A U–Pb and 40Ar/39Ar time scale for the Jurassic
A U–Pb and 40Ar/39Ar time scale for the Jurassic
复制标题
侏罗纪的 U-Pb 和 40Ar/39Ar 时标
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
J. Mortensen
中科院分区：
文献类型：
--
作者：
J. Pálfy;Paul L. Smith;J. Mortensen
已公布的时间标尺对侏罗纪阶段界线提供了不一致的年龄估计，并带有很大的不确定性。对已知地层年龄的火山碎屑岩进行U-Pb或40Ar/39Ar定年是提高刻度的首选方法。编制了一个由50个U-Pb年龄和40个Ar/39Ar年龄组成的放射性年龄数据库，建立了一个修正的侏罗纪年表。接受年龄的精度为±5 Ma(2σ)或更高，并限定为不超过两个相邻的阶段。这些校准点大多数来自北美科迪勒拉西部的综合生物年代学和地质年代学测年，以前从未在时间尺度上使用过。Di-rect测年仅适用于三叠系-侏罗系界线以及Crassicosta计时和卡洛夫阶段的初始界线。用年代学方法估算了所有早、早中侏罗世带界线(首次在此尝试)、中侏罗世晚期界线和晚侏罗世阶段界线。确定了6个连续带界线的普连斯巴契期和托尔克期，取得了明显的改善。得到的地带性持续时间是不同的，在0.4~1.6 Ma之间变化。最新的侏罗纪同位素数据库仍然过于稀疏，因此使用基于磁年代学的插值法改进了年代学估计。侏罗纪阶段的初始界线如下：Berriasian(侏罗纪-白垩纪)：1418 18
Published time scales provide discrepant age estimates for Jurassic stage boundaries and carry large uncer - tainties. The U-Pb or 40 Ar/ 39 Ar dating of volcaniclastic rocks with precisely known stratigraphic age is the preferred method to improve the calibration. A radiometric age database consisting of fifty U-Pb and 40 Ar/ 39 Ar ages was com- piled to construct a revised Jurassic time scale. Accepted ages have a precision of ±5 Ma (2σ) or better and are con- fined to no more than two adjacent stages. The majority of these calibration points result from integrated bio- and geochronologic dating in the western North American Cordillera and have not been previously used in time scales. Di- rect dates are available only for the Triassic-Jurassic boundary and the initial boundary of the Crassicosta chron and the Callovian stage. The chronogram method was used to estimate all Early and early Middle Jurassic zone boundaries (attempted here for the first time), late Middle Jurassic substage boundaries, and Late Jurassic stage boundaries. Signif - icant improvement is achieved for the Pliensbachian and Toarcian, where six consecutive zone boundaries are deter- mined. The derived zonal durations are disparate, varying between 0.4 and 1.6 Ma. The latest Jurassic isotopic database remains too sparse, therefore chronogram estimates are improved using interpolation based on magnetochronology. The initial boundaries of Jurassic stages are proposed as follows: Berriasian (Jurassic-Cretaceous): 1418 18