Revisions to the Paleoproterozoic Sequence A, based on reflection seismic data across the western plains of the Northwest Territories, Canada

Abstract

Abstract New insights into Proterozoic Sequence A were gained from analysis of reflection seismic data acquired across the western plains of the Northwest Territories, Canada, a re-examination of geological maps of the Coppermine Homocline, and recently published studies in the Cordillera. Results show that the sequence contains four unconformity-bounded sub-sequences and should be, therefore, subdivided. They are informally named here, from oldest to youngest, as A1, A2, A3 and A4. Sequence A1 is laterally restricted and consists of the Bigbear and Fault River formations of the Hornby Bay Group on Coppermine Homocline, seismic Sequence A1 in the subsurface, and is potentially equivalent to the very thick Wernecke Supergroup of the Cordillera. Sequence A2 on Coppermine Homocline consists of the clastic Lady Nye Formation, carbonates of the East River Formation, and the syntectonic clastics of the Kaertok and LeRoux formations of the Hornby Bay Group. Sequence A2 in the subsurface consists of the Basinal, Platformal, and Syntectonic seismic units and does not correlate with strata of the Cordillera. A2 strata in the subsurface and on the homocline were deformed by the intracratonic style Forward Orogeny (ca. 1.66 Ga), which is likely an expression of the Racklan Orogeny, described from the Cordillera. Sequence A3 consists of the Dismal Lakes Group on Coppermine Homocline, seismic Sequence A3 in the subsurface and the Pinguicula Group in the Cordillera. It overlies a regional unconformity that bevelled the underlying Forward Orogeny and Racklan Orogeny structures and completely removed Sequence A2 strata from the region of the present Cordillera. Sequence A4 is made up of the Coppermine River Group on the homocline and the Tweed Lake basalts in the subsurface. No correlative strata have been reported in the Cordillera.