Controls of eustasy and diagenesis on the 238U/235U of carbonates and evolution of the seawater (234U/238U) during the last 1.4 Myr

The δ(234U) data suggest that the (234U/238U) ratio of the seawater has remained within ∼20‰ of the modern seawater value during the last 1-1.4 Myr. Furthermore, we find that small-scale (1-15‰) variations in seawater δ(234U) mirror sea-level changes during the penultimate glacial-interglacial period (∼140 to ∼200 ka), thus confirming the record of lower δ(234U)SW during periods of low sea-level stand and expanding it to at least the last two glacial-interglacial events (i.e., ∼0.23 Ma). Such fluctuations in δ(234U)initial values should be taken into account when screening carbonate sediments U-Th ages on the basis of the initial (234U/238U) ratios of the samples.