High-resolution chronostratigrahic studies of the Triassic-Jurassic biotic crisis

三叠纪-侏罗纪生物危机的高分辨率年代地层学研究。基于高分辨率地质年代学的三叠纪-侏罗纪（Tr-J）时间尺度的校准对于现实地评估各种观察到的生物和古环境异常的原因和相互关系是必不可少的，这些异常是这种转变的特征。目前还不清楚在几种相互竞争的假说中，哪一种对Tr-J大灭绝的原因，特别是时间的假设是最准确的。这一争论的主要原因是：（1）众所周知，海洋和陆地沉积档案的严格对比是非常困难的，（2）缺乏生物地层学校准的海洋剖面中精确和准确的放射性同位素年龄。从现有的地质年代学数据中可以得出一些可能的情况，但没有一种情况是可以明确接受或拒绝的。其中有可能（1）陆地和海洋的灭绝是历时性的，或者（2）生物危机在两种环境中是同步的，地质年代学，特别是在海洋环境中，需要显着改进。PI将分析几个海洋Tr-J剖面中火山灰层中所含的矿物。具体而言，我们将应用U/Pb技术的封闭系统锆石和补充40 Ar/39 Ar定年含钾矿物。此外，他们还将在可能的情况下对大陆剖面中的CAMP（Central Atlantic Magmatic Province）火山岩进行U/Pb和40 Ar/39 Ar分析，通过将U/Pb和40 Ar/39 Ar年代学与磁性地层学和生物地层学的结合，将大大改善晚三叠世至早侏罗世的时间尺度。预期对陆地和海洋部分进行的校准将有助于详细比较陆地和海洋事件的时间顺序，并有助于对生物危机的潜在原因进行更现实的评价。

High-resolution chronostratigrahic studies of the Triassic-Jurassic biotic crisisRoland Mundil and Paul R. RenneBerkeley Geochronology LaboratoryEAR-0617733ABSTRACTA calibration of the Triassic-Jurassic (Tr-J) time scale based on high-resolution geochronology is essential to realistic evaluation of the causes of, and interrelationships between, the various observed biotic and paleo-environmental anomalies that characterize this transition. It is as yet unclear which of several competing hypotheses for the cause, and in particular the timing, of the Tr-J mass extinction is most accurate. The main reasons for this controversy are that (1) a well-constrained correlation of marine and terrestrial sedimentary archives is notoriously difficult, and (2) precise and accurate radio-isotopic ages in biostratigraphically calibrated marine sections are lacking. A number of potential scenarios arise from the currently available geochronological data, none of which can be unambiguously accepted or rejected. Among them is the possibility that (1) the extinction on land and in the ocean was diachronous, or (2) the biotic crisis was synchronous in both environments and the geochronology, particularly in marine environments, needs significant improvement.PIs will analyze minerals contained in volcanic ash-layers in several marine Tr-J sections. Specifically we will apply the U/Pb technique to closed system zircons and complementary 40Ar/39Ar dating to K-bearing minerals. In addition they will target CAMP (Central Atlantic Magmatic Province) volcanics within terrestrial sections with both U/Pb and 40Ar/39Ar analyses where possible.Through careful integration of U/Pb and 40Ar/39Ar geochronology with magnetostratigraphy and biostratigraphy, the time scale of the Late Triassic through Early Jurassic will be greatly improved. The anticipated calibration of terrestrial and marine sections will permit detailed comparison of the chronology of events on land as well as in the ocean and contribute to a more realistic evaluation of potential causes for the biotic crisis.