Search

Geomagnetic excursions during Brunhes epoch have been brought to the forefront topic in paleomagnetic study, as they provide key information about Earth’s interior dynamics and could serve as another tool for stratigraphic correlation among different lithology. Loess-paleosol sequences provide good archives for decoding geomagnetic excursions. However, the detailed pattern of these excursions was not sufficiently clarified due to pedogenic influence. In this study, paleomagnetic analysis was performed in loess-paleosol sequences on the northern piedmont of the Tianshan Mountains (northwestern China). By radiocarbon and luminance dating, the loess section was chronologically constrained to mainly the last c.130 ka, a period when several distinct geomagnetic excursions were involved. The rock magnetic properties in this loess section are dominated by magnetite and maghemite in a pseudo-single-domain state. The rock magnetic properties and magnetic anisotropy indicate weakly pedogenic influence for magnetic record. The stable component of remanent magnetization derived from thermal demagnetization revealed the presence of two intervals of directional anomalies with corresponding intensity lows in the Brunhes epoch. The age control in the key layers indicates these anomalies are likely associated with the Laschamp and Blake excursions, respectively. In addition, relative paleointensity in the loess section is basically compatible with other regional and global relative paleointensity records and indicates two low-paleointensity zones, possibly corresponding to the Blake and Laschamp excursions, respectively. As a result, this study suggests that the loess section may have the potential to record short-lived excursions, which largely reflect the variation of dipole components in the global archives. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]