Xian Center

Fengcheng, China

Xian Center

Fengcheng, China
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Zhu Y.,CAS Institute of Earth Environment | Cheng P.,CAS Institute of Earth Environment | Cheng P.,Xian Center | Yu S.-Y.,CAS Institute of Earth Environment | And 10 more authors.
Radiocarbon | Year: 2010

Technological and theoretical advancements in modern radiocarbon chronology make the precise dating of archaeological and geological events possible. Here, we show examples of how these state-of-the-art methods can be used to establish and refine the archaeological cultural chronology for the Shangluo area in the Qinling Mountains of central China. In this study, the Donglongshan and Zijing sites were dated using the high-precision accelerator mass spectrometry (AMS) 14C method. Also, detailed magnetic-susceptibility measurements were conducted at both sites to gain preliminary information about past climate changes. The 14C dates, after being treated with Bayesian statistics, provide a firm constraint on the archaeological chronological framework for this area. Within this framework, the Malan loess-Holocene soil transition can be placed at 10,400-10,090 BC, while the duration of the Yangshao and Longshan cultures was dated to ~4200-2900 and ~2900-2100 BC, respectively, revealing an undisrupted history of human occupation in this area until the early dynastic period. Magnetic susceptibility values began to increase in the early Holocene, indicating a progressive amelioration of regional climate. The widespread development of paleosol during the middle Holocene indicates that warm and wet climate conditions prevailed, providing a favorable environmental context within which the Yangshao culture thrived. Magnetic susceptibility values then decreased from ~2100 BC when the Xia Dynasty started, and loess accumulated again, pointing to cooling and drying climate conditions that may have led to a cultural transition from the Neolithic to the dynastic civilization. © 2010 by the Arizona Board of Regents on behalf of the University of Arizona.

Zhou W.,CAS Institute of Earth Environment | Zhou W.,Xian Center | Zhou W.,Xi'an Jiaotong University | Zheng Y.,CAS Institute of Earth Environment | And 4 more authors.
Earth and Planetary Science Letters | Year: 2010

The peat sequence at Hani in northeastern China accumulated over the past 16. cal. kyr in a percolation mire in which rain water and ground water seeped through the peat system. The molecular compositions of n-alkanes, n-alkanols, and n-alkanoic acids extracted from the Hani peat sequence reveal different responses to the progressive evolution of climate and changes in the nature of the peat-forming vegetation. Long chain length components that originate from the waxy coatings of subaerial vascular plants dominate the n-alkane distributions throughout the Hani peat sequence. The paleoclimate integrity of these biomarker molecules appears to be well preserved. Most of the n-alkanol distributions are similarly dominated by long chain components that indicate their origins from subaerial plants. In contrast, n-alkanoic acid distributions are dominated by secondary components that record the importance of post-depositional microbial activity in this peat sequence, which evidently can be extensive in a percolation mire.Elevated n-alkane Paq values and C23/C29 ratios, which are both molecular proxies for water-loving plants, record an especially moist local climate in the Bølling-Allerød (14.5 to 12.9ka), Younger Dryas (12.9 to 11.5ka), and Pre-Boreal (11.5 to 10.5ka) portions of the Hani peat sequence. Depressed Paq values and C23/C29 ratios and larger n-alkane average chain length values indicate that the Holocene Climatic Optimum (10.5 to 6ka) was a period of warmer climate with lower effective precipitation, which contrasts with evidence of wetter climates in most of East Asia. © 2010 Elsevier B.V.

Cheng D.-H.,Chang'an University | Wang W.-K.,Chang'an University | Hou G.-C.,Xian Center | Yang H.-B.,Chang'an University | And 2 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2012

The relationship between vegetation and groundwater in the hinterland of Mu Us Desert with 6 indicators, such as vegetation populations and cover, groundwater depth and mineralization, vadose zone moisture content and salinity, were investigated. We established the suitable depth of groundwater, unsaturated zone moisture content, groundwater salinity and the vadose zone salinity for dominated vegetation, Artemisia, Salix psammophila and Carex. The results showed that vegetation populations is very sensitive to groundwater depth and vadose zone moisture content, while vadose zone salinity and groundwater mineralization are non-sensitive indicators. In addition, the vegetation, the moisture of which for growth obtained from groundwater, its cover is more sensitive to groundwater depth, while the total coverage is non-sensitive indicators.

Qiao G.,Xian Center | Wang P.,Petrochina | Wu Y.,Xian Center | Du W.,Chang'an University | And 3 more authors.
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2015

Karakorum metallogenic belt is one of the hot area for the mineral resource exploration and development in West China with a great prospecting potential. According to the metallogenic theories established by the geologists of China, Karakorum metallogenic belt are further researched based on the metallogenic characteristics and its feature of geological formation. In the light of the time-space relationship of the mineralization and the geological formation, the related metallogenic series can be divided into syngenetic, epigenetic, and superficial weathering metallogenic series. These metallogenic series existed in the same geological formation naturally constitute a metallogenic serie family. In this study, 9 metallogenic serie families and 12 metallogenic series are summed up for the main mineral deposits of Karakorum metallogenic belt. On the basis of the mineralization pedigree, from their tectonic evolution angle, we further discussed its dynamic background of the formation for the metallogenic serie families, which provides the basis for clarifying the regional metallogenic regularity. ©, 2015, Jilin University Press. All right reserved.

Zhang H.,Chang'an University | Liu J.,Chang'an University | Peng S.,Xian Center | Zhang S.,Chang'an University | Wang D.,Chang'an University
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2014

Plagioclases with special zonal structure were seen occasionally in diorite intrusion in Pingshun, southern Taihang Mountains. The plagioclases is characterized by high Ca-riched basic plagioclases (An>63) in the core and Na-riched in the rim, and a corrosion zone formed between the core and the rim that composed epidote and sericite. In addition there are distinctive compositional differences between core and rim of the plagioclase xenocrysts. Based on the evidences from the components and textures of the plagioclause, the following scenario about the magma evolution is tentatively suggested. Mantle magma originating from the EMI underplated to lower crust and crystallized Ca-riched basic plagioclases under high temperature. Crustal source magma originated by melting of lower crust with the help of heat-carrying mantle magma. Mantle magma and crustal magma ascended quickly along Taihang deep fault, intruded into shallow crust, and mixed. Meanwhile, early-formed basic plagioclases dissoluted because of sudden reduced pressure and formed corrosion zone with irregular shape. The crust-mantle magma crystallized Na-riched plagioclases on the basis of Ca-riched basic plagioclases and formed plagioclases with special zonal structure, providing the most direct evidence to magma mixing in the study area.

Jiang H.-B.,Xian Center | Yang H.-Q.,Xian Center | Dong F.-C.,Xian Center | Tan W.-J.,Xian Center | And 2 more authors.
Northwestern Geology | Year: 2012

Metallogenic unit is a geological unit on the metallogenic significance. The latest classification scheme about Chinese metallogenic units released by the national mineral resource potential assessment project include level I (metallogenic domain), level II (metallogenic provinces) and level III (metallogenic belts). This article revises the boundaries of the six level III metallogenic units (metallogenic belts) in the East Tianshan-Beishan area on the basis of the inheritance of this classification scheme. Then the six level III metallogenic units are divided into 11 class IV metallogenic units (metallogenic sub-zone) as a symbol of sgnificant stratigraphic, tectonic and magmatic belt and associated mineralization. Furthermore, there is a summary about geology and mineral characteristics of every class IV metallogenic unit (metallogenic sub-zones).

Zhang P.,Northwest University, China | Zhang P.,CAS Institute of Earth Environment | Liu W.,CAS Institute of Earth Environment | Ma J.,Northwest University, China | And 4 more authors.
Arabian Journal of Geosciences | Year: 2016

The global expansion of C4 plants during the Late Cenozoic is an important event in the Earth’s environmental-ecosystem evolution. Taking into account the nonglobal expansion of C4 plants, the CO2 concentration is not the only prerequisite for C4 expansion. The direct driving factors for C4 expansion may be associated with regional arid and/or warm seasonal precipitation and temperature variations. However, a large change in the CO2 concentration occurred, varying from 100∼300 to >2000 ppm during geological history; thus, it is necessary to understand the impact of such changes in the atmospheric CO2 concentration on the δ13C values of C3 and C4 plants during different geological periods. In this article, we analyzed the δ13C values for seven C4 and C3 plants grown under different CO2 concentrations for 10, 20, and 30 days. According to our study, the δ13C records for all the C3 and C4 plants show a rapid decrease followed by a slowly stable decreased trend with increasing CO2 concentration when the plants were grown for 10, 20, and 30 days. Comparing with the value averaging about −26 to −27 ‰ for C3 plants and about −12 ‰ for C4 plants, when the CO2 levels reach 20,000 ppm, all of the δ13C values of C4 plants become more negative, varying from −27.5 to −36.1 ‰, which fall into the range of δ13C values for C3 plants. Namely, the increase of carbon dioxide can limit the identification of C4 plants by carbon isotope composition. Thus, the expansion of C4 plants as reconstructed from the geological records of carbon isotopes possibly does not reflect the origin and expansion of C4 plants when atmospheric CO2 concentration was reduced to a threshold value, as previously thought. However, another possible explanation is that the atmospheric CO2 concentration was reduced to a threshold value from which the carbon isotope values of C3 and C4 plants can be distinguished. Therefore, we suggest that it is necessary to understand the δ13C range for C3 and C4 plants, to accurately evaluate the origin and expansion of C4 plants, for geological periods when a high CO2 concentration occurred. © 2016, Saudi Society for Geosciences.

Yu X.,CAS Institute of Earth Environment | Yu X.,Xian Center | Zhou W.,CAS Institute of Earth Environment | Zhou W.,Xian Center | And 4 more authors.
Holocene | Year: 2011

Previous sedimentological studies on peat sequences from the eastern Tibetan Plateau showed that there have been eolian dust inputs to the wetlands on the eastern Tibetan Plateau, thereby providing an opportunity to reconstruct the history of the Asian winter monsoon at a higher temporal resolution. Here the dust flux and the content of trace metallic elements (Ti, Ni, and V) in a peat sequence from the Hongyuan Swamp (32°46.7′N, 102°31.0′E) are used to reconstruct variations in the intensity of the Asian winter monsoon during the Holocene. This record, when compared with the summer monsoon proxy, can help elucidate the phase relationship between these two systems. Our proxy-based reconstructions show different patterns of changes in the Asian winter and summer monsoons before and after 5.5 cal. ka BP. Generally, the two monsoons varied reciprocally before 5.5 cal. ka BP; however, after 5.5 cal. ka BP, these two systems exhibit synchronous changes. Moreover, both the frequency and amplitude of the variations in these two monsoons are different before and after 5.5 cal. ka BP. The rate of changes in the solar insolation during the Holocene matches well with these monsoon records, implying that the mid-Holocene climate transition may have resulted from orbital forcing. © The Author(s) 2011.

Cheng D.H.,Chang'an University | Wang W.K.,Chang'an University | Chen X.H.,University of Nebraska - Lincoln | Hou G.C.,Xian Center | And 2 more authors.
Environmental Earth Sciences | Year: 2011

A model, influence of water and salt on vegetation (IWSV), was developed to evaluate their influence on plant species. The main function of this model was to calculate a comprehensive index value for evaluating the suitability of plant growth. This model consists of five explanatory variables (vadose zone moisture content, vadose zone salinity, vadose zone lithology, depth to the water table, and groundwater mineralization) and two response variables (plant species and their cover). A set of independent data on three plant species, Artemisia ordosica, Salix psammophila, and Carex enervis, which are dominant species in the Mu Us Desert of northern China, were used to validate the model. Validation results show an overall correct prediction for the distribution of these three species. The results demonstrated that the IWSV model can be a useful tool for groundwater management and nature conservation in a semi-arid desert region, especially for predicting the vegetation distribution in areas with groundwater extraction. © 2010 Springer-Verlag.

Zheng Y.,Northwest University, China | Zheng Y.,CAS Institute of Earth Environment | Zhou W.,CAS Institute of Earth Environment | Zhou W.,Xian Center | And 2 more authors.
Organic Geochemistry | Year: 2011

Most research on long chain methyl ketones has focused on their origins and distributions. Their application in paleoclimate studies is less common than that of other n-alkyl lipids. The goal of this research was to explore this potential by studying n-alkan-2-ones from the Hani peat sequence in northeastern China. They were identified using gas chromatography-mass spectrometry (GC-MS) and showed a distribution ranging from C19 to C31 with a strong odd/even predominance. This type of distribution is considered to derive from Sphagum and microbial oxidation of n-alkanes. Comparison with climate sensitive indicators and macrofossil analysis shows that microbial oxidation of n-alkanes derived from higher plants was enhanced during the warm early Holocene period. This led us to develop three n-alkan-2-one proxies - C27/ΣC23-31 (C27/HMW-KET), carbon preference index (CPIH-KET) and average chain length (ACL(27-31)-KET) - as possible indicators of paleoclimate in the peat-forming environment. These proxies, in combination with C27 n-alkane δD values and peat cellulose δ18O records, might allow examination of paleo-ecosystem behavior during climatic evolution in northeastern China over the past 16,000yr. © 2010 Elsevier Ltd.

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