Magnetic, granulometric and geochemical characterizations of loess sections in the eastern Arid Central Asia: Implication for paleoenvironmental interpretations

摘要

Loess deposits in the Arid Central Asia (ACA) contain sensitive messages concerning the evolution of the Westerlies and the interior aridification of Asia. In this study, we conducted a combined study of geophysical and geochemical characterization on loess sections in the eastern ACA, to discuss possible paleoclimate development since the late Pleistocene Era. Results show that the ACA loess chiefly exhibited similar geophysical and geochemical compositions with loess deposits in other regions, like the Chinese Loess Plateau. There are various accumulation rates that would have been responsible for the depositional difference within the ACA loess profiles. In addition, there are three magnetic responses to the bulk grains and geochemical proxies in this study. At the bottom segment of the section, magnetic enhancement was associated with coarse grain sizes and water leaching. Magnetic enhancement responded to stronger pedogenesis and moderate paleo-wind intensity in the uppermost parts. Moreover, there is a transitional segment in the middle part of the section, characterized by inordinately detrital inputs and weak pedogenic contributions. Thus, it may be better to evaluate the magnetic climatology of the ACA loess through different depositional stages. Furthermore, this study generally reveals that the paleoclimate pattern in the ACA was probably characterized by relatively low moisture during warm intervals, and vice versa, in the middle and bottom parts of the profiles. But relatively enhanced moisture was indicated during the Holocene period. Further studies are still necessary to obtain reliable proxies and chronology for a detailed paleoclimate interpretation of the ACA loess.