Taconic orogeny Taconic orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the East coast of the United States. As the mountain chain eroded in the Silurian and Devonian periods, sediments from the mountain chain spread throughout the present-day Appalachians and midcontinental North America. Beginning in Cambrian time, about 550 million years ago, the Iapetus Ocean began to close. The weight of accumulating sediments, in addition to compressional forces in the crust, forced
Svecofennian orogeny and thick continental crust collapsed under the influence of gravity and spread out. By 1850 millions years ago this collapse had evolved to a dynamic of extensional tectonics. In this extensional milieu short-lived sedimentary basins formed. The Svecobaltic orogeny developed when subduction bought the Fennoscandian Craton into an oblique collision with the Sarmatian Craton. The mentioned sedimentary basins were destroyed by basin inversion 1830 million years ago. This last event of basin inversion was associated with a period of metamorphism in southern Finland that peaked about 1820 million years ago. Two models exist regarding the origin of the Nordic orogeny: