The problems and potential of using animal fossils and trace fossils in terminal Proterozoic biostratigraphy

Despite the discovery of soft-bodied megascopic fossils of late Neoproterozoic age at numerous localities world-wide, there has been slow acceptance of their potential for intercontinental correlation. The stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the Cambrian is very varied. Basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance. Recent geochronological studies support notions of a narrow time distribution.

Well studied Neoproterozoic sequences in Eurasia, eastern and western North America and southern Australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft-bodied megascopic remains up-section, though strata immediately preceding the Cambrian are relatively barren other than for a sparse palynoflora and compressions of “primitive” plants. Trace fossils from Australian sections relating to an early part of the “Ediacaran” apparently overlap a time of abundance of large process-bearing acritarchs and big leiosphaerids. This overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance.

Rare discoveries of forms resembling Rangea Gürich in the Flinders Ranges of South Australia precede the classical Ediacara assemblage and may provide a possible correlation with occurrences of this genus in Namibia. The distinctive remains and trace fossils at this level constituting the “Rangeid-Hiemalora Assemblage Zone” resemble a biota from the Podolia region of the Ukraine and show a similarity to finds in parts of the Windermere Supergroup of the Northwest Territories, Canada. Similarly, the offshore, frondose assemblage of Newfoundland is comparable with the biota of Charnwood Forest, England.