Hettangian ammonite faunas and a Triassic-Jurassic boundary succession at Williston Lake, British Columbia.

摘要

Within the Fernie Formation, Hettangian strata are present at just a few locations, among which the best-preserved outcrops are in the Williston Lake area of north-central British Columbia. The most fossiliferous section is at Black Bear Ridge on the north shore of Peace Reach of Williston Lake. At this location, the studied succession overlies the Upper Triassic Pardonet Formation (Norian, with possibly a thin Rhaetian sequence) with apparently continuous marine deposition. The Triassic-Jurassic boundary is present somewhere within a 2.33m thick interval; the study provides new biostratigraphic data which, combined with geochemical analysis, allows better definition of the Triassic-Jurassic System boundary in the Williston Lake area. The overlying 22m-thick Hettangian interval contains a fairly complete and rich succession of ammonite faunas represented by 40 taxa, used as a basis for the recognition of six local biozones and 13 horizons.; Study of the ammonite faunas has permitted refining and improving of the biozonation and biostratigraphic correlation with Hettangian strata elsewhere in Western Canada.