Xiuming Liu

Eolian evidence from the Chinese Loess Plateau: the onset of the Late Cenozoic Great Glaciation in the Northern Hemisphere and Qinghai-Xizang Plateau uplift forcing

On the basis of a newly-constructed record of magnetic susceptibility (SUS) and the depositional rate change of eolian loess-red clay sequences in the last 7.2 Ma BP from the hea Plateau, together with a cornperison of a record of °18O values from the equatorial East Pacific Ocean and eolian Quartz flux variations fmm the North Pacific Ocean, the evolutiomuy process of the Late Cenozoic Great Glaciation in the Northern Hemisphere can be divided into three stages: the arrival stage around 7.2–3.4 Ma BP, the initial stage at about 3.4—2.6 Ma BP, and the Great Ice Age since 2.6 Ma BP. The evolution of the East Asian monsoon is characterized by paid winter and summer monsoons, and it is basically composed of the initial stage of weak winter and summer monsoons, the transitional stage of simultaneous increase in intensity of winter and summer monsoons, and the prevailing stage of strong winter and week summer monsoons, or weak winter and strong summer monsoons. The Late Cenowic global tectonic uplift, paaicdarly the Qinghai-Xizang Plateau uplift and the associated CO2 concentration variation, controls the dng processes of the onset of Great Glaciation and the long-term changes of East Asian monsoom climate in the Northern Hemisphere to a large extent. The accelerating uplift of the Qinghai-Xizang Plateau between 3.4 and 2.6 Ma BP provided an important driving force to global climiatic change.

Magnetic properties of the Tertiary red clay from Gansu Province, China and its paleoclimatic significance

The study on magnetic properties of the red clay indicates that the red clay and loesspaleosol sequence have a common magnetic mineralogy, with magnetite, maghemite, hematite (and possibly goethite) contributing to the magnetic behavior. The red clay magnetic susceptibility is also found to have a positive relation with extrafine superparamagnetic grains. This suggests that, like the Quaternary loess-paleosols, an ultrafine ferrimagnetic component produced during pedogenesis in the red clay under humid conditions also plays an important role in susceptibility enhancement in the soil units. This is supported by the correlation between Rb/Sr ratio and magnetic susceptibility. This signifies that, like the above loess-paleosol sequence, the magnetic susceptibility of the red clay can be used as a general proxy paleoclimatic indicator, although whether its susceptibility in the red clay is comparable to pedogenesis intensity and requires further investigation. Magnetic susceptibility variation in the red clay thus also provides an eolian/pedogenic record of paleoclimatic evolution. Study of the background susceptibility indicates that, on average, the absolute scale of the paleoclimatic shift from red clay development to Quaternary loess deposition is similar to the climatic shift from stage 5 (S1) to stage 2–4 (L1). This may suggest that during the Quaternary there is an evident strengthening of the absolute wind intensity to bring more (about double) coarser and less weathered (non-SP fraction) eolian magnetic input from the source regions to the Loess Plateau than during the Pliocene. The presence of eolian red clay since 7.5 Ma BP in central-northern China implies an important environmental change from the underlying Cretaceous red sandstone. The red clay development was closely related to global drying and climate cooling since the Cretaceous and closely associated with the abrupt uplift of the Qinghai-Xizang Plateau at about that time. This uplift of the plateau intensified the East Asia monsoon system and started red clay deposition.

High resolution climate record from the Beijing area during the Last Glacial‐Interglacial Cycle

The Zhaitang loess section, located in the western suburbs of Beijing has yielded a very high resolution magnetic susceptibility record for the last-glacial and interglacial period. All substages can be clearly defined in marine isotope stage (MIS) 5 (S1) and even also in substage 5a, demonstrating comparable detail with Vostok and parts of the GRIP ice record. Rapid climate shifts during the Eemian period may have extended to continental Asia, but exerted only a weak influence on the Zhaitang record. Abrupt climate transitions (5b/5c/5d/5e) recorded in this section from the NE edge of the Plateau show more detrial than most other Chinese loess records. These three well defined peaks in substage 5a, imply sensitivity of the east Asian monsoon to rapid hemisphere-scale climate change and the prospect of finding more information on orbital and non-orbital events in the loess sequence.

Response of the high‐resolution Chinese loess grain size record to the 50°N integrated winter insolation during the last 500,000 years

The global ice volume change regulates the Earths climate and has been characterized by 100,000 year cycles over the last 700,000 years. The Asian inland winter climate change is proposed to show primary 100,000 year cycles that mimic ice volume changes. Here we calibrate the age of a high-resolution grain size record over the last 500,000 years with a grain size age model. The results show a primary 41,000 year cycle and a weaker 100,000 year cycle during the last ~ 500,000 years. We suggest that the primary 41,000 year cycle in the grain size record can be ascribed to the 50°N integrated winter insolation. Our findings suggest that ice volume changes have a limited effect on the Asian inland winter climate. Asian continental winter climate changes respond to the 50°N integrated winter insolation in addition to ice volume changes.

Identification of aeolian loess deposits on the Indo-Gangetic Plain (India) and their significance

Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment. For example, paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades. Compared to Chinese loess, research on Indian loess is lacking. Currently, most studies focus on the Kashmir area located in the southern Himalayas, and studies on other areas are rare. However, field observations demonstrate that the sediments around the New Delhi-Agra-Jaipur Plain are similar to Chinese loess-paleosol sequences. For example, the boundary between two strata is transitional and without horizontal bedding. Moreover, obvious pedogenic horizons developed among sediment sequences, probably indicating unrecognised aeolian deposits in the Indo-Gangetic Plain (IGP). To confirm this, pilot samples were obtained from the IGP and detailed indoor measurements conducted. The results indicate that the distribution patterns of particle size and rare earth elements (REE) of the pilot samples are similar to Chinese loess. Furthermore, the scanning electronic microscopy (SEM) images of pilot samples show obvious conchoidal fractures, dash-shaped concavities, and abundant small pits that usually form through mechanical impact. These are typical characteristics of aeolian particles. In addition, environmental and rock magnetic measurements indicate that the dominant magnetic minerals in the pilot samples are magnetite and maghemite, and that they likely contain small amounts of hematite. Furthermore, conventional magnetic parameters are comparable with Chinese loess. Based on this, aeolian loess deposits are widely distributed in the IGP, which may have promoted the development of Indian farming and contributed towards the prosperity of ancient Indian civilisation. This study also provides a new and valuable record for the research on paleoclimate changes in the study area in the future.