High-resolution U-Pb dating of the Croles Hill Diamictite, Tasmania: Near-synchroneity of widely separated mid-Ediacaran glacial deposits

Ediacaran glacial deposits are widespread, but their distribution in space and time is still poorly understood, hindering global correlation and a better understanding of their association with environmental and biological change. Of these deposits, the Gaskiers Formation and nearby Trinity Diamictite in eastern Newfoundland are the best constrained radiometrically at ca. 579––581 Ma, although recent evidence suggests glaciation initiated several million years earlier. Here we report two new U-Pb (zircon) CA-ID-TIMS dates on rhyodacite units immediately below, and within the Croles Hill Diamictite in northwest Tasmania previously interpreted as glacial in origin: 579.20 ± 0.09 Ma and 578.86 ± 0.23 Ma respectively. These ages make the Croles Hill Diamictite slightly younger than the Gaskiers Formation (>579.88 ± 0.44 Ma) but permit correlation with the Trinity Diamictite. Deposition of all three diamictites took place in a narrow (<2.7 m.y.) temporal window. Features consistent with a glacial origin for the Croles Hill Diamictite include rare, laminated mudstones with dropstones, a single, consistent stratigraphic position within the Togari Group, and compositional diversity of clasts.