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Oil and Gas … and Potash

Colour image of globe showing changing position of continents 360 million years agoThe Carboniferous Period is named for the widespread occurrences of coal deposited during this time and the high carbon content of these sedimentary rocks. Geologists divide the period into the ‘Lower’ and ‘Upper’ Carboniferous. New Brunswick’s Lower Carboniferous Period rocks are mostly found between Saint John and the Dorchester area. In New Brunswick the sedimentary rocks of the Devonian and Carboniferous are part of the Maritimes Basin. The basin consists of mountains and valleys created as continents were coming together to form the supercontinent of Pangea. The land that would become New Brunswick was located near the equator and Pangea was surrounded by one ocean called the Panthalassic.

During the early part of the Lower Carboniferous, the Albert Formation was formed in valleys that were filled with lakes, rivers and swamps. Near the village of Albert Mines fine-grained lake deposits have yielded specimens of small bony fish called paleoniscids. Further west near Norton the rocks reveal what has been described as the oldest fossil forest in Canada. Remains of almost 700 trees, most in life position, have provided insight into an early lycopsid forest growing along the banks of meandering rivers. Algae growing on lakes in the Maritimes Basin created thick mats on the bottom of the lakes. As the deposits were buried, they formed the oil shales that are now producing oil and gas in southern New Brunswick.

During the Carboniferous global sea level rose and fell as the southern polar ice cap melted and froze. Oceans periodically flooded low-lying parts of the Maritimes Basin to create the Windsor Sea. When sea level dropped and the oceans retreated from the continent, the dry conditions caused the remaining salt water to evaporate, leaving concentrated minerals in the form of carbonate and evaporate rocks such as gypsum, potash, and halite deposits. Sedimentary rocks formed from deposits in the Windsor Sea are found from Hillsborough to Sussex.