Abstract

The Ediacaran-Cambrian boundary, arguably the most important in the stratigraphic column, is based on the first appearance of the ichnospecies Treptichnus pedum. However, most trace fossils have long temporal ranges and occur in a narrow range of facies, and are typically of little use in biostratigraphic studies. Therefore, understanding the environmental tolerance and range offset of T. pedum is essential to evaluate the reliability of the Ediacaran-Cambrian boundary. Our study in Fortunian units in the Vanrhynsdorp Group of South Africa shows a broad environmental tolerance for the T. pedum producer in shallow-marine clastic settings. This ichnotaxon is not only present in low-energy offshore wave-dominated marine settings, but it also occurs at considerably shallower water in intertidal and shallow-subtidal zones of tide-dominated systems. T. pedum seems to have high values of peak abundance in the upper offshore and lower intertidal sand flats. In many sections, the Ediacaran-Cambrian transition occurs in successions containing a sequence boundary due to incision of valleys that were filled with coarse-grained deposits of fluvial or estuarine origin, both representing facies that are unsuitable for T. pedum. The range offset of this ichnotaxon is typically greater above sequence boundaries and within transgressive systems tracts, providing some constrains on its use. However, the broad environmental tolerance of T. pedum in shallow-marine clastic settings supports evolutionary innovations rather than facies controls as the main mechanism underlying the observed vertical pattern of distribution of this ichnospecies in the relatively continuous succession of the Ediacaran-Cambrian boundary Global Standard Stratotype Section and Point.

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