Globally Synchronous Marinoan Deglaciation Indicated by U-Pb Geochronology of the Cottons Breccia, Tasmania, AustraliaGeology
AbstractU-Pb zircon data from the uppermost Cottons Breccia, representing the Marinoan glacial-postglacial transition on King Island, Tasmania, provide the first direct age constraint on the Cryogenian-Ediacaran boundary in Australia. Zircons in four samples from the topmost meter of the Cottons Breccia, dated by sensitive high-resolution ion microprobe, exhibit two modes ca. 660 Ma and ca. 635 Ma. The younger component predominates in the uppermost sample, a possibly volcanolithic dolomitic sandstone, apparently lacking glacially transported debris, in the transition to cap carbonate. Chemical abrasion–thermal ionization mass spectrometry (CA-TIMS) U-Pb dating of euhedral zircons from that sample yields a weighted-mean age of 636.41 ± 0.45 Ma. Equivalence to published TIMS ash bed dates from Cryogenian-Ediacaran transitional strata in Namibia (635.51 ± 0.82 Ma, within glacial deposit) and China (635.23 ± 0.84 Ma, 2 m above glacial deposit) supports correlation of those strata to the Australian type sections and globally synchronous deglaciation at the end of the Cryogenian Period.
Citation InformationC. R. Calver, J. L. Crowley, M. T. D. Wingate, D. A. D. Evans, et al.. "Globally Synchronous Marinoan Deglaciation Indicated by U-Pb Geochronology of the Cottons Breccia, Tasmania, Australia" Geology (2013)
Available at: http://works.bepress.com/mark_schmitz/23/