Magnetotelluric Study of the Saskatchewan Elbow Impact Structure and Applications of Finite-Element Modeling

Abstract:

The Elbow structure (50°59’N, 106°43’W) is located in south-central Saskatchewan on an elbow of the South Saskatchewan River. It was initially discovered using seismic methods by Carter Oil in 1943 and was then verified through drilling by Imperial Oil in 1945. Initially, the structure was interpreted to be formed by either anticlinal or salt tectonism, but it was later argued to be a result of meteorite impact. The Elbow structure is 8 km in diameter and circular in plan, with a central structurally uplifted area of fractured and brecciated target rocks surrounded by a ring depression. The impact occurred between 370 to 420 million years ago during the Devonian Period. Although seismic and gravity studies had been done by oil companies in the last century, which lead to the discovery of the Elbow structure, no electromagnetics studies (in particular magnetotellurics) have been used for the crater exploration since then. In September 2019, a magnetotellurics (MT) survey was carried out at the Elbow structure to investigate any subsurface geoelectric disturbance caused by the impact. Both conventional MT impedance tensor study and phase tensor and dimensionality analysis were done. The MT survey identified three layers of distinct conductivity associated with changes in lithology. However, The MT survey was unable to detect uplift associated with the impact structure due to an insufficient subsurface lateral resistivity variation. Nonetheless, the survey may have detected a change in the underlying geoelectric dimensionality which may be associated with fracturing induced by the impact. Additionally, applications of magnetotellurics on impact structure studies were investigated by using the finite-element modeling software Comsol Multiphysics.