A LATEST EDIACARAN DOUSHANTUO-TYPE LAGERSTÄTTE FROM NORTHERN MONGOLIAN PHOSPHORITES

Phosphatic microfossils, including possible animal embryos, from the Doushantuo Formation of South China have provided critical insights into Ediacaran paleobiology. Norwegian and Indian deposits contain similar phosphatized fossils but their diversity and preservation do not match that of the Doushantuo Formation. A newly discovered Doushantuo-type microfossil Lagerstätte is preserved in phosphorites of the upper Khesen Formation, Khuvsgul Group, northern Mongolia. The three-dimensionally preserved assemblage occurs in the lower of two phosphorite horizons in foreland basin deposits. Lithostratigraphic and δ¹³C correlation with the Zavkhan terrane of southwestern Mongolia establish a latest Ediacaran age for the assemblage. Eight genera include the second occurrence of the putative multicellular fossil animal embryo Megasphaera (likely represented by a new species) outside the Doushantuo Formation, the Doushantuo-Pertatataka-type acanthomorphic acritarchs Appendisphaera and Variomargosphaeridium, and the possible alga Archaeophycus yunnanensis. A probable new species of Variomargosphaeridium is identified. Some fossils are tentatively interpreted as the acanthomorphic acritarch Cavaspina. The Khesen biota represents the youngest Doushantuo-Pertatataka-type assemblage yet reported. It extends the range of Megasphaera, filling a gap in the record of phosphatized embryo-like forms between the ~600 Ma Doushantuo Weng’an Biota and Cambrian examples. The Khesen fossil assemblage emphasizes the potential of Mongolian phosphorites to provide new paleontological data on the Ediacaran–Cambrian transition, and to resolve the phylogenetic debate surrounding Megasphaera embryo-like taxa.