Determining the Duration of the Ediacaran Shuram C-isotope Excursion using Rock Magnetic Cyclostratigraphy

使用岩石磁旋回地层学确定埃迪卡拉舒拉姆 C 同位素偏移的持续时间

• 批准号: 1322002
• 负责人: Kenneth Kodama
• 金额: $ 21.58万
• 依托单位: Lehigh University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-15 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322002&HistoricalAwards=false
• 关键词: Determining; Duration; Ediacaran; Shuram; isotope

Determining the Duration of the Ediacaran Shuram C-isotope Excursion using Rock Magnetic CyclostratigraphyPI: Kenneth P. Kodama, Lehigh University, EAR-1322002ABSTRACTThis award is designated as an OIIA/ISE Global Venture Fund Award and is being co-funded by NSF's OIIA International Science and Engineering Section. This project will develop high-resolution time sequences, or chronostratigraphies, for the sedimentary rocks that carry a record of the Ediacaran (~555 Ma) Shuram negative carbon isotope excursion at two distant localities, one in South China and the other in South Australia. The chronostratigraphies will be determined by a new technique, rock magnetic cyclostratigraphy, which can detect global climate cycles that are driven by variations in the magnitude and direction of Earth's axial tilt and the ellipticity of Earth's orbit around the Sun. The astronomically-forced global climate cycles have been very regular throughout Earth history, so they provide a high-resolution metronome to develop time sequences for sedimentary rocks. The rock magnetic chronostratigraphies should provide up to 15,000 year resolution for the duration of the Shuram carbon isotope excursion recorded by the Doushantuo Formation in South China and by the Wonoka Formation in South Australia, both marine, silt-carbonate sedimentary rocks. Magnetizations applied in the laboratory to samples collected at close stratigraphic spacing (10-30 cm) will measure variations in the concentration of depositional magnetic minerals in the rocks. PIs previous work shows that the magnetic mineral concentration variations can record astronomically-forced global climate cycles. Oriented samples will also be collected from the Wonoka and Doushantuo rocks for standard paleomagnetic analysis to detect polarity reversals of the Earth's magnetic field. The reversal stratigraphy developed will help constrain the duration of the rock magnetically detected cycles to ensure they are astronomically-forced climate cycles. Comparing the rock magnetic cyclostratigraphies from two widely separated localities will provide a strong test of the primary nature of the Shuram carbon isotope excursion. Post-depositional alteration of the rocks is one explanation for the Shuram excursion. Identical high-resolution durations for the excursion in Australia and China would support a primary origin and would bolster the interpretation that the Shuram excursion is a singular event in Earth history and resulted from the oxidation of the world ocean just before life exploded into multi-cellular diversity. The development of the rock magnetic cyclostratigraphy technique for Ediacaran rocks that will result from this project will afford higher resolution relative time assignment for these ancient rocks than afforded by current geochronological techniques.

使用岩石磁旋回地层学确定埃迪卡拉舒拉姆 C 同位素偏移的持续时间PI：Kenneth P. Kodama，利哈伊大学，EAR-1322002摘要该奖项被指定为 OIIA/ISE 全球风险基金奖，并由 NSF 的 OIIA 国际科学基金共同资助和工程科。 该项目将为沉积岩开发高分辨率时间序列或年代地层学，这些沉积岩携带着埃迪卡拉纪（~555 Ma）舒拉姆负碳同位素偏移在两个遥远地点（一个在华南，另一个在南澳大利亚）的记录。年代地层将通过一种新技术——岩石磁旋回地层学来确定，该技术可以检测由地球轴倾斜的大小和方向以及地球绕太阳轨道的椭圆度的变化驱动的全球气候循环。在整个地球历史中，天文学迫使的全球气候循环非常有规律，因此它们提供了高分辨率的节拍器来开发沉积岩的时间序列。岩石磁性年代地层应该能够为华南陡山沱组和南澳大利亚沃诺卡组（这两种海相粉砂碳酸盐沉积岩）记录的 Shuram 碳同位素偏移持续时间提供高达 15,000 年的分辨率。在实验室中对以紧密地层间距（10-30 厘米）收集的样品应用磁化，将测量岩石中沉积磁性矿物浓度的变化。 PI之前的工作表明，磁性矿物浓度的变化可以记录天文强迫的全球气候周期。还将从沃诺卡和陡山沱岩石中收集定向样本，用于标准古地磁分析，以探测地球磁场极性反转。所开发的反转地层学将有助于限制岩石磁力探测周期的持续时间，以确保它们是天文强制的气候周期。比较两个相距甚远的地区的岩石磁性旋回地层将为舒拉姆碳同位素偏移的主要性质提供强有力的检验。岩石沉积后的蚀变是舒拉姆偏移的一种解释。澳大利亚和中国的这次旅行的相同高分辨率持续时间将支持主要起源，并支持这样的解释：舒拉姆旅行是地球历史上的一个奇特事件，是生命爆炸成多细胞之前世界海洋氧化的结果多样性。 该项目所开发的埃迪卡拉岩石磁性旋回地层学技术将为这些古老岩石提供比当前地质年代学技术更高分辨率的相对时间分配。