Biostratigraphy and Palaeoecologic Turnovers at the Ediacaran-Cambrian Type Section in Newfoundland, Canada

In 1992, the Fortune Head section of the Chapel Island Formation exposed at Burin Peninsula, Newfoundland, Canada, was selected as Cambrian Global Boundary Stratotype Section and Point (GSSP). For twenty years, a Working Group of the Subcommission on Cambrian Stratigraphy actively visited sections in Africa, North America, Asia, Australia, and Europe, and agreed on the placement of the Precambrian–Cambrian boundary point at the first appearance of Treptichnus pedum, a complex trace fossil that unequivocally attests of the presence of triploblastic animal life. Here, I will present a revision of the biostratigraphic scheme developed in the Chapel Island Formation for the Ediacaran–Cambrian boundary interval based on new data collected during extensive fieldwork since 2016, and demonstrate that this framework is still sound and robust. In a second part, I will showcase how major events of animal behavior evolution can be deciphered by analysing all-encompassing ichnological data gathered in the Chapel Island Formation through high-resolution time-environment matrices. This powerful approach highlights a first turnover from an Ediacaran matground ecology to a Fortunian firmground ecology corresponding to the appearance of several new body plans related to the Cambrian Explosion. A second turnover is evidenced across the Fortunian–Cambrian Age 2 boundary interval with the development of thick and pervasive sediment mixed layers reminiscent of modern substrates (mixground ecology) alongside the colonization of deeper infaunal niches. These events are not local, but global, as can be observed on palaeogeographic maps created from the compilation of ichnological data gathered from several other localities worldwide and preserved both in siliciclastic and carbonate deposits. These conclusions, built upon state-of-the-art approaches developed in ichnology and sedimentology, demonstrate that cutting-edge methods of data analysis can finely resolve key events of the history of life.