Geological Journal of China Universities

The lake environment changes in China and its mechanical explanation

WANG Su-ming, XUE Bin, SHEN Ji, YAO Shu-chun

2009, 15(2): 141-148.

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All the information from the lake environment changes could be well archived in th lacustrine sediments. The changes in lake environment on the different time-scale are resulted from the tectonic movement, climatic change and human impact respectively and meanwhilely. The major tectonic movement in China is the uplifting of Tibetan Plateau, and the climate system is the east Asian monsoon, however, the human impact seems to be more implicated, e.g. the indirect impact such as the vegetation and land use changes in the catchment, or the direct impact such as the lake reclamation and the lake enclosure from large river system. Delineating the mechanism of the lake environment changes and distinguishing the human impact from the natural influence are presently highlighted by the paleolimnologists.

Cycles and forcing mechanism of wet-dry variations in north China during the past 11 million years revealed by wind-blown silt deposits

LU Hua-yu, HU Ting, Wang XIAN-yan

2009, 15(2): 149-158.

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There occur thick wind-blown silt deposits which are regarded as a good geological archive of paleoclimatic changes in Late Cenozoic in North China and the central Asia. In these aeolian sequences, the Quaternary loess deposits were widely investigated and the Milankovitch cycles were found in the paleoclimatic changes. However, the frequencies and forcing mechanism of wet-dry changes in Pliocene and Miocene are not clear to date. In this study, the representative aeolian silt sequences in Chinese Loess Plateau and northeastern Qinghai-Tibetan Plateau are systemically sampled and measured for grain size distribution. On the basis of the previous optically stimulated luminescence dating and magnetostratigraphic investigations,the time series of the grain size variations of the past 11.0 Ma is established, which is a good proxy indicator of the wet-dry changes in North China and the interior Asia. We slice the new time series into 11~7.3 Ma, 8.0~5.0 Ma, 5.3~2.5 Ma, 2.5~1.2 Ma and 1.2~0 Ma, and utilize Blackman-Turkey spectrum analysis and wavelet transfer to detect cycles of the long-time climatic changes. Our results show that the cycles of ~20 ka of the precession, ~40 ka of the obliquity and~100 ka of the eccentricity have been dominated in the time series, demonstrating that insolation has forced the paleoclimatic changes in the past 11.0 Ma. Atthe same time, the non-orbital cycles found in this new time series might be caused by harmonics of the orbital cycles and/or the spurious time scale, induced by a vulnerable depositional process of the aeolian sediments. We suggest perturbation of the Earth orbital trajectory, which caused the insolation changes in the north Hemisphere, might drive the replacement of the Westerlies and the Asian monsoon changes, and controlled the wet-dry variations in North China and the central Asia. Further investigation on seeking for complete aeolian records and strengthening modeling work would improve our understanding of environment changes in North China and the central Asia.

Sr-Nd isotopic characteristics of different particle-size fractions of eolian sands in the deserts of northern China

RAO Wen-bo1,3, CHEN Jun2, YANG Jie-dong2, JI Jun-feng2, LI Gao-jun2

2009, 15(2): 159-164.

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Sr-Nd isotopic compositions of different grain-size fractions of eolian sand samples collected from Gurbantunggut,Tengger and Ordos deserts are investigated in detail. TheεN（d 0） and 87Sr/86Sr values vary from -3 to -5.3 and from 0.712452 to 0.716895, respectively in the Gurbantunggut desert, between -9.9 ~ -12.3 and 0.716753 ~ 0.723033, respectively in the Tengger desert, and between -13.1 ~ -18 and 0.714028 ~ 0.716780, respectively in the Ordos desert. These desert sands with different Sr-Nd isotopic ratios imply their distinct provenances. The Nd isotopic values of eolian sands are dependent on geology and relief of the deserts. The Sr isotopic ratios of eolian sands are affected not only by geology and relief of the deserts, but also by particle sorting and mineral weathering. The isotopic compositions of different particle-size fractions of eolian sands in the Gurbantunggut desert have similar variations to those in the Tengger desert, but distinct from those in the Ordos desert. Fine and coarse sands in the Ordos desert have different sources, of which, the fine sand (especially the < 2 μm fraction) perhaps came partially from foreign sources. However, different grain-size fractions of eolian sands in other deserts have same provenances without the input of foreign sources.

Advance in study of oxygen and carbon isotope variations in cave stalagmites as Palaeo-climate proxies

KONG Xing-gong

2009, 15(2): 165-170.

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Stalagmites are now regarded as valuable archives in study of climatic conditions on the continents. They are ideal materials for precise U-series dating, yielding ages in calendar years, coupled with annual layer counting, the chronology of stable oxygen-isotope then be made with the resolution higher than year. These absolute precise dating and high resolution records offer a number of advantages relative to other continental climate proxy recorders such as lake sediments and peat cores. In many cases, stalagmite records may provide climate conditions that rival those obtained from marine sediments and ice cores. The controls on stalagmite δ18O are numerous, under equilibrium condition, the δ18O values of stalagmites are related to intensity of summer monsoon or amount of the monsoon precipitation at the typical monsoon area. This emphasis on global climate teleconnections has replaced attempts to constrain absolute palaeotemperature, allowing the scientific community to place global climate changes on a firm chronological and climate dynamical footing. Unlike the global comparison of δ18O, under equilibrium open system conditions, the δ13C of the dissolved species reflects the isotopic composition of the soil CO2, with no detectable isotopic imprint from the carbonate host-rock. Thus the stalagmite δ13C is mainly controlled by the vegetation covering the cave, normally by the C3/C4 ratio of the local vegetation. The δ13C can still be related to the change of precipitation and temperature at special region.We should pay special attention to these processes including evaporation, rapid degassing of cave dripwaters, kinetic fractionation,CO2 degassing of dripwaters and consequent calcite precipitation in the vadose zone above a cave that could affect the carbonisotope to a relatively heavier signature. The literature is reviewed briefly to provide for the readers a sense of the current research work of the stable isotope of stalagmite and provide some ideas for future research directions.

Model assessment of the possible contribution of increasing marine biogenic aerosol in Late Cenozoic cooling

LI Gao-jun, CHEN Jun, JI Jun-feng, SHENG Xue-fen, LI Tao

2009, 15(2): 171-183.

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Geochemical model coupled with marine isotopic records of carbon, strontium and osmium indicates a late Cenozoic increase in chemical weathering associated with enhanced physical erosion. Marine bio-productivity is largely promoted by the fertilized oceans in response to the increasing riverine phosphorus input. The increasing biogenic aerosol caused by marine biobooming result in elevated cloud albedo and cloud cover, which would act as a significant negative radiative forcing of about 16.5 W m-2 over the past ~7 Ma that is equivalent to about 13 ℃ global cooling in equilibrium temperature. The increasing atmospheric aerosol also reduces the precipitation efficiency of cloud, which would enable penetration of ocean vapour into high latitudes and ultimately facilitate the accumulation of polar ice sheets.

Rapid quantification of calcite in north Atlantic sediments by DRIFTS and its climate significance — Example of drilling site U1308

GE Yun, LIU Lian-wen, JI Jun-feng, BALSAM William

2009, 15(2): 184-191.

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A rapid and simple method based on diffuse reflectance coupled with lnfrared Fourier Transform Spectroscopy (DRIFTS)was developed for the quantification of calcite content in deep sea sediments. Taking the drilling site U1308 from North Atlantic as an example, the standard sediment sample was put on DRIFTS detection and the area ratio of calcite peak 713 cm-1 to quartz peak 800 cm-1 was set as independent variable. The calcite content was obtained by Vacuum-Gasometric technique, and the correlation between DRIFTS area ratio and calcite content was analysed and a regression equation was validated. The results show that the DRIFTS method can clearly quantify the calcite in sediments, which is especially sensitive for the low calcite content with good mesure precision and detection limit. In this way, we determined the calcite content for drilling site U1308 sediments of recent nearly 1 Ma, which displays typical Atlantic carbonate cycle. It reflects intensified changes in calcite preservation during mid-Brunhes event (MBE) and mid-Pleistocene evolution (MPE). In response to global climate change, it also reflects the driven force mechanism of global carbon reservoir changes in North hemisphere ice sheet expansion and influence of deep water circulation on calcium carbonate preservation.

Development and mechanism of desiccation cracking of clayey soil under different temperatures

SHI Bin1, TANG Chao-sheng1, WANG Bao-jun1, JIANG Hong-tao2

2009, 15(2): 192-198.

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An experimental project was undertaken to investigate the effect of temperature on initiation and propagation of desiccation cracks of clayey soil, and the computer image processing techniques and programming were applied to quantify the geometric structure and morphologic characteristics of surface crack networks after drying under different temperatures.The results show that the soil cracking generally experiences four stages of development which is significantly influenced by temperature. With increasing temperature, the crack patterns of soil samples tend to be simpler, and the crack width increases;Under lower temperature condition, the crack pattern is more complicated, the crack width is finer and the soil surface is more fractured; A new interpretation on the cracking mechanism is proposed based on double-layer theory of clay; An interesting phenomenon was discovered in the testing that most of the cracks intersect almost perpendicularly, and most of the polygons separated by cracks are quadrangular. The future research work on desiccation cracking is proposed.

Characteristics of ground temperature variations in superficial soil layers for Nanjing in cecent 30 years

WANG Bao-jun1, SHI Bin1, JIANG Hong-tao2, ZHAO Li-zheng1

2009, 15(2): 199-205.

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Through collecting the measured data, including the atmospheric temperatures of recent 50 years and the ground temperatures at different depths of recent 30 years at an observation station in Nanjing city, the relationship of the ground temperatures with the atmospheric temperatures and the changing trend of ground temperatures are analyzed. The variations of ground temperatures, variation of daily mean ground temperatures and daily ranges of ground temperatures are also studied. The results show that, the ground temperature changes have a good correlation with the atmospheric temperatures, however, with a lag.The change regularity of monthly mean ground temperatures of Nanjing city is basically similar, and the maximum values occur in July or August, and the minimum in January or February each year. In general, the ground temperatures increase gradually during the recent 30 years, with the maximum increment on the ground surface of 2.8 ℃， at the 20 cm depth of 2.0 ℃ and at the 40 cm depth of 1.75 ℃. The greatest temperature difference on the surface reaches 84.5 ℃, and at the 40 cm depth reaches 27.5 ℃.Therefore, some possible influence due to ground temperature rising on the engineering geological properties of superficial soil layers inside the Nanjing city area can not be ignored.

A study on the engineering classification of chemically modified soils

IANG Hong-tao, LIU Jin, WANG Yuan, ZHAO Li-zheng

2009, 15(2): 206-212.

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Based on the existing research achievements and the authors’ recent work, the chemical modified soils are classified into five categories i.e. inorganic soils, organic soils, inorganic-organic compound soils, chemico-physical soils and polluted soils. The definitions of the five categories of chemical modified soils are presented, and their origins, engineering properties, mechanisms, applications, advantages and disadvantages are also analyzed and summarized in this paper. The research indicates that the five chemical modified soils have different engineering properties, formation mechanisms and engineering applications; The effect of modified soils depends on the modified material properties, soil properties and modifying technology. The chemicophysical soils are the best one in improving the engineering property, while the polluted soils can only be used after an effective treatment because in general their engineering properties and environmental effect can not meet the engineering requirement. The chemically modified soils have wide application prospect in the field of environmental geotechnical engineering.

Laboratory study on influence of tempereture on shear strength of unsaturated clayey soil

SHAO Yu-xian, SHI Bin, GAO Lei, GU Kai, ZHAO Li-zheng

2009, 15(2): 213-217.

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In order to assess the urban heat island effect on the engineering properties of clayey soil，some laboratory tests have been done on moisture contents and dry densities of the clayey soil under different environmental temperatures, and some thermodynamic characteristics of clayey soil are revealed. The research results indicate that the temperature has complicated influence on the shear strength of clayey soil. When the moisture content of soil is more than 18 %, the shear strength of soil decreases with the increasing temperature, showing the thermal softening on strength; When the moisture content is less than 18 % and dry density is 1.67 g·cm-3, the temperature hardly affects the soil strength; However when the dry density is less than 1.67 g·cm-3, the soil strength increases with the temperature rising, showing the thermal hardening on strength. Finally, the mechanisms of the thermal softening and hardening of soil are analyzed.

Study on application of GIS in environmental impact assessment of mineral resources planning

SONG Zhen1， HUA Jian-wei1,2， WANG Bao-jun1， SHI Bin1， LI Hai-tao1

2009, 15(2): 218-225.

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According to the current situation of environmental impact assessment of mineral resources planning, the methods of this domain at home and abroad are systematically illustrated in this thesis. Based on comparative analysis of existing methods,the thought and technical framework of environmental impact assessment using GIS (Geographic Information System) is proposed.Moreover, some key techniques of GIS are analyzed in this thesis, such as spatial information storage, raster data layer creating,buffer analysis, DEM (Digital Elevation Model) creating, raster superposition and model analysis, distance analysis, typesetting，etc. Finally, the feasibility of thought and technical framework using GIS is verified by taking environmental impact assessment of mineral resources planning of Jiangsu Province as an example, and its results will provide valuable references for other relevant work.

Sedimentary characteristics and source provenance in the Early Cretaceous Tenggeer Formation of Baiyinchagan Sag, Erlian Basin

LIN Chun-Ming1, ZHANG Zhi-Ping1, LI Yan-Li1, YUE Xin-Dong2,1,XU Shen-Mou1, ZHANG Xia1, QI Bin-Wen3,1

2009, 15(2): 226-239.

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Based on core description, electric logging, mud logging, core analysis data, seismic survey, etc., the sedimentary facies types and characteristics of early Cretaceous Tenggeer Formation, Baiyinchagan Sag, were studied in detail, as well as their distribution pattern. The research shows that fan delta, braided delta, lacustrine facies and turbidity fans were developped in this formation, of which the fan delta is located along the steep northern border and the braided delta found along the gentle southern slope. In addition, from the margin to the depocenter of Baiyinchagan Sag, the sedimentary environment gradually changed from fan delta or braided delta to semi-deep and deep lakes, and on the flank of fan delta or braided delta, the shore and shallow sediments were deposited. The turbidity fans are distributed in the delta front zone, pro-delta and semi-deep and deep lacustrine zones. Generally speaking, the sedimentary facies are different from the east to the west of Baiyinchagan Sag and were differentiated between the southern and the northern parts, which was controlled by the neighboring faults and the basin palaeotopography. Based on the analysis of sandstone detrital components and heavy minerals, the sediments of Tenggeer Formation in Baiyinchagan Sag came from the Bayinbaolige swell and Saihuduge salient, with the characteristics of multiphase,spasm and closing to the source rocks. The results also illustrate that the source rocks were mainly the sedimentary, and in lesser amount the igneous, with little contribution of the metamorphics.

Karst collapse hazard zoning based on group decision-making around West Lake

ZHAO Zeng-yu1, PAN Mao1, CONG Wei-qing1, LIANG He2, FU Jun-he2

2009, 15(2): 240-245.

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Karst collapse hazard zoning around West Lake is an important aspect of urban geological harzard analysis and evaluation, which is a part of urban geological data management and service system for the Hangzhou city. In the model of the karst collapse hazard zoning, the analytic hierarchy process (AHP) is introduced to get the weights of individual contributing elements, based on the advices of project geologists before group decision-making. The most compatible weights of contributing elements are obtained by considering the geologists weights during process of decision-making, based on the principle of individual analyses and coefficient variations. Weight results of AHP are fully utilized in this model, which avoids the extreme weights by a few geologists. Hence, the results seem to be more reasonable than those of the conventional method. Zoning results show that the development of karst collapse harzard and the geological structure are two main important elements that affect karst collapse hazard around the West Lake, which is quite well accepted by most of the experts. Although there is no distribution of the most risk area, the government should take attention to more susceptible and sub-susceptible area which could be potentialy hazard collapse area more seriously, especially when the area is considered as an engineering site.

Sandbox modelling on genetic mechanism of fault system in Weixinan Depression of the Beibu-Gulf Basin and its inspirations

Meng Ling-jian, Tong Heng-mao, Cai Dong-sheng, Liu Ming-quan, Li Xu-shen

2009, 15(2): 246-255.

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The fault system of Weixinan Depression in the Beibu-Gulf Basin is very complex. In order to reveal the genetic mechanism, this paper applies sandbox modelling technologies to make a systemic analysis on the formation mechanism of Weixinan Depression fault system on the basis of systematic structural analysis of 3D seismic data. After several physical simulation experiments, the south-north direction experimental model of disharmonic extension can successfully reproduce the complicated fault system of Weixinan Depression, and the major characteristics have clear appearance in this experimental model.The complicated fault system of Weixinan Depression was formed gradually during progressive deformation on the basis of the preexisted basement structure, and the fault system of main rifting phase (Late Eocene-Oliqocene) was formed just by one extension stage (NS trending), but not the result of multi-stage superimposed deformation. This understanding not only can interpretet the fine structure of 3D seismic data in Weixinan Depression, but also can provide a reference for studying the formation and evolution of the peripheal basins of the South China Sea.

Study on the enthalpy variation during adsorption processes of Acidithiobacillus ferrooxidans ATCC23270 on the surface of minerals and its metabolic thermogenesis under different conditions

WANG Xiu-mei1, 3, LIU Jian-she2*, LI Bang-mei1, ZHU Jian-yu1,WANG Hua-tai1, YAN Yin1, QIU Guan-zhou1

2009, 15(2): 256-262.

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The influencing factors of the enthalpy variation during adsorption processes of Acidithiobacillus ferrooxidans ATCC23270 on the surface of sulfide minerals and the metabolic thermogenesis of the bacteria under different conditions (different concentrations of the bacteria, different initial pH values and different media) were studied using microcalorimetry. The results show that the concentration of pulp at 0.03 g/mL and concentration of bacteria at 1.7×108 were the best environment for enthalpy variation during adsorption processes of A. ferrooxidans ATCC23270 on the surface of minerals. A. ferrooxidans cultured in different media with different contents of extracellular polymers (EPS) create different heat of reaction attaching on the surface of minerals. Bacteria cultured with pyrite having the highest EPS create the biggest heat of reaction, which proves the important role of EPS in the process of adsorption. The growth thermograms of bacteria can be determined by using the mircocalorimetric method. These perfect thermogram curves reflect the changes of bacteriaI growth patterns. For A. ferrooxidans ATCC23270, the best condition for the metabolic thermogenesis is at pH = 2.0 or 2.3, and concentration of bacteria at 3.0 × 108 cell/ mL. The bacteria cultured in different media create different growth thermograms. Media of 2039+ FeSO4 is the best one for metabolic thermogenesis.

Water content of peridotite xenoliths from Cenozoic basalt in Yangyuan, Hebei province

ZHU Bei-bei1, WANG Qin1,*, WANG Liang-shu1, CHEN Li-hui1, ZHANG Hong-fu2

2009, 15(2): 263-272.

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Water in the upper mantle plays a critical role in the strength and partial melting of lithosphere. Investigation on water contents of peridotite xenoliths from the North China Craton (NCC) gives important constraints on mechanism for its lithospheric thinning since the Mesozoic. Spinel peridotite xenoliths were collected from Cenozoic basalt in Yangyuan, Hebei province, to study the water contents of the lithospheric mantle in the northern Trans-North China Orogen of NCC. Using microscopic Fourier transform infrared spectrometry (FTIR), we measured the water contents of major minerals in five samples. All olivine, orthopyroxene and clinopyroxene grains exhibit characteristic hydroxyl absorption peaks in FTIR spectra. Olivine has relatively low amount of water (4×10-6~9×10-6), while orthopyroxene and clinopyroxene have (105~201)×10-6 and (260~440)×10-6, respectively. Based on the modal composition, the water contents of bulk samples are estimated to be (49~75)×10-6. It is worthy to note that metasomatism and late alteration significantly increase the water contents of clinopyroxene in our amphibole-bearing harzburgite sample. Water contents in clinopyroxene and orthopyroxene from Yangyuan peridotite xenoliths display positivecorrelation with the water partition coefficient D cpx/opx OH =2.4±0.9, which is consistent with the average value (D cpx/opxOH =2.2±0.1) for the global peridotite xenoliths. Olivine, orthopyroxene and clinopyroxene in Yangyuan peridotite xenoliths contain much more hydroxyl than those from Hannuoba, which may be caused by fluid-rich metasomatism in the upper mantle beneath Yangyuan.Statistical analysis of available water measurements on natural peridotites shows that olivine from basalt-borne spinel peridotites is relatively dry with water contents of 0~10×10-6. In contrast, variable water contents in orthopyroxene and clinopyroxene from basalt-borne spinel peridotites reflect heterogeneous water distribution in the upper mantle. Olivine, orthopyroxene and clinopyroxene from kimberlite-borne garnet peridotites contain much more water than those from basalt-borne spinel peridotites.This is probably because kimberlite is characterized by greater depth of origin, more fluids and faster ascending rate than basalt.

Identification criteria and prediction of reef and shoal facies reservoirs of the Changxing Formation in the Eastern Kaijiang-Liangping area intraplatform trough

ZHANG Bing1, ZHENG Rong-cai1, WEN Hua-guo1, Hu Zhong-gui1,LUO Ai-Jun2, WEN Qi-bing3, ZHU YI-xin3

2009, 15(2): 273-284.

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The reef and shoal facies reservoir in Changxing Formation, Upper Permian, is located in Kaijiang－Liangping intraplatform trough. In the region of interest the intraplatform trough（ deep water basin） , platform slop, platform edge and open platform sedimentary facies are developed. The platform edge is the important layer for oil and gas exploration. The lithology of the reservoirs in Changxing Formation is mainly reef facies dolomites, shoal facies dolomites and crystal dolomites, and is characterized by huge distribution area and thick reservoirs. According to the analyses of core observation, thin sections and sedimentary facies and by using geology, bore wells and seismic data, the electrofacies and seismic facies models are established to recognize the reef and shoal facies reservoirs. The chimney effect which is used to confirm the mess of wave resistance, interception and pulldown in seismic cross section is an effective sign of looking for reef and shoal facies reservoirs anabled gas reservoirs. Based on it, reef and shoal geologic model acting to seismic inversion constraining condition of predicting favorable reef and shoal facies zone, combined with the thickness distribution map of dolomites，the favorable area for reservoir evaluation is estimated.

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