Seismic reflection interpretation of the Carboniferous Cumberland Basin, Northern Nova Scotia

Abstract

An interpretation of approximately 1700 km of seismic data was completed in 1996. The seismic analysis, together with well information and geological map data, were used to map thirteen seismic horizons in the Cumberland Basin. Ten of the horizons were mapped only in limited areas, whereas three horizons could be mapped regionally. These are: BW (base of the Windsor Group), BP (base of the Boss Point Formation), and PG (base of the Pictou Group). The BW horizon is the deepest regional horizon mapped. The horizon generally dips southerly toward the Cobequid Highlands. It is affected by faults adjacent to the Scotsburn Anticline and the Hastings Uplift; the horizon was not recognized over part of the uplift. On the seismic reflection data, the horizon varies between 500 ms and 3200 ms two-way travel time (approximately 800-7600 metres) and rocks corresponding to this horizon do not outcrop in the basin. The BP and PG horizons can be traced to outcrop on the flanks of the major anticlines. Time structure maps of these horizons mimic the distribution of synclines mapped from outcrop geology. The BP horizon is affected by more faults and is more tightly folded than the PG horizon south of a major fault (Beckwith Fault). North of the Beckwith Fault, both horizons are essentially flat and not deformed. Several geological relationships were documented during this study. A thick (up to 1600 m) clastic unit was recognized in the central portion of the southern margin of the Cumberland Basin. It is interpreted as Windsor Group equivalent. Seismic reflections from within the Falls and Millsville conglomerates were recognized and suggest that these rocks correlate with the Windsor Group. Seismic profiles that cross the southern margin of the Cumberland Basin image parts of the asement complex to the south of the basin (Cobequid Highlands) and show reflection patterns consistent with mountain fronts. The seismic data image the folded and faulted Cobequid Highlands basement complex, which is interpreted as a thrusted structural wedge.