A gravity and magnetic interpretation of the Bay St. George Carboniferous Subbasin in western Newfoundland

Peavy, Samuel Thomas (1985) A gravity and magnetic interpretation of the Bay St. George Carboniferous Subbasin in western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Gravity and magnetic data were used to model and interpret the subsurface structure of the Bay St. George Carboniferous Subbasin in western Newfoundland. -- A total of 236 gravity stations with an average spacing of 4.0 km were used. Magnetic data were digitized on a 0.8 km grid from existing 1:63360 scale aeromagnetic maps. Regional and residual anomaly maps for a 5th-order polynomial were obtained for both gravity and magnetic maps using a trend analysis program. -- Densities and magnetic susceptibilities from 242 samples of evaporites, representative sedimentary rocks, and anothositic samples of inferred basement type were determined. -- Program for 2-D and 2.5-D gravity inversion, 2.5-D forward gravity modelling, and 3-D gravity and magnetic modelling were written in FORTRAN and tested. These were used to determine the basement topography, and to delineate faults, obtain thickness estimates of the sedimentary infill, and locate possible new evaporite deposits. -- Results from the 2.5-D inversion compared favorably to the final 3-D gravity model, showing that the 2.5-D process can be used to estimate basement topography. 3-D magnetic modelling confirmed that the basement shape defined by gravity modelling was correct geometrically. -- The results of the modelling were combined with a qualitative interpretation of the gravity and magnetic maps to yield a model of the subsurface geology. Several new faults were located in the subbasin, and several of the old faults were extended. Three possible new evaporite deposits were also located. The maximum thicknesses of the sediments in the basin were discovered to be~6 km in the St. Davids Syncline and 4 to 5 km in the Barachois Synclinorium. The throws of the Crabbes Brook and Shoal Point faults were found to be between 0.5 and 3 km, and 4.5 km, respectively.

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