Discovery of a 1.0 Ma Yellow River terrace and redating of the fourth Yellow River terrace in Lanzhou area

Based on the aeolian loess sequence-stratigraphic division and paleomagnetic datings on terraces, we found that an undiscovered terrace with the age of 1.0 Ma BP lies between the Dunwashan terrace and Wuyishan terrace. This terrace recorded an intensive Yellow River incision event during that period. Results of paleomagnetic dating and optically stimulated luminescence (OSL) dating of the Wuyishan loess section and Zaoshugou loess section on the fourth Yellow River terrace (T4) show that the age of the fourth Yellow River terrace in Lanzhou area is 0.86 Ma BP rather than the previously believed 0.6 Ma BP. This result answers a long-term question in the geomorphology community of whether there exists a 0.8 Ma terrace in Lanzhou area. The discovery of the 1.0 Ma Yellow River terrace and redating of the age of 0.6 Ma terrace in Lanzhou area provide new insights into further research on the evolution of Yellow River.     

Progress in the stratigraphy and geochronology of the Shuidonggou site, Ningxia, North China

In the past years we carried out further stratigraphy division in field and it is found that rich stone artifacts can be found in fluvial-shallow lake-alluvial sediments on the terrace Ⅱ of Biangou River, inShuidonggou site, Ningxia and they are SDG1, 2 and 7. More luminescence and AMS ^14C dating in laboratory show that Paleolithic culture develops during the Upper Paleolithic period with ages of 35--20 ka. The Paleolithic culture of SDG 1 is a little earlier than that of SDG 2 similar to SDG 7. The sandy sediments on terrace Ⅱ of Biangou River deposits in the past 72--18 ka, corresponding to Last Glacial. SDG2 has a stable sedimentary environment, resulting in the continuous stratigraphy, thickest deposits and rich environment and culture information, which can be regarded as the important and classic paleoanthropological section of Late Pleistocene in this region.     

Discovery of a 1.0 Ma Yellow River terrace and redating of the fourth Yellow River terrace in Lanzhou area

Based on the aeolian loess sequence-stratigraphic division and paleomagnetic datings on terraces, we found that an undiscovered terrace with the age of 1.0 Ma BP lies between the Dunwashan terrace and Wuyishan terrace. This terrace recorded an intensive Yellow River incision event during that period. Results of paleomagnetic dating and optically stimulated luminescence (OSL) dating of the Wuyishan loess section and Zaoshugou loess section on the fourth Yellow River terrace (T4) show that the age of the fourth Yellow River terrace in Lanzhou area is 0.86 Ma BP rather than the previously believed 0. 6 Ma BP. This result answers a long-term question in the ge-omorphology community of whether there exists a 0. 8 Ma terrace in Lanzhou area. The discovery of the 1. 0 Ma Yellow River terrace and redating of the age of 0.6 Ma terrace in Lanzhou area provide new insights into further research on the evolution of Yellow River.     

U-series dating of Zhangkou Cave in Yiliang,Yunnan Province:Evidence for human activities in China during 40—100 ka

The cultural deposits at pits T1 and T2 in Zhangkou Cave are intercalated with several flowstone layers. U-series dates show that the capping and 2rid flowstone layers are Holocene of age. The 4th and 5th flowstone layers are ca. 55 and 110 ka old respectively. The lithic artifacts bracketed by them provide unequivocal evidence for hominid presence during this time interval. The ““temporal gap““ of hominid fossil, widely quoted as in support of the out-of-Africa hypothesis, is most probably an artifact due to systematic errors of dating techniques. The infillings under 6th flowstone layer date to ＞300 ka, much older than the previous estimate at 15 ka based on classical 14C dating of fossil bones, providing one more example of the limited reliability of this chronometer. With rich relics and favorable conditions for precise dating, this site is promising for further multidisciplinary studies to address issues concerning recent human evolution in China.     

Formation mechanism of ferromagnetic minerals in loess of China： TEM investigation

The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eolian detrital particles. The magnetite can be classified into two categories, high-titaninm and low-titanium, which may be the indicators of magmatic rocks and metamorphic rocks,respectively. TEM investigation at nanometer scale shows that primary detrital magnetite of micron scale had been partially weathered to magnetite of 5-20 nanometer during the pedogenic process, which maintain the pseudomorphism of the aeolian debris. Some chlorite particles were also weathered to nanometer scale magnetite or maghemite in the pedogenic process. So weathering of the two minerals leads to formation of superparamagnetism, which may be the important mechanism of magnelic-susceptibnlty increase in paleosols. The mgnelite or maghhemite resulting from the weathering of chlorite contains a small amount of P and S,which is the signal of microbe-mineral interaction, and indicates that microbes may play a certain role in chlorite weathering and formation of Superparamagnetic particles.     

Nd isotopic characteristics of post-Archean sediments from the Eastern Nanling Range： Evidence for crustal evolution

A systematic Sm-Nd isotopic study was carried out for sediments and metasediments of different ages from Mesoproterozoic to early Mesozoic era in southwestern Fujian, Eastern Nanling Range. The results show that Nd model age (tDM) and εNd(t) value of most sediments are closely similar to those of Paleoproterozoic Mayuan Group, indicating that they may mainly be the recycling product of Paleoproterozoic crustal materials. However, the Nd model age significantly decreases with a corresponding increase in the εNd(t) value at Neoproterozoic (ca. 0.8-0.7 Ga) and Late Paleozoic (ca. 0.25 Ga), respectively. This is manifested by prominent vales and apexes on the diagrams of tDM VS. tStr. (stratum age) and εNd(t) VS. tstr. The decrease in tDM and the increase in εNd(t) are explained as a result of the significant incorporation of juvenile crustal materials that originated from depleted mantle due to strong lithospheric extension during both periods. It appears that tectonic magmatism in the Neoproterozoic and the Late Paleozoic is of prominent importance in affecting the geochemical nature of sediments in South China.     

Single grain Rb-Sr dating of euhedral and cataclastic pyrite from the Qiyugou gold deposit in western Henan, central China

The Rb-Sr isotopic dating of pyrite mineral from ore deposits can directly provide mineralization age. However, many geological factors may affect the Rb-Sr isotopic system,which baffles application of this method. Employing ultra-low procedural blank Rb-Sr method,we have dated pyrites separated from the No. 4 breccia pipe of the Qiyugou gold deposit,western Henan Province. Single grains of euhedral pyrite crystal with few microcracks yield an isochron age of 126 ± 11 Ma, which represents time of the main mineralization stage of the deposit. Pyrite grains of cataclastic type show nevertheless scattered Rb-Sr isotopic composition and no reasonable isochron can be defined. Crystal morphology and mineral inclusion studies reveal that Rb and Sr of pyrite mineral probably are preserved mainly in biotite, K-feldspar, and sericite mineral inclusions. The dating results likely suggest that cataclastic pyrite is not suitable for the Rb-Sr dating due to modification of the Rb-Sr isotopic system by later hydrothermal activity of fluid.     

U-Pb zircon dating constraints on formation time of Qilian high-grade metamorphic rock and its tectonic implications

In order to constrain the formation time of high-grade metamorphic rocks in the Qilian Mountains, U-Pb zircon dating was carried out by using LA-ICPMS technique for a paragneiss of the Hualong Group in the Qilian Mountains basement series and a weakly foliated granite that intruds into the Hualong Group. Zircons from the paragneiss consist dominantly of detrital magma zircons with round or sub-round shape. They have 207Pb/206Pb ages mostly ranging from 880 to 900 Ma, with a weighted mean age of 891 ±9 Ma, which is interpreted as the magma crystallization age of its igneous provenance and can be taken as a lower age limit for the Hualong Group. Magma crystallization age for the weak-foliated granite is 875±8 Ma, which can be taken as an upper age limit for the Hualong Group. Accordingly, the formation time of the Hualong Group is constrained at sometime between 875 and 891 Ma. A few zir- cons from both paragneiss and weak-foliated granite display old inherited ages of 1000 to 1700 Ma and young metamorphic ages of Early Paleozoic. The zircon age distribution pattern confirms that the Qilian Mountains and the northern margin of Qaidam Basin had a united basement, with geotectonic affinity to the Yangtze Block. The results also reveal that sediments of the Hualong Group formed by rapid accumulation due to rapid crustal uplift-erosion. This process may result from intensive Neoproterozoic orogenesis due to assembly of the suppercontinent Rodinia.     

Elemental composition in the sediments of the Yangtze and the Yellow Rivers and their tracing implication

Elemental compositions in the surface sediments of the Yangtze River and the Yellow River are quite different. The Yangtze River' s sediment is rich in K, Fe, Mg, Al and most of trace elements, and its elemental composition show remarkable spatial variations, whereas the Yellow River s sediment has higher contents of Ca, Na, Sr, Ba, Zr and Hf, and the elemental composition remains relatively stable. The ratios of some elements are also different in the sediments of the two rivers. The elemental composition of the Yangtze River sediment results from widely distributed igneous rocks and complicated source rocks and strong chemical weathering in the Yangtze River catchment basin, while the main provenance of the Yellow River sediment is the Loess Plateau which has dominant influence on the elemental composition, and the intense physical weathering is another controlling factor. The elements such as Cu, Zn, Sc, Ti, Fe, V, Ni, Cr, Co, Li and element ratios such as La/Sc, La/Co, Th/Co, Ti/Zr and Zr/Y can be used as the tracers to distinguish the Yangtze River sediment from the Yellow River s. The tracers can be used in the study of the mixing and distribution of the substances of the two rivers matters in coastal zones of China.     

Trace element geochemistry during chemical weathering——As exemplified by the weathered crust of granite, Longnan, Jiangxi

The granite weathering in Longnan, Jiangxi, is represented by mineralogical changes of feldspars → montmorillonite, illite → kaolinite, halloysite f66 bauxite, with Na, Ca, Si, P, V, U and Sr being in a mobile state while Ti, Al, Fe, Sc, Th, Zr and Hf remaining relatively conservative. With the exception of Zr/Hf, Nb/Ta, Th/Sc, Zr/Nd and Sm/Nb, changes are notable in ratios between most of the trace elements. Re-distribution of REE and Y has taken place during the chemical weathering, and the REE patterns of weathered samples in the profile, with original characters of the parent rock still recognizable, has undergone some fractiona-tion. Generally, the extent of chemical weathering is the critical factor determining the mineralogical and chemical characteristics of the profiles and this must be taken into account in any study of tracing the provenance on the basis of mineralogical and trace element characteristics of the sediments.     

Paleomagnetic dating of the topmost terrace in Kouma,Henan and its indication to the Yellow River＇s running through Sanmen Gorges

In the east of Xiaolangdi, many river terraces are developed at the exit of the Yellow River Gorges. Among them the terraces in Kouma, Yanshi of Henan Province are most typical, where the Yellow River developed three staircase terraces, among which the altitude of gravel stratum of the topmost terrace is 30-35 m higher than the river level.The top of the gravel stratum was covered by 60 m eolian loess deposits which have many brownish-red paleosol strips.And the paleosol $14 is at its bottom. Research on systematic magnetostratigraphy and paleosol-loess matching indicates that the bottom age of the loess on the topmost terrace is 1165 ka. Therefore, it can be concluded that the terrace develops no later than 1.165 Ma and the situation that the Yellow River runs through Sanmen Gorges and inpours into East China Sea happened at least before 1.165 Ma.     

Does chemical index of alteration （CIA） reflect silicate weathering and monsoonal climate in the Changjiang River basin？

Chemical weathering of continental silicates significantly influences global climate change,earth surface processes,material cy-cling and oceanic chemical composition.How to quantitatively reconstruct chemical weathering history has become an important issue in global change research.Chemical index of alteration(CIA) has been widely used as a quantitative indicator for estimating the degree of silicate weathering.However,its method of calculation and the limitations of its application are not well understood.In this study,we calculated CIA values from suspended particulate matter collected from the mainstream and major tributaries of the Changjiang River.The values yielded considerable variations at different temporal and spatial scales.The average CIA values increased from the upper to middle-lower reaches,and were lower in the suspended samples taken during the flood than in the dry season.The spatial variation in the CIA is predominantly controlled by basinal monsoon climate.In contrast,the temporal varia-tion in the Changjiang River basin is controlled mainly by the changing provenance of suspended samples in relation to the shift of the precipitation zone.The CIA probably indicates the integrated weathering history in the river basin,and thus,cannot be used as a reliable proxy of instantaneous chemical weathering.Furthermore,the calculation method and hydrodynamic sorting also influence the CIA values.Therefore,caution should be taken when using the CIA as a proxy for studying chemical weathering from different regions.     

Environmental and biogeo-chemical process of accumula-tion of iron-phosphorus in marine sediments

This paper discusses the environmental andbiogeochemical process of accumulation of iron-phosphorusin marine sediments for the north aktian of the South ChinaSea and analyzes the relationships between the contents ofiron, phosphorus and calcium carbonate as well as their ex-istent characteristics. The results show that the variances ofphosphorus and calcium carbonate contents with depths areopposite and those of iron and calcium carbonate contentsare almost accordant. It is not only related to the biogeo-chemical process of accumulation of biogenous calcium car-bonate in sediments, which resulted from the fact that themarine primary productivity was stimulated by part of ter-rigenous phosphorus dissolved into seawater due to declineof superficial water temperature and increase of carbon di-oxide content in the glacial period, but also related to ironimpelled oxidation and accelerated deposit by the dissolvedoxygen from the atmosphere and the photosynthesis of hy-drophytes in seawater. The variance of soluble iron-phos-phorus species (Fe-P) in sediment columns can sensitivelyreflect the changes of climate and environment, which sug-gests that the accumulative characteristics and existent statesof iron-phosphorus species (Fe-P) in marine sediments havethe significance as an indicator of the changes of paleocli-mate and paleoenvironment.     

Variations of geochemical compositions and the paleoclimatic significance of a loess-soil sequence from Garzê County of western Sichuan Province, China

The West Sichuan Plateau is located in the southeast margin of the Tibetan Plateau, where the climate is mainly influenced by the Indian southwest summer monsoon and the Tibetan Plateau monsoon. In this study, detailed geochemical analysis has been carried out on Ganzisi loess-paleosol sequence in Ganzê County of western Sichuan Province. The results indicate that Ganzê loess and paleosol have experienced the incipient stage of chemical weathering in dust source regions, characterized by the decomposition of plagioclase which caused the depletion of mobile elements Na and Ca. The post-depositional chemical weathering is characterized by carbonate dissolution and oxidation of Fe2＋. The variations of some geochemical indexes （such as CIA values, Na/K and Fe2＋/ Fe3＋ ratios） in Ganzisi loess-paleosol sequence indicate a gradually decreased chemical weathering intensity in the dust source regions and deposition areas since 1.15 Ma BP consistent with the general increase of global ice volume, reflecting that the arid trend since 1.15 Ma BP in the southeast Tibetan Plateau is a regional response to the global climate change. The geochemical indexes in this section also reveal an obvious drying step occurred at about 250 ka BP in this region. We interpret this drying step as a result of decreased influence of the Indian southwest summer monsoon. This decrease in monsoon moisture is probably attributable to the uplift of the southeast margin of the Tibetan Plateau at about 250 ka BP.     

4.1 Ga old detrital zircon in western Tibet of China

4.1 Ga old detrital zircon was found by SHRIMP U-Pb dating for quartz schist from Buring County in western Tibet, Southwest China. This is the oldest zircon U-Pb age found in China so far. The detrital zircon is a zircon of magmatic origin because its Th/ U ratios are 0.76 to 0.86. Two dates older than 4.0 Ga were measured only in one grain. U-Pb ages of 35 measured spots in 24 zircons can be subdivided into 6 groups, corresponding to at least 6 episodes of magmatic activity in the target area. The present results provide an important geochronological constraint on the geological evolution of Qinghai-Tibet Plateau.     

Dating recent lake sediments using spheroidal carbonaceous particle （SCP）

Dating lake sediment using sedimentary event is the supplement and calibration to traditional dating by radionuclide such as ^210Pb and ^137Cs. Based on the change of spheroidal carbonaceous particle (SCP) concentration, the age sequence of lake sediments can be deduced. It is one of the dating methods using sedimentary event. SCP is formed from combustion of fossil fuel at high temperature up to1750℃ and at a rate of heating of approaching 104℃/s. It can be dispersed to several hundred kilometers away from its source and deposited with precipitation or dryly deposited, and kept in sediments. Compared with Cs or Pb, there is no evidence for SCP that it decays in lake sediments and is unremovable once stored except by physical disturbance because it is mainly composed of element carbon. Handy method to extract, identify and calculate has been developed. Although fossil fuel has been used early in China, combustion at high temperature started later since emergence of electricity generation. The productivity of SCP is positively related with the generated thermal power, which is reflected as the SCP concentration in lake sediments increases with the increase of generated thermal power. Therefore, reliable sediment markers from the start of the SCP record and the remarkable variation can be used for dating purpose. In China, electricity industry started from the 1950s, and rapid increase of generated power took place since 1978. Based on these time markers, SCP time sequences of lake sediment cores LH and LL-4 from Longgan Lake, the middle reach of the Yangtze River, have been established, which is comparable with the results from ^137Cs and ^210pb, and has eliminated the errors of dating using ^137Cs and ^210pb.     

Late Pleistocene human skull from Jingchuan,Gansu Province

Jingchuan human fossil, found in Gansu Province in 1976, was given a preliminary report in 1984, but questions remained con- cerning the age and character of the fossil. We conducted field investigation at Jingchuan in May of 2006 to examine the stratum yielding the human fossil and to obtain sediment samples for optically stimulated luminescence (OSL) dating. Three samples collected from different stratigraphic levels at the fossil locality yielded OSL dates of 15, 48 and 7.9 thousand years ago (ka), respe...     

Porphyry Cu-Mo deposits in the eastern Xing’an-Mongolian Orogenic Belt: Mineralization ages and their geodynamic implications

The eastern Xing’an-Mongolian (Xing-Meng) Orogenic Belt (XMOB) is one of the important areas of porphyry copper (Cu)-molybdenum (Mo) deposits in China. However, studies on the exact ages of mineralization and their geodynamic significance are very limited. In this study, granodioritic rocks from the Duobaoshan Cu deposit and Daheishan Mo deposit were selected to make zircon SHRIMP U-Pb analyses in order to constrain their mineralization ages. Geochronological data indicate that two episodes of mineralization took place in the Duobaoshan Cu deposits. The granodiorite related to the Duobaoshan porphyry Cu deposit was formed in the Early Paleozoic with zircon U-Pb age of 485±8 Ma, whereas the granodiorites related to the Sankuanggou skarn-type Cu deposit were emplaced in the Jurassic with zircon U-Pb ages of 176±3 and 177±3 Ma. In the Daheishan area of Jilin Province, the emplacement age of the granodiorite porphyry related to the porphyry Mo deposit was dated at 170±3 Ma, and the unmineralized monzogranite at 178±3 Ma. Therefore, two episodes of Cu-Mo mineralization were developed in the eastern XMOB, at ~485 Ma and ~175 Ma, respectively. Based on the geological history and spatial-temporal distribution of the granitoids in northeastern (NE) China, it is proposed that the Duobaoshan Cu deposit was related to the collision of the Xing’an and Erguna blocks in the Early Paleozoic, and the Sankuanggou Cu and Daheishan Mo deposits were related to subduction of the Paleo-Pacific plate during the Jurassic.     

Geochronologic constraints on magmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gangdese,Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion mi-croprobe(SHRIMP) . The ages can be divided into two separate groups,reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystalli-zation of the Zhunuo ore-forming porphyry. Finally,a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3 ±0.2 Ma,representing the time of copper mineraliza-tion. These ages,in combination with available literature data,indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward,and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.     

Geochronolosic constraints on masmatic intrusions and mineralization of the Zhunuo porphyry copper deposit in Gansdese, Tibet

In situ zircon U-Pb ages for the recently discovered Zhunuo porphyry copper deposit in the western part of the Gangdese metallogenic belt in Tibet were determined by sensitive high-resolution ion microprobe （SHRIMP）. The ages can be divided into two separate groups, reflecting more than four major tectono-magmatic events in the area. The 62.5±2.5 Ma age of inherited zircons may be related to the volcanic eruption of the Linzizong Group formed shortly after the India-Asia continental collision. The 50.1±3.6 Ma age most likely corresponds to the time of underplating of mantle-derived mafic magma in Gangdese. The 15.6±0.6 Ma age obtained from magmatic zircons is interpreted as the age of crystallization of the Zhunuo ore-forming porphyry. Finally, a molybdenite Re-Os isochron age of 13.72±0.62 Ma is consistent with another zircon U-Pb age of 13.3±0.2 Ma, representing the time of copper mineralization. These ages, in combination with available literature data, indicate that magmatic crystallization and copper mineralization in the Gangdese metallogenic belt became gradually younger westward, and further suggest that the Zhunuo porphyry copper deposit was formed in the same tectonic stage as other porphyry copper deposits in the eastern and central Gangdese belt. This conclusion provides critical information for future exploration of porphyry copper deposits in western Gangdese.