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Trilobite zones in the Murray Range, Pine Pass map-area, British Columbia Street, Peter John

Abstract

Trilobites and other fossils from three measured sections in the Murray Range, Pine Pass map-area, British Columbia, are described and their zonal significance is discussed. Zones represented by fossil assemblages are the Upper Olen-ellus subzone (uppermost Lower Cambrian), the Ogygopsis klotzi and Tonkinella stephensis subzones of the Bathyuriscus-Elrathina zone (upper Middle Cambrian), the upper Conaspis zone and Ptychaspis subzone of the Ptychaspis-Prosaukia zone (Upper Cambrian, Franconian Stage), the Lower or Middle Saukia zone (Trempealeau-an Stage), and Zones A, B and D of the Lower Ordovician (Canadian Series). The lower Middle Cambrian, Dresbachian and lower Franconian zones, and the Lower Ordovician Zone C, appear to be missing. Early Cambrian assemblages show some affinities with faunas of the southern hemisphere (the archaeocyathid genera Sigmocya-thus, Syringocnema and Monocyathus) and eastern Canada and the United States (species of Bonnia, Kootenia, Paedeumias and Eo-ptychoparia). However, these affinities become weaker in Middle Cambrian and later assemblages, and all the present collections are predominantly Cordilleran in character. They are considered representative of the intermediate extracratonic biofacies realm as defined by Lochman-Balk and Wilson (1958). The sections provide a further example of the transition, well-known in other parts of the Canadian Cordillera, from Lower Cambrian argillaceous and arenaceous clastic rocks to more or less argillaceous limestone and dolomite of the Middle Cambrian and later Series. Throughout Cambrian and early Ordovi-cian time the original area represented by the present sections was covered by miogeosynclinal seas which progressively encroached upon the craton. This marine transgression was interrupted at times, and the comparatively local uplift of the Peace River Arch was responsible for extreme reduction in thickness of the Middle and Upper Cambrian portions of the early Palaeozoic section.

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