Ediacaran periglacial sedimentary structures

Abstract

Ediacaran fossils are sometimes reconstructed as colorful organisms of clear azure seas like tropical lagoons, or as ghostlike forms in deep, dark oceans. Alternatively, they can be envisaged as sessile organisms in frigid soils, to judge from associated Ediacaran periglacial paleosols and tillites. Additional evidence of cool Ediacaran paleoclimate now comes from reinterpretation of two supposed trace fossils: (1) grooves radiating from Ediacaran fossils interpreted as radular feeding traces (“Kimberichnus”) of supposed molluscs (Kimberella), and (2) chains of fossil impressions interpreted as feeding traces (“Epibaion”) of supposed worms or placozoans (Yorgia, Dickinsonia). The grooves are not curved with rounded ends like radular scratches, but with sharp or crudely bifid tips like frost flowers and frost needles extruded from plant debris. Fossil impressions in chains are not sequential feeding stations, but in polygonal arrays, like vagrant lichens and mosses displaced by wind gusts and periglacial frost boils. Thus, neither the taphomorph “Epibaion”, nor the ice crystal pseudomorphs “Kimberichnus” are valid ichnogenera. These newly recognized frost boils, needle ice, frost feathers, frost hair and frost shawls are additions to isotopic and glendonite evidence that the Ediacaran was another period in Earth history when even low paleolatitudes were cool.