EARLY TONIAN MACROALGAL ECOSYSTEMS FROM NORTHWESTERN CANADA

The diversification of macroalgae during the early Neoproterozoic led to dramatic changes in marine ecosystems including reorganizing benthic habits, altering biogeochemical cycles and influencing oxygenation. However, this important transition remains poorly documented owing to the rarity of macroalgal preservation and the generally simple morphologies of those preserved that are common to both prokaryotes and early eukaryotes. The Proterozoic inliers of northwestern Canada preserve strata spanning over one billion years of Earth’s history, including the early evolution and ecological expansion of macroalgae. The Dolores Creek Formation of the Mackenzie Mountains Supergroup (Yukon Territory, northwestern Canada) contains a diverse macroalgal assemblage with three unique macroscopic forms. The first to be taxonomically defined, Archaeochaeta guncho has been taxonomically defined and interpreted as a benthic green macroalga characterised by unbranching, uniseriate thallus with uniform width n=304, width = 0.20 to 0.85 mm) and an elongated holdfast. A larger size class of ribbon-like forms is interpreted as Vendotaenia sp. (n=19, width = 1.0 to 1.7 mm), while smaller branching specimens (n = 90, width = 0.03 to 0.06 mm) remain undefined based on their lack of morphological characteristics. A new macrofossil locality was documented during 2022 with an additional 130 slabs of specimens collected approximately 10 km north of the of the original locality. Preliminary analyses suggest this assemblage contains Archaeochaeta guncho and previously undocumented ribbon-like forms. Analytical microscopy, including scanning electron microscopy, will provide insight into the fossil preservation and morphology. The new locality contributes to the growing record of macroalgal ecosystems documented during the Tonian Period, supports the hypothesis that algae were increasing in morphological complexity and ecologically expanding their habitats.