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Tianjin, China

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

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.

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.

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.

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.

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