浙江碓边剖面江山阶旋回地层学研究

Currently four Global Stratotype Section and Point (GSSP) are recognized in Cambrian, three GSSPs are located in South China. The GSSP for the base of the second stage of the Furongian Series Cambrian System, the Jiangshanian Stage, is located at the Duibian Bsection, near Duibian Village, western Zhejiang, China. The average duration for a single agnostoid zone, together with the closest rather reliable U-Pb zircon age, which is derived from a crystal-rich volcaniclastic sandstone in Dolgellau Formation of North Wales, Englland, yields a best estimated age for the base of the Jiangshanian Stage. And this U-Pb zircon age constrains the top of the Lotagnostus americanus Zone of South China and elsewhere to a great extent. Further research about this estimated age for the base of the Jiangshanian Stage is necessary, because there is only one reliable U-Pb zircon age in the Furongian Series..Choosing magnetic susptibility as a succedaneous paleoclimatic proxy, this project plan to launch cyclostratigraphic research at all the Duibian B section and part of Dubian A section. The purpose of this research is to recognize signals of Milankovitch cycles in the given beds, and establish a floating Astronomical Time Scale on the basis of numbers of Milankovitch cycles. Furthermore, combined with the reliable U-Pb zircon age mentioned above, this reseach could calibrate the age of the base of Jiangshanian Stage. With our calibrated age, the best estimated age so far for the base of the Jiangshanian Stage could be confirmed from a cyclostratigraphic angle.

寒武系已正式确立四个“全球标准层型剖面和点位”，三个落户中国华南地区。江山阶为寒武系芙蓉统第二阶，其“全球标准层型剖面和点位”位于浙江碓边B剖面。江山阶底界年龄为依据球接子带平均年龄和取自英国北威尔士Dolgellau组火山砂岩的U-Pb年龄得出的估算值，该U-Pb年龄在很大程度上能限定华南或其他地区球接子三叶虫Lotagnostus americanus带顶界年龄。因芙蓉统中仅有一个可靠的同位素年龄，急需对江山阶底界的估算年龄做进一步研究。本项目选择碓边B剖面和附近的碓边A剖面作为研究对象，计划以岩石磁化率作为古气候替代性指标，在江山阶底界以上地层中开展旋回地层学研究。目的是在该段地层中识别出米兰科维奇旋回信号；进而根据米兰科维奇旋回个数建立具有相对时间概念的天文年代标尺，并结合芙蓉统唯一可靠U-Pb年龄对江山阶底界进行年代标定，从旋回地层学的角度对江山阶底界最佳估算年龄作出进一步验证。