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.