MACROSTRATIGRAPHY OF THE EDIACARAN SYSTEM OF NORTH AMERICA

The Ediacaran marks the termination of Cryogenian ‘Snowball Earth’ glaciations, contains the earliest known metazoan fossils, and exhibits the most extreme negative δ¹³C excursion (Shuram-Wonoka) in the stratigraphic record. Although Ediacaran successions are typically framed in the context of proxies for glaciation, biological evolution, and geochemical perturbations, the stratigraphic record also identifies the Ediacaran as a critical transition from an enduring Precambrian nadir to an early Paleozoic zenith. Quantifying the geologic record of the Ediacaran is, therefore, critical to assessing both the context of our sampling of Earth history and the potential drivers of Earth systems evolution. Here we present a comprehensive compilation of Ediacaran successions in North America to quantify spatiotemporal patterns in the geologic record of North America. We find that the Ediacaran system has much reduced preserved rock volume in comparison to the Cambrian and most younger systems. As noted by previous sequence stratigraphic work, the Cambrian transition is marked by long-lived marine flooding, which culminated in the inundation of most of the continent and its burial by primarily Cambrian sediments with a combined total volume ~6 times greater than that of the entire Ediacaran. Decomposing continent-scale Ediacaran macrostratigraphy into separate tectonic terranes/provinces identifies potential global mechanisms, including sea level rise/fall, as well as signals of regional tectonism and volcanism. Metazoan fossils within each realm/terrane co-occur with an increase in the volume flux of preserved sediments and disappear from the record through intervals of decreasing volume flux. The Shuram-Wonoka carbon isotope excursion co-occurs with a rise in the abundance of metazoan-bearing fossil localities and the first major increase of carbonate volume flux during the Ediacaran; a subsequent and even larger carbonate volume increase is not associated with a rise in metazoan-bearing fossil localities or a δ¹³C excursion. There is little quantitative signature of the Gaskiers in the quantity or composition of Laurentian sediments. The extent to which the timing and transitional nature of the Ediacaran of North America is reflected globally remains to be seen, but we hypothesize that the marked transition in the geologic record from the Ediacaran to the Cambrian over at least 15% of Earth’s modern continental crust provides critical insight into drivers of geochemical and biological evolution at the dawn of animal life.