“Foldastic” and “Faultastic” Deformation Features at the Base of the Lewis Thrust Sheet in the Kananaskis Area

Speaker: Normand Bégin (Nanook Geo-Exploration Inc.)

CSPG Structural Geology Division Luncheon Talk, November 7, 2019

ABSTRACT

The Lewis Thrust Fault extends over 450 km in mapped view
length, from the Rockies in Montana to the Southern Canadian Cordillera, where
it dies into folded carbonate beds of the Mississippian-age Rundle Group at
Mount Kidd in the Kananaskis Area. South of Mount Kidd and along the Highway
40, the thrust juxtaposed steeply SW-dipping (50-70 degrees) carbonaceous units
of the Rundle Group in the hangingwall, against also steeply SW-dipping clastic
units of Mesozoic-age in the footwall. Although complex folding is somewhat visible
in the hangingwall, when driving by the highway and looking up to the various
summits of the Lewis Range, hiking and scrambling up peaks and ridges reveal
far more spectacular views of the deformation features in the basal part of the
Lewis Thrust Sheet. In the summer of 2019, several named and unnamed summits
from King Ridge and northward to Opal Ridge South were climbed, capturing a
series of photos that outline a range of complex deformation features in the
Lewis Thrust Sheet, otherwise not present further south along the Lewis Range in
the vicinity of  Highwood Pass.

Heading from the Highway 40 and northeastward to about three
quarters of the way up those summits, in the structurally highest levels of the
Lewis Sheet, a train of broad open folding (100’s meters in wavelength) with
essentially no faulting is observed. Higher up towards the summits and structurally lower where the deformed panel gets at its
steepest for this portion of the Lewis Range examined, duplexes and ramp
anticlines are common. Thrust faults have m’s to 10’s m of displacement with a
NE sense of displacement. Multiple detachment horizons are present in the
thinly laminated carbonaceous units, with faulted offsets on thickly and
massive carbonate layers. The basalmost part of the Lewis Thrust hangingwall
section, on the backside (NE) of the summits, display folded units with the
interlimb angle typical of a tight to almost isoclinal geometry. C-S fabrics
(top to the NE) in cataclasites are observed in thinly laminated interbeds.

Collectively, those structures
described above could represent a broad strain gradient from higher up to lower
down in the basal part of the Lewis Thrust Sheet in the Kananaskis Area. The folds,
detachment and other shear-related structures would have been passively tilted
to the SW, as a result of motion on the easterly and underlying major
imbricates like the Rundle and Misty thrust sheets. Further south in the Lewis
Range such as Little Highwood Pass, the hangingwall section structurally above
the Jurassic units consists mainly of a SW-dipping homocline in Mississippian
units, with a much thinner sheared package above the thrust.


BIOGRAPHY

Normand
graduated with a BSc in Geological Engineering at Laval University in 1985, then completed a Ph.D. in
Geology at Queen’s University in 1989. He worked as a
Postdoctoral Fellow at the University of Calgary (1990-1992), then in mining
exploration in the NWT for 2 years as a structural geologist and field mapper.
He worked with the Foothills Research Project (U of C) from 1994 to 1996,
before joining Talisman Energy as an exploration geologist and structural
specialist in various deformed belts around the world. Along with his teammates,
he has successfully geosteered over 50 wells with several commercial
hydrocarbon discoveries in thrust-fold belts of the Canadian Rockies Foothills,
Llanos Foothills of Columbia, Zagros Belt of Kurdistan. For the last four years
with Repsol Canada, he worked on projects in Papua New Guinea, Russia, Algeria
and Bolivia. Since the late 1990’s, he has led several structural geology trips
for the industry Alberta, Kurdistan and Australia.

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