Champlain Thrust Fault
June 29, 2004
This photo of the Champlain Thrust Fault was taken on a Geological Society of America sponsored field trip in late winter while the frozen surface of Lake Champlain afforded easy access to Lone Rock Point and the thrust fault. Lone Rock Point isn't far from Burlington, Vermont. The fault is visible here as the contact between the light colored Dunham Dolostone above and the dark shale of the Iberville Formation below. The Cambrian aged Dunham Dolostone was thrust eastward (essentially toward the camera here) an estimated 35 to 50 miles (56 to 80 km) over the younger (Ordovician) Iberville Formation, as the Iapetus Ocean closed during the mid-Ordovician Taconic Orogeny. The contact between the 2 formations is characterized by grooves and corrugations preserved in the Dunham Formation as it slid over the Iberville Shale. These "slickenlines" are revealed as the weaker Iberville shale is eroded away at the shore of the lake.