Macrostratigraphy of the Ediacaran System in North America

Abstract

Ediacaran sediments record the termination of Cryogenian ‘Snowball Earth’ glaciations, preserve the first occurrences of macroscopic metazoans, and contain one of the largest known negative δ13C excursions (the Shuram-Wonoka). The rock record for the transition between the Proterozoic and Phanerozoic in North America is also physically distinct, with much of the continent characterized by a wide variety of mostly crystalline Proterozoic and Archean rocks overlain by early Paleozoic shallow marine sediments. Here, we present quantitative macrostratigraphic summaries of rock quantity and type using a new comprehensive compilation of Ediacaran geological successions in North America. In keeping with previous results that have identified early Paleozoic burial of the ‘Great Unconformity’ as a major transition in the rock record, we find that the Ediacaran System has greatly reduced areal extent and volume in comparison to the Cambrian and most younger Phanerozoic systems. The closest quantitative analogue to the Ediacaran System in North America is the Permian-Triassic interval, deposited during the culminating assembly and early rifting phases of the supercontinent Pangea. The Shuram-Wonoka carbon isotope excursion occurs against the backdrop of the largest increase in carbonate and total rock volume observed in the Ediacaran. The putatively global Gaskiers glaciation (~580-579 Ma), by contrast, has little quantitative expression in these data. Although the importance of Ediacaran time is often framed in the context of glaciation, biological evolution, and geochemical perturbations, the quantitative expressions of rock area, volume, and lithology in the geologic record clearly demarks the late Ediacaran to early Cambrian as the most dramatic transition in at least the past 635 Myr. The extent to which the timing and nature of this transition is reflected globally remains to be determined, but we hypothesize that the large expansion in the extent and volume of sedimentation within the Ediacaran, particularly among carbonates, and again from the Ediacaran to the Cambrian, documented here over approximately 17% of Earth’s present-day continental area, provides important insights into the drivers of biogeochemical and biological evolution at the dawn of animal life.

Building a multi‐scale, collaborative, and time‐integrated digital crust: The next stage of the Macrostrat data system

“…(c) Section G3 (Moynihan et al, 2019, vertical axis = meters ) with a single stable‐isotope record (part of a and b compilations). (d) Column footprints: Grey, core holdings; magenta, Ediacaran compilation (Segessenman, 2020).…”

“…Columns and their constituent units are sourced primarily from regionally defined, representative stratigraphic summaries compiled at basin and continental scales (e.g., COSUNA; Childs, 1985). However, more localized scales of data are increasingly being ingested as part of data‐assimilation projects (Segessenman, 2020, Section 4.1.2).…”

“…This system allows new datasets to be compiled separately from the ‘core’ Macrostrat dataset. It is being used to organize ocean‐drilling cores (Section 4.1.2) and mesoscale compilations targeting Ediacaran and Mesozoic basins in North America (Segessenman, 2020) as essentially stand‐alone data products within the larger Macrostrat cyberinfrastructure. Altogether, 3,992 columns have been entered into various Macrostrat projects that are not yet part of the core public dataset of 1,534 columns.…”