Abstract
DIRECT radiometric age determination of Phanerozoic carbonates has been a long-standing problem in geochronology. Rb–Sr and K–Ar dating schemes, commonly used to constrain the chronology of Phanerozoic sediments, have so far proved to be unsuccessful in dating these rocks because of their poor enrichment in radiogenic 87Sr and 40Ar and also because of analytical difficulties. Recent studies1,2 have demonstrated that large amounts of radiogenic Pb exist in some carbonates and that they could be dated by the Pb–Pb method. However, the precision of this method is severely limited to samples having very high uranium to lead ratios because by the beginning of the Phanerozoic (∼590 Myr ago) 98% of 235U originally present in the Earth had decayed to 207Pb. Here we report the first isochron age of carbonates using the 238U–206Pb method on corals. This method, which gives good accuracy even for low U concentrations, has great potential for the direct dating of sedimentary sequences and should be valuable for refining the Phanerozoic timescale.
Published Version
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