Book excerpt: Previous studies of the lower Palaeozoic in the Eagle Plain & Richardson Mountain area of north-west mainland Canada in the Yukon & Northwest Territories have dealt either with outcrop or surface sections, or with subsurface well sections, but did not integrate these data. This has led to the development of inconsistent stratigraphic nomenclatures and an inability to form a consistent sequence stratigraphic model for the lower Palaeozoic in this area. This bulletin presents a stratigraphic synthesis based on data from surface exposures in the mountains surrounding Eagle Plain and on subsurface borehole data from beneath Eagle Plain and from the interior plain bordering the east flank of the Richardson Mountains. An internally consistent stratigraphic framework is developed, including reaffirmation of some previous nomenclature, restriction to certain areas of others, and definition of new stratigraphic units. The positions of carbonate-to-shale transitions which commonly exert a strong control on structural evolution and on the occurrence of sedimentary mineral deposits & hydrocarbons are more accurately delineated. A detailed sedimentological analysis of the Ogilvie Formation, the most prospective lower Palaeozoic unit for the occurrence of hydrocarbon reservoirs, is also included, along with a map of thermal maturity at the top of the unit.