July 10. Joggins Formation, Nova Scotia

With the collision of Gondwana and the combined North America-Europe, a pretty significant mountain range was formed. The deformation was mostly the Alleghenian Orogeny in eastern North America and the Variscan in southern Europe, and while it made some new mountains it probably rejuvenated some old mountains as well, including parts of the Caledonian mountain belt between Maritime Canada – Nova Scotia and Newfoundland – and Greenland on one side and the British Isles and Scandinavia on the other.  

Within the mountain belts, quite a variety of environments formed, including extensive swampy basins in which abundant plant life lived, and died to make the coal that gives the Carboniferous its name. One such swampy basin was in what is now western Nova Scotia, where a low-lying area received sediments that became the Joggins Formation. 

Photo of upright Pennsylvanian tree fossil in
Joggins Formation by Michael C. Rygel.

The tectonic deformation that was associated with the continental collisions wasn’t all just a big crunch, a big squeeze. In places, because of the angle of collision, actual extension could occur, leading to down-dropped areas that became basins. In some places including parts of what is now Nova Scotia, older salt deposits might have been dissolved and flowed so that there was very rapid subsidence and infill of sediments. This is one explanation, suggested by geologists John Waldron and Michael Rygel, for the many upright tree fossils that are found in the Joggins Formation. The trees could have been buried during life by incursions of sediment. The sediment was brought from the Caledonian highlands by complex river systems, resulting in the alternating coal swamps and the sands and silts that buried them, pretty much the standard example of Pennsylvanian coal deposits.

The package of rocks is one of the best examples of Pennsylvanian coal strata in the world. At least Charles Lyell thought so. Lyell was the author of the books entitled the Principles of Geology, which arguably made geology into a modern science, and Lyell wrote that these were the finest examples of coal-age rocks on earth.

The upright fossil trees at Joggins contain animal fossils as well, including the oldest known reptile. We’ll talk more about them in a couple days.

The fossiliferous cliffs at Joggins are a World Heritage Site, designated in 2008.

—Richard I. Gibson

References:
Joggins Formation 
Alluvial sedimentology and basin analysis of Carboniferous strata near Joggins, Nova Scotia, Atlantic Canada, by Michael C. Rygel, 2005
Five more articles
Historical perspective on the Joggins cliffs geology 
Jogins Fossil Cliffs

Photo of upright Pennsylvanian tree fossil in Joggins Formation by Michael C. Rygel.