基于XRF岩芯连续扫描的藏南哲古错沉积物近4400年地球化学分布及环境演变

XRF岩芯连续扫描在近30年间被广泛用于获取不同地理环境的湖泊沉积序列元素分布及其指示的环境意义，特别是湖泊密集的"亚洲水塔"青藏高原。然而，XRF扫描数据的准确性受沉积岩芯物理属性的显著影响，可能导致记录信息的过度或错误解释。本研究基于青藏高原南部哲古错（ZGC）内近4400年以来由植物和泥沙混合沉积而成的2.16 m完整岩芯（ZGC21），利用XRF岩芯连续扫描获取其元素信号值和色度分布，结合含水量、粒度、烧失量等物理特征分析，表明ZGC岩芯层理清晰、定年精准、气候信息记录全面，是重建印度夏季风和青藏高原南部气候变化的最佳载体之一。稳定元素（Al、K、Fe、Mn、Rb、Si、Ti、Zr）信号值分布均不能用于指示ZGC岩芯不同层理的碎屑物质输入比例，但Zr/Rb比值则可反映流域内物质输入的真实特征；Ca和Br元素信号值分布分别指示ZGC21岩芯的碳酸盐和有机质含量变化。基于可靠元素信号分布和AMS-14C精确定年，青藏高原南部在太阳辐射强度变化驱动下于4400~3500 a B.P.和850~80 a B.P.年间均处于寒冷气候环境中，低温不足以支撑湖内植被的生存，而在2750~1830 a B.P.和1320~850 a B.P.年间则相反。上述结果为XRF岩芯连续扫描数据的正确应用和准确解释提供科学示范，也为重建该地区过去4400年人地关系提供年代际尺度环境演变框架。

Geochemical distributions of sediments from the Zhegu Co by XRF core scanning and revealed environmental evolutions in the southern Qinghai-Xizang Plateau during the past 4400 years

High-resolution XRF core scanning has been applied for acquiring the distribution of elements along lacustrine sedimentary sequences at different geographical environments over the past 30 years. Especially, the produced data has widely used to indicate environment change at plenty of lake catchments in the Qinghai-Xizang Plateau, which was known as "Asian Water Tower". Nevertheless, the accuracy of data by XRF core scanning is subject to physical properties of lake sediments(i.e. water content, grain size, etc.), which further results in excessive or false interpretations of recorded environmental information. In this study, a-2.16 m sedimentary core(28°38'1″N, 91°40'41″E, labeled as ZGC21) from the Zhegu Co(ZGC) basin(28°35'~28°50'N, 91°12'~91°50'E) in the southern Qinghai-Xizang Plateau was drilled in 2021, which was deposited successively by the mixture of plants and silts during the past 4400 years. Firstly, the distributions of element signal values and chroma were acquired by XRF core scanning along split lengthwise core surface. Subsequently, the ZGC21 core was vertically subsampled using semicircular plastic sheets according to visible sedimentary beddings(1 cm intervals at the same bedding) and a total of 215 discrete samples were collected in the ZGC21 core with the thickness ranging from 0.7 cm to 1.5 cm. In addition, water content, grain size, and loss on ignition of each sample were analyzed for identifying the physical characteristics of the ZGC21 core. As a result, the sedimentary sequence from the ZGC was thought as one of the best carriers to reconstruct the Indian summer monsoon and climate change in the southern Qinghai-Xizang Plateau due to its clear bedding, accurate dating and comprehensive environmental information. In detail, the signal distributions of stable elements(Al, K, Fe, Mn, Rb, Si, Ti and Zr) could not indicated the input of detrital material at different beddings of the ZGC21 core. Conversely, the ratio of Zr/Rb clearly showed true situation of material input in the ZGC catchment. Moreover, the distribution of Ca and Br signal values by XRF core scanning indicated the changes of carbonate and organic matter content in the ZGC21 core, respectively. Based on reliable elements signal distributions and precise AMS-14C dates, it was a cold climate in the southern Qinghai-Xizang Plateau during the periods of 4400~3500 a B.P. and 850~80 a B.P. under the influence of solar radiation intensity variation. Aquatic plants in the ZGC were less likely to survive due to low temperature at the same periods. On the other hand, it was warm over 2750~1830 a B.P. and 1320~850 a B.P. in the southern Qinghai-Xizang Plateau. Finally, all above results provided scientific basis for correct interpretation of elements signal values by XRF core scanning. Besides, those also provided inter-decadal environmental evolution processes for reconstructing human-environment interaction in the southern Qinghai-Xizang Plateau during the past 4400 years.