Gravity and magnetic modelling of the Sackville Sub-basin, New Brunswick

Abstract

The Sackville Sub-basin is part of the Maritimes Basin, an accumulation of Carboniferous sediments in Atlantic Canada. The goal of this thesis is to construct a model of the sub-basin using available gravity and aeromagnetic data, complemented by seismic information. Of the results obtained from interpretation of the magnetic data, most important with respect to the hydrocarbon potential of the sub-basin is the discovery that the sedimentary section is at least 3500 m thick. Magnetic modelling shows that the Fairfield fault, a basement fault within the sub -basin, has a vertical offset of the order of 700 m. Furthermore, the presence of a large basement intrusive of a facies more mafic than granite is suggested by the magnetic modelling. A regional scale gravity map and a map of the second vertical derivative of the gravitational field have been prepared. Interpretation of these maps suggests that the northern and southern boundaries of the Sackville Sub-basin are well defined by normal faults having large vertical displacements. However, there are no clearly distinguished boundaries at the eastern and western ends of the sub-basin. Basal seismic reflectors cannot be identified using the available gravity and magnetic data. Due to a lack of independent geological information, it is not possible to resolve the inherent ambiguity the gravity and magnetic models constructed. The composite gravity/magnetic model presented most part, geologically plausible. However, one of many models which may satisfy the equally well. Three Fortran programs have been written to complement the data editing facilities of the modelling software used. These allow the user to subtract a regional gradient from the survey data, splice a modified dataset to the original and strip the synthetic output for one or more model bodies from the survey data.