INTERPRETATION OF SEISMIC REFLECTION DATA PROVIDES NEW INSIGHTS INTO STRUCTURE OF SUSITNA BASIN

Located approximately 80 km northwest of Anchorage, the Susitna Basin is a complex sedimentary basin whose tectonic history has been poorly understood. Recent interpretation of 2D seismic data integrated with well, aeromagnetic, and gravity data provides new insights into the structural and stratigraphic nature of the basin. We present the results of the interpretation of forty-three 2D seismic reflection lines, acquired by industry from the 1960s to the 1980s. Our interpretation of the seismic data focused mainly on picking two Eocene stratigraphic units and a presumed base of Tertiary horizon on the seismic sections. Based on our interpretation of the seismic data, the structural features in the basin appear to be mainly contractional, as evidenced by the presence of many reverse and thrust faults and folds. This result is contrary to conclusions from several previous geologic studies that showed normal faults. Several regional reverse faults have been identified in the seismic data and appear to divide the basin into three regions or “sides”: east, west, and south. The eastern seismic lines show evidence of numerous short-wavelength antiforms that appear to correspond to a series of northeast-trending lineations observed in filtered aeromagnetic data, which have been interpreted as being due to folding of Paleogene volcanic strata (Shah and others, 2014). The eastern side of the basin is also cut by a number of localized reverse and thrust faults, the majority of which strike north-south. The western side of the Susitna Basin is cut by a series of four regional reverse faults and is predominantly characterized by synformal structures. These synforms are progressively deeper to the west in the footwalls of the east-vergent Skwentna and northeast-vergent Beluga Mountain reverse faults. Although the seismic data are limited to the south, we interpret a regional south-southeast-directed reverse fault striking east-northeast across the entire southern portion of the basin, based on integration of the seismic reflection and aeromagnetic data.