Insights into the drivers of Ediacaran-Cambrian phosphogenesis from phosphorites of the Khuvsgul Group, Mongolia

Dr Eliel Antilla, ETH Zurich Cambridge Fluids Network - fluids-related seminars 25 November 2025 12:00pm Department of Earth Sciences, Tilley Lecture Theatre Phosphorus, a limiting nutrient for life on geological timescales, can accumulate in concentrated, ore-grade deposits, called phosphorites. A secular increase in the size and abundance of phosphorites in the stratigraphic record across the Ediacaran-Cambrian boundary has been putatively linked to an increase in nutrient flux to the global oceans, and further associated with concomitant changes in the redox state of Earth’s surface environments and the rise and diversification of animals. However, the precise age and depositional setting of many phosphorites from this ~130 Myr interval remain poorly constrained, preventing quantitative tests of hypothesized drivers of the Ediacaran-Cambrian phosphogenic episode. In this talk, I will discuss how new age and tectonostratigraphic models for the Cambrian phosphorites of the Khuvsgul Group, Mongolia, provide new insights into the timing and mechanisms of Ediacaran-Cambrian phosphogenesis. The Khuvsgul Group phosphorites, which include a Doushantuo-Pertatataka-type microfossil assemblage, were deposited in the pro-foreland basin between 534 and 531 Ma, at least 40 million years later than the phosphatized Weng’an Biota of the Doushantuo Formation of South China. Tectonically-mediated basinal topography associated with foreland development was a necessary condition for phosphogenesis along the Cambrian Tuva-Mongolia-Zavkhan margin, with different styles of phosphate mineralization associated with variable sediment starvation and migrating redox boundaries across the margin. In conjunction with an updated compilation of ages and geological context of other Ediacaran-Cambrian phosphorites, our models for the Khuvsgul Group suggest that the Ediacaran-Cambrian increase in preserved phosphorite deposits represents the opening of a taphonomic window in which a long-term, sustained increase in redox potential enabled increased authigenic phosphate accumulation over a protracted period in marginal marine environments with the requisite tectono-stratigraphic and sedimentological conditions.