700-540 MA TIME-SLICE IN NORTH AMERICA

The 700-540 Ma time-slice spans the great climate and biological changes of the Cryogenian and Ediacaran periods. This time-slice also encompasses the final break-up of the supercontinent Rodinia and the assembly of the megacontinent Gondwana with a hypothesized intervening supercontinent Pannotia. North America preserves abundant stratigraphic, magmatic, and thermochonological records for exploring proposed relationships between tectonic and environmental change.

Since the “Inside-Out” hypothesis of Hoffman (1991), Laurentia was envisioned as the core of Rodinia with its breakout resulting in an extroversion to form Gondwana. Since then, reconstructions of Gondwana have instead suggested assembly through introversion around the Congo. This difference, which frees up North America from the core of Rodinia, is important not only for geodynamic models, but also opens up potential new avenues for research in the nature and timing of the rifting of North America’s margins beyond the idealized Rodinian rifting between major cratons. Both the Cordilleran and Appalachian margins of North America preserve evidence for at least two episodes of Cryogenian-Ediacaran extension and rift-related magmatism. And yet for both margins, it remains unknown if the earlier rifts were successful, and the identities of the conjugate margins are debated. These uncertainties in the number, timing and nature of rifting remains an outstanding problem for paleogeographic reconstructions.

In cratonic settings of North America, Cryogenian-Ediacaran time is missing below the Great Unconformity. Erosion under the Great Unconformity has been variably linked to climate and environmental change as well as dynamic or tectonic exhumation. A new frontier for Cryogenian-Ediacaran records has emerged by extracting Cryogenian-Ediacaran exhumation histories for North America from thermochronology on older cratonic rocks. Together, new models, new tools that can extract records from the craton, and improved resolution on tectonic forensics is ushering in an exciting era of research on the 700-540 Ma time-slice in North America, which promises to provide the needed resolution to test links between tectonic and environmental change through this critical interval.