Gravity modelling of the Marysville, New Brunswick subbasin

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University of New Brunswick


This report investigates the economic potential of the Marysville Carboniferous Subbasin using existing regional gravity survey data to estimate sediment thickness and basement shape. The geometry of the Marysville Subbasin (MSB) was investigated by modelling o f existing regional gravity data supplied by the New Brunswick Department of Natural Resources & Energy (NB DNRE). Geologic models for subsurface structure were developed based on a review of Carboniferous Basin geology in New Brunswick. Rock densities were obtained from a New Brunswick DNRE complication (Hassan, 1996) and Thomas and Willis (1989). An 85 km linear profile of Bouguer gravity values at 71 stations across the Marysville Subbasin was imported into a 2.75 dimensional gravity modelling software package in order to model Marysville Subbasin geometry. Pre-existing information on the regional geology of the Marysville Subbasin that helped guide the gravity modelling process included a NB DNRE geology map of southwest New Brunswick (Plate NR-5), and reports by Thomas and Willis (1989), and Spector and Pichette (1980). The observed gravity profile contains a central low over the Marysville Subbasin flanked by highs related to Shin Formation mafic volcanics. The gravity highs on the perimeter of the basin are in turn flanked by lows related to the low density Pokiok and St. George Batholiths. Precambrian basement structure is fault-controlled with subvertical movement on the Fredericton and Belleisle Faults. The maximum depth of the Marysville Subbasin was estimated to be 2.3 km near Fredericton Junction. Gravity modelling o f a hypothetical salt diapir indicated an observable gravity effect only when fully developed and 800 m in height. The Marysville Subbasin contains sufficient sediment thickness to host Windsor evaporites and therefore justifies more detailed geophysical surveys including a gravity component.