Organic-walled microfossils from the Ediacaran-Cambrian boundary stratotype section, Chapel Island and Random formations, Burin Peninsula, Newfoundland, Canada: Global correlation and significance for the evolution of early complex ecosystems

Although a variety of trace and body fossils have been described from the Cambrian strata in the stratotype section (global stratotype section and point) of the Precambrian-Cambrian boundary in the Burin Peninsula, Newfoundland, a detailed analysis of its organic-walled microfossils has been missing. The basal Cambrian Treptichnus pedum Ichnozone of the Chapel Island Formation is dominated by leiosphaerids and filamentous sheaths. The appearance of Granomarginata approximates the base of the overlying Rusophycus avalonensis Ichnozone. Common process-bearing acritarchs, represented by small Asteridium and Comasphaeridium, first appear in the middle of the overlying Random Formation, and a more diverse acritarch assemblage at its top. The Random Formation also yields small carbonaceous metazoan fossils, the first report of this type of fossil in this formation. The initial low diversity of phytoplankton in the basal Cambrian strata, a holdover from Ediacaran extinctions, indicated that they have limited potential for precise global correlation of the global stratotype section and point. The pattern of increasing diversity of acritarchs through the lower Fortunian strata lagged behind and was potentially a response to the Cambrian radiation of metazoans, as most clearly represented by ichnofossils. The timing of phytoplankton radiation reflects a dynamic lag driven by metazoan-induced changes in early Cambrian food webs.