ORGANIC-WALLED MICROFOSSILS FROM THE EDIACARAN-CAMBRIAN GLOBAL BOUNDARY STRATOTYPE SECTION, CHAPEL ISLAND, RANDOM, AND BRIGUS FORMATIONS, SOUTHEASTERN NEWFOUNDLAND, CANADA

New data for organic-walled microfossils from coastal sections on the Burin Peninsula, southeastern Newfoundland, add significant detail about the distribution of these biostratigraphically important fossils. Filamentous sheaths and leiosphaerids dominate the Ediacaran-Cambrian transition interval of upper member 1 to lower member 2A of the Chapel Island Formation. Probable Cochleatina and problematic forms of uncertain identity are also present, including an acritarch with rigid processes. The first specimens of Granomarginata prima approximate the base of the Rusophycus avalonensis Ichnozone in member 2A. The first abundant process-bearing acritarchs were encountered in the middle of the Random Formation, comprising Asteridium tornatum, A. lanatum, and Comasphaeridium agglutinatum. A more diverse assemblage appears near the top of the formation, including Fimbriaglomerella membranacea, Skiagia ornata, S. orbicularis, Comasphaeridium mollicum, and C. brachyspinosum. The overlying Brigus Formation yielded scarce acritarchs with Heliosphaeridium dissimilare, H. longum, Globosphaeridium cerinum, Archaeodiscina umbolunata, Skiagia orbicularis, and Skiagia sp. Heliosphaeridium longum is indicative of the Volkovia-Liepaina Zone.

The association from near the top of the Random Formation indicates the Skiagia-Fimbriaglomerella Zone of Baltica, considered to approximate, or somewhat precede, the first global appearance of trilobites. Acritarchs from the mid-portion of the Random Formation indicate the Asteridium-Comasphaeridium Zone, which on Baltica has been suggested to have a first appearance that approximates the base of the Cambrian. Granomarginata, considered elsewhere to first appear in the Cambrian, appears first much closer to the base Cambrian GSSP than do Asteridium or Comasphaeridium.  Strata of the Treptichnus pedum Ichnozone are devoid of any “Cambrian” acritarchs. This study further shows that in Newfoundland, the first appearance of Watsonella crosbyi, a candidate fossil for the base of Cambrian Stage 2, is within the range of Granomarginata, but below the first appearances of Asteridium and Comasphaeridium. Data from the Brigus Formation are consistent with the time gap between the Random and Brigus formations on at least this part of the Burin Peninsula.