Geoscience

Attempt to the Late Cretaceous Ostracod Carapace Stable Isotope Measurement — Case Study on the SK1 Drill Cores

MO Xiao-Qiao, WANG Chao, Ci-Wei-Min

2011, 25(3): 401-408.

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Rapid isotopic variation affected by Late Cretaceous greenhouse is of globe implication, and can be used as proxy of climate change in the Earths history. In continental sedimentary system, relatively continuous paleoclimate signal is recorded in lacustrine sediments. It is an ideal record to recover highresolution paleoenvironment and paleoclimate changes. The Songliao lacustrine basin is a large Cretaceous sedimentary basin. A coring program, the“Cretaceous Continental Scientific Drilling Programme of China (SK1)”, was initiated to the study of Cretaceous climate change. Under this programme, an ambitious effort is now underway to develop an oxygen and carbon isotopic record for a nearly complete Cretaceous lacustrine section in the Songliao basin to reveal paleoclimate change in innercontinental area. Bulk samples were normally used to the Cretaceous stable isotope analysis. The compositions of terrestrial stable isotopes are complicated and can be affected by various factors. The present authors attempt to select ostracod carapaces as analytical materials. As a result, ostracods were handpicked from samples collected from drill cores. After removing them from rock matrix, the ostracod carapaces, matrix and filling materials were then visually examined for possible secondary calcite, such as sparry calcite, respectively. The result indicates that ostracod carapaces are avoided from secondary calcite and /or diagenesis. They are reliable materials for the isotopic study. Specifically, we demonstrate that the carbon and oxygen isotopes recorded in the ostracod carapaces of the Songliao basin seemingly track the corresponding contemporaneous isotopic records during Late Cretaceous. The isotopic curves will be the criterion of terrestrial isotopic succession in China after detailed study.

Progress in the Study of Cretaceous Rapid Climate Change— Evidence of Glaciation in a Greenhouse World

CHEN Xi-1, 2 , WANG Cheng-Shan-1, 2 , HUANG Yong-Jian-1, 2

2011, 25(3): 409-418.

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The Cretaceous, representing the warmest period during Phanerozoic, contains sparse and frequently equivocal evidences for glaciers or even polar ice sheet. Recently, more and more geoscientists have been interested in the hypothesis of Cretaceous glaciation. This paper compiled the evidences from previous publications including dropstones, tillites, glendonites, eustasy fluctuations and δ18O values. The potential glaciations most possibly existed in the following intervals: BerriasianValanginian, late Valanginian, Barremian, AptianAlbian transition, AlbianCenomanian boundary, middle and latest Cenomanian, middle Turonian, middle Coniacian, early Santonian, late Campanian, CampanianMaastrichtian transition and latest Maastrichtian. The Cretaceous glaciers were small and ephemeral if they did exist. It is suggested that the Cretaceous glaciers could exist during short intervals of peak Milankovitch insolation.

“Earthtime” Project: Dating Precision and Temporal Resolution in the “Deep Time” Record

TUN Fu-Chun-1, 2 , WANG Cheng-Shan-1, 3 , ZHANG Shi-Gong-1, 3 , YANG Tian-Shui-1, 3 , MO Xiao-Qiao-1, 3

2011, 25(3): 419-428.

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The level of achievable geological time precision, accuracy and resolution determines the nature of the deeptime ecological, climatic, biological evolution and basic geological questions for which a reasonable answer may be expected. The main dating and correlation techniques include radiometric isotopic geochronology, biostratigraphy, magnetostratigraphy and cyclostratigraphy, and each has its own advantage and disadvantage. There might have some inconsistencies between the dating results of different techniques. Earthtime is an organized, communitybased, extensive international cooperation project. Its scientific objectives are to integrate, calibrate and improve highprecision geochronology and quantitative chronostratigraphy, to develop the geochronological techniques necessary to produce geological time with uncertainties approaching to 01%, and finally to precisely determine the ages and sequences in the deep time of Earth history. The continuous terrestrial Cretaceous developed in the Songliao Basin, northestern China, provides a unique opportunity to carry out high resolution integrated geochronological research, and its accomplishment will be an important complement and contribution of the Earthtime project applied in the Mesozoic continental records.

Tectonic Compression and Rapid Sediment Filling of Bohai Sea

LUAN Ti-Wu-1, LIU Feng-1, 2 , SUN Dian-Ai-1, 2 , LI Xiao-Yun-1, 2

2011, 25(3): 429-439.

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Based on longtime data of base line, water depth, geological structure, satellite image and hydrology, the issue of the Bohai Sea Closing was discussed in this paper. The GPS observation results clearly show that the Bohai Sea is in the process of tectonic contraction. The geologic record and results of longterm tidal stations show that the sea level of the Bohai Sea is falling. The seismic profiles and drilling data show that the basement subsidence of the Bohai Sea basin has stopped. There are three key factors which determine the evolutionary direction of the Bohai Sea, namely the tectonic contraction, falling of sealevel and stopping of the basement subsidence of the Bohai Sea, and all these factors commonly lay the foundation for the Bohai Sea finally inevitably toward closing. The advancing of coastline of the Bohai Sea toward the sea and becoming shallow of the depth of the Bohai Sea are taken as powerful geological evidences which response geological processes of the Bohai Seas closing. The deposition of the Yellow River delta and the Liaohe River delta have been constantly carrying forward the Bohai Sea under the geological background which the Bohai Sea is destined to close, and the effect of silt creating land is very apparent, thus it becomes the main factor for the Bohai Sea fast towards closing. It is expected that the Yellow River estuary and the Liaohe River estuary will combine in the Bohai Sea in 400 years later, so the Bohai Sea will disappear; and that the Laizhou bay will be closed in 100 years later. With the Bohai Sea circulation change, more substances of the Yellow River may deposit towards the Bohai Sea, as a result, the closing rate of the Bohai Sea could also be accelerated. The remote effect of the Himalayas uplift causes tectonic shrinkage of the Bohai Sea, and a large number of deposits are carried into the Bohai Sea by Yellow River, thus fundamentally causing the closing of the Bohai Sea. As a whole, these geological effects in the short term will not change, and will even not change with human being activities.

Activity Characteristics on the Xigeda Fault in Late Quaternary and Recrudescing Interval of Strong Earthquake

LEI Hai-Feng-1, 2 , JI Zhi-Jie-3

2011, 25(3): 440-446.

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The paper studied the Late Quaternary activity of the Xigeda fault carefully based on the geomorphologic analysis of the landsat ETM data combined with field tectonogeomorphic observations and measurement. Results reveal that shape of the rivers and ridges along the fault showed the “S” or anti“Z”, or more “S”shape, which are end to end connected with each other, and an echelon oblique columns; the faulting way is sinistral strike slip with left step, and a series of pullapart basins and fracture lakes (lake distributed popularly)developed; that as Holocene active strikeslip fault, its latest active time was later than (1283±109) ka, generally, which is west dipping, with smaller (trend) strikeslip component and slip rates of 170 mm/a since late Pleistocene; that according to the seismic remnant and active characteristics of the fault, recrudescing interval of the fault activity is 10-12 ka or shorter.

Dynamic BasinOrogen Coupling and Sequence Response Process：Taking LanpingSimao Basin, Western Yunnan as a Case

YANG Xin-1, 2 , ZHENG Jian-Jing-1, LIU Xin-Wang-1, 2 , SU Long-1, LIU Yu-Hu-1, 2 , LIU Yan-Gong-3

2011, 25(3): 447-455.

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Accompanied with the orogenic belt evolution stage from collision to postcollision and intraplate stage, the coupled basins transform from foreland basin to extensional basin and strikeslip structural basin, which is considered as the dynamical basinorogen coupling model. The MesozoicCenozoic basinorogen coupling of Sanjiang region of western Yunnan is a typical example of this conceptual model. Based on strata and outcrops, we divide Mesozoic strata of LanpingSimao basin into 3 second sequences and 11 third sequences. The 3 second sequences corresponded to the evolutional stage of foreland basin, extensional basin and strikeslip structural basin, on behalf of each single prototype of the sedimentary basin filling. The growth of 11 third sequences controlled by several times noncyclical basin basement activities including repeatedly deflection response to thrust load, episodic faulting activity of basement, and strikeslip structural function.

Sedimentary Environment of Paleogene Lacustrine Oncoids in Pingyi Basin, Shandong Province

TANG Xin-Ping-1, 2 , Huang-Wen-Hui-1, 2 , DENG Hong-Wen-1, 2 , ZHANG Kuang-Meng-1, 2 , Liu-Jia-Ji-1, 2 , Mu-Na-Na-1, 2

2011, 25(3): 456-463.

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There are a great many oncoids in the limestone of Pingyi basin. By means of field inspection and microscope observations, the host rocks as well as associated fossils and sedimentary structures were investigated. Some of the chemical compositions were also measured to discuss the environmental features. Oncoids were found intensively distributed in the environment which was characterized by shallow water, medium or mediumlow energy. Slight amount terrigenous influx was discovered to contribute to the growth of oncoids, while superfluous influx was found adverse. Oncoids were divided into 3 types: regular micrite laminaes oncoids (type A), regular microspar laminaes oncoids (type B), irregular micrite laminaes oncoids (type C). Type A, which was mainly represented by macrosize, multinucleus, regular multilaminaes, could be considered as the mark of shallow water, mediumenergy, slight amount influx. Type B, which was characterized by light color, wellsorted microsize, microspar laminaes, could represent shallow water, relatively highenergy environment. Type C was identified by irregular laminaes, and could represent the low energy condition. Type A and B indicated lowporosity rocks, while type C indicated comparatively favorable pore space.

Analysis of Sediment Provenance and Sedimentary Control Factors in Yaoshang Formation, Weining County in Guizhou Province

KONG Fan-Cui, YANG Rui-Dong, HAN Xiao-Tong, WEI Fu-Rui, CHENG Ma-Li, GAO Jun-Bei, LIN Hai-Li, LONG Jie

2011, 25(3): 464-475.

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The feature of major elements and REEs composition of lake sediments of Yaoshang Formation in Guizhou, Weining County, are analyzed. The provenance features, climatic evolution and control factors of sediment accumulation have been discussed. The results show that: The change of abundance of Al, Mg, Ca, K, Na and Ti is consistent in the section. Their correlations between 0522 and 0985 are very high. Fe and Mn form a positive correlation, while they negatively correlate with Al, Mg, Ca, K, Na and Ti. The abundance of Fe2O3 in the yellow clay of iron layer is very high. The chondritenormalized REE distribution patterns of samples are similar with that of soil and red clay of karst areas in Guizhou, almost similar with that of weathering crust of carbonate rocks in Guizhou, and are inconsistent with Emeishan basalt. The abundance of REEs is slightly lower than that of the weathering crust of carbonate rocks. The provenance mainly comes from carbonatites of which the strong weathering results in the abnormal enrichment of REEs in this section (ΣREE average 21938 μg/g). The climatic indicators of Mg/Ca, MgO/Al2O3, (CaO+K2O+Na2O)/Al2O3, (Fe2O3+Al2O3)/(MgO+CaO) and (K+Na+Ca+Mg)/(Fe+Mn) show that the climate has experienced the conversion from warm and humid to cold and dry. (Al+Fe+Mn)/(K+Ca+Mg) and (MgO+Na2O+CaO)/Al2O3 can also be used as the climatic indicators of lake sediments. The formation of deposits is controlled by provenance properties, iron rocks，tectonic movements and climate.

Characteristics of the Detrital Response to Oligocene/Miocene Geological Events in Baiyun Sag, Pearl River Mouth Basin

LI Yun-1, ZHENG Rong-Cai-1, GAO Bo-Yu-2, HU Xiao-Qiang-2, DAI Chao-Cheng-1

2011, 25(3): 476-481.

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The source areas changed obviously during Oligocene/Miocene in the northern South China Sea. With the pointcounting method of thin sections of Miocene Zhujiang Formation and Oligocene Zhuhai Formation in Baiyun Sag, Pearl River Mouth Basin, the characteristics of detrital components were studied in detail. The results show that: the lithic fragments in Zhuhai Formation were dominated by plutonic magmatic fragments, and there were also many feldspar and sedimentary lithic fragments, in agreement with the fact that the source was mainly from Mesozoic granite rock in the South China; in contrast, the lithic fragments were dominated by metamorphic fragments in Zhujiang Formation, and there were some magmatic fragments, sedimentary fragments and more feldspar, indicating more supply of the sources in Zhujiang Formation. With the various Oligocene/Miocene geological events, especially accompanied by weathering and increasing erosion caused by the uplift of QinghaiTibet Plateau, the source areas expanded within the ancient South China land and even to eastern Tibetan Plateau. The change of clastic components was the result of these various geological events.

Sedimentary Record in Core OS031 from the Southern Okhotsk Sea since the Last Interglacial and the Paleoenvironmental Significance

CI He-Wan, HOU Xue-Jing, DING Xuan

2011, 25(3): 482-488.

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Core OS031 was retrieved from the southern Okhotsk Sea (150°00′36″E, 49°29′51″N; 975meter water depth). The core consists of 381 m of silty clay and 96 samples were taken. Based on the analysis of AMS 14C ages of planktonic foraminifera, oxygen isotopes of benthic foraminifera, opal content, organic carbon content, planktonic foraminifera assemblage, icerafted debris (IRD) content and grain size distribution of sediments, the research reconstructed the paleoenvironmental records over the past~140 ka. The results reveal that the relative abundance of Neogloboquadrina pachyderma (sinistral) is very good negative correlation with Globigerina bulloides, and both of the two species can be used as the sea paleotemperature proxy compared with the curve of oxygen isotopes. The absolute abundance of the planktonic foraminifera, opal content and organic carbon content show that the climate variation of the study area is obviously affected by glacialinterglacial cycle, and the paleoproductivity in the interglacial period was relatively higher than in the glacial period. The analysis of IRD and sediment grain size indicates that the coarse grain content of the southern Okhotsk Sea in the interglacial period was higher than in the glacial period.

Mineralogy of the Xiba Granitoid Pluton in the Southern Qinling Orogenic Belt and Its Implications for Petrogenesis

HONG Huan-1, 2 , WANG Jian-Beng-1, 2 , LIU Jia-Jun-1, 2 , CAO Rui-Rong-3, HUI De-Feng-3, CHENG Jian-Jun-3

2011, 25(3): 489-502.

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The Xiba granitoid pluton, as an important part of the IndoChinese Wulong granitoid series, is located in the middle section of the Southern Qinling orogenic belt and spatially related to the Shuangwang gold deposit. It mainly consists of quartz monzodiorite and granodiorite containing many mafic microgranular enclaves (MME). Systematic petrological and mineralogical studies indicate that the rocks belong to I type granite. The petrographical studies of granite and MME suggest that magma mixing plays a great role during magma crystallization. The pressure of the granite estimated by Alinhornblend barometer is from 167×108 to 366×108 Pa. Amphiboleplagioclase thermometry yields a forming temperature of 64972~70384 ℃. The plutons equilibrated under high oxygen fugacities (lg fO2) ranging from -1616×105 to -1706×105 Pa, moderate water fugacities (fH2O) between 4682×105 and 13685×105 Pa, and also moderate hydrogen fugacities (fH2) from 032×105 to 091×105 Pa. The high oxygen fugacities provide suitable conditions for Au entering into melt and fluid, thus favor the formation of gold deposit.

Seismites from Bayan Obo Group in the Bainaimiao Area of Inner Mongolia
and Their Tectonic Implications

JIAO De-Yang-1, CUI Xiao-Huan- 1, SU Hong-Wei-2

2011, 25(3): 503-509.

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The MiddleUpper Proterozoic Bayan Obo Group is located at the northern margin of the North China Craton, and was deposited under intraplate tectonic setting of extension in MiddleLate Proterozoic. From the Halahuogete Formation of Bayan Obo Group in the Bainaimiao area of Inner Mongolia, the authors discovered a set of structures resulted from softsediment deformation for the first time. They occur within the crystalline limestone at the lower section of this group, and include remobilisation breccias, synsedimentary folds, faultgrading, molar tooth and so on. These characteristics demonstrate they belong to the seismites. According to further comparisons between the Bayan Obo Group and the contemporary Sailinhudong Group nearby, we found they exhibit similar features of softsediment deformation as well as the same age of formation. This discovery of the seismites from Bayan Obo Group indicates the northern margin of the North China Craton was undergoing a rapid and intense extension and divergence in MiddleLate Proterozoic, which provides fundamental observations for further studies on tectonic evolution of the North China Craton.

Zircon U-Pb Age of Xiaomiao Formation of Proterozoic in the Eastern Section of the East Kunlun Orogenic Belt

CHEN Wei-Xin, FEI Xian-Chi, LI Rui-Bao, LIU Zhan-Qiang, LI Zuo-Chen, ZHANG Xiao-Fei, CHEN Guo-Chao, LIU Zhi-Gang, DING Sa-Beng, GUO Dun-Feng

2011, 25(3): 510-521.

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After detailed means of field geological survey, petrologic study and LAICPMS zircon UPb chronology method about Xiaomiao Formation, the age of the metamorphic basement formed in PreCambrian in Kekesha area of Xiangride Town in the eastern section of the East Kunlun orogenic belt is discussed. The results show that Xiaomiao Formation is mainly a suite of quartzconsisted metamorphic rocks, which can be categorized into 4 classes, such as rock assemblages of biotite quartz schistquartzite, gneissschist, hornblende schistbiotite quartz schist and quartzitemarble. These characteristics reveal that the original rock assemblage of the rocks may be a suite of volcanosedimentary formation, which belongs to sedimentary system from shallow sea to continental margin in environment and lowamphibolite facies of middle pressure in metamorphic condition. Furthermore, the zircon UPb chronology indicates that there were geotectonicthermal events in 1,600-2,729 Ma in source area of Xiaomiao Formation, most ages of which are distributed in 1,683-1,554 Ma of the Middle Proterozoic in geological time.

Petrological Characteristics and Genesis of Qingtian Stone in Zhejiang Province

CHEN Yan-Fang-1, YU Hua-Hui-2, JIANG Liang-Zhi-2

2011, 25(3): 522-530.

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Petrologically, Qingtian stone is a kind of rock comprising clay mineral of pyrophyllites, which formed by hydrothermal metasomatism and metamorphism and is a kind of secondary quartzite. The present work focuses on petrography, mineral composition and varieties of Qingtian stone, suggesting that hydrothermal metasomatism and metamorphism of intermediateacid volcanic rocks lead to the formation of the stone. Our investigations include petrographical observations, physical and chemical characteristics, geochemical compositions, field environments and reviews of previous papers of Qingtian stone. The studies show that Qingtian stone can be classified into several types, according to its main mineral components which are closely related to its protolith, features of the hydrothermal fluid, and temperature pressure conditions. Its color and quality are closely related to the mineral component, microstructure, and colorcausing cations. High quality Qingtian stone had undergone extensive metasomatism and metamorphism, whereas others with lower quality commonly had undergone slight metasomatism and metamorphism. It is suggested that determination of alteration zone of volcanic rocks of Mesozoic and Cenozoic Era by means of geological mapping is an effective way of looking for the high quality Qingtian stone, and must be concerned in the identification and subsequent evaluation of the stone.

Analysis of Orecontrolling Structure and Prospecting of Tectonogeochemistry in Jinshan AuAg Mining Area，Guangxi

JIAN Jian-Beng, XIE Biao-Wu, CHEN Hong-Yi, BAI Yan-Ping, TUN Xiao-Lei

2011, 25(3): 531-544.

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Through the field investigation and structural maping of the Jinshan AuAg mining area in Guangxi Province，the orecontrolling structural regularities have been summarized. On this basis, the prospecting study of geochemistry was carried out in the main orecontrolled fault zone. There are two deposit types in the mining area，one is altered rock type gold deposit which was hosted in the main orecontrolled fault zone，and the other is quartz vein type gold deposit which was hosted in the flank pinnate tension fracture. The different mineralization types were controlled by the different tectonic environment，and they can be a prospecting criteria for each other. The orebody was controlled by the tectonic interface. The mineralization have obviously subenrichment regularity because the orecontrolling fault opened heterogeneously in the mineralization period. The tectonic activities in mineralization period shows the hanging wall of the main fault obliqueslipped toward southeast, accordingly the orebody is SWlateral trending and its depth is greater than extension. The middle of orebody is thicker than both sides，and the exploration line No11 is the enrichment center of mineralization. The concentrations of metallogenic elements,Ag,Au,Cu,Pb,and Zn increased with increasing alteration. Factor analysis show the main metallogenic elements association is Ag,Au,Cu,Pb,and Zn,which can be used as indicator elements.The elements distribution patterns，combination analysis and fractal dimension statistics show that multistage silver and gold mineralization. The zoning sequence of tectonogeochemical primary halo is AuHgAsBiSnSb→MnVAgNiTiCrCoW→MoPbZnCu from upper to down，which shows that the deposit is a shallow denudated deposit and may be superimposed by latestage hydrothernal fluids. On the basis of the analysis of oreforming structures，the magmatic activities，the characteristics of alteration zone and tectonogeochemical primary halo zoning，it can be proposed that the deep and periphery of the mining area have still better prospecting potential. The key zone of prospecting is in the southwest of the exploration line No11.

REE Geochemistry of Baijian Iron Deposit in Shahe City, Hebei Province

Hao-Dun-Jie, SHEN Jian-Hong, DIAO Xin-Wei, FENG Dong-Dong

2011, 25(3): 545-552.

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Based on the study of REE geochemistry of Baijian iron deposit in Shahe, Hebei Province, REE in skarns, ores and strata limestone have the similar characteristics, and ores are closely related to magmatic rocks (diorites). REE pattern of ores show the same distribution pattern of limestones of wallrocks. A probable reason of the phenomenon is infered that oreforming fluids or magma experienced long distance transportation after forming, went through structures such as faults to the deposition place, and then acted metasomatism with wallrocks, and that during metasomatism, oreforming fluids extracted oreforming materials from wallrocks. The skarns and ores have similar chondritenormalized REE distribution patterns and are enriched in LREE, with an obvious Eu negative anomaly and a moderate Ce anomaly, implaing that they were formed by magmatic fluids in reductive environment characterized by low temperature and strong enrichment of Eu.

Organic Carbon Decomposition and Its Temperature Sensitivity of Black Soils in Different Land Use Types in the Songnen Plain

LIAO Yan-1, YANG Zhong-Fang-1, JIA Hua-Ji-1, GAO Lei-1, FENG Hai-Yan-1, DIAO Xiu-Fang-2

2011, 25(3): 553-561.

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The black soil samples from three different land use types in the Songnen Plain were incubated for 90 days in the laboratory. It was found that after reaching a maximum value at the initial stage, the rates of soil respiration declined continuously and then stabilized. At the four different temperature conditions(5 ℃, 15 ℃, 25 ℃ and 35 ℃), the rates of soil respiration simultaneously increased with increasing temperatures. At the same temperature conditions, intensity sequence of soil respiration rates of the different samples was as followed: black soil from the paddy field>black soil from the grassland>black soil from the dry land. The values of temperature sensitivity coefficient Q10 of soil respiration decreased with increasing temperatures, which means that the feedback of soil organic carbon to the climate warming would be more sensitive at the colder regions. Soil respiration dynamics was fitted with the firstorder kinetic equation. It was showed that among the three types of black soils, black soil from the paddy field had the highest content of active organic carbon, followed by that from the dry land and then that from the grassland; as to the proportion of active organic carbon to total organic carbon, black soil from the grassland was the highest, followed by that from the dry land and then that from the paddy field. Light fraction and heavy fraction of organic carbon in the samples were divided by the density separation, and it was found that more than 95% of total organic carbon in the samples was in the form of heavy fraction, which was much higher than the amount of light fraction. The result from the density separation coincides with that from the model fitting, and the proportion of light fraction (active carbon) to total organic carbon was arranged as followed: black soil from the grassland>black soil from dry land>black soil from paddy field, while that of heavy fraction (slow carbon) was the opposite.

The Relationship between Soil Acidification and Nitrogen Inputs in the Poyang Lake Area, Jiangxi Province, China

WEN Bang-Yong-1, YANG Zhong-Fang-1, HOU Jing-Xie-1, YANG Xiao-Yan-1, YIN Guo-Qing-2, ZHONG Cun-Di-2

2011, 25(3): 562-568.

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The Poyang Lake area in Jiangxi Province is one of the most soil acidification areas in China. This paper aims to study the relationship between soil acidification and soil nitrogen inputs through fertilization, atmospheric deposition and irrigation in this area. Firstly, soil pH variation in the last two decades was investigated by comparing data from the multipurpose regional geochemical survey carried out in the early 21st century and that from the second soil survey in the 1980s, and the result showed that the area of serious acidification had increased from 5822% to 7844%. Nitrogen input fluxes from fertilization, atmospheric deposition and irrigation are 12384 kg·hm-2·a-1, 7413 kg·hm-2·a-1 and 1102 kg·hm-2·a-1, respectively. With these nitrogen inputs, protons enter into soils, which causes soil acidification. Anthropogenic activities bring proton input to soil by 1867 kmol·hm-2·a-1. Nitrogen fertilization is the first factor for soil acidification of the Poyang Lake area. The negative correlation between soil pH and N implies that organic N has little concern with soil acidification and so enhancing organic fertilization and reducing chemical N fertilization are good measures for preventing further acidification. Soil pH has a positive correlation with Ca, so Cariched matter will reduce soil acidification.

Evaluation of Soil Elements in Topsoil of Hebei Plain

CUI Geng-Chao-1, LUAN Wen-Lou-1, LI Jun-2, LI Sui-Min-1, SONG Ze-Feng-1

2011, 25(3): 569-574.

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This paper evaluates the elements of Hebei plain topsoil by referring to the three aspects of soil quality. Study shows that elements reflecting soil fertility quality are in a rich or fitting state, but the other ones including TOC, N, P, alkalihydrolyzable N, Zn, Mo, effective Mo, effective B are insufficient, especially TOC, Mo, effective Mo are deeply lacking. According to Soil Environmental Quality Standard (GB-15618-95), it suggests that the environment of Hebei plain heavy metal elements are favorable, and the exceedingstandard rate of these elements is very low. And the analysis of these heavy metal elements form shows that the bioavailability and potential harmfulness of Cd is much large and it is the most ecologically harmful element in the area. Among the elements which reflect the quality of soil health, F is rich or fitting while I is in relatively lacking state.

Dispersion and Migration of Gold Under Landscape Evolution in Gobi Desert Terrains

ZHANG Bi-Min-1, 2 , 3 , WANG Hua-Qiu-1, 3 , CHI Qing-Hua-1, 3 , LV Qiang-Tian-2

2011, 25(3): 575-580.

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Some Gobi desert terrains in northwestern China are peneplains formed by a long period of erosion. Dispersion pattern of elements is changed under this kind of landscape evolution. Jinwozi gold deposit was selected for study of element dispersion and migration in the process of pediplanation by using overburden drilling sampling. The results show that (1) gold tends to concentrate in the top and bottom of the vertical profile over the ore body; (2) gold is enriched in the finegrained fractions of soils with clayrich horizons at surface or near surface and the largest gold anomalies occur in fine grained samples (-100 mesh) over the ore body; (3) gold distribution in different size fractions of soils at the bottom of the weathering regolith display no obvious difference but tend to be anomalously enriched in bedrock troughs. This indicates that gold was concentrated in the lowest places by erosion and lateral transportation during the process of pediplanation. Vertical migration to the soil surface and entrapment by clays and amorphous FeMn oxides leads to the formation of geochemical anomalies directly over the ore body.

Apatite Fission Track Analysis of Tectonothermal History in the Northeast of Ordos Basin

DING Chao-1, 2 , CHEN Gang-1, 2 , LI Zhen-Hua-1, 2 , MAO Xiao-Ni-1, 2 , YANG Fu-1, 2

2011, 25(3): 581-588.

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Apatite fissiontrack analysis offers the opportunity to reveal Mesocenozoic tectonothermal history of different sections and different sequences in the Northeast of Ordos Basin，and to provide new constraints on forecast and prospect oil, gas and other mineral. Simulation results show that: the temperature of stratum slowly rose at the rate of 09 ℃/Ma during 250-150 Ma; and rapidly rose at the rate of 21 ℃/Ma during 150-120 Ma in the northeast of Ordos Basin. At this time, all temperatures that are higher than 130 ℃ reach the highest. After that, strata of the north margin in the northeast of Ordos Basin rapidly uplift and cool at the rate of 13 ℃/Ma during 120-65 Ma and slowly uplift and cool at the rate of 04 ℃/Ma during 65-10 Ma; and strata of the south margin and subsidence of basin slowly uplift and cool at the rate of 09 ℃/Ma during 120-30 Ma and rapidly uplift and cool at the rate of 15 ℃/Ma during 30-10 Ma. The northeast of basin rapidly uplift and cool at the rate of 65 ℃/Ma since at least 10 Ma. Therefore, it is considered that （120±10) Ma is the key time of MidYanshan tectonic thermal event, which brought about the mature hydrocarbon generation and the largescale petroleum accumulation in the northeast of Ordos Basin. The north margin passed the 110 ℃ closed temperature in the 65 Ma±, and the south margin and subsidence area passed 110℃ closed temperature in the 30 Ma±, which were beneficial to the protopetroleum enrichment and preservation. Since Paleogene late (30 Ma), especially Neogene late (10 Ma), the rapid upliftcooling process has most probably become the key factor of the protopetroleum adjustment and the secondary reservoir formation.

Characteristics of Present Geothermal Field of the Wuerxun Depression in Hailaer Basin, Inner Mongolia

CUI Jun-Beng-1, 2 , LIN Zhan-Li-1, 2

2011, 25(3): 589-593.

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Wuerxun depression is one of the sags with the most abundant oil and gas resources in Hailer basin, Inner Mongolia, but the characteristics of geothermal field of this depression have not been researched. The characteristics of present geothermal field in Wuerxun depression was analyzed according to the continuous temperature data of 5 wells and reservoir temperatures of 42 wells and heat conductivity data. The present geothermal gradient is 28-37 ℃/hm with average value of 335 ℃/hm; the present heat flow is 422-594 mW/m2 with average value of 560 mW/m2. This result shows that Wuerxun depression has middletemperature field; the present geothermal gradient and heat flow in the north of the depression are higher than those in the south, which are mainly caused by the activity of the ground water and fault and volcanic rock. The present temperature is an important control factor on oilgas generation of source rocks. The Wuerxun depression has undergone continuous burial with increasing temperature, and the present temperature is the maximum temperature that the source rock has experienced; the present temperature in the west is the maximum, which causes the source rocks in Tongbomiao, Nantun and Damoguaihe formations in a high temperature environment, thus the source rocks is still in the stage of oilgas generation now, so the west area is the main oilgas exploration region in the Wuerxun depression.

5Research on the Formation Stages of Oilgas Reservoirs in Beier Depression of Hailaer Basin

QIN Wen-Long-1, 2 , 3 , CUI Jun-Beng-1, 2

2011, 25(3): 594-598.

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On the basis of illite dating method, hydrocarbon generated and hydrocarbon expulsed process and homogenization temperatures of fluid inclusion, formation stages of oilgas reservoirs in Beier depression of Hailaer basin are studied. It shows that there are two main formation stages of oilgas reservoirs in Beier depression of Hailaer basin. The first stage is about 120-80 Ma, which is corresponding to sedimentary period of Yimin Formationearly sedimentary period of Qingyuangang Formation, which is the main formation time of oilgas reservoirs in Beier depression of Hailaer basin. The great majority of formation period of oil and gas is 105-90 Ma, which is corresponding to secondthird segment sedimentary period of Yimin Formation. It is the abundant period of hydrocarbon generated and expulsed process, and sufficient migration force is helpful to formation of oil and gas reservoirs. The second stage is from Qinyuangang Formation to now which is second formation process of oilgas reservoirs. The oilgas reservoirs formed in the first stage is adjusted in the second stage.

Characteristics and Oilsource Investigation of the Oils in the Nanpu Oilfield, Bohai Bay Basin

MO Zhong-Hua-1, 2 , LI Su-Mei-1, 2

2011, 25(3): 599-607.

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Nanpu oilfield is a recently discovered field with substantial petroleum reserves. Totally 43 oils and 31 rock samples were collected for performing detailed geochemical analyses to unravel the characteristics and oil source for the oils. Three oil families have been recognized according to biomarkers and compound specific carbon isotope of nalkanes, namely Tertiary oils in No1 and 2 structural belts (OFⅠ), Tertiary oils in No3, 4 and 5 structural belts (OFⅡ) and Ordovician oils (OFⅢ). The OFⅠ is characterized by relatively low ratios of diasteranes to regular steranes but high ratios of steranes to hopanes, 4methyl steranes to C29 regular steranes and gammacerane to C30 hopane with a little heavier δ13C values of the compound specific isotope of nalkanes relative to the OFⅡ. The OFⅢ is distinguished from both the OFⅠ and OFⅡ with relatively higher thermal maturity and heavier δ13C values of nalkanes. Detailed oilsource rock correlation showed that the OFⅡ and OFⅢ were mainly derived from the source rocks of Ed3-Es1 and Es2+3 respectively, and the OFⅠ was derived from both the Es2+3 and Ed3-Es1 source rocks. We suggested that the Es2+3 is one of the most important source rocks of the Tertiary oils in the Nanpu oilfield, which is different from the previous idea that only the Ed3-Es1 is responsible for the Tertiary oils. This study should be helpful to petroleum resources evaluation and further petroleum exploration of the Nanpu oilfield.

Feasibility of Gas Production from Hydrate Reservoir Considering Heat Conduction：Taking Shenhu Area in the South China Sea as an Example

SU Zheng-1, 2 , 3 , CAO Yun-Cheng-1, 4 , YANG Rui-1, 2 , 3 , ZHANG Ge-Ni-5, TUN Nai-You-1, 2 , 3

2011, 25(3): 608-616.

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How the gas to be effectively produced from hydrate deposits has become a hot research topic. Heat stimulation is regarded as another important way for producing hydrate besides depressurization. However, the production efficiency and economic feasibility of gas production by heat stimulation have not been clearly understood. In this paper, a model for predicting gas production from hydrate deposits by heat stimulation was developed. The model was idealized and simplified by neglecting the effects of heat convection and pressure in sediment. We computed the heat consumption efficiency and gas energy efficiency of gas production by heat stimulation, only considering effect of hydrate dissociation. This model can be used to predict the maximum production efficiency. After thorough analysis of the characteristics of hydrate reservoirs and significant parameters from drilling and sampling research, we calculated the production potential of Shenhu hydrate deposits and investigated the production efficiency and feasibility. The result shows that the maximum amount of cumulative gas production at Shenhu is about 509 m3 per meter in three years, and the production potential is much lower than the industrial criterion for marine production. Therefore, it is concluded that hydrate dissociation rate is very low, and production cost is high and economic value is low under the current production technology.Thus it is unfeasible to produce gas from Shenhu hydrate deposits only considering the thermal conduction.

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