Silurian Rocks at Arisaig, NS

Silurian rocks from Arisaig, Nova Scotia, Canada.

The Northumberland Strait shoreline of Arisaig Provincial Park in Nova Scotia, Canada, is described as one of the best sections of Silurian rock in the world. The strata are shales, sandstones, and siltstones from the Arisaig Group which was deposited in the early Silurian Period dating from about 443 to 424 million years ago.

I was fascinated by the way that some of the rocks were made up hundreds of extremely fine layers that were breaking up very easily. As far as I understand it, these darker shale layers were the result of deposits created in the coastal waters of the time by storm events rather than by tides or currents; and they are known as tempestites.

Hickman Hild and Barr (2015) say that the uninterrupted accumulation of fine-grained sediment during the Silurian Period, exposed here along a continuous 5 kilometre stretch, suggests that the area was tectonically quiet for at least 20 million years.

REFERENCES

Donohoe, H. V. Jnr, White, C. E., Raeside, R. P. and Fisher, B. E, (2005) Geological Highway Map of Nova Scotia, Third Edition. Atlantic Geoscience Society Special Publication #1.

Hickman Hild, M. and Barr, S. M. (2015) Geology of Nova Scotia, A Field Guide, Touring through time at 48 scenic sites, Boulder Publications, Portugal Cove-St. Philip’s, Newfoundland and Labrador. ISBN 978-1-927099-43-8, pp 50-53