Timing and Spatial Distribution of Loess inXinjiang, NW China

Central Asia is one of the most significant loess regions on Earth, with an important role in understanding Quaternary climate and environmental change. However, in contrast to the widely investigated loess deposits in the Chinese Loess Plateau, the Central Asian loess– paleosol sequences are still insufficiently known and poorly understood. Through field investigation and review of the previous literature, the authors have investigated the distribution, thickness and age of the Xinjiang loess, and analyzed factors that control these parameters in the Xinjiang in northwest China, Central Asia. The loess sediments cover river terraces, low uplands, the margins of deserts and the slopes of the Tianshan Mountains and Kunlun Mountains and are also present in the Ili Basin. The thickness of the Xinjiang loess deposits varies from several meters to 670 m. The variation trend of the sand fraction (>63 μm) grain-size contour can indicate the local major wind directions, so we conclude that the NW and NE winds are the main wind directions in the North and South Xinjiang, and the westerly wind mainly transport dust into the Ili basin. We consider persistent drying, adequate regional wind energy and well-developed river terraces to be the main factors controlling the distribution, thickness and formation age of the Xinjiang loess. The well-outcropped loess sections have mainly developed since the middle Pleistocene in Xinjiang, reflecting the appearance of the persistent drying and the present air circulation system. However, the oldest loess deposits are as old as the beginning of the Pliocene in the Tarim Basin, which suggests that earlier aridification occurred in the Tarim Basin rather than in the Ili Basin and the Junggar Basin

Geoconservation and geotourism in Luochuan Loess National Geopark, China

The Chinese Loess Plateau (CLP) is the largest area of loess deposits in the world. Loess sediments in the CLP have high scientific value for global climate change research and are also important resources for tourism, especially science-based tourism. Unfortunately, loess conservation and geotourism do not attract much attention from the general public in China. This study briefly introduces the history of geoconservation and geotourism in China and uses Luochuan Loess National Geopark (LLNG) as an example to review problems with the development of geotourism and geoconservation. The main problems identified are inadequate measures to protect the loess geoheritage, a conflict between ecological restoration and scientific observation, ineffective interpretation of geological features for visitors, a lack of an engaging way to exhibit the materials in the Loess Museum and insufficient financial support. We propose new strategies for the sustainable development of LLNG, such as improving infrastructure, improving management actions, planting grass rather than trees for ecological restoration, popularizing science and increasing its practical use, developing a modern geological museum, and integrating the park into a global network of geological parks.</p

Clay mineral records of the Erlangjian drill core sediments from the Lake Qinghai Basin, China

Located at the northeastern margin of the Qinghai-Tibet Plateau (QTP) in the Asian interior, the Lake Qinghai is sensitive to environmental change and thus an outstanding site for studying paleoenvironmental changes. Thick deposits in the Lake Qinghai provide important geological archives for obtaining high-resolution records of continental environmental history. The longest drilling core obtained from the Lake Qinghai, named Erlangjian (ELJ), reached about 1109 m and was investigated to determine its clay mineral assemblage and grain size distributions. Clay mineralogical proxies, including type, composition, and their ratios, as well as the illite crystallinity (KI) and chemical index (CI), in combination with grain size data, were used for reconstructing the history of paleoenvironmental evolution since the late Miocene in the Lake Qinghai Basin. The clay mineral records indicate that the clay mainly comprise detritus originating from peripheral material and has experienced little or no diagenesis. The proportion of authigenic origin was minor. Illite was the most abundant clay mineral, followed by chlorite, kaolinite, and smectite. Variations of clay mineral indexes reflect the cooling and drying trends in the Lake Qinghai region, and the grain size distribution is coincided with the clay minerals indexes. The paleoclimatic evolution of the Lake Qinghai Basin since the late Miocene can be divided into five intervals. The climate was relatively warm and wet in the early of late Miocene, then long-term trends in climate change character display cooling and drying; later in the late Miocene until early Pliocene the climate was in a short relatively warm and humid period; since then the climate was relatively colder and drier. These results also suggest multiple tectonic uplift events in the northeastern QTP.</p

OSL and ESR dating of glacial deposits and its implications for glacial landform evolution in the Bogeda Peak area, Tianshan range, China

The Bogeda Peak area is the largest center of modern glaciation in the eastern Tianshan range in China. Four moraine complexes and associated fluvioglacial deposits are well preserved in the valleys, indicating multiple Quaternary glaciations in this region. Optically stimulated luminescence (OSL) and electron spin resonance (ESR) dating were used to determine the ages of the glacial tills and associated sediments in the Gubanbogeda and Heigou valleys. A total of eighteen samples were collected from moraines and fluvioglacial deposits. Fourteen samples were dated using OSL with a single-aliquot regenerative-dose (SAR) protocol, and the other four samples were analyzed by ESR dating of germanium (Ge) centers in quartz grains, which are sensitive to both sunlight and grinding. The results indicate that the fluvioglacial deposits are more suitable for OSL dating than the tills. Most ages show good agreement with the geological setting and field investigations, and the OSL and ESR ages are consistent with each other for the samples collected from the fourth set of moraines. Based on the ages as well as geomorphic and stratigraphic, the first and second moraine complexes of the Bogeda Peak area were deposited during the Little Ice Age (LIA) and Neoglaciation respectively. The low and high glacial terraces of the third set of moraines in the Gubanbogeda and Heigou valleys were deposited during marine oxygen isotope stages (MIS) 2 and 4. The fourth set of moraines has MIS 6 ages associated with the penultimate glaciation.</p

Paleomagnetic and Fission-Track Dating of a Late Cenozoic Red Earth Section in the Liupan Shan and Associated Tectonic Implications

The north-trending Liupan Shan is an important tectonic boundary between the Tibetan Plateau and the Ordos platform. The Late Cenozoic red earth deposits of the Liupan Shan record its tectonic history and environmental effects. In this article we report a new Late Cenozoic red earth section from an intermontane basin in the southern part of the Liupan Shan. Lithofacies analysis, paleomagnetic and fission-track chronologies, and paleocurrent analysis have been employed to identify the tectonic uplift events of the Liupan Shan. Based on the age constraints of mammal fossils, the paleomagnetic polarity zones of the Huating Section can be approximately correlated with the standard polarity zones that lie between C3An.2n and C5n.1n of the Geomagnetic Polarity Timescale; the bottom age of this section is approximately 10 Ma. Based on this and the previous studies, we infer that a tectonic event commenced in the southern Liupan Shan in this interval between 8.3 and 8.7 Ma, accompanied by a remarkable increase in sediment accumulation rate. Field observations, fission-track dating, determinations of grain-size frequency distributions and the vertebrate fossils found there suggest that the red earth deposits were reworked by water and mainly transported by fluvial-alluvial processes from the adjacent area.</p

Magnetic parameter variations in the Chaona loess/paleosol sequences in the central Chinese Loess Plateau, and their, significance for the middle Pleistocene climate transition

A high-resolution rock magnetic investigation was performed on the Chaona Quaternary loess/paleosol sequences in the Central Chinese Loess Plateau. Based on a newly developed independent unturned time scale and magnetic records, we reconstructed the history of the East Asia monsoons during the last 3 Ma and explored the middle Pleistocene climate transition (MPT). Rock magnetic results show that the loess layers are characterized by relatively high coercivity and remanent coercivity, lower magnetic susceptibility (MS), and that the paleosol layers are characterized by relatively high MS, saturation magnetization and remanent saturation magnetization. Spectrum analyses indicate that there are various periods in addition to orbital periodicities. According to the onset and stable appearance of 100 kyr period, we consider that the MPT recorded in this section began at similar to 1.26 Ma and was completed by similar to 0.53 Ma, which differs from previous investigations based on orbitally tuned time scales. The forcing mechanism for the MPT was more complicated than just the orbital forcing. We conclude that the rapid uplift of the Tibetan Plateau may have played an important role in the shift of periodicities during the middle Pleistocene.</p

Evaporite minerals of the lower 538.5 m sediments in a long core from the Western Qaidam Basin, Tibet

Qaidam Basin is a tectonically controlled Mesozoic-Cenozoic depression on the northern margin of the Tibetan Plateau. A 938.5 m-long core was drilled in the Qahansilatu sub-basin in the western Qaidam Basin, with an average core recovery of 95%. It revealed alternating salt layers and carbonate clay layers. Samples were collected at 10-40 cm intervals for mineralogical analysis by XRD and chemical analysis by ICP-OES. The lower 538.5 m sediments are composed of halite, gypsum, anhydrite, gaylussite, calcite, aragonite, ankerite, dolomite, and an unnamed mineral (Mg(0.92)Ca(0.0)8CO(3)center dot 3H(2)O), with trace eugsterite. The mother brines could be Na-type, Na-Ca-type, Na-Ca-(Mg)-type, Ca-(Na)-type, Ca-(Mg)-(Na)-type, and trace Ca-Mg-(Na). Reflux and bacterial activity could be suitable for the formation of dolomite. Deep burial diagenesis could have played an active role in the formation of ankerite and anhydrate. The continuous presence of halite suggested the paleo-lake water was highly brackish or saline, with high evaporation since 2.77 Ma. Salt layers in the lower 538.5 m-long sediments were present from 2221 ka to 2052 ka, corresponding to Pleistocene salt formation in the Qaidam Basin. As hydrated carbonate minerals, both gaylussite and the unnamed mineral are deposited under high precipitation rates with microbial activity. Gaylussite was deposited from Na-Ca-enriched solutions with molar ratios of Na/Ca more than 2 from 691 m (2226 ka) to 413.6 m (1222 ka). The un-named mineral (Mg0.92Ca0.08CO3 center dot 3H(2)O) was found from 523.4 m (1728 ka) to 724.2 m (2308 ka). Anhydrite could be transformed from gypsum under deep burial from 657.42 m (2052 ka) to 867 m (2556 ka). Alternating salt and clay layers in the lower part of the core recorded arid and relatively wet climatic oscillations and the evolution of brine. As a tectonic sub-basin, tectonic activities could change the local climate during episodes of uplift and subsidence. The dominant minerals in the Chahansilatu sub-basin are similar to those of the other sub-basins in the western Qaidam Basin, but have asynchronous evolutionary stages of brine.</p

Evaluating OSL-SAR protocols for dating quartz grains from the loess in Ili Basin, Central Asia

Late Pleistocene records of loess deposition are a critical archive for understanding terrestrial paleo-environment changes in Central Asia. The age of loess is not well known for the deserts regions and surrounding high plateaus in Central Asia. Previous studies have shown that there remains a disparity between ages for loess deposition by luminescence and C-14 dating. This study evaluates the potential of optically stimulated luminescence (OSL) to date a loess sequence resting on fluvial sands in the east Ili Basin, Central Asia. The single-aliquot regenerative-dose (SAR) protocol on coarse grain quartz was employed for equivalent dose determinations. The basal fluvial sand returned a secure OSL age, with low overdispersion value in equivalent doses (19 +/- 2%) of ca. 36 ka and provides a close, but maximum age estimate (within 5 ka) on the initiation of loess deposition. However, the loess yielded high overdispersion values for equivalent doses and age reversals, coincident with diffuse paleosols; indicating that pedoturbation with loess deposition may be a dominant process. OSL ages between ca. 45 and 14 ka calculated using a maximum age model and OSL ages from other sites in the Basin suggests that the latest major period of loess deposition was between 70 and 10 ka ago. A future hypothesis to test based on these analyses is that there may be three periods of heightened loess deposition at ca. 45, 35 to 19 and 14 ka, when desert source areas to the west were particularly dry.</p

Interplay between the Westerlies and Asian monsoon recorded in Lake Qinghai sediments since 32 ka

Two atmospheric circulation systems, the mid-latitude Westerlies and the Asian summer monsoon (ASM), play key roles in northern-hemisphere climatic changes. However, the variability of the Westerlies in Asia and their relationship to the ASM remain unclear. Here, we present the longest and highest-resolution drill core from Lake Qinghai on the northeastern Tibetan Plateau (TP), which uniquely records the variability of both the Westerlies and the ASM since 32 ka, reflecting the interplay of these two systems. These records document the anti-phase relationship of the Westerlies and the ASM for both glacial-interglacial and glacial millennial timescales. During the last glaciation, the influence of the Westerlies dominated; prominent dust-rich intervals, correlated with Heinrich events, reflect intensified Westerlies linked to northern high-latitude climate. During the Holocene, the dominant ASM circulation, punctuated by weak events, indicates linkages of the ASM to orbital forcing, North Atlantic abrupt events, and perhaps solar activity changes.</p