Terrestrial Age Constraints for the Dicynodon Assemblage Zone, South Africa: Implications for the Timing of the End-Permian Mass Extinction

南非双齿兽组合带的陆地年龄限制：对二叠纪末大灭绝时间的暗示。GastaldoColby学院深度时间记录为生物多样性和生态系统破坏和恢复的变化提供了证据，并作为了解影响地球的潜在变化的模型。据报道，二叠纪末大灭绝事件影响了超过90%的海洋生物和80%的陆地生物，崩溃同时发生在2.522亿±0.2百万年前。最近的工作表明，来自南非卡鲁盆地的古生物学记录，即陆地突然塌陷的想法的基础，不能用来识别一个独特的事件。相反，用于分配一个二叠纪末的生物模式的标准是不准确的基础上字段的关系。确定这一事件发生时间的最可靠方法是使用基于火山灰沉积物中单晶锆石放射性测年的计时技术。迄今为止，这是不可能的，因为它被认为是这样的存款没有？在东开普省的瓦帕兹堡山口，一个被火山灰掩埋并保存下来的化石化森林凋落物，位于据报道灭绝事件发生的海拔以下70米处。由EARTHTIME倡议分发的使用ET 535示踪剂（加标）溶液的同位素稀释热电离质谱法（ID-TIMS）分析单晶锆石的初步研究得出了一套年龄，表明锆石的碎屑来源。年龄范围为新元古代（1038.78 ± 1.42 ~ 606.76 ± 1.0 Ma [3粒]）至早中生代（252.0 ± 0.5 ~ 251.8 ± 0.038 Ma [3粒]）。该项目的目标包括从Wapadsberg Pass和其他地方的几个地层层位中采集一套更大的碎屑锆石，并对其进行年龄测定。这些将与收集地点沉积环境的变化相关联，以便对卡鲁盆地确定的生物多样性趋势施加年龄限制。该项目测试的假设，即？妈妈？在所有大灭绝中，有一种现象仅限于海洋，陆地上生物多样性趋势的变化与其他地方的记录无关。如果大陆生物多样性的更替与海洋中确定的模式不同时发生，那么就必须开发一种新的模型来描述地球历史上最大的大灭绝。

Terrestrial Age Constraints for the Dicynodon Assemblage Zone, South Africa: Implications for theTiming of the End-Permian Mass ExtinctionRobert A. GastaldoColby CollegeDeep time records provide evidence for changes in biodiversity and ecosystemdisruption and recovery, and act as models for understanding the potential changes nowrecognized affecting Earth. The End Permian Mass Extinction Event is reported to haveimpacted more than 90% of life in the oceans and up to 80% of life on land, with thecollapse occurring simultaneously at 252.2±0.2 million years ago. Recent work of the PIand collaborators demonstrates that the paleontological records from the Karoo Basin,South Africa, on which the idea of sudden collapse on land is based, can not be used toidentify a distinct event. Rather, criteria used to assign an end-Permian age to the biologicalpatterns are inaccurate based on field relationships. The most reliable way to identify thetiming of this event is by using chronometric techniques based on radiometric dating ofsingle crystal zircons from volcanic ash deposits. To date, this has not been possiblebecause it was believed that such deposits didn?t exist near the boundary.A fossilized forest litter, located 70 m below the level where the extinction event isreported, is buried and preserved by volcanic ash deposits in Wapadsberg Pass, EasternCape Province. A pilot study of single crystal zircons analyzed by isotope dilution thermalionization mass spectrometry (ID-TIMS) using the ET535 tracer (spike) solution, distributed bythe EARTHTIME initiative, resulted in a suite of ages indicating a detrital source for thezircons. Ages range from the NeoProterozoic (1038.78 ± 1.42 to 606.76 ± 1.0 Ma [3 grains]) tothe early Mesozoic (252.0 ± 0.5 to 251.8 ± .038 Ma [3 grains]). The project goals include theacquisition of a larger suite of detrital zircon from several stratigraphic horizons inWapadsberg Pass and elsewhere that will be age dated. These will be correlated withchanges in sedimentary environments in the collection sites to place an age constraint onthe biodiversity trends identified in the Karoo Basin. The project tests the hypothesis thatthe ?Mother? of all Mass Extinctions was a phenomenon restricted to the oceans, andchanges in biodiversity trends on land were decoupled from those documented elsewhere.If turnover in continental biodiversity did not happen simultaneously with the patternsidentified in the oceans, a new model for the greatest mass extinction in Earth history willhave to be developed.