Aeromagnetic survey data used to map features of the Cook Inlet and Susitna basins, Alaska
Tuesday, August 25, 2015: 9:40 AM
When sedimentary basins contain strata with enhanced magnetic properties, vertical offsets in these layers, such as those caused by faults and folds, can generate measurable magnetic anomalies. Mapping of these anomalies has the potential to delineate structures of interest within the basin. In order to distinguish anomalies due to sedimentary sources from those due to changes in the crystalline basement, however, targeted processing is typically needed. The Cook Inlet and Susitna basins of south-central Alaska are bordered by volcanoes and magnetite-bearing bedrock. Measurements of magnetic susceptibility of Pliocene strata in Cook Inlet and late Paleocene/early Eocene sedimentary rocks in Susitna Basin layers show values as high as 10x10-3 SI; those associated with other measured Tertiary units are not as high. Aeromagnetic flight line data over these basins show low amplitude, short wavelength anomalies that persist from track to track but are narrower than the flight line spacing (~800 m). Such anomalies would typically be filtered out with standard gridding approaches. We applied several types of filters that enhance short-wavelength anomalies to flight line data. In the Cook Inlet basin, 2-25 nT, 400-800-m wide noise-like anomalies are clustered in areas near glacial moraines, with some focusing along rivers and other features. Noticeable differences in the magnitudes of anomalies within these clusters appear to be related to the provenance of the glacial sediments. Similar anomalies are also seen in areas where outcropping igneous rock is present. The filtered magnetic data also show linear 5-100 nT anomalies in both basins that persist for more than 10 km in some areas. Comparisons to seismic reflection data show that these anomalies correspond to structural highs in the strata formed by folds and faults. These anomalies help with mapping of such features and provide insight into the structural history of the basin.