The Indicator Lake Formation was introduced by Chown (1971) to designate the lower sequence of the Otish Group. It was later renamed the Otish Group Indicator Formation by Chown and Caty (1973). In its synthesis of the Otish Basin, Genest (1989) later elevated this unit to the rank of group, leading to the redefinition of the Otish Group as a supergroup. Correlations between the different nomenclature used in previous work is summarized in the Otish Supergroup record and in the summary table of Genest (1989, p. 21). The Ministère‘s compilation maps (2010a-c) are essentially based on descriptions from Genest (1989) and are summarized in the following section. The name comes from Indicator Lake in SW Otish Basin (sheet 22M13).

Despite wide variations in thickness, the Indicator Group is always composed of two sedimentary cycles corresponding to the Matoush Formation, at its base, overlain by the Shikapio Formation. Each cycle consists of a basal quartz pebble oligomictic conglomerate unit overlain by a sandstone unit (Members A and B of Genest, 1989, respectively). Beds, which can be more than a metre thick, are massive and resistant to erosion (Genest, 1986). Sedimentary rocks are mainly grey, with some beige or greenish beds. The Indicator Group is characterized by the absence of plagioclase and high diagenetic alteration of K-feldspar grains.

Chown and Caty (1973) described the type section of the Indicator Formation (now Indicator Group) on the north side of the hill north of Conflans Lake:

Thickness and distribution

The Indicator Group corresponds to the peripheral units of the Otish Basin, except at the SW end, and appears to follow the trace of a regional synform of general NE-SW orientation. Its thickness varies considerably from one area to another, from 225 m in the type area (sheet 23D07) to over 1200 m in the Indicateur Lake area (sheet 22M13). Paleoproterozoic units in the Otish Basin generally have shallow dips. The distribution of the different sedimentary units is largely controlled by the underlying Archean basement paleotopography, fault zones and topography of the area.

Dating

The Indicator Group is cut by gabbro dykes and sills associated with the Otish Gabbro dated to 2169 Ma (Hamilton and Buchan, 2016; Miligragovic et al., 2016), giving it a minimum sedimentation age.