Stratigraphic comparison of the Lardeau and Covada Groups: implications for revision of stratigraphic relations in the Kootenay Arc

The Lardeau Group is a heterogeneous assemblage of lower Paleozoic, outer continental margin strata present in the Kootenay Arc in southeastern British Columbia. A correlation between the Lardeau Group and the Covada Group and Bradeen Hill assemblage, both in north-eastern Washington is proposed. The latter contain the same stratigraphic elements, in the same structural order, as those of the Lardeau Group. However, the sense of facing, and hence the stratigraphic sequence in the Covada Group and Bradeen Hill assemblage, is reversed in relation to the Lardeau Group, with the quartzo-feldspathic wacke unit the oldest and slate and argillate the youngest. Because the degree of preservation of the units in northeastern Washington is superior to that of the Lardeau Group, it is suggested that: 1) the Lardeau Group may be inverted relative to the sequence as originally defined; 2) the Lardeau Group may range from Late Cambrian to Devonian; and 3) further work is warranted to test this hypothesis. -from Authors