Marc S. Tremblay
Found: 73 Million Years Old Fossil
Updated: Sep 27, 2022
Last week at low tide, Dana and I visited Campbell Bay. The bay is home to one of the Island's best beaches, with a relatively debris-free, pebbly-sandy beach. Many people swim there because it's calm, the water is a bit warmer and there is even a swim dock with a diving board.
As I combed the beach for interesting shells and rocks, I found what looked to be either, an intricately carved stone, or a fossilized piece of wood with leaves. I posted a photo of it on the Mayne Island Photo Facebook page to see if anyone had ever seen something like it or could identify it.
Some people offered their best guesses, and one suggested I post it on the Vancouver Island Rockhounds Facebook page for proper identification.
It wasn't long before several people identified it as a piece of a large Ammonite.
Ammonites are shelled mollusks that roamed the world's oceans 65-400 million years ago.
Here are five photos of it, with the last photo being one I received from the Vancouver Island Rockhounds, to show the same kinds of "sutures." You can see the same pattern if you look closely at the photo of the entire shell.
Sutures are lines that formed inside the shell. Apparently, these are called "Ammonitic sutures" and are characteristic of ammonites from the Jurassic period (145-201 million years ago), to the Cretaceous period (66-145 million years ago).
So, how old is this piece I found on Mayne Island, you ask?
Let's figure that out...
About 68 to 80 million years ago, Mayne Island was under water, making up the seafloor, hundreds of meters below sea level.
Of course, it wasn't an island yet, but sediment was slowly accumulating on the ocean floor. Over millennia, the seafloor compacted and sediment formed rocks, which were slowly pushed up by tectonic forces.
For info, there are three main types of rock formations on Mayne Island: conglomerate, sandstone and mudstone. The type of stone formed was determined by underwater channels that made specific deposits based on how fast water flowed in specific sections, sometimes accumulating larger rocks and stones, sometimes sand, or fine silt in other areas.
Formations found on the south-east of the island are generally "older" than those found on the north-west of Mayne Island.
Geologists estimate there is a 12 million years old difference from one side to the other, with those making up St. John's Point at about 80 million years old, compared to rocks at Georgina and Edith Points, estimated to be about 68 million years old.
Seeing as Campbell Bay is relatively close to the Edith Point, we can probably assume its in the lower range of the 68-80 million years old, so let's call it 73 million years old, plus or minus 5 million years.
What an amazing find...