Paleozoic Tectonics and Paleogeography

What Did the World Map Look Like 541 to 252 Million Years Ago??

During the Paleozoic Era, sea levels rose and fell four times. With each sea-level rise, most of North America was covered by a shallow tropical ocean. Evidence of these submersions is the abundant marine sedimentary rocks such as limestone with fossils, corals, and ooids. Widespread unconformities document extensive sea-level falls. Today, the midcontinent has extensive marine sedimentary rocks from the Paleozoic. Western North America has thick layers of marine limestone on block faulted mountain ranges such as Mt. Timpanogos near Provo, Utah.

The assembly of supercontinent Pangea, sometimes Pangaea, was completed by the late Paleozoic Era. The name Pangea was originally coined by Alfred Wegener and means “all land.” This supercontinent existed when all the major continents were grouped by a series of tectonic events, including subduction island-arc accretion, continental collisions, and ocean-basin closures. The Appalachian Mountains are the erosional remnants of these mountain-building events in North America. Surrounding Pangea was a global ocean basin known as the Panthalassa. Continued plate movement extended the ocean into Pangea through rifting, forming a large bay called the Tethys Sea that eventually divided the land mass into two smaller supercontinents, Laurasia and Gondwana. Laurasia consisted of Laurentia and Eurasia, and Gondwana comprised the remaining continents of South America, Africa, India, Australia, and Antarctica.

While the east coast of North America was tectonically active during the Paleozoic Era, the west coast remained mostly inactive as a passive margin during the early Paleozoic. The western edge of the North American continent was near the present-day Nevada-Utah border and was an expansive shallow continental shelf near the paleo equator. By the end of the Paleozoic Era, the east coast of North America had a very high mountain range due to continental collision and the creation of Pangea. North America’s west coast had smaller, isolated volcanic highlands associated with island arc accretion. During the Mesozoic Era, the size of the mountains on either side of North America would flip, with the west coast being a more tectonically active plate boundary and the east coast changing into a passive margin after the breakup of Pangea.