Seismic investigation of the precambrian basement in the Northern Williston Basin

Abstract

This study utilizes nearly 2000 km of reflection seismic data which forms a pseudo-3D grid over the northern portion of the Williston Basin. The Precambrian unconformity is mapped within an area of 25000 km2 after removal of multiple interferences by application of the Karhunen-Loeve transform. Experiments designed to determine the severity and location ofmultiple reflections within the basement reveal that a combination of travel paths between the top of Second White Specks, Bakken, and Winnipeg Formations can explain the majority of multiples within the upper Precambrian basement.

The attenuation of multiple reflections allows exploration of the structural setting of the Precambrian unconformity and the features within the basement. The Precambrian structural map indicates a distinct change in basement character along an approximate north-south trend which bisects the study area. Structural features to the west of this division are more pronounced, indicating a complex tectonic history in relation to the eastern portion of the data coverage.

The seismic sections which image the upper crust to a depth of 10 km outline several prominent features. A number of steeply dipping north-south fault zones are identified which seem to be associated with anomalous aeromagnetic signatures. These fault zones influence the overlying Precambrian unconformity which, in turn, affects the Phanerozoic sediments as recently as the Cretaceous. Slightly east of these major fault zones, a band of reflection fabrics dip to the west at 10-15° and appear to be associated with the western boundary of a large crustal entity. These dipping reflection fabrics and seismic transparency within the basement of the eastern portion of the sections is interpreted as an indication of northward extension of the Dakota block within the Trans-Hudson Orogen.