New conodont data constraining the age of the 'Bear Rock assemblage' in the Colville Hills, Northwest Territories

Abstract

In the Colville Hills region of the Northwest Territories, the Lower to Middle Devonian succession consists of variably brecciated limestone and dolostone that historically has been assigned to the Bear Rock Formation. Nonbrecciated strata within this interval can be assigned to the Arnica and Landry formations, but bedrock exposure is too sparse to permit these units to be mapped. In view of the internal complexity of this stratigraphic succession, the term 'Bear Rock assemblage' is applied to this interval. Only limited age constraints on these strata have been reported. Conodont assemblages collected in 2015 demonstrate that the succession ranges from lowermost Emsian to lower Eifelian (dehiscens to costatus zones). This is comparable to the inferred age of Bear Rock Formation in the Franklin Mountains and Mackenzie Mountains. Thermal alteration of most samples is low, but one sample records evidence of higher maximum temperatures, possibly related to hydrothermal alteration.