A hand holds up an erractic fossil. There is a boat and Bute Inlet in the background.

Glacier-borne fossils in the Discovery Islands

Over the past 20 years, Christian Gronau has documented 149 fossiliferous rocks in our area. 

Fossil #144 was recently installed at the Cortes Island Museum, but the German-born and trained palaeontologist said, “Palaeontology became a question for me when I was settled here. I looked around, of course was interested in the local geology, and realized that Cortes is just a big pile of granite with very little exceptions to that rule and started wondering what I was going to do with my interest in fossils.”

Image credit: The important pieces of evidence in support of Bute Inlet having been the main conduit for the transport of Buchia erratics from the Potato Range to Cortes Island. Fossil #129 found by Barry Saxifrage, Fossil #130 by Christian Gronau – photo courtesy Christian Gronau

He moved to Canada in 1972 and met his partner, Aileen Douglas, while working in the mining sector. 

Regarding their decision to move to Cortes Island in 1978, he explained, “it’s a winding path, a complicated path, but a happy path that led me here and palaeontology didn’t feature into the decision making. More the landscape, the political climate of Canada, people of Cortes. This was a long time ago.”

He and Aileen moved to a water access only property without hydro or telephone and became shellfish farmers, but palaeontology is very important to Christian Gronau.  

“It’s one of the major aspects of defining our existence, explaining our origins, putting us in some context and giving us an identity on this planet. It gives us a real sense of deep time, because we can trace our ancestry as far back as life itself, which I think is pretty profound, pretty important.”

The Lead Scientist  (Lead as in Pb), Christian Gronau examining specimens at Shoal Bay, East Thurlow Island – Photo by Aileen Douglas
Fossil #1 from Gorge Harbour, Cortes Island – Photo courtesy Christian Gronau

Everything changed after fossil #1 turned up in Gorge Harbour.  

Gronau learned of it after complaining, “I don’t know what I’m doing here. There are no fossils here.” 

“A neighbour responded, ‘Yes, there are.’” 

“I said, ‘No way!’ 

“And he said, ‘yes, my son Mikey found one, and sure enough, he produced a tiny  inch size pebble that had fossil imprints in it.’  

It was a beach pebble, well rounded and clearly not coming out of Cortes Island’s granite hills. 

So if the pebble wasn’t local, where did it come from? And how did it get here?  

Gronau wrote to an acquaintance at the Geological Survey of Canada in Vancouver, Dr. Jim Haggard, who ‘got quite excited.’ He recognized the clam like shells in the pebble. They were bivalves from the Lower Cretaceous era, 130 million years ago. Haggard also had an idea where the fossil rocks might have originated. 

Erratics have been found as far as West Thurlow Island. Before – Fossil #76, West Thurlow Island – Photo courtesy Christian Gronau
After – Fossil #76, West Thurlow Island – Photo courtesy Christian Gronau

“There are outcrops on the west coast of Vancouver Island, not far from Kyuquot, for instance. He envisioned an inland sea stretching all the way from Haida Gwaii across Northern Vancouver Island, passing by Kyuquot and then across Cortes island. He was hoping that further research could find the source of this one little pebble near Cortes Island,” said Gronau.

“After hearing that, I took photographs of the one little specimen, put posters out, asked people about it, and I got responses. That’s how it all started, well over 20 years ago, and now we are almost at 150 such fossil finds that have been documented and photographed.”

So far, none of the fossils have originated locally. 

“Every single specimen that we have in our possession or that we have documented is an ‘erratic.’ In other words, it has been transported by glaciers,” he explained.  

Erratics have been found as far south as Smelt Bay on Cortes Island. David Ellingsen with Fossil # 63, which he found at Smelt Bay – Photo courtesy Christian Gronau
Fossil #25, which Niko Mense found at Plunger Pass, Cortes Island

“You can usually tell at first glance, because the piece is well rounded. It has been rolled, pushed, and tumbled by the glaciers. Sometimes you have scratch marks on the surface called striae that glaciers will leave behind.”

After 20 years of research, he has come to the conclusion that glaciers transported most, possibly all, of the fossiliferous erratics from the Potato Range, about 200 kilometres away in the Chilcotins. They would have been carried down the Homathko River, into Bute Inlet and south into the Discovery Islands. This would have occurred 14,000 to 16,000 years ago, during the last advance of the Ice Age. 

 “The fossils themselves are, as I mentioned, much older. They’re 130 million years old. They’re Lower Cretaceous and they have been sitting in the rocks of the Potato Range for a very long time until erosion and the last Ice Age scraped them loose and pushed them all the way down to Cortes. The farthest occurrence, the far south location that we have documented for these fossil erratics is Smelt Bay. That’s where it stands right now. The total is 149 recorded specimens,” explained Gronau.

Map panel from the Cortes Island Museum – Photo courtesy Christian Gronau

“The answer that we were looking for came last year, when we actually went up Bute Inlet and sampled its rocky shores looking for erratics that had Buchia in them.” 

Gronau emailed, “This is very simplified.  We had looked at Bute in 2008 once, but the probabilities of finding Buchia-erratics in this steep-sided fjord are very small (for glaciological reasons).  We revisited Bute in 2021 and spent a lot of time looking, before we succeeded in finding a total of 5 tell-tale specimens.”

“Buchia is the genus that basically all the fossils that we find in these erratics belong to. It’s a very monotonous fauna. It could compare to our modern blue mussel beds that are immense,  thousands and thousands of them packed together. If you imagine them turned to stone and then scraped down Bute Inlet and all the way to Cortes Island , you kind of get the idea. There are few other species of invertebrates that have been documented but, all in all, it is dominated by the Buchia Bivalves.”

Christian Gronau with Fossil #59 on Read Island – Photo by Aileen Douglas

The other invertebrates they found were:

  • Belemnites – ‘squid-like creatures that have a torpedo shaped  internal skeleton like the cuttlebone in a Cuttlefish only more cylindrical and heavier.  They are a classic Mesozoic fossil, well known from the Jurassic and specifically from the Cretaceous.’
  • several other species of Bivalves, including a primitive scallop 
  • a couple of Ammonite fragments. ‘It would be nice to find a good specimen of an Ammonite because they are very precisely identifiable. And it would give us an even more clear idea of how old the original rocks are.’ 
Illustration courtesy Christian Gronau

“This winter, I hope to be able to sit down and write a much more concise, readable and entertaining account for the museum,” said Gronau. “I like to call it a never ending story because there are more and more finds that are coming our way and more and more detailed descriptions that can be made, but it is a never ending story with the conclusion since we know the probable source of these erratics,  the travel path that they took, and  that enables me to write it down because I have a last chapter for that.”

Top image credit: Fossil #129 – proof positive : Buchia erratic a long way up Bute Inlet – Photo courtesy Christian Gronau

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