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

对三叠纪-侏罗纪生物危机的高分辨率年代地层学研究Roland Mundil和Paul R.RenneBerkeley地质年代学实验室EAR-0617733伯克利地质年代学实验室基于高分辨率地质年代学对三叠纪-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具有这种转变特征的生物和古环境异常的原因及其相互关系至关重要。目前还不清楚关于Tr-J大灭绝原因的几种相互竞争的假设，特别是时间上的哪一种最准确。引起这一争议的主要原因是：(1)海洋和陆地沉积档案的严格对比是出了名的困难，(2)生物地层学校准的海洋剖面缺乏准确的放射性同位素年龄。根据目前可用的地质年代学数据，出现了一些可能的情况，其中没有一个可以明确地接受或拒绝。其中有一种可能性是：(1)陆地和海洋的灭绝是历时的，或者(2)生物危机在这两个环境中是同步的，地球年代学，特别是海洋环境，需要显著改善。PI将分析几个海洋Tr-J剖面中火山灰层中包含的矿物。具体地说，我们将把U/Pb技术应用于闭合系统的锆石，并将补充性的40Ar/39Ar年龄应用于含钾矿物。此外，他们还将尽可能以陆地剖面内的CAMP(中大西洋岩浆省)火山岩为目标，进行U/Pb和40Ar/39Ar分析。通过U/Pb和40Ar/39Ar年代学与磁性地层学和生物地层学的仔细结合，将大大改善晚三叠世至早侏罗世的时间尺度。预计将对陆地和海洋部分进行校准，这将使我们能够详细比较陆地和海洋事件的年表，并有助于对生物危机的潜在原因作出更现实的评估。

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.