The aim of this study is to develop a better understanding of the Howley Basin and
its hydrocarbon potential using a magnetotellurics (MT) survey. This sedimentary
basin is located in western Newfoundland, and is covered by the Howley formation
which is only found in this basin. Very little is know about the basin and its structure.
The Rocky Brook formation, which consists of organic rich mudstone that is known
for generating hydrocarbons, is found in the adjacent Cormack Basin and is believed
to be present in the Howley Basin as well.
The MT method is a passive electromagnetic method that is sensitive to the electrical
conductivity structure of the subsurface. The source for MT is completely natural,
resulting from the flow of charged particles in the ionosphere (e.g. from solar storms)
and from lightning strikes. These cause natural variations in the Earth’s magnetic
field which in turn result in induced currents in the subsurface.
MT sounding of an 18 km long profile was conducted in August and September 2013,
crossing from the Topsail Igneous Complex formation into the Howley formation at
about 3 km from the southeast end of the survey and extending to the anticipated
location of the boundary between the Howley and Cormack Basins in the northwest.
The Howley Basin is characterized by higher conductivities than the surrounding igneous basement. Strike analysis reveals the basin has a preferred geo-electric orientation
of 9⁰ with the deeper structures having a preferred strike of 33⁰. A range of 2D
inversions were performed for both strikes. TM mode only inversion yielded the best
results with misfit (least square fit to the observed impedances) of 3.9 for the strike
of 9⁰ and 2.4 for the strike orientation of 33⁰. The MT data suggest a maximum
thickness of the basin along the profile of approximately 2 km and that the basin
is decreasing in thickness towards its eastern boundary. There are also indications
of a conductive feature or features extending beneath the basin, possibly related to
faulting through the basin and into the basement or of a step in the base of the basin