Railroad Valley and Adjacent
Structures, Nevada: Analogues and
Clues from the Flathead Valley, South-eastern
British Columbia, Canada
Jones, Peter B.1 (1) Wedge
Energy Inc, Calgary, AB
For more than twenty years, Railroad Valley, Nevada, was the site of some
of the most prolific onshore oil wells in the U. S. A., Two neighbouring wells
in Railroad Valley produced over 21
million barrels of oil, but ongoing exploration is severely restricted by lack
and complexity of subsurface and surface data and uncertain structural
relationships.
Comparable structural relationships occur
in a simpler setting in the Flathead Valley, British Columbia, a half-graben in
the Rocky
Mountains,
formed by the post-Laramide Flathead extensional fault. Paralleling the fault
for more than 150 km south-eastward into northwest Montana, the Tertiary Kishenehn
basin occupies the half graben, containing up to 3300 metres of Paleogene
fine-grained lacustrine deposits and valley fill, overlying an irregular
surface of Paleozoic carbonates and younger rocks. Fill includes
reservoir-scale slide blocks of Proterozoic, Paleozoic, and Mesozoic carbonates
and clastics, and oil seeps.
In the Flathead region, the Jurassic
Fernie shale is a major detachment horizon separating overlying structures
above from those below it, a function similar to that of the Mississippian
Chainman shale of Nevada. Both units involve
huge and anomalous thickness variations. The Flathead valley has the potential
for discoveries comparable to those in Nevada, without the structural
complexity that has hampered Railroad Valley exploration. The
comparison can benefit exploration in both areas.