Tectonic Cross-sections of the United States during the Triassic

During the Triassic Period, North America was on the western margin of the supercontinent Pangaea. During the latter part of the period this supercontinent began to disintegrate. Along the future eastern continental margin, large fault-bounded basins formed. These basins were filled with red clastics eroded from the surrounding highlands. At the end of the Triassic an episode of volcanism began, wherein magma flowed to the surface along the fracturing continental crust. This episode of volcanism, known as CAMP volcanism (Central Atlantic Magmatic Province), is responsible for the formation of the Roundtop Hills and Seminary and Cemetery ridges at Gettysburg National Battlefield Park, and the Palisades along the Hudson River.

Along the western edge of North America, the collision of the ancient Farallon ocean plate with Pangaea produced an arc of volcanic islands, and an intervening sea filled with volcanic sediments.

Graphic: David K. Brezinski