ice ages. They came in almost the blink of an eye, geologically speaking (so recent in fact that some oral history appears to survive), brining walls of moving ice up to kilometres in thickness.

This had two major effects:
First, as covered above, they removed the fossiliferous paleozoic rocks from surrounding regions. As it did this much of the rock was crushed forming the Leda clay. Second, the glaciers depressed the continent's crust causing seawater to move inward from the ocean.

The result was an inland sea, the Champlain sea, in which arctic whales swam and seals gave birth to pups on ice flows in this area (10,500 years ago). This was followed by giant fresh water rivers during the last stages as the glaciers melted and then our modern "relatively dry" period. What is left is a system of bogs and sandbars among the other glacial features and in them a fauna of shells, nodules (some containing fishes) and even some mammal bones.

Further reading:
Geoscape Ottawa-Gatineau lesson plan (NRcan)
The Geology of Montreal (Mcgill)

P.S. Watch out for erosion: After all it is thought that the Gatineau hills were once higher than Everest (mind you they were already their current height by 600 million years ago). Of course, millenia ago and looking out at the receeding melt waters from the top of these hills, we would see how the roots of mountains become shoreline.

One question though: If these mountains saw the Iapetus come and go as well as the Champlain, how long will it be before these hills see another sea come ...in this "history of water"?

- Jonas Weselake-George

The Cenozoic

As mentioned above there is a diverse salt and mixed water fauna, including a wide variety of shells, nodules with teleost fish and even rare mammal bones (and even a frog). Most of this was only a few thousand years ago and there is little mineral replacement ("fossilisation"). For the most part these are found in sand deposits, or in the case of nodules in some stream beds.

Gallery: Remnants of the ice walls

The Paleozoic

Our fossils touch the late Cambrian, but include mainly Ordovician, as well as some Silurian strata. These are all aquatic (with the exception of the earliest evidence for amphibious behaviour found further southwest).

The fossils include a variety of (the ultra charismatic) Trilobites, sessile (stationary) organisms in the form of Blastoids, Crinoids and Brachiopods, all filter feeders, most of which who grew stalks in this period. In addition there are some sponges and worm burrows. Finally, we find fossil cephalopod shells - top predators of this period (who eventually shed their shells to become the fastest and most intelligent marine invertebrates)

Can't get your trilobite taxonomy taxonified? Are you unable to develop an obsession with ocular furrows? Check out Sam Gon III's Guide to the Orders of Trilobites

Gallery: Crinoids, Blastoids & Brachiopods

Gallery: Trilobites 1

Gallery: Trilobites 2

It is good to note that many of these fossils have been professionally prepared (using special air abrasers). When they are first found they are covered in mud and buried in the mud. Here is a set of before and after pictures (the before has been split from the rock and possibly glued and washed).

The Precambrian?

Rocks that have survived the six hundred or so million years are rare, rarer still are those rare conditions that were able to preserve silhouettes of those early soft bodied progenitors of modern multicellular life and their finer single celled counterparts. For these reasons the only known fossils that may have precambrian origins in the Ottawa area are some possible stromatolites (colonies of encrusted cyanobacteria). This is still under investigation.

J.A. Donaldson has some good information on some more recent Paleozoic stromatolites in the area