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Tianjin Center

Tianjin, China
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Chen X.,China Agricultural University | Li Y.,Tianjin Center | Wang F.,China Agricultural University
Acta Mechanica Sinica/Lixue Xuebao | Year: 2017

A new instantaneous mobile bed thickness model is presented for sediment transport in skewed asymmetric oscillatory sheet flows. The proposed model includes a basic bed load part and a suspended load part related to the Shields parameter, and takes into account the effects of mass conservation, phase-lag, and asymmetric boundary layer development, which are important in skewed asymmetric flows but usually absent in classical models. The proposed model is validated by erosion depth and sheet flow layer thickness data in both steady and unsteady flows, and applied to a new instantaneous sediment transport rate formula. With higher accuracy than classical empirical models in steady flows, the new formula can also be used for instantaneous sediment transport rate prediction in skewed asymmetric oscillatory sheet flows. © 2017 The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg

Fan C.,Chinese Academy of Geological Sciences | Fan C.,Tianjin Center | Koeniger P.,Leibniz Institute for Applied Geophysics | Wang H.,Tianjin Center | Frechen M.,Leibniz Institute for Applied Geophysics
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2011

Modern living and mid-Holocene shells of Crassostrea gigas from the western Bohai Sea in China were subjected to sclerochronological analysis with the aim of determining whether their concave bottoms and growth breaks on resilifer surfaces, as well as corresponding translucent growth bands visible in cross-section, have seasonal significance. An additional aim was to obtain ontogenetic information from mid-Holocene fossil shells. We compared δ18O and δ13C profiles compiled with high and low sampling resolution for the same shell in order to test the consistency of the results and identify a suitable sampling strategy for future sclerochronological studies. The results show that concave bottoms on the resilifer surface and corresponding translucent growth bands in cross-section formed during the cold season. These features are appropriate indicators of annual growth increments in fossil C. gigas shells. Moreover, growth breaks located near convex tops indicate annual growth increments for that part of the shell which grew when the organism was sexually mature. Therefore, spawning-related growth breaks and alternating winter freeze shocks (concave bottoms) are excellent morphological features in determining annual growth increments. Consequently, the life span, growth rate, and timing of spawning and death can be determined from the increments of ligament growth of these fossil oyster shells. For future sclerochronological studies, an adaptive micro-sampling strategy could be used for different increments of ligament growth that represent different seasons. Such a strategy would be more efficient in providing reliable insights into growth history of shells with variable growth rates of annual increments. © 2010 Elsevier B.V.

Wu W.,Peking University | Zhao L.,Peking University | Pei Y.,Tianjin Center | Ding W.,Wuhan University | And 2 more authors.
Organic Geochemistry | Year: 2013

Glycerol dialkyl glycerol tetraethers (GDGTs) and bulk organic geochemical parameters were examined for a short core from the Bohai Sea, a Yellow River-dominated continental margin. A three end member mixing model using branched/isoprenoid tetraethers (BIT) index, δ13C and C/N shows that the average fractions of soil, marine and plant organic matter (OM) during the period of 1933-2011 are 67.7% (38-92%), 26.1% (0-58%) and 6.2% (0-23%), respectively. Abrupt changes of sedimentary OM compositions around 1953, 1976 and 1996 are synchronous with the Yellow River mouth relocations. The BIT index values (0.33-0.80) present a stronger correlation with crenarchaeol abundance (R2=0.88) than branched GDGTs abundance (R2=0.27), suggesting that variations of marine Thaumarchaeota abundance rather than soil OM inputs is the first order factor controlling the BIT index values, although this proxy has been widely used for soil OM. The comparison between the BIT index, nutrient status and historical Yellow River sediment load indicates that the high sensitivity of the BIT index to the Yellow River channel shifts cannot be explained by a nutrient stimulation mechanism, but instead is likely caused by the restriction of Thaumarchaeota growth in highly turbid water due to the enormous sediment inputs from Yellow River. Our study demonstrates that local conditions should be considered when applying the BIT index as an environmental proxy. © 2013 Elsevier Ltd.

Sun D.,Peking University | Tan W.,Peking University | Pei Y.,Tianjin Center | Zhou L.,Peking University | And 3 more authors.
Organic Geochemistry | Year: 2011

Bulk geochemical characterization (total organic carbon, grain size distribution, carbon isotope composition) and molecular biomarkers (lignin phenols, straight chain aliphatic hydrocarbons, glycerol dialkyl glycerol tetraethers) were analyzed for a 21m core from the Bohai Sea (North China), spanning ca 21kaBP. These paleo-proxies presented remarkable differences between the late glacial period and the Holocene, reflecting continental and coastal environments, respectively. Two peat layers were deposited during the period of ca 9000-8460yrBP. Thereafter the core site has been consistently covered by seawater until recent reclamation of land from the sea. The occurrence of a total organic carbon maximum from ca 6000-3800yrBP was attributed to delivery of organic carbon enriched sediments via the Yellow River, consistent with increased vegetation density and higher development of soil under warm and humid mid-Holocene climate conditions. The distributions of lignin phenol compositions and C31/C29 n-alkane ratio suggested the largest expansion of woody plants between ca 5300 and 4000yrBP, corresponding to the extremely favorable climatic conditions. Since ca 3800yrBP, an abrupt increase in the C31/C29 n-alkane ratio suggested higher abundance of grasses, consistent with a drying climate trend after the mid-Holocene. Since our coastal sediments close to the Yellow River outflow contain catchment-integrated environmental signals of the river basin, molecular proxies demonstrate that the variability of vegetation distributions in the Holocene is a widespread phenomenon in those areas adjacent to Yellow River Basin. © 2011 Elsevier Ltd.

Xue C.,China University of Geosciences | Chi G.,University of Regina | Li Z.,Tianjin Center
Ore Geology Reviews | Year: 2014

The Uragen Zn-Pb deposit in Wuqia County, Xinjiang, China, is hosted in sandstones and conglomerates of the Lower Cretaceous Kezilesu Group and argillaceous dolomite of the Paleocene Aertashi Formation in the Kashi sag, northwestern Tarim basin. The deposit is characterized mainly by low grade (Zn+Pb~3wt.%) and large tonnage (~3Mt metals in the southern ore zone, potentially 10Mt metals for the whole deposit), with an average Zn/Pb ratio of about 5.8. The orebodies are tabular and stratiform, mainly distributed in a syncline. The ores are characterized by disseminated sulfides with minor massive, veinlet, patchy structures, and fine-grained, locally colloform and framboidal, textures. The main primary metallic minerals are sphalerite, galena, pyrite and marcasite, and minor supergene minerals include smithsonite, hydrozincite, anglesite, calamine, jarosite, and limonite. The ore minerals mainly occur as replacement of cements, matrix and framework grains of the host rocks and as open space filling to a lesser extent. Based on the fact that orebodies straddle across a hiatus between the lower Cretaceous and Paleocene host rocks and on the replacement and open-space filling textures and structures, the mineralization is interpreted to be epigenetic. The tightly clustered Pb isotopic values of the main-stage ore minerals (206Pb/204Pb ranging from 18.608 to 18.663, 207Pb/204Pb from 15.619 to 15.669, 208Pb/204Pb from 38.677 to 38.839) suggest that a single source supplied the metals, whereas the wide range of S isotopes (δ34S from -27.9‰ to 14.6‰ VCDT) indicates multiple sources of reduced sulfur including those from thermal sulfate reduction (TSR) and bacterial sulfate reduction (BSR). The organic matter in the ores is characterized by relatively low concentrations of saturated hydrocarbons, high concentrations of aromatic hydrocarbons, asphaltenes and non-hydrocarbons, and low maturity compared to that in the host rocks and equivalent strata away from mineralization. Both hydrocarbons in the ores and host rocks show little biodegradation. These characteristics of organic matter suggest that the site of mineralization was buried to significant depths and heated to above 80°C before the charging of hydrocarbons (thus non-development of biodegradation), that some of the hydrocarbons were consumed in mineralization (thus decreased maturity), probably used as reducing agents for sulfate reduction in situ, and that bacteria-derived sulfur in the ores was not generated in situ. Mineralization probably resulted from mixing of a metal-rich fluid with multiple fluids carrying reduced sulfur from different sources (including some reduced sulfur from in situ TSR). However, it remains unclear whether the metal-carrying fluid was derived from a near-surface groundwater system and flowed downward to the site of mineralization at burial conditions, or was derived from deeper parts of the basin and flowed up to the site of mineralization as part of a hydrothermal system; the distinction of the two models requires a better understanding of the thermal profile across the deposit. © 2014 Elsevier B.V.

Wu W.,Peking University | Ruan J.,Peking University | Ding S.,Peking University | Zhao L.,Peking University | And 5 more authors.
Marine Chemistry | Year: 2014

To assess the source of glycerol dialkyl glycerol tetraethers (GDGTs) and their usefulness as proxies for terrestrial organic matter inputs and temperature in the Yellow River-dominated margin, we measured isoprenoid and branched GDGT concentrations in surface sediments along a lower Yellow River-estuary-coast transect. Branched GDGTs dominated over isoprenoid GDGTs in the riverbed sediments and had similar compositions from river to coast. In contrast, isoprenoid GDGTs displayed an increasing abundance and a decreasing GDGT-0 to crenarchaeol ratio (1.6 to 0.6) toward the sea. Such distribution patterns of GDGTs, combined with the result from a principal component analysis (PCA), confirmed the different origin of branched and isoprenoid GDGTs with branched GDGTs being primarily from soil erosion of the Chinese loess plateau (CLP) whereas, in addition to allochthonous terrestrial inputs, aquatic Thaumarchaeota partially contributes to the isoprenoid GDGT pool in estuarine and coastal areas. The branched GDGT-derived temperature (avg. 11°C) is consistent with the annual mean air temperature (MAT) of the CLP in the middle river basin, a major source region for the Yellow River sediments, whereas the isoprenoid-derived temperature (12.7 to 28.4°C) deviated widely from the annual mean temperature in the study region. Application of a binary mixing model based on δ13C, the branched and isoprenoid tetraether (BIT) index and branched GDGT concentrations showed consistent decreases in the relative amount of terrestrial organic carbon toward the sea, but estimates from the latter two proxies were lower than those from the δ13C. © 2013 Elsevier B.V.

Zhang Q.,Jilin University | Lu W.,Jilin University | Chen S.,Tianjin Center | Liang X.,Jilin University
Theoretical and Applied Climatology | Year: 2016

Drought is a recurrent disaster that occurs in virtually all climatic zones of the world. However, drought characteristics vary substantially among different climatic regions. In this study, multifractal and wavelet analyses are used to characterize drought based on monthly precipitation. The rainfall data of 28 precipitation stations from 1958 to 2011 in Jilin province were collected to calculate the standardized precipitation index (SPI), and the negative monthly SPI time-series is used in a multiscaling approach to determine drought characteristics in Jilin province. Simple scaling and multiscaling analyses show significant variations in monthly droughts in the region. Morlet wavelet analysis also shows that significant cycles and multiple time-scales of drought exist in all stations. Cross wavelet analysis shows that drought occurrence in the region is mainly influenced by different climatic factor scales. However, different factors have different degrees of influence at different regions. The enduring influence of medium and long-term climatic patterns (such as El Niño events) may lead to the simple scaling behavior of drought for some regions. © 2016 Springer-Verlag Wien

Zhang Z.,China University of Geosciences | Kang J.,Tianjin Center | Kusky T.,Wuhan University | Santosh M.,China University of Geosciences | And 3 more authors.
Precambrian Research | Year: 2012

Two layers of basaltic flows intercalated with Late Neoproterozoic (Sinian) sandstones have been identified in the Sugetbrak region in the northwest Tarim block, Northwest China. The basaltic rocks are composed of augite and plagioclase phenocrysts set in a groundmass of plagioclase laths with interstitial subophitic clinopyroxene grains and minor anhedral opaque minerals (magnetite and ilmenite). LA-MC-ICP-MS U-Pb dating of zircons from the lower basaltic flows yields a crystallization age of 783.7±2.3Ma. Both layers of the basaltic rocks are characterized by low SiO 2 and high total FeO (>12wt.%), TiO 2 (>3wt.%) and P 2O 5 (>0.5wt.%) contents and extremely high Na 2O/K 2O ratios, and display a Fenner trend of differentiation that could be ascribed to significant fractional crystallization of clinopyroxene and plagioclase. The mineralogical and geochemical characteristics suggest the affinities of a transitional series between alkaline basalt and tholeiite. However, the lower basaltic flows have higher Nb/Y ratios than the upper ones, indicating that they are more alkaline. Positive age-corrected Nd isotope ratios [e{open} Nd(t)=+0.24-1.07] and positive e{open} Hf(t) values (+1.1-4.5) of the basaltic rocks suggest absence of any significant crustal contamination. High e{open} Nd(t) lavas are isotopically similar to those of several modern oceanic hotspots, and have ocean island-like patterns of incompatible elements. The estimated potential mantle temperature is ∼100-150°C higher than normal asthenospheric mantle, consistent with a plume-head origin. Moderate ratios of light rare earth elements (REE) to heavy REE indicate that the source magma was probably generated by partial melting of garnet-spinel transition facies of peridotite, but the upper basaltic rocks were derived from a relatively shallower mantle source, reflecting progressive lithosphere thinning possibly through plume-lithosphere interaction. We correlate the Sugetbrak basalts to the second Neoproterozoic mantle plume event (780-745Ma) related to the breakup of the Rodinia supercontinent. © 2012 Elsevier B.V.

Zhong Y.,Tianjin Center | Chen Y.L.,CAS Institute of Geology and Geophysics | Zhai M.G.,CAS Institute of Geology and Geophysics | Ma X.D.,Chinese Academy of Geological Sciences
Yanshi Xuebao/Acta Petrologica Sinica | Year: 2016

The khondalite series, located in the western part of the North China Craton (NCC), is one of the most significant objects that are essential for understanding formation and evolution of the NCC. To date, a great number of researches suggested that the khondalite series, a suite of high-grade metamorphic alumina-rich sedimentary rocks, had witnessed two important metamorphic events during 1. 95 ∼ 1. 82 Ga, including high pressure/high temperature metamorphism and high to ultra-high temperature/medium to low pressure metamorphism. The available data from drilling samples of the Mesozoic-Cenozoic Ordos Basin revealed that its basement rocks were similar with the khondalite series in petrology, provenance, depositional age and metamorphic timing. It appears that a larger part of the Ordos Block had been covered by the protolithes of the khondalite series and been involved by the subsequent high-grade metamorphic events. However, the debates on the distribution, isochronism and depositional environment of the protolithes of the khondalite series are still ongoing. These points are invaluable for constraining temporal-spatial distribution of the khondalite series and understanding tectonic evolution of the western NCC. As an attempt to facilitate deciphering the protolith basin, three typical sections of the khondalite series in the Helanshan, Daqingshan and Jining areas were chosen for deposition sequence subdivisions, stratigraphie correlation and lithofacies paleogeographic rebuilding. These results in this paper suggest that: (1) the khondalite series in the northern margin of the Ordos Block are composed of three correlatable deposition sequences; (2) an epeiric sea over the Ordos Block (Ordos Epeiric Sea) might be responsible for the planar distribution of the khondalite series and its transgressive direction was mainly from the Helanshan-interior of the block to the Daqingshan and Jining areas: and (3) the Ordos Epeiric Sea induced accumulation was completed during the inactive period (2.5 ∼ 2. 3Ga) and the khondalite series might be the first sedimentary cover after the cratonization of the NCC.

Guo L.,China University of Geosciences | Meng X.,China University of Geosciences | Zhang G.,Tianjin Center
Journal of Applied Geophysics | Year: 2014

We present the 3D correlation imaging approach for the total magnitude magnetic anomaly and the normalized source strength data for reducing effects of strong remanent magnetization. We divide the subsurface space into a 3D regular grid and then calculate the cross correlation between the observed total magnitude magnetic anomaly or normalized source strength and the theoretical total magnitude magnetic anomaly or normalized source strength at each grid node due to a magnetic dipole. The resultant correlation coefficients are used to describe the equivalent magnetic dipole distribution underground in a probabilistic sense. The two approaches were tested both on the synthetic magnetic data and the real magnetic data from a metallic deposit area in the middle-lower reaches of the Yangtze River, China. The results show that the two approaches can considerably reduce effects of remanent magnetization and delineate magnetic sources in the subsurface, and that the approach for the normalized source strength is less sensitive to strong remanent magnetization than that of the total magnitude magnetic anomaly. © 2014 Elsevier B.V.

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