A combined study of magnetic, granulometric and geochemical properties from lacustrine sediment in the arid Central Asia: Implications for paleoenvironmental variations

Abstract

Lacustrine sediments in areas of arid Central Asia are sensitive records for paleoenvironmental variations largely associated with the westerlies, targeting the possible transitional linkage between the North Atlantic climate zone and monsoonal eastern Asia. An extensive cognition of paleoenvironmental proxies is a precondition for better deciphering and refining the paleoenvironmental setting. In this study, a combined analysis of magnetic, granulometric and geochemical properties was carried out on lacustrine sediment from the northeastern part of the Yili Basin in northwest China. Results show that magnetic properties within different sedimentary layers may largely respond to the mineral preservation in relation to hydrodynamic inputs and post-depositional alteration. Magnetic concentration was potentially dominated by the input flux of detrital materials, but the depletion of magnetic concentration in the middle part of the section probably arises from post-depositional alteration of the ferrimagnetic phases in sediment with high organic content. This depletion also leads to an enhancement of the fine-grained magnetic phases. Based on the analysis of magnetic and other non-magnetic proxies, three phases of paleoenvironmental variation were identified with regard to the changes in hydrodynamic conditions. Strong hydrodynamic conditions dominated in the lower part of the sections, while there were weaker conditions operated in the middle part of the section, which also underwent post-depositional processes. The upper part of the section experienced undulating hydrodynamic conditions. In addition, this study proposed that the χARM/SIRM ratio possibly has the potential to indicate paleoenvironmental changes and emphasized that the sole usage of magnetic data alone would not deliver comprehensive information of paleoenvironmental evolution. Furthermore, this study also suggests that interdisciplinary study of magnetic transformation in lacustrine sediments is still essential in the future.