Permian to Present 1: Reading Bedrock
Welcome to the first installment of my new series “Natural History of PEI: Permian to Present”. I’ll be posting these occasionally among my other two series on plants & habitats and wildlife tracks & sign on Prince Edward Island, Canada. If you’re interested in this stuff, follow me here or on Facebook so you don’t miss any posts! 😊
Prince Edward Island’s story starts during the late Carboniferous and early Permian Periods, roughly 300 million years ago. At this time, we weren’t an island on the north-east edge of a continent but instead located near the equator, in the middle of the supercontinent Pangea (Photo 1).
The earlier collision of continents that formed Pangaea created the Appalachian Mountains. The slow erosion of these mountains over millions of years produced the sediment that became the Island’s famous red sandstone bedrock (Photo 2).
These sedimentary layers record history in a way similar to tree rings. Oldest layers are at the bottom, and each one tells us about the environment when it was formed. Green-grey layers are unoxidized and often point to very wet periods; the pebbly conglomerate above the green-grey layer in Photo 3 records a period of fast-flowing floodwater.
That thick layer of finer sediment (called mudstone) between the green-grey layers in Photo 4 was formed beneath standing water such as an ancient lake or slow-moving river.
Ripples in the rock (Photos 5 and 6) were formed under shallow water with lapping waves, just like we see ripples in the sand of intertidal zones and sandbars on PEI beaches today.
The width of the ripples is proportional to the width of the waves: faster, shorter waves create narrower ripples than do the slower, longer waves of slightly deeper water. This all points to an ancient lake shore.
Sedimentary layers are always horizontal when formed. Finding them on an incline (Photo 7), is evidence of the immense geological forces associated with movement of the continents – strong enough to tilt the entire landscape! The tilt shown is only about 20 degrees or so, but you can find even more dramatic examples around the Island’s coast.
Our sandstone bedrock not only preserved information about our pre-historic climate, but also evidence of pre-historic plants (and animals) that flourished in this topical, monsoonal world. In the next edition of Permian to Present, I’ll show you some examples.