An integrated gravity, magnetic and seismic interpretation of the Carboniferous Bay St. George Subbasin, western Newfoundland

Kilfoil, Gerald Joseph (1988) An integrated gravity, magnetic and seismic interpretation of the Carboniferous Bay St. George Subbasin, western Newfoundland. Masters thesis, Memorial University of Newfoundland.

	[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (14MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)
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Abstract

Gravity, magnetic and reflection seismic data were compiled and interpreted to determine the basement and internal structure in the Carboniferous Bay St. George Subbasin of Western Newfoundland. Gravity data, compiled from portions of several datasets for onshore regions, were complemented by those from a recent underwater gravimetry survey of St. George's Bay. Magnetic data from published aeromagnetic maps, a private aeromagnetic survey and a sea magnetometer survey were integrated into a single data set by application of corrections and offsets to bring each to a similar datum. Reflection seismic data of 1971 and 1973 vintage cover an area of the outer St. George's Bay. -- The geophysical interpretation strongly supports the hypothesis of a subbasin opened by northeast-directed right-lateral wrench tectonics. In addition, less prominent structural features are discussed in the text and a basement structure map is produced. Evidence in support of structure within the sedimentary section is also discussed. -- Sedimentation in the early history of the subbasin was controlled by vertical displacements along the northeast directed strike-slip faulting of the Cabot Fault system that initiated the basin opening during Famenian time. The Long Range Fault, which borders the subbasin to the southeast, is readily identified from the contoured datasets by its strong geophysical signature. A fault identified as trending northeast along the southeast St. George's Bay coastline exhibits a similar but less prominent geophysical character. The latter fault bounded the early subbasin on its northwest margin during deposition of the Anguille Group. -- North-northeast oriented faults, which are associated with vertical displacement of Lower Paleozoic rocks on the Port au Port Peninsula, are extrapolated offshore on the basis of a series of magnetic highs whose maxima define an east-west trend south of the peninsula's southern coastline. -- Basement picks on the reflection profiles delimit the offshore subbasin as a half-graben dipping monoclinally to the southeast and interrupted locally by strike-slip faults. Gentle gravity gradients to the southeast attest to the agreement of datasets and enable depth mapping in the inner reaches of the bay. Results of the present interpretation show the subbasin as transected by several east-west dextral strike slip faults spaced on the order of 10 km, and laterally displacing features resulting from the earlier faulting by distances of the order of 5 km. Vertical displacements along these faults is minimal with the single exception of a fault at 5365N (UTM km) where a northward throw of greater than 2.0 km has been identified from offsets in the basement seismic reflector. Timing of secondary faulting is uncertain, but is considered to largely postdate deposition of the Missippian-aged Codroy Group, with possibilities of initiation as early as the Mississippian/Pennsylvanian time boundary. -- Gravity and magnetic data profiles, selected where best constrained by the seismic interpretation and geology, were modelled using available physical parameters and developed modelling techniques to obtain estimates of depth to basement, configurations of major lithologic units and the extent of large evaporite structures within the Carboniferous strata.

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