Radiolaires des complexes d'accrétion de la Cordillère canadienne (Colombie-Britannique)

Abstract

Ninety-two collections of radiolarian faunas have been recovered from siliceous strata of the Cache Creek, Bridge River, and Hozameen accretionary complexes in the Coast and Intermontane Belt of southern British Columbia, and from local units comprising the Chilliwack Group, the Camp Cove Formation, and chert clasts from regional Cretaceous conglomerates. Radiolarian fauna range in age from Late Devonian to Middle-Late Jurassic, including Early Carboniferous, Early and Late Permian, Middle and Late Triassic, Early and Middle Jurassic. The Bridge River Complex, which contains radiolarians from Early Carboniferous to Middle-Late Jurassic, almost spans this entire age range. Taxonomic descriptions comprise 78 genera and 172 species, including 4 new genera, 24 new species and 38 new morphotypes. Most of the radiolarian associations were extracted from radiolarian ribbon chert, although some of the youngest productive samples are from siliceous argillite associated with fine- or coarse-grained clastic sedimentary strata. Radiolarian chert, a rock-type resulting from the accumulation of radiolarian shells, is widespread in time and space in the terranes studied. This favours the hypothesis of radiolarian planktonic predominance in proto-Pacific ocean basins of Late Paleozoic and Mesozoic times Most of radiolarian associations discovered in chert-bearing terranes of southern British Columbia have low paleolatitude faunal affinities. Some of them are known only from western Pacific terranes such as those in Japan, not only in Permian or Triassic times, but also in the Middle-Late Jurassic when these terranes were supposedly closer to the west American margin(s). This favours the idea of paleoenvironmental and/or paleolongitudinal controls in addition to proposed paleolatitudinal differentiation of radiolarian fauna in the Mesozoic. Twenty-eight plates illustrate 313 micrographs of radiolarians and 15 micrographs of conodonts (identified by M.J. Orchard, Geological Survey of Canada).