Organic geochemistry, sedimentology and palaeontology of the Khatyspyt Formation, Arctic Siberia: Towards an integrated view of Ediacaran biofacies

The terminal Ediacaran Khatyspyt Lagerstätte (ca. 550–544 Ma) of Arctic Siberia has been a prime target for geobiological research. Previous evidence suggested that Ediacaran macroscopic soft-bodied organisms could be highly sensitive to sedimentary processes and various environmental factors such as water column stratification and seawater redox-conditions. By integrating organic geochemistry, sedimentology, and palaeontology of the Khatyspyt Formation, we identified three biofacies. The most proximal Longifuniculum biofacies consists of outer- to mid-ramp debris flow deposits and is characterised by a high taxonomic diversity and biomarker proxies pointing to a non-stratified non-euxinic water column. The most distal Aspidella biofacies comprises outer-ramp thin-bedded calcareous turbidites and is also marked by a high taxonomic diversity, although the associated biomarker proxies provide evidence for a stratified euxinic environment. Transient between those is the Nenoxites biofacies, consisting of outer- to mid-ramp debris flow deposits and characterised by a low taxonomic diversity, with biomarker proxies indicating redox instability. This systematic pattern suggests that the distribution of Ediacaran organisms was influenced by a heterogenous redox landscape. More specifically, the highest diversity of benthic soft-bodied organisms, including the iconic Charnia masoni, appears in stratified euxinic environments, while the highest diversity of macroalgae is found in non-stratified settings. The occurrence of a complex Ediacaran community in a stratified euxinic environment suggests that anoxia might have driven ecological differentiation of organisms, and that heterogeneous and dynamic redox landscapes were far more significant in early animal evolution than hitherto appreciated.