Gravity surveying, potential-field modeling, and structural mapping and analysis of the Howley Basin, western Newfoundland

Ernst, Linden (2018) Gravity surveying, potential-field modeling, and structural mapping and analysis of the Howley Basin, western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The northeast trending Cabot Fault transects western Newfoundland. Early Carboniferous, possibly late Devonian, activation and continued strike-slip movement throughout the late Paleozoic has led to the deposition of non-marine, fluvial and lacustrine facies, in an isolated sedimentary basin in western Newfoundland, the Deer Lake Basin. The Howley Basin is the northeast depocenter within the Deer Lake Basin. It is separated from the Humber Basin depocenter to the west by a northeast trending, elongated ridge of inverted older Carboniferous sedimentary units. Active oil seeps, bitumen in shallow drill core, organic rich lacustrine shales and mudstones, porous sandstones, and a large negative gravity signal over the Howley Basin make it an attractive hydrocarbon exploration target. Poor exposure, limited shallow drilling along the margins, and a lack of high-resolution geophysics leaves much of the Howley Basin’s internal stratigraphy and structure unknown. Integration of potential-field geophysics and detailed structural mapping and analysis is used to asses the Howley Basin’s structure and hydrocarbon potential. A large lake overlies most of the Howley Basin. Full coverage of gravity surveying required acquisition of gravity stations over the lake. A Ground Penetrating Radar was used in conjunction with the gravity survey to determine the bathymetry of the lake and was used to remove the anomalous mass of the water column in the complete Bouguer gravity anomaly. Gravity data collected in this study was combined with reprocessed pre-existing gravity datasets. A high-resolution aeromagnetic survey and the gravity data was used to model the Howley Basin. Interpretations show that the basin forms an asymmetric half-graben deepening to the east, reaching a depth of 4.3 km, well into the predicted oil window. Structural mapping of the Howley Basin revealed that the basin has been affected by episodes of transtension and transpression throughout the Carboniferous and likely continuing into the Permian. Hydrocarbon maturation is predicted to have peaked in the late Pennsylvanian to early Permian. Late-stage transpressional inversion of the Howley Basin is interpreted to have been focused on its margins, potentially creating large wavelength structural traps in the center of the basin.

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