The informal name Knob Lake group was proposed by Harrison (1952) to designate the entire sequence of predominantly sedimentary origin containing iron-bearing rocks of the southern part of the Labrador Trough (Burnt Creek strip area, sheet 23J). The name comes from a lake with a knob located near Schefferville. At that time, three other groups completed the Proterozoic succession in the Trough, namely the Howse, Murdock and Doublet groups (Harrison, 1952). These groups were higher in the stratigraphic column than the Knob Lake Group. In 1949, Labrador Mining and Exploration geologists divided the Knob Lake group sequence into three series called Hamilton River, Ferriman and Point. The usefulness of these terms could not be corroborated by Harrison (1952) following his work near Schefferville. In proposing the Knob Lake group name, Harrison (1952) was already considering eventually abandoning the name.

According to Harrison (1952), the Knob Lake group consisted of, from bottom to top, the following formations: Attikamagen, Denault, Fleming, Wishart, Ruth, Sokoman and Menihek. Frarey and Duffell (1964) added the Seward and Purdy formations to the group. Considered a formal designation, the Knob Lake Group now included the following revised list of formations from base to top: Seward, Attikamagen, Denault, Fleming, Wishart, Ruth, Sokoman, Purdy and Menihek. Frarey and Duffell (1964) and Baragar (1967) recognized the presence of the Knob Lake Group in the Wakuach Lake area (sheet 23O), north of the Schefferville area. Subsequently, Dimroth (1968, 1969, 1970, 1972, 1978) extended the distribution of the Knob Lake Group northward (to latitude 56° 30′ N) to include all predominantly sedimentary rocks stratigraphically underlying volcanic rocks of the Doublet Group. He divided the Knob Lake Group, from bottom to top, into four subgroups: Seward, Pistolet, Swampy Bay and Ferriman. Subsequently, Knob Lake Group formations were recognized between latitudes 56°30′N and 57°15′N by Dressler (1979), and between latitudes 57°15′N and 58°N by Clark (1977, 1978, 1979, 1980). In contrast, during the initial mapping work north of latitude 58°N, cartographers did not use the same stratigraphic nomenclature; consequently, the Knob Lake Group was not recognized in these areas (e.g. Bérard, 1965; Sauvé and Bergeon, 1965; Hardy, 1976). Following the recommendations of the North American Stratigraphic Code (NACSN, 1983), Clark and Wares (2004) elevated each of the subgroups to the rank of group, thus creating the Seward, Pistolet, Swampy Bay, Attikamagen, and Ferriman groups. At the same time, these authors recommended that the name Knob Lake Group be abandoned.

The name Knob Lake Group became inappropriate following the discontinuation of the subgroups that comprised the Knob Lake Group (Dimroth, 1972, 1978), which were reclassified as groups (Clark and Wares, 2004). In addition, the part of the Knob Lake Group containing iron-bearing rocks was interpreted as the chronostratigraphic equivalent of part of the Doublet Group (see Le Gallais and Lavoie, 1982). For Clark and Wares (2004), it made more sense to give another group name to the restricted sequence of the second cycle containing these iron-bearing rocks. Thus, the sequence was named the Ferriman Group. The name Knob Lake Group was no longer useful and Clark and Wares (2004) recommended that it be abandoned.

References