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

南非二齿兽聚集区的陆地年龄限制：对二叠纪末大规模灭绝时间的影响

• 批准号: 1123570
• 负责人: Robert Gastaldo
• 金额: $ 12.5万
• 依托单位: Colby College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-15 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1123570&HistoricalAwards=false
• 关键词: Terrestrial; Age; Constraints; Dicynodon; Assemblage

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.

深时间记录为生物多样性的变化、生态系统的破坏和恢复提供了证据，并作为理解目前公认的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%的海洋生物和高达80%的陆地生物，同时发生在2.522±20万年前。pii和合作者最近的工作表明，来自南非卡鲁盆地的古生物学记录——陆地上突然崩塌的想法的基础——不能用来确定一个独特的事件。相反，根据野外关系来确定生物模式的二叠纪末期的标准是不准确的。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的放射性定年法的年代测定技术。到目前为止，这是不可能的，因为人们认为这样的沉积物不会形成。T在边界附近存在。在东开普省的瓦帕德斯堡山口，一堆森林凋落物化石被火山灰掩埋并保存了下来，它位于报道的灭绝事件发生的高度70米处。通过同位素稀释热化质谱法（ID-TIMS）分析单晶锆石，使用ET535示踪剂（尖峰）溶液（由EARTHTIME计划分发），得出了一套锆石碎屑来源的年龄。年龄范围从新元古代（1038.78±1.42 ~ 606.76±1.0 Ma[3粒]）到中生代早期（252.0±0.5 ~ 251.8±）。038 Ma[3粒])。该项目的目标包括从wapadsberg山口和其他地方的几个地层中获取一套更大的碎屑锆石，并对其进行年龄测定。这些将与收集地点的沉积环境变化相关联，从而对卡鲁盆地确定的生物多样性趋势施加年龄限制。该项目验证了？妈妈吗?生物大灭绝是一种局限于海洋的现象，陆地生物多样性趋势的变化与其他地方记录的变化是分离的。如果大陆生物多样性的变化没有与海洋生物多样性的变化同时发生，那么地球历史上最大规模物种灭绝的新模式就必须建立起来。