Detection of subtle basement faults with gravity and magnetic data in the Alberta Basin, Canada: A data-use tutorial

Abstract

Editor's note: This paper is based on a presentation at the 2003 Canadian Society of Petroleum Geologists/Canadian Society of Exploration Geophysicists Joint Convention in Calgary. Exploration for a wide range of mineral deposits is critically dependent on knowledge of the location and age of fractures and faults. Oil and gas fields in many sedimentary basins are distributed along fault-controlled linear trends, and fault identification is often used effectively for target-area selection in hydrocarbon exploration. Similarly, mineral deposits in various geologic settings are commonly associated with fluid-conducting faults. In the platformal, Phanerozoic Alberta sedimentary basin in western Canada (Figure 1), two fundamentally different types of crystalline-basement structure, formed in different tectonic conditions, are recognized (Lyatsky et al., 1999): Figure 1. Location of the northern Alberta study area in relation to main regional geologic features. 1. Archean and Early Proterozoic (Hudsonian and older) ductile orogenic structures, and 2. Middle Proterozoic to Recent cratonic ones. The influence of ancient ductile structures on the Alberta Basin seems largely confined to the control on Early Paleozoic depositional and drape patterns by the Precambrian erosional basement relief, which may to some extent be related to the basement lithology distribution controlled by ductile ancient structures. These structures were mostly healed and innactive during the Phanerozoic development and evolution of the Alberta Basin, and thus of limited significance to fluid migration. Their geophysical expression typically consists of large magnetic and gravity anomalies, which often obscure the potential-field signatures of the desirable brittle faults. The steep, brittle basement faults in the western Canadian platforms and Cordilleran foreland, although much more subtle than their spectacular counterparts in western United States, exerted considerable syn- and postdepositional influence on the Phanerozoic sedimentary cover. Occasionally, brittle faults and fractures follow the older orogenic basement structures, but commonly cut across them. Even when subresolution seismically, many …