Subsurface Proterozoic stratigraphy and tectonics of the western plains of the Northwest Territories
Authors: Cook D G , MacLean B C 
Published: November 2010

Reflection seismic records from the northwestern plains of the Northwest Territories reveal about 14 km of Proterozoic strata deformed to varying degrees, including spectacular large-scale faults and folds. The Proterozoic section, subdivided into four seismic
assemblages representing five unconformity-bounded sequences, can be reasonably correlated with outcropping strata on Coppermine Homocline and Brock Inlier to the east and in the Cordillera to the west. Correlations are based largely on recognizing similar stratigraphic and tectonic histories. The
HB Assemblage at the base of the subsurface stratigraphic column contains two unconformity-bounded sequences, the lower of which is correlated with the Bigbear and Fault River formations (of the Hornby Bay Group) on Coppermine Homocline, and with the Wernecke Supergroup in the Cordillera. The upper
sequence, comprising the Basinal, Platformal, and Syntectonic units (of the HB Assemblage), is correlated with the deltaic Lady Nye Formation, platformal East River Formation, and syntectonic Kaertok and LeRoux formations, (of the Hornby Bay Group) on Coppermine Homocline, but has no known
correlatives in the Cordillera. The DL Assemblage is the third sequence and is correlated with the Dismal Lakes Group on Coppermine Homocline, and the Pinguicula Group in the Cordillera. The fourth sequence, the Tweed Lake Assemblage, is correlated with the Coppermine River Group on Coppermine
Homocline (a correlation supported by chemical analyses of basalts) and has no known correlative in the Cordillera. The fifth and stratigraphically highest sequence, the M/S Assemblage, is correlated with the Shaler Supergroup on Coppermine Homocline, and the Mackenzie Mountains Supergroup and
Hematite Creek Group in the Cordillera (correlations that are supported by the presence of 'Grenville-age' detrital zircons, and macro- and microfossils).

The subsurface tectonic history includes compressional and extensional events, and parallels remarkably well the history of Coppermine Homocline. The most important compressional event, the thick-skinned, intracratonic Forward Orogeny, identified in the subsurface and on Coppermine Homocline, is
probably related to the Racklan Orogeny, identified in the Wernecke Mountains of the Cordillera. Forward Orogeny basement-cored structures affected HB Assemblage and older strata and were peneplaned by regional erosion before deposition of the DL Assemblage and correlative strata. The most important
extensional event postdated DL Assemblage deposition and occurred primarily as a reactivation of Forward Orogeny faults.

Other structures include early extensional faults related to Basinal Unit subsidence, and late, long-wavelength folds affecting the Tweed Lake Assemblage, M/S Assemblage, and correlative strata.

Strong, discordant seismic reflections are mostly interpreted as representing intrusive sheets that are correlated with Western Channel Diabase sheets on Coppermine Homocline. Younger sheets imaged in M/S Assemblage strata are correlated with the Tsezotene sills exposed in the Mackenzie Mountains.

The Cambrian Mackenzie Trough, grabens and half-grabens developed at various times (Early Cambrian, post-Devonian/ pre-Cretaceous, and post-Cretaceous), the transpressional (Laramide?) Colville Hills, and the Laramide Imperial Anticline, are all Phanerozoic elements whose development was influenced
by Proterozoic history.