THE MIDDLE CAMBRIAN BURGESS SHALE AND ITS RELATIONSHIP TO THE STEPHENFORMATION IN THE SOUTHERN CANADIAN ROCKY-MOUNTAINS

The Burgess Shale has been an anomalous geologic unit ever since Walco tt named it in 1911 as the geographic equivalent of the Ogygopsis Shal e in the Middle Cambrian Stephen Formation of southeastern British Col umbia, but it has never been recognized outside of its type locality, so its status relative to the Stephen Formation remained uncertain. Th e geologic setting of the Burgess Shale was determined by Aitken and F ritz in 1968, when they recognized the Cathedral Escarpment and divide d the Stephen Formation into a ''thin'' platformal succession on top o f the Escarpment, and a ''thick'' basinal succession, which included W alcott's Burgess Shale, in front. Fieldwork by Royal Ontario Museum pa rties between 1982 and 1997 has now demonstrated that the thin and thi ck Stephen successions lie within different facies belts and should be regarded as separate formations; the Stephen Shale Formation is part of the Middle Carbonate Belt succession, whereas the name Burgess Shal e Formation is applied to the thick basinal succession within the Oute r Detrital Belt Chancellor Group. Ten distinct members are recognized in the Burgess Shale: Kicking Horse Shale, Yoho River Limestone, Camps ite Cliff Shale, Wash Limestone, Walcott Quarry Shale, Raymond Quarry Shale, Emerald Lake Oncolite, Odaray Shale, Paradox Limestone, and Mar pole Limestone. In contrast to the Stephen Shale Formation with its no nsequences, the thicker Burgess Shale Formation seems to represent con tinuous deposition spanning the Glossopleura to Bathyuriscus-Elrathina zonal boundary, incorporating the Polypleuraspis insignis and Pagetia bootes subzones and the main part of the Pagetia walcotti subzone.