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

使用岩石磁性旋回地层来确定埃迪卡拉舒拉姆碳同位素漂移的持续时间PI：利哈伊大学的Kenneth P.KoDama，EAR-1322002ABSTRACT该奖项被指定为OIIA/ISE全球风险基金奖，由NSF的OIIA国际科学和工程部共同资助。该项目将为两个遥远的地点，一个在南中国，另一个在南澳大利亚，为携带埃迪卡拉纪(~555 Ma)舒拉姆负碳同位素漂移记录的沉积岩开发高分辨率时间序列或年代地层学。年代地层学将由一种名为岩石磁性旋回地层学的新技术来确定，该技术可以探测由地球轴向倾斜的大小和方向以及地球绕太阳轨道的椭圆度变化所驱动的全球气候周期。天文强迫的全球气候周期在整个地球历史上都是非常有规律的，因此它们提供了一个高分辨率的节拍器来开发沉积岩的时间序列。岩石磁性年代地层学应该为南中国陡山坨组和南澳大利亚Wonoka组记录的Shuram碳同位素漂移提供高达15,000年的分辨率，这两种沉积岩都是海相的粉砂碳酸盐沉积岩。在实验室中，对以近地层间距(10-30厘米)采集的样品进行磁化，将测量岩石中沉积磁性矿物浓度的变化。PIS以前的工作表明，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Wonoka和陡山坨岩石中收集定向样本，用于标准的古地磁分析，以探测地球磁场的极性反转。开发的反转地层学将有助于限制岩石磁检测到的周期的持续时间，以确保它们是天文强迫的气候周期。对两个相距甚远的地区的岩石磁性旋回地层学进行比较，将为舒拉姆碳同位素漂移的主要性质提供强有力的测试。岩石的沉积后蚀变是舒拉姆漂移的一种解释。在澳大利亚和中国观测到的相同的高分辨率持续时间将支持一个主要起源，并将支持这样的解释，即舒拉姆漂移是地球历史上的一个独特事件，是在生命爆发为多细胞多样性之前世界海洋氧化的结果。该项目将带来埃迪卡拉纪岩石磁性旋回地层学技术的发展，将为这些古老岩石提供比现有地质年代学技术更高分辨率的相对时间分配。

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.