Analysis of high resolution aeromagnetic anomalies from the south‐central Alberta Foothills, Canada

Abstract

Summary High resolution aeromagnetic (HRAM) data from the south-central Alberta Foothills were processed to enhance near-surface sources of magnetic anomalies and suppress regional gradients. The processed HRAM anomalies are not related to the topography and are induced by the magnetic properties of the rock units underlying the survey area. Siliciclastic strata dominate the surface geology; they have low magnetic susceptibility (10 -5 – 10 -2 SI), and therefore induce small magnetic anomalies (ranging between 9.8 and –10.8 nT). A remarkable correlation can be observed between lithostratigraphic units and HRAM anomalies. Short ground magnetic profiles show good correlations between the magnetic anomalies, lithology, structure and the measured magnetic susceptibilities of the outcropping sedimentary rocks. The magnetization model constructed to reproduce the HRAM data generates anomalies that closely matched the observed values, and reflects the structural and lithological complexity of the study area. HRAM data show the different magnetic signatures of the Middle Blaimore, Brazeau and Lower Coalspur strata and can be used to effectively map near-surface lithology and structure. Methods The surface geology, topographic and well data from the study area were compiled using MapInfo GIS software. To determine the magnetic properties of the sedimentary strata from the area, field and laboratory magnetic susceptibility measurements were carried out. The HRAM data (Figure 1) were processed using different filtering techniques to enhance the shallow, high frequency features, and to suppress the regional gradients. The best results were obtained using a spatial band-pass filter 0.3125– 1.25 km -1 (800-3200 m wavelength), with the output shown in Figure 2. The filtered magnetic anomalies were contoured and displayed over the surface geology data. The information obtained was utilized to constrain a 55.35 km long cross-section that was used to model the magnetic anomalies. A ground magnetic survey was used to delineate magnetic features along the profile, and to compare the results with the HRAM data and magnetic susceptibility measurements.