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
Nevadan orogeny deformation from the Nevadan Orogeny in the Eastern Belt is somewhat limited. It was determined that the deformation was minimal in the Eastern Belt by looking at dikes that had intruded the rocks which appeared to be mostly undeformed. These mostly undeformed dikes were dated using the K-Ar method and were determined to be between 169 and 209 Ma in age, which implies they were placed well before any deformation related to the Nevadan Orogeny would have occurred. As the age of these dikes are older than the deformation of the Nevadan Orogeny, it is evident that most of the