U-Pb Dating of Carbonates

研究表明，238 U-206 Pb等时线 来自碳酸盐岩的产量数据与 沉积年龄尽管证据的成岩作用在主机 碳酸盐。 观测到的同位素比值在 碳酸盐岩足以提供潜在的年龄分辨率 的+ 1 Ma的古生代;然而，迄今为止的研究 实现了不超过大约+10 Ma的2 o误差极限 由于分散在等时线（“误差线”）之外， 这是由于分析错误。 本研究的目的 是通过以下方式了解这种分散的原因 研究原始和近原始低- 下侏罗纪的镁方解石化石， 保存完好的海相和成岩碳酸盐相 从二叠纪珊瑚礁群。 成岩作用的重要性 和可能的痕量相（铁氧化物，磷酸盐矿物， 有机物）将通过使用 微量取样方法、部分沥滤，以及适用时， 监测各种同位素和化学物质 追踪器 更好地理解 控制碳酸盐238 U/204 Pb的初始变异 比值，并随后改变U-Pb同位素体系 将导致更可靠和精确的碳酸盐238 U-206 Pb 207 Pb-206 Pb等时线。 碳酸盐岩的直接定年 直接适用于许多问题， 地球科学，包括地球上的 前寒武纪的时间尺度、定年及对比 沉积物和成岩作用的年代测定。

Studies have demonstrated that 238U-206Pb isochrons derived from carbonate rocks yield dates consistent with depositional ages despite evidence of diagenesis in the host carbonates. The spread of observed isotope ratios in carbonates is sufficient to give a potential age resolution of + 1 Ma for the Paleozoic; however, studies to date have achieved 2o error limits of no better than roughly + 10 Ma due to scatter about the isochron ('errorchron') beyond what is attributable to analytical error. The aim of this study is to gain an understanding of the causes of this scatter by studying U-Pb systematics in pristine and near-pristine low- Mg calcite fossils from the Lower Jurassic and in a number of well-preserved marine and diagenetic carbonate phases from the Permian Reef Complex. The importance of diagenesis and possible trace phases (Fe oxides, phosphate minerals, organic matter) will be assessed through the use of microsampling methods, partial leaching and, as applicable, the monitoring of a variety of isotopic and chemical tracers. A better understanding of the processes that control l the initial variability of carbonate 238U/204Pb ratios and that subsequently alter U-Pb isotopic systems will lead to more reliable and precise carbonate 238U-206Pb and 207Pb-206Pb isochrons. The direct dating of carbonates has immediate application to a number of problems in the earth sciences, including the calibration of the Phanerozoic time scale, the dating and correlation of Precambrian sediments, and the dating of diagenesis.