Globally synchronous marinoan deglaciation indicated by U-Pb geochronology of the cottons Breccia, Tasmania, Australia

C.R. Calver, J.L. Crowley, Michael Wingate, D.A.D. Evans, T.D. Raub, M.D. Schmitz

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    Abstract

    U-Pb zircon data from the uppermost Cottons Breccia, representing the Marinoan glacialpostglacial 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. © 2013 Geological Society of America.
    Original languageEnglish
    Pages (from-to)1127-1130
    JournalGeology
    Volume41
    Issue number10
    DOIs
    Publication statusPublished - 2013

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