洛阳盆地古洪水剖面地球化学指标的古气候指示意义^*

Significance of palaeoclimate indicators of geochemical indexes of palaeoflood profiles in Luoyang Basin,China

摘要

地球化学指标在古气候研究中多用于黄土、湖泊等沉积物的分析,河流沉积物由于沉积水动力变化大,对其化学元素及其古气候指示意义的研究较少。文中对洛阳盆地4~3.8 ka BP龙山晚期古洪水(SQ)剖面地球化学指标的古气候指示意义进行了探讨。分析显示,古洪水剖面的化学元素含量与中值粒径相关性显著。在排除物源、沉积再旋回和成岩钾交代作用对于化学元素的影响后,根据各化学元素与中值粒径的相关系数进行分组,并在同组内按照元素迁移强弱建立化学元素参数指标,其结果与CIA粒度效应校正结果具有一致性,均在距今4 000年前后的古洪水层呈低值,指示相对干凉的气候。结合该剖面孢粉的分析结果,认为洛阳盆地温凉的气候条件是距今4 000年前后古洪水事件发生的重要环境背景。虽然河流沉积过程的复杂性导致本研究具有一定的局限性,但是通过相关系数分组建立比值参数的方法,为探讨河流沉积物化学元素指标的古气候指示意义提供了新的思路。

Abstract

In paleoclimate studies,geochemical indexes are predominantly employed in the analysis of loess,lake and other sediment types. However,the role of chemical elements in indicating palaeoclimate conditions in river sediments has been rarely investigated,primarily due to significant variations in sedimentary dynamics. In this paper,the significance of paleoclimate indicators derived from the geochemical index of the late Longshan Paleoflood section(SQ)dating from 4 to 3.8 ka BP in the Luoyang Basin. The analysis reveals a significant correlation between the chemical elements in the SQ profile and the median particle size. After accounting for the influences of provenance,sedimentary recycling and diagenetic potassium metasomatism on the chemical elements,the chemical elements were grouped based on the correlation coefficients with median particle size. Subsequently,we established chemical element parameter indexes according to the migration strength of the elements within the same group. The results are consistent with the CIA particle size effect correction findings,both indicating low values in the paleoflood layer,which suggests a dry and cool climate. Based on the results of palynology in this profile,it is concluded that the relatively mild,warm and cool climate in the Luoyang Basin serves as a significant environmental background for the occurrence of paleoflood events around 4 000 years ago. However,the complexity of the river deposition process presents limitations for this study. The method of grouping parameters offers a valuable approach to exploring the palaeoclimatic significance of chemical element indicators found in river sediments.

关键词

洛阳盆地 / 古洪水 / 地球化学指标 / 相关性分析 / 气候事件

Key words

Luoyang Basin / palaeoflood / geochemical indexes / correlation analysis / climate event

基金资助

*国家自然科学基金项目(编号: 41971114)、 国家社科基金重大项目(编号: 21&ZD223,18ZDA172)和国家社科基金一般项目(编号: 20BKG001)联合资助