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

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评估三叠纪-侏罗纪（Tr-J）时间尺度的原因和相互关系至关重要，各种观测到的生物和古环境异常表征了这一转变。目前还不清楚，关于Tr-J大灭绝的原因，特别是时间的几个相互竞争的假设中，哪一个是最准确的。这一争议的主要原因是：(1)海洋和陆地沉积档案的良好约束对比是出了名的困难，(2)在生物地层校准的海洋剖面中缺乏精确和准确的放射性同位素年龄。从目前可获得的地质年代学数据中产生了许多可能的情景，其中没有一个可以明确地接受或拒绝。其中包括：(1)陆地和海洋的灭绝可能是历时性的，或者(2)两种环境中的生物危机是同步的，地质年代学，特别是海洋环境的地质年代学需要显著改进。pi将分析几个海洋Tr-J剖面的火山灰层中含有的矿物。具体来说，我们将把U/Pb技术应用于封闭体系锆石，并对含k矿物进行40Ar/39Ar互补测年。此外，在可能的情况下，他们将针对陆地剖面内的CAMP（中大西洋岩浆省）火山进行U/Pb和40Ar/39Ar分析。通过U/Pb和40Ar/39Ar年代学与磁地层学和生物地层学的精细结合，将大大提高晚三叠世至早侏罗世的时间尺度。预期的陆地和海洋部分的校准将允许对陆地和海洋事件的年表进行详细的比较，并有助于对生物危机的潜在原因进行更现实的评估。

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.