Baotian Pan

Loess plateau storage of northeastern Tibetan plateau-derived Yellow River sediment

Marine accumulations of terrigenous sediment are widely assumed to accurately record climatic- and tectonic-controlled mountain denudation and play an important role in understanding late Cenozoic mountain uplift and global cooling. Underpinning this is the assumption that the majority of sediment eroded from hinterland orogenic belts is transported to and ultimately stored in marine basins with little lag between erosion and deposition. Here we use a detailed and multi-technique sedimentary provenance dataset from the Yellow River to show that substantial amounts of sediment eroded from Northeast Tibet and carried by the rivers upper reach are stored in the Chinese Loess Plateau and the western Mu Us desert. This finding revises our understanding of the origin of the Chinese Loess Plateau and provides a potential solution for mismatches between late Cenozoic terrestrial sedimentation and marine geochemistry records, as well as between global CO2 and erosion records.

Age and genesis of the Shagou River terraces in eastern Qi- lian Mountains

The fluvial terrace sequence in eastern Qilian Mountains is a record of periodic uplift events of the Tibetan Plateau. Based on paleomagnetic dating, thermoluminescence dating, radio carbon dating and loess-paleosol sequence on terraces, we preliminarily determine the ages of five major terraces of the Shagou River, northern side of the Qilian Mountains. The ages of five terraces were about 830, 418, 250, 140 and 10 ka, respectively. Analysis on characteristics of terraces show that five major terraces were mainly tectonic genesis. Therefore, five major terraces recorded five strong rising events in the Qilian Mountains during the past 830 ka. The ages of those rising events are about the same as those terraces formation. Sub-terraces, constituting a main terrace, were perhaps mainly formed by climatic changes.

Distribution features and controls of heavy metals in surface sediments from the riverbed of the Ningxia-Inner Mongolian reaches, Yellow River, China

Fifty-six riverbed surface sediment (RSS) samples were collected along the Ningxia-Inner Mongolian reaches of the Yellow River (NIMYR). These samples were analyzed to determine their heavy metal concentrations (Co, Cr, Ni, Cu, V and Zn), grain sizes, sediment sources and the causes of their heavy metal contamination. The cumulative distribution functions of the heavy metals in RSS of these reaches are plotted to identify the geochemical baseline level (GBL) of each element and determine the average background concentration of each heavy metal. Principal component analysis and hierarchical cluster analysis are conducted based on the grain sizes of RSS, and the samples are classified into two groups: coarse grained samples (CGS) and fine grained samples (FGS). The degree of heavy metal contamination for each sample is identified by its enrichment factor (EF). The results reveal that the coarse particle component (medium sand and coarse sand) in the bed materials is chiefly from the bordering deserts along the Yellow River. The clay and silt in the bed materials chiefly originate from the upper reaches of the Yellow River, and the fine sand is identified as a hybrid sediment derived from the upper reaches of the Yellow River and the bordering deserts. The CGS primarily appear in the reaches bordering deserts, and the sites are near the confluence of gullies and the Yellow River. The FGS are located adjacent to cities with especially strong industrial activity such as Wuhai, Bayan Nur, Baotou and Togtoh. The Cr, Ni, Cu, V and Zn concentrations (mg kg(-1)) are 84.34 ± 49.46, 30.21 ± 7.90, 25.01 ± 7.61, 73.17 ± 18.92 and 55.62 ± 18.93 in the FGS and 65.07 ± 19.51, 23.86 ± 6.84, 18.04 ± 3.8, 53.47 ± 10.57 and 34.89 ± 9.19 in the CGS respectively, and the concentrations of Co in the CGS (213.40 ± 69.71) are notably higher than in the FGS (112.02 ± 48.87) and greater than the Co GBL (210). The most contaminated samples in the NIMYR are adjacent to the cities of Wuhai (EF(Cr) = 5.19; EF(Ni) = 1.96), Bayan Nur (EF(Cr) = 5.88; EF(Ni )= 2.08) and Baotou (EF(Cu) = 1.55; EF(Zn) = 1.68) where the Cr, Ni, Cu, V and Zn concentrations are above the correlated GBLs (85, 34, 27, 75 and 62 mg kg(-1), respectively), which are mostly affected by industrial processes, and samples that are only moderately contaminated by heavy metals are found in the reaches bordering desert (Wuhai-Baotou) because contaminated sediments are diluted by uncontaminated desert sand. In contrast, all of the Cu, Cr, Ni, V and Zn concentrations in RSS of the Qingtongxia-Wuhai reach are lower than the correlated GBLs of elements.

Paleomagnetic dating of the Jiuquan Gravel in the Hexi Corridor: Implication on mid-Pleistocene uplift of the Qinghai-Tibetan Plateau

The sediments in the foreland basins around the Qinghai-Tibetan Plateau preserved crucial information to reveal its tectonic history. In the Hexi Corridor, north periphery of the Qinghai-Tibetan Plateau, the angular unconformity between the Jiuquan Gravel and the Yumen Conglomerate has been well known to represent an intensive tectonic event of the plateau. However, its age is poorly constrained. Our paleomagnetic dating at the Laojunmiao section in the Jiuxi Basin show that the bottom of the Jiuquan Gravel reaches 0.84 MaBP, the top of the Yumen Conglomerate is about 0.93 MaBP. This result clearly demonstrates that the northern Qinghai-Tibetan Plateau experienced an intensive movement at mid-Pleistocene.

Late Quaternary glacial chronology on the eastern slope of Gongga Mountain, eastern Tibetan Plateau, China

The Gongga Mountain is the largest area of modern glaciation in the Hengduan Mountains and, with a summit elevation of 7556 m, is the highest mountain on the eastern margin of the Tibetan Plateau. During the Quaternary glacial-interglacial cycles the Gongga Mountain was extensively and repeatedly glaciated, and glacial landforms and outwash deposits from multiple glaciations are well-preserved in valleys, in basins, and on piedmonts. To constrain the glacial chronology of the eastern slope of Gongga Mountain, sample sites were selected based on the distribution and weathering of glacial tills, relationships among glacial deposits, and soil development on moraines. Dating of the tills and glaciofluvial deposits was undertaken with electron spin resonance (ESR) and optically stimulated luminescence (OSL). The ages of the glacial deposits can be divided into four clusters: 2.2±0.5, 11.9±0.6, 35.9±2.7-58.0±6.3 and 119.2±15.9-194.2±32.8 ka. Five glacial advances in this region have been identified, which are equivalent in age to the Little Ice Age (LIA), Neoglaciation, marine oxygen isotope stage (MIS) 2, mid-MIS3, and MIS6. The largest local last glacial maximum (LGML) occurred on Gongga Mountain during mid-MIS3, characterized by a cold-humid climate, rather than the global Last Glacial Maximum (LGMG) of MIS2. The Gongga, Nanmenguangou (NMGG) and Yajiageng Glaciations occurred during the late part of the last glacial cycle, the middle of the last glacial cycle and the penultimate glacial cycle, respectively. On the basis of geomorphological, sedimentological, and compositional characteristics, landforms of the Moxi Platform and terraces can be grouped by facies and geochronology. In combination with the dating results, this analysis indicates the basal part of the Moxi Platform between Xinxin and the Moxi Hotel is correlative with the till of the Nanguanmen Glaciation (mid-MIS3). This basal unit has occasional lenses of glaciofluvial sandy gravel and lacustrine sediments. The remainder of the Moxi Platform and the terraces beside the platform are glaciofluvial deposits occasionally mixed with debris flow deposits and range in age from MIS3 to Holocene.

Rates and kinematics of active shortening along the eastern Qilian Shan, China, inferred from deformed fluvial terraces

In the eastern Qilian Shan, a flight of fluvial terraces developed along the Jinta River valley are deformed across the Nanying anticline. Four individual fluvial terraces are preserved at different elevations above the river, and higher terrace treads are draped by systematically thicker aeolian loess. Optically stimulated luminescence dating of deposits at the base of the loess provides constraints on the timing of surface abandonment; terraces were abandoned at 69 +/- 4 ka B.P. (T4), 57 +/- 4 ka B.P. (T3), and between 34 +/- 3 ka B.P. (T2), respectively. Differential GPS measurement of the terrace profile across the anticline allows reconstruction of subsurface fault geometry; we model terrace deformation above a listric thrust fault with a tip line at 2.2 +/- 0.1 km depth and whose dip shallows systematically to 23 +/- 3 degrees at depth of 5.8 +/- 1.1 km. Combining terrace ages with this model of fault geometry, we estimate a shortening rate of 0.8 +/- 0.2 mm/a across the Nanying fold and a shortening rate of similar to 0.1 mm/a across the mountain front fault since similar to 70 ka B.P. This rate suggests that the frontal fault system along the eastern Qilian Shan accomplishes crustal shortening at rates of approximately 0.9 +/- 0.3 mm/a during late Pleistocene time.

A 60 000-year loess-paleosol record of millennial-scale summer monsoon instability from Lanzhou , China

The 28-m high-resolution Shajinping loess section in Lanzhou on the Chinese western Loess Plateau records a detailed history of millennial Asian summer monsoon change since the earlier last glaciation. Summer monsoon proxies of soil magnetic susceptibility, carbonate content and soil color show that Asian summer monsoon experienced a series of rapid episodic pulse enhancements spanning only ca. 1–2 ka and have sub-Milankovitch cycles of progressive weakening in low frequency domain since ca. 60 kaBP. Soil formation responds to these by deepening colors, accumulating organic matter, increasing biological channels and leaching certain carbonates. The pedogenic degree generally increases with the degree of enhancement of summer monsoon. These may reflect the impact of the last glacial fast climatic change in the North Atlantic region on Asian summer monsoon.

Apatite fission track constraints on the pattern of faulting in the north Qilian Mountain

The Qilian (祁连) Mountain is an active orogenic belt located at the northeastern margin of the Tibetan Plateau. During the process of continuous convergence between Indian and Eurasian plates, the Qilian Mountain grow correspondingly by means of reaction of old faults and generation of new ones. Here we present apatite fission-track data along a river profile crossing three minor fault (the Minle (民乐)-Damaying (大马营) fault, the Huangcheng (皇城)-Taerzhuang (塔尔庄) fault and the Kangningqiao (康宁桥) fault) which compose the North Qilian fault (NQF) to test the timing and patterns of the fault activities. Apatite fission-track (AFT) results indicate that these minor faults experienced two active phases in the Cretaceous and the Oligocene-Miocene. Further research indicate that the initiation timing of faulting became younger northward in both active periods and the later phase probably more active than the former phase. These tectonic activities might be highly related to the docking of the Lhasa Block to the south in the Cretaceous and uplift and expansion of the Tibetan Plateau in the Cenozoic.

Dust Storms in Northern China: Long-Term Spatiotemporal Characteristics and Climate Controls

AbstractAirborne dust derived from desertification in northern China can be transported to East Asia and other regions, impairing human health and affecting the global climate. This study of northern China dust provides an understanding of the mechanism of dust generation and transportation. The authors used dust storm and climatological data from 129 sites and normalized difference vegetation index (NDVI) datasets in northern China to analyze spatiotemporal characteristics and determine the main factors controlling dust storms occurring during 1960–2007. Dust storm–prone areas are consistent with the spatial distribution of northern China deserts where the average wind speed (AWS) is more than 2 m s−1, the mean annual temperature (MAT) ranges from 5° to 10°C, and the mean annual precipitation (MAP) is less than 450 mm. Dust storms commonly occur on spring afternoons in a 3- to 6-h pattern. The three predominant factors that can affect DSF are the maximum wind speed, AWS, and MAT. During 1960–2007, dust s...

Analysis of trace elements (heavy metal based) in the surface soils of a desert–loess transitional zone in the south of the Tengger Desert

It is very important to strengthen the research about the heavy metal pollution of soil in vulnerable ecological regions of the south-central arid area of Northwest China for regulating and guiding local industrial and municipal activities and for protecting the environment. In this study, 48 surface soil samples were collected in the desert–loess transitional zone in the south of the Tengger Desert. The distributions of elements (heavy metal based) and the differences between urban and natural soils were analyzed. We observed that As, Pb, Cu, Zn and S were clearly enriched in the Baiyin area, and Ni and Cr were mainly enriched in the Zhongwei area. V, Mn, Ti, Bi, Co and W were enriched in the southeast margin of the Tengger Desert, where there is relatively little human activity. Over the entire study area, Ce, La and Nd were widely distributed across regions whether with strong or weak human activity. Based on the distributions of elements, we suggest that in the desert–loess transitional zone in the south of the Tengger Desert, the distribution and abundances of element As, Pb, Cu, Zn, S, Ni and Cr are strongly related to the human activities in the area, but the elements V, Mn, Ti, Bi, Co, W, Ce, La and Nd are derived mainly from natural sources.