湖南寒武系古丈阶底界GSSP剖面旋回地层学研究

发布时间：2018-05-21 15:09

本文选题：旋回地层学 + “浮动”天文年代标尺　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：寒武纪是显生宙的第一个纪,发生了包括多细胞生物的大爆发,以三叶虫为代表的大量无脊椎动物的繁盛,碳同位素漂移事件(TOCE,SPICE,BACE)以及磁极倒转事件在内的众多地质和生物事件。对这些地质事件的理解离不开精确的年代框架。国际地质年代表(GTS)2012中,寒武系年代地层界线年龄由放射性同位素年龄和生物带拟合计算得出,但误差接近3.0 Myr,这对发生的地质、生物和环境事件持续时间的估计造成很大影响。旋回地层学是解决这个问题的有效的方法,通过对地质记录中天文轨道旋回的识别和天文校准,可以建立一个高精度的年代标尺并对重大地质事件进行天文年代估计。本次研究的古丈剖面是古丈阶底部GSSP剖面,跨越了鼓山阶上部和古丈阶的下部,自下而上包括4个重要的化石带。本次选择该剖面开展旋回地层学研究的目的是:1)识别出古丈剖面里的米兰科维奇旋回;2)建立古丈剖面的“浮动”天文年代标尺,估算地层沉积时期的平均沉积速率和各个生物带的持续时间;3)探讨在野外使用手持磁化率仪和自然伽玛能谱仪直接测量剖面获取古气候替代性指标进行旋回分析的可行性。本文分别以2cm为间距对研究剖面进行连续的磁化率(MS)数据野外测量和5cm为间距对研究剖面进行连续的自然伽玛(GR)数据野外测量,共获得测量数据11284个。对MS序列和自然伽玛序列进行频谱分析和滑动窗口频谱分析,在古丈剖面里识别出稳定的米兰科维奇旋回。由长、短偏心率、斜率和岁差周期控制的地层沉积旋回厚度分别是24.8 m、7 m、1.8 m和1.2 m。剖面记录了3.5个稳定的长偏心率旋回。依据405 ka长偏心率信号天文校准结果,建立了“浮动”天文年代标尺,估算出Goniagnostus nathorsti带持续时间为0.49 Myr,Lejopyge armata带持续时间为0.14 Myr。古丈剖面花桥组下部地层沉积持续时间为1.33 Myr,沉积速率变化不大,平均沉积速率约为6.5 cm/kyr。
[Abstract]:The Cambrian is the first period of the Phanerozoan. There are many geological and biological events, including the explosion of multicellular organisms, the prosperity of a large number of invertebrates represented by trilobites, the carbon isotope drift event (TOCE-SPICEBACEE) and the magnetic pole inversion event. These geological events cannot be understood without a precise chronological framework. The age of Cambrian chronostratigraphic boundary was calculated by the fitting of radioisotope age and biological belt, but the error was close to 3.0 Myr, which had a great influence on the estimation of the duration of geological, biological and environmental events. Cyclic stratigraphy is an effective method to solve this problem. By identifying and calibrating astronomical orbit cycles in geological records, a high precision chronological scale can be established and astronomical age estimation of major geological events can be carried out. The Guzhang section in this study is the GSSP section at the bottom of the ancient Zhang stage, which spans the upper part of the Gushan step and the lower part of the ancient Zhang stage, and includes four important fossil belts from the bottom to the top. The purpose of this study is to identify the Milankovich cycle in the Guzhang section. (2) to establish the "floating" astronomical scale of the Guzhang profile. To estimate the average deposition rate of stratigraphic deposition period and the duration of each biological belt, the feasibility of using hand-held magnetic susceptibility meter and natural gamma energy spectrometer to obtain paleoclimate alternative indexes for cycle analysis in the field is discussed. In this paper, continuous magnetic susceptibility measurements are carried out on the study profile with 2cm as the spacing, and field measurements on the study profile are carried out with 5cm as the spacing. A total of 11284 measured data are obtained. The spectrum analysis and sliding window spectrum analysis of MS sequence and natural gamma sequence are carried out, and the stable Milankovich cycle is identified in the Guzhang section. The thickness of sedimentary cycle controlled by long, short eccentricity, slope and precession period is 24.8 m ~ 7 m ~ (1.8 m) and 1.2 m ~ (-1) m respectively. A total of 3.5 stable eccentricity cycles were recorded in the section. Based on the astronomical calibration results of 405ka long eccentricity signals, a "floating" astronomical age scale is established, and the duration of the Goniagnostus nathorsti band is estimated to be 0.49Myrn Lejopyge armata band duration of 0.14Myr. The sedimentary duration of the lower part of Huaqiao formation in Guzhang section is 1.33 Myr, and the deposition rate is not changed much, the average deposition rate is about 6.5 cm / kyr.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P534.41

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