Geochronological constraints on an Ediacaran ice age in northern Virginia

Radiometric constraints from volcanic ash within an ice age deposit of mid-Ediacaran age (ca. 582 Ma) in Newfoundland narrowed the known temporal gap between widespread ice ages and the evolution of complex metazoans (preserved as fossil impressions beneath volcanic ash) to several million years. 

Bedding plane of Ediacara animals (ca. 550 million-years-old) at Mistaken Point, Newfoundland. The animals died during a volcanic eruption and were buried and preserved beneath volcanic ash (see grey veneer on surface).

We evaluated this claim in a study of an Ediacaran glacial diamictite at the base of the Fauquier Formation in northern Virginia, and discovered a conformable relationship (indicated by the fluidization of carbonate between pillow basalt and hyaloclastic textures, suggesting the rapid generation of steam and the shattering of carbonate sediments) between the post-glacial cap carbonate and overlying volcanic rocks of the Catoctin Formation.

The shattered appearance of the carbonate below the pillow basalt suggests the rapid generation of steam when the volcanics flowed over unconsolidated carbonate sediments.

U/Pb zircon age constraints for the rift-related volcanic flows suggest initial emplacement around 571 million years ago. Application of the Catoctin age to the Fauquier succession constrains the Fauquier ice age to be about 10 million years younger than the 582 Ma Gaskiers event, supporting the view of multiple Ediacaran Period glaciations. Furthermore, the age constraint from eastern Laurentia falls within radiometric uncertainty of fossiliferous strata in Avalonia, indicating that the Fauquier glaciation was coincident with early metazoan evolution.

 A paper related to this study can be found at http://www.geol.umd.edu/%7Ekaufman/pdf/Hebert10_PCResearch.pdf