宜昌埃迪卡拉系陡山沱组中—下部旋回地层学研究  

CYCLOSTRATIGRAPHY OF THE LOWER—MIDDLE EDIACARAN DOUSHANTUO FORMATION IN YICHANG, SOUTH CHINA

作　　者：薛乃华 王伟[1] 关成国[1] 房亚男 赵向东 张海春[1] XUE Nai-hua;WANG Wei;GUAN Cheng-guo;FANG Ya-nan;ZHAO Xiang-dong;ZHANG Hai-chun(State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology and Center for Excellence in Life and Paleoenvironment,Chinese Academy of Sciences,Nanjing 210008;University of Science and Technology of China,Hefei 230026)

机构地区：[1]中国科学院南京地质古生物研究所和生物演化与环境卓越创新中心,现代古生物学和地层学国家重点实验室,江苏南京210008 [2]中国科学技术大学,安徽合肥230026

出　　处：《地层学杂志》2020年第3期250-259,共10页Journal of Stratigraphy

基　　金：国家自然科学基金(41572010、41622201、41688103、42072036);中国科学院战略性先导科技专项(B类)(XDB18000000、XDB26000000、XDB10010101);中国科学院青年创新促进会、国家科技重大专项(2017ZX05036-001-004)共同资助。

摘　　要：华南埃迪卡拉纪早期地层记录了多次碳同位素负漂移事件(例如:EN1/CANCE、WANCE、EN2/BAINCE),并产出"蓝田生物群"、"瓮安生物群"和大型带刺疑源类等化石生物群。然而由于缺乏高分辨率的年代格架,使得这些地质事件的年龄及地层对比问题长期存在争议。本研究使用自然伽马测井曲线作为古气候替代指标,对宜昌地区九龙湾岩芯陡山沱组中—下部沉积地层进行了高分辨率旋回地层学研究,发现该段约1m的沉积旋回代表405 kyr的长偏心率周期。根据长偏心率周期进行天文年代校准,并采用九龙湾岩芯陡山沱组Ⅱ段底部火山灰层的锆石TIMSU-Pb年龄(635.2±0.6Ma)作为绝对年龄锚点,得到陡山沱组Ⅱ段顶部年龄为591.4±0.6Ma,并将EN2/BAINCE结束年龄约束为约591 Ma,这远早于Gaskiers冰期发生的时间(约580 Ma)。本研究为进一步探讨陡山沱组中—下部所记录的古环境和生物演化事件提供了高分辨率年代格架。The early Ediacaran strata of South China occur negative carbon isotope excursions(e.g.,EN1/CANCE,WANCE,and EN2/BAINCE),and also yield the Lantian Biota,Weng’an Biota and Doushantuo-Pertatataka acritarchs.However,the widespread absence of continuous high-resolution time scale causes extensive controversy in the timing of those geological events.In this study,we used gamma-ray logging curve as paleoclimate proxy to conduct a cyclostratigraphic research on the lower-middle Ediacaran Doushantuo Formation from the Jiulongwan drill-core,Yichang,South China.We interpreted that about 1 m sedimentary wavelength as the 405 kyr long eccentricity period.The long-eccentricity cycles calibration was anchored to 635.2±0.6 Ma zircon TIMS U-Pb age originating from a volcanic ash bed at bottom of the MemberⅡof the Doushantuo Formation in the Jiulongwan drill core.The calibration reveals an age of 591.4±0.6 Ma for the top of the MemberⅡand constrains the age of EN2/BAINCE to about 591 Ma,that is about 10 Myr earlier than the Gaskiers glaciation(~580 Ma),respectively.This study provides a high-resolution time scale for the lower-middle Doushantuo Formation,and also displays a high-resolution age framework for geochemical and evolutionary events during the early Ediacaran Period.

关 键 词：埃迪卡拉纪 陡山沱组 华南扬子台地 旋回地层学 自然伽马测井曲线 

分 类 号：P534.1[天文地球—古生物学与地层学]